Olympus E-M1 Mark II
versus OM System OM-1

I wrote this review as a current user of the Olympus E-M1 Mark II. Therefore, I concentrated on the differences between OM-1 and E-M1 II, although I mentioned several times other Olympus cameras. I rarely use these cameras for video, so I do not discuss video capabilities here.

This page is not meant to be a complete review of all capabilities of the OM-1. For a more extensive review, see for example dpreview.com. For a complete description of the OM-1 functions, see the OM-1 user guide, the OM-1 quick guide, or one of the OM-1 books. I have, and recommend, Tony Phillips' "The complete guide to the OM System OM-1". If you buy a version printed on paper, make sure that you also get the PDF version of the book for free (the book contains instructions on how to do this). This additionally registers you to get free access to the extra materials available from the author and described in the book. Registering also makes sure that you will receive a link to the PDF of updated book versions (v. 1.1 came out at the end ov November 2022).

Note that you can find two printed versions of Phillips' book (color and B/W) in several online bookstores, but if the PDF version is enough for you, you can save some money by buying it from the author or from the Friedman Archives Press.

I also have Joe McDonald's "The OM-1 menu", which is cheaper than the former book but far more limited in scope and amount of information. However, don't forget the OM-1 user guide, which is free but does contain plenty of useful information.

I once prepared an Excel sheet of the E-M1 Mark II settings (not updated to later firmware versions), and found it useful at times for my work, and as a complement to the user guide. A comparable Excel sheet of the OM-1 settings has been made available for free by BobCS on dpreview. Pages 311-326 of the PDF user guide contain tables of the default settings. Another Excel sheet with the OM-1 settings is available for free to buyers of Tony Phillips' book (see above).

In 2020, Olympus announced that they no longer wanted to make digital cameras, and sold their imaging division to Japan Industrial Partners (JIP), a large "private equity fund focused on corporate carve-outs" (but Olympus retained 5% of the ownership). JIP seems to have no experience in the camera business, but has very large economic resources, so much so that their purchase from Olympus is not even listed among their significant acquisitions.

Currently (August 2022), Olympus is in talks with the US-based Bain Capital private equity company to sell them the Olympus scientific instrument division, so the sale of their imaging division two years ago was not just a one-off reaction to low camera sales but one of multiple symptoms of widespread dysfunction of the whole Olympus company. While Olympus cameras are better known than Olympus microscopes and biomedical equipment to the general public, the latter has been the core of Olympus since its very start. If Olympus continues to shed off its most important divisions at this rate, it will not take long before it is reduced to just a brand name, like Kodak and Polaroid.

On the other hand, if, as we are seeing with the imaging division, selling the scientific instrument division will result in a positive revival of the now moribund Olympus microscope business, I for one will welcome the change of ownership.

There are still plenty of "official" links to Olympus camera products on the web, but most of them now lead to pages re-branded "Olympus System". If this sounds confusing, repeat with me: Olympus System is not Olympus.

The new company was initially called Olympus Digital Solutions, but now most of the time it sports the name OM Digital Solutions, or sometimes just OM Digital. The name OM System is also increasingly used, instead of Olympus System. Perhaps the transfer of ownership was such a rushed affair, almost as chaotic as the US retreat from Afghanistan, that JIP did not have time to decide on a proper, permanent name for the new company, or perhaps this gradual shift away from "just Olympus" is intentional, to give enough time to photographers to learn that the new company is not an upstart but literally the heir to the Olympus camera legacy, expertise, product development teams, and factories.

The company name is not the only thing shrouded in confusion. The headquarters of Olympus Digital Solutions are said to be located in Shinjuku, Tokyo, while the headquarters of OM Digital are reportedly in the less glamorous, more picturesque Takakura-machi, Hachioji-shi, Tokyo.

Most observers believed that JIP only planned to liquidate piecewise the assets of the Olympus Imaging Division, like they did with other acquisitions. Quite the opposite happened: Not only did the new company continue to produce the current Olympus camera models at the existing factories, they introduced new high-end lenses, a new PEN camera, a new high-resolution digital sound recorder and, roughly one year after the ownership transfer, no less than a new flagship camera, the OM-1. I have just been informed that they will release a new 90 mm f/3.5 Pro macro lens, with in-lens IS working in tandem with sensor-shift IS and 2x maximum magnification (not 4x as erroneously reported by several sources, including the OM System marketing web site - note that it makes no sense to apply a format‑relative factor to magnification, it only creates more confusion, as we just saw in this case).

OM System has just officially announced the new OM-5 second-tier camera, a significant upgrade of the Olympus E-M5 line, albeit delayed by the world-wide long-term shortage of electronic components. Early rumors suggested it would use the same stacked sensor of the OM-1 and the same BLX-1 battery. It turned out neither is true. The OM-5 uses the BLS-50 battery (much smaller than the BLX-1 of the OM-1 and already used in several Olympus cameras), a single card slot and a single TruePic IX (i.e. 9) image processor inherited from the E-M1 III, instead of one or two of the newer TruePic X (i.e. 10) of the OM-1. While the OM-5 is quite expensive, it lacks some of the advanced features of the OM-1, including Subject Tracking.

Externally, the OM-5, besides being the first camera sporting OM System on the fascia, seems to be identical to the E-M5 III and is said to use the plates and grip of the latter. The OM-5 even has the same Micro USB connector of the E-M5 III. Without PD (only available on USB 3), this makes in-camera battery charging slow. The small battery size makes this less of a problem than charging a BLX-1 without PD, but the lower battery capacity of the BLS-50 also makes an external charger and an extra battery practically obligatory for extended use. Incidentally, the EU legislated that all rechargable mobile devices will have to be equipped with a USB C connector for recharging. This will make the OM-5 illegal to sell in the EU from January 1, 2024.

OM System is partly, but not totally, to blame for the general lack of innovative features in the OM-5. This camera likely had been in the works for a substantial time already under the Olympus leadership. In fact, the OM-5 is a lack-luster upgrade of the E-M5 III in a way very similar to how the E-M1 III was a lack-luster upgrade of the E-M1 II.

As expected, OM System discontinued several of the camera models it inherited from Olympus, in particular the E-M1 III, E-M5 III and (according to rumors) E-M1X. If you are interested in any of these, now is the time to look for a bargain. I am not aware of the E-M10 line being discontinued or upgraded, but clearly either decision is likely to be among the next steps. The new PEN did not sell much, so the logical step would be either to discontinue the PEN line, or to develop it into a much more powerful camera. Interviews say that OM System is considering the development of a "mini OM-1", which may or may not turn out to be a "super-PEN".

For several years, the earliest contributions by Olympus to Micro 4/3 were limited to low-end cameras and lenses targeted to occasional amateur users. Afterwards, starting with the E-M5, came the golden years of Olympus Micro 4/3, which combined highly innovative cameras and lenses with reasonable prices. This happened when Olympus gradually (and perhaps reluctantly) gave up its E-series 4/3 DSLR and lenses, thus freeing resources for the development and production of more advanced Micro 4/3 cameras and lenses. Micro 4/3, developed by Olympus together with Panasonic but technically an offshoot of the Olympus 4/3 E-series DSLRs, became the first successful mirrorless system, with Olympus concentrating mostly on still imaging and Panasonic mostly on video with their respective flagship models.

This golden period came to an end for Olympus in the years immediately preceding the sale of the Olympus Imaging Division. These years show a lack of vision by the company leadership of the time. The 2013 E-M1 had been the first Micro 4/3 camera worth considering by professional photographers and advanced amateurs. The 2016 E-M1 Mark II had been a remarkable improvement over the E-M1 "Mark I" in almost every respect, but the 2020 E-M1 Mark III was such a modest improvement on the Mark II that it should have been skipped entirely. The 2019 E-M1X is a large, heavy and expensive dual-grip camera that gives up the Micro 4/3 advantage in size and weight, in return for an only moderately better performance and a small number of new features.

Today, the E-M1X sells for a recommended price just 150 € below the more capable and much smaller OM-1. I cannot see why anyone, today, would choose the E-M1X, except perhaps a few professional photographers who cannot live without a dual grip (albeit the OM-1 can be equipped with a battery grip if desired), or who need to impress customers with a camera bigger than anything else in the mirrorless world (at the time of introduction - this dubious record is now claimed by Canon).

As far as I know, the only main feature available in the E-M1X but not in other models (including the OM-1) is GPS. If you regard it as indispensable, then the E-M1X is the camera for you.

The Olympus M-1 SLR was announced in 1972, half a century ago. When Leica complained loudly that the M-1 name was encroaching on their own M-series telemeter cameras, Olympus complied and renamed its new camera OM-1, then went on to make camera history with this small and lightweight SLR and its successors (various iterations of the OM-1/2/4/10/20/30). Decades later, Olympus re-used the OM name in its OM-D (OM Digital) series of mirrorless digital cameras, subsequently renamed E-M. Perhaps Olympus' E‑M (Electronic M) name was a link-back to the original M-1 name, and at the same time to the E-series, the Olympus DSLR system cameras. It is no accident that the new OM System flagship camera is called OM‑1. It is a statement that this is a new start, as well as a return to the original spirit of the OM series.

I cannot avoid pointing out, however, that "OM System OM-1" sounds kind of repetitive. Additionally, the OM-1 SLR and its own original OM system are still famous enough that many cannot avoid thinking of this 20th century camera. On the web, plenty of search results for OM-1 still lead to pages on the legacy SLR. For now, I can live with the new company name. While this camera still sports the "Olympus" name on its fascia, there is still time for JIP to come up with a stroke of genius for a really catchy brand name for their new cameras.

Like other former Olympus cameras, the OM-1 is made in Vietnam, although many parts and subassemblies come from other countries.

From specifications, reviews, and my experience with the camera, it appears that the OM-1 incorporates several innovations that Olympus designers wanted to introduce, while remaining true to the essence of the original OM-1 and of the Micro 4/3 system. Perhaps, the JIP leadership's lack of significant experience in the camera business is a good thing, in the sense that they left the former Olympus designers free to implement the ideas that had been stymied for years by their previous management.

As for me, the E-M1 Mark III was such a disappointment that I never upgraded to it. The E-M1X is too large for me to look at it twice. An important part of my decision, almost two decades ago, to switch from DSLRs to Micro 4/3 was the physical size advantage of Micro 4/3 cameras and lenses. Besides, both the E-M1X and E-M1 III use the same sensor as the E-M1 II, so the basic image quality cannot be much different from the one I already had.

A further, frustrating peculiarity of the E-M1 III and E-M1X is that neither model has a full complement of features. For example, the E-M1X has Subject Tracking, but not the E-M1 III (in spite of the latter using one-generation newer processors). On the other hand, just to remain within AF-related features, the E-M1 III did get Starry Sky AF as a firmware update, but in the E-M1X this update is said not to be possible, because its graphic processors lack some required hardware functions. Why did Olympus expect buyers to choose among two different sets of features, without being able to have one camera with the full complement of features? The whole idea of a flagship camera model is that a buyer gets everything and the kitchen sink in terms of firmware functionality, none barred among what is currently available. So why didn't Olympus provide one real flagship model, and instead two almost-flagship models with different and incomplete sets of features? Perhaps the plan was to introduce a successor to the E-M1X, but Olympus never got around to it (which in itself is a good thing in my opinion).

I cannot shake the impression that someone high up on the Olympus command chain decided the release of the E-M1 III just to show customers that Olympus cameras were not a dead end, but without giving the imaging division a sufficient mandate and resources to do a good job of it, and on the contrary intentionally crippled the E-M1 III feature set in order to prevent this model from competing with the supposedly flagship E-M1X.

The OM-1, on the other hand, is only slightly larger and heavier than the Mark II (599 vs. 574 g), uses two image processors like all E-M1 models after the Mark I (albeit much faster than in any earlier models), and as far as I know has inherited or bettered all features of both the E-M1X and E-M1 III, including e.g. multi-shot live ND and subject tracking. The OM-1 also adds a new sensor and viewfinder. In particular, for the first time since I switched to mirrorless, when looking through the OM-1 viewfinder I have the same feel of looking through the optical viewfinder of a DLSR, without the color-shifts, delays and lower resolution associated with a relayed electronic image. In retrospect, my decision to hold back on the E-M1 III and E-M1X was fully vindicated.

Pixel count and light gathering of Micro 4/3 sensors

Much has been written about the light-gathering properties of sensors of different sizes, and about the optimal amount of megapixels in an image. Apparently, this discussion cannot be avoided while considering the purchase of a Micro 4/3 camera. You can read my thoughts here. If you want the short-short version:

the 20 Mpixels images from a Micro 4/3 camera are large enough for 95% of commercial uses. For much of the remaining 5%, you may consider using the 50 Mpixel or 80 Mpixel images produced by sensor-shift on a camera like the OM-1.
A larger sensor with the same number of pixels does collect more light per pixel. With a subject at infinity, this advantage is only two stops (and therefore only moderate). In macro photography, the advantage decreases to one stop (i.e. a small advantage) because a Micro 4/3 camera needs to work at only 0.5x to produce the same field of view of a full-frame camera at 1x.

Physical camera appearance

Branding

As mentioned above, the OM-1 is still branded OLYMPUS on the front of the viewfinder (but there is no branding on the rear of the LCD screen, unlike in Olympus-made models). On the other hand, the image EXIF metadata identifies the camera maker as OM Digital Solutions. A small tag near the bottom right of the lens mount says OM System, and so do the plastic cap covering the lens mount, the battery, the USB power brick, and the SD card once it has been formatted in the camera. The camera strap is branded OLYMPUS OM SYSTEM OM-1, and a label at the rear of the camera, normally hidden under the LCD screen, says OM Digital Solutions Corporation. The OM-1 identifies itself as buildroot when connecting to a WiFi router. The optional BCX-1 battery charger is branded OM Digital Solutions Corporation. These inconsistencies in brand profiling are rather unusual in the camera business.

E-M1 Mark II (left) and OM-1 (right), front view.

E-M1 Mark II (left) and OM-1 (right), rear view.

Physical controls

It is obvious that the external appearance of the OM-1 inherits several elements from the E-M1X. Compared to the E-M1 II, the front and rear dials are no longer at the top of the camera, and leave the top of the camera much less crowded than in the E-M1 II, in spite of the moderately larger mode dial. Both front and rear dials are now sunk into the body and no longer operable with two fingers. The rightmost portion of the top panel in the E-M1 II is so crowded that the rear dial, when turned, can rub against the eyelet for the camera strap (or the camera strap itself). For this reason I removed the right eyelet, as visible in the above pictures, and fastened the camera strap to the right side of an Arca-compatible base plate. This has the added advantage that, with a moderately large lens, the camera tilts with the lens front element pointing downward instead of outward, protecting the front element better against accidental impacts when carrying the camera hanging from its strap in tight or crowded quarters.

I also use two models of Sony Alpha cameras, which have dials very similar to the OM-1, so for me this change is a good thing.

The top of the power switch mount, with its two buttons, is concave (versus flat in all E-M1 models) and more difficult to operate accidentally.

The power lever itself is shorter but thicker than in the E-M1 II, with a more positive "click" feeling like in the EM-1X, but angled more unobtrusively to the right rather than to the rear like in the E-M1X. The three buttons on top of the power lever of the E-M1X are thankfully reduced to two in the OM-1, like in the E-M1 I/II/III.

The shutter button has been more clearly separated from other controls. It is also more flush with the surrounding surface and more difficult to trip accidentally by brushing against the camera. I am not quite used yet to this style of shutter button, and sometimes I need to fumble before finding it. A better tactile feedback, for example by texturing the button surface, or a ring around the button, might help.

Among other small differences from the E-M1 II, the hot shoe on the OM-1 is no longer black but chrome-plated (like in the E-M1 III and E-M1X), which may conceivably make it easier to locate in low light, and probably is also more durable than the old black enamel.

The eye sensor for switching between LCD screen and viewfinder is placed under the viewfinder, instead of at its right side like in earlier models. As a result, the rubber eyecup now has a different shape.

Menu is the only button that has substantially moved with respect to the E-M1 II. The new position is similar to the Menu button of my Sony Alpha cameras, and of the E-M1 III (but not the E-M1X, which strangely exiled the Menu button to the bottom left of the camera rear). Most buttons on the rear of the camera are smaller in the OM-1 than in the E-M1 Mark II.

All cable connectors behind the rubber doors on the left and right sides of the body have remained the same (with the microphone connector being placed slightly higher in the OM-1, which makes it slightly easier to open the LCD screen when this connector is in use). The OM-1 comes with a lightly-built strain reliever that screws to the connector plate, keeps the rubber door open, and houses the USB and video connectors. Some third-party video cables have a connector shell too large to fit into the strain reliever, and the camera does not come with a video cable.

The right-hand handle is slightly larger than in the E-M1 II and fills the palm of my right hand better. This also means that brackets for the E-M1 II/III do not fit the OM-1. The thicker BX-1 battery, compared to the BH-1 of the Mark II/III/X, means that the door of the OM-1 battery compartment is also significantly larger, which makes it difficult to design a bracket exactly covering the outline of the bottom of the handle. The RRS base plate I use on the Mark II simply does not fit on the OM-1, because of the numerous dissimilarities in shape. For the same reason, the add-on battery handle for earlier Olympus cameras cannot be used on the OM-1 (the electronics and battery are incompatible, anyway).

Third-party accessory makers like RRS and Smallrig (see below) initially solved these problems by cutting off entirely the rightmost portion of the bottom plate. The unfortunate consequence is that, with the plates designed so far, the little finger of most male photographers is left partly floating in the air, unable to grip the handle. My hands are only medium-sized, and the handle of the OM-1, slightly larger than in previous cameras, allows me to use half of my little finger, but not in a comfortable way. As a past user of the Japanese katana, I appreciate the importance of the left little finger in holding and controlling a two-handed sword, and holding a camera similarly becomes much more comfortable when the right little finger can be used.

In the summer of 2022, on their web page for the BOM-1 bracket, RRS silently replaced the picture of their prototype OM-1 base plate, with chopped-off right side, with a completely redesigned model that covers the entire base of the camera.

A few months later (November 2022), they still only accept pre-orders, with no date set for production.

As for myself, I am not going to place a pre-order for this base plate because (1) there is no sign yet that RSS will actually start producing it, and (2) a better and/or cheaper bracket might become available at any time from another maker. With the exception of my E-M1 Mark II, which uses an RSS base plate, I used no-name base plates made in China for all my cameras of the last two decades, and found no fault with them.

Unlike in the past, manufacturers of camera plates and brackets seem to have little to no interest in producing a model for the OM-1. In fact, I found only two alternatives available online for the OM-1. The first is the Smallrig Cage. It is not a bracket or plate, it does not provide a gripping point for the little finger, and it is designed as a small and lightweight video cage, but at least it is available today and reasonably priced. It is, however, not available from EU mail-order retailers. This cage leaves the OM-1 hot shoe fully usable, and adds a cold shoe nearby. The numerous threaded sockets on the top, left side and bottom are potentially useful for electronic flash and other equipment, especially in field macro photography.

This cage does not block access to the cable sockets on the left side of the camera (but the cable strain reliever that comes with the OM-1 is not compatible with the cage). It also allows the articulated LCD screen to fully open (as long as no cables are plugged into the left side cable sockets). One problem is that the rail on the left side of the cage is a NATO gun rail, not Arca-compatible (only the bottom plate is), so you need to attach an Arca plate to the left rail if you want to mount the camera in portrait orientation on a tripod head.

The OM-1 bracket from the Taiwanese STC is a second alternative, and apparently only available by mail-order from Taiwan. Its design with a folding rest for the palm of the right hand is somewhat odd, and the position of the eyelet for the camera strap at the bottom right (not at the right side) of the camera body even more questionable, but nonetheless it is a potential new choice among the almost total lack of alternatives.

Controls layout and camera shape

The E-M1 Mark III is so similar to the Mark II that the only significant differences in external appearance are the addition of the 8-way joystick and a minor reshuffling of the buttons. The OM-1 inherits the joystick and button layout from the Mark III (like the E-M1X mostly did). The OM-1 does look thicker and more rectangular than the E-M1 II/III, especially when looking at the base of the camera. The more squarish frame of the viewfinder also contributes to this impression, together with the new location of the eye proximity sensor. It appears that most of the increase in volume of the OM-1 was achieved by "filling up" the corners and oblique surfaces of the preceding models and making the OM-1 surfaces more orthogonal. However, the OM-1 is only 19 g heavier than the Mark II, so the impression of solidity and larger volume of the OM-1 is, largely, just an impression.

Menu system

The menu system is an important part of both the appearance and ergonomics of a digital camera. The unusually large number of settings and functions of the OM-1 has been arranged in a redesigned menu that moves the top-level tabs from the left side of the LCD screen in previous cameras to the top of the screen in the OM-1.

These tabs are not very different than in past models, but they tell a little better what settings one can expect to find in each tab:1, 2, AF, , , , and My. A new thing is that each tab is color-coded in pastel colors. Each tab contains a number of pages, color-coded in the same color scheme and numbered, in addition to their text title. The title of each page tries to describe what types of settings are contained in the page, although not all page titles are successful in their aim.

One scrolls from tab to tab with the front dial, and from page to page with with the rear dial or with the left and right buttons of the 5-way selector. The menu wraps around automatically from the last back to the first page of the same tab, or vice versa. The menu also wraps around from the last tab to the first one, or vice versa.

Each page displays all the settings available on the page. There are no hidden lines beyond the top or bottom of a page, that in previous cameras had to be brought into view by scrolling vertically. The up and down buttons of the arrow pad move between rows in the current page. The joystick also scrolls horizontally from page to page and vertically from line to line.

The center button (OK) of the arrow pad is used to move deeper into the menus and to accept choices. The Menu button brings the user one level up, or out of the menu. The INFO button often, but not always, displays a brief help on the current item.

1 (8 pages) and 2 (3 pages) are still a mixed bag, covering everything from saving the C1-C4 settings to bracketing. The page titles are, respectively:

Basic Settings/Image Quality
Picture Mode/WB
ISO/Noise Reduction
Exposure
Metering
Flash
Drive Mode
Image Stabilizer
and:

Computational modes
Other Shooting functions
Bracketing

The AF tab (6 pages) contains pretty much everything that has to do with focusing, except focus bracketing and focus stacking.

AF 1
AF 2
AF 3
Movie AF
AF Target Settings & Operations
MF

The (movie) tab (6 pages) contains movie settings (except for Movie AF, which is in the AF tab).

Basic Settings/Image Quality
Picture Mode/WB
ISO/Noise Reduction
Image Stabilizer
Sound Recording/Connection
Shooting Assist

The (playback) tab (3 pages) contains everything used during playback, including customization of the camera controls while in playback mode.

File
Operations
Displays

The (gear) tab (5 pages) contains all remaining operational settings.

Operations
Operations
Live View
Information
Grid/Other Displays

The (wrench) tab (6 pages) contains card, folder and file settings.

Card/Folder/File
Information Record
Monitor/Sound/Connection
Wi-Fi/Bluetooth
Battery/Sleep
Reset/Clock/Language/Others

The My menu (introduced, less informatively, as the star menu with the E-M1X) contains the custom menu, initially empty. Here you can put your most frequently used menu items, where you can quickly find them. The OM-1 has space for 6 settings in each of 5 pages of this menu, so in total 30 frequently-used menu items. A few individual sub-menu items, selected at the discretion of the OM-1 designers, can also be placed here. The My menu has the potential of becoming the most frequently used menu, possibly replacing the SCP (see below) in popularity.
What you need now is a way to instantly open the My menu. There are two settings that can do much of this for you:

→ 2. Operations → Menu Cursor Settings → Menu Start Position → My. When you press the Menu button, this setting always opens the menu at the My tab. An alternative setting value is Save, which remembers the last menu position used and re-opens it automatically. This may be a better choice if you don't use the My menu that often.
→ 2. Operations → Menu Cursor Settings → Page Cursor Position → Save. This remembers the last selected setting on a menu page, and selects it for you when you return to the same page.

Super Control Panel (SCP)

While in live view mode, by default pressing OK displays the SCP, like in previous models. This is the fastest way to access many of the commonly used shooting settings, including several that have no dedicated physical controls. In the Mark II, when I need to change a setting but I do not exactly remember how, I go to the SCP first, and afterwards dive into the menu if I cannot find what I am looking for in the SCP.

In the OM-1, the SCP has been re-designed to use a larger portion of the LCD screen area (up to the sides and bottom screen edges) and to display a smaller number of settings (by default 22, compared to 29 in the Mark II) with thinner grid lines between adjacent settings. As a whole, the SCP of the OM-1 feels more readable and much less crowded. In the Mark II, the SCP is further crowded by the wide unused margins at the sides of the SCP, and of the bottom of the screen being occupied by a row of read-only settings (largely duplicates of the settings are also visible in the Live View screen overlays). As a whole, the SCP in the Mark II feels too crammed with settings to be reliably operated via the touch-screen, although in practical use this proves to be more of an impression than a real problem.

Types of exposure compensation

The choice of settings available on the SCP is, in my opinion, more rational in the OM-1 than in earlier cameras. For example, on the OM-1 SCP one can set the flash exposure compensation, which on the OM-1 can be set independently of the exposure compensation in A mode. This is done with menu setting 1 → 6. Flash → + → Off, which breaks the linkage between the two types of compensation and allows each of them to be set independently of the other. In this way, you can use by default the front dial for , which is based on ambient illumination, and the SCP to adjust , which sets the flash exposure compensation. This allows you to decide the relative strength of ambient versus flash illumination in a shot that combines both illumination types, for example just enough for the flash to fill up the shadows without completely washing out the shading caused by sunlight.

Functional improvements

The most important improvements of the OM-1 over the E-M1 Mark II, in my opinion:

OM-1	E-M1 Mark II
1,023 cross-type AF points, spread over "100%" (actually more like 90-95%) of sensor area, that can also record image information. Phase-detect pixels placed in the corners of the sensor cannot work reliably, which explains why even the current improved phase detectors cannot cover 100% of the sensor.	121 hybrid AF points, spread over 70% of sensor area. Each AF point consists of multiple dedicated pixels and can only perform AF. The "blind spots" left on the sensor are interpolated from adjacent image pixels, using the same technology that remaps dead and stuck pixels.
Sequence shooting up to 50 fps with CAF, 120 fps with locked AF and AE, no viewfinder blackout (except during long exposures).	Sequence shooting up to 18 fps with CAF, 60 fps with locked AF and AE.
Each pixel of the 20 Mpixel sensor consists of four, individually readable photodiodes under a shared microlens and Bayer filter. Thus, properly speaking, this is not an 80 Mpixel sensor, but neither is it a "plain" 20 Mpixel sensor. Perhaps, subsequent firmware versions will make use of the quad-pixel structure also for new functions.	Ordinary Bayer-array sensor, one photodiode per pixel.
Rear-illuminated stacked sensor.	Standard front-illuminated sensor.
Up to ND64 (6 stops) electronic neutral density filter, optionally with preview of the results in the viewfinder/LCD screen. Several other enhancements of the computational imaging methods.	No ND filter.
IS can be used simultaneously with several other functions, e.g. it can be active in Live View and Live Composite.	IS not usable simultaneously with most other functions.
Subject-tracking AF on trains, cars, aircraft, birds, and pets (the subject category must be manually chosen in advance). Face and eye AF cannot be combined with subject-tracking (it would make no sense anyway, because none of the current subject tracking modes are for human subjects).	Only face and eye AF, no predictive tracking other than "sticky" AF.
Mode dial: P-A-S-M-B, Movie, C1…C4.	Mode dial: P-A-S-M, Movie, C1…C3, Art, iAuto.
No bundled dedicated mini-speedlight, but can use the FL-LM3.	Bundled dedicated mini-speedlight FL-LM3.
One BLX-1 battery. No external charger. USB 3 power brick included, can recharge the battery in the camera and operate the camera simultaneously.	One BLH-1 battery. Single-battery external charger, no in-camera recharging, no mains-powered operation (mains operation requires both an optional battery grip and an optional dedicated AC adapter).
50 and 80 Mpixel tripod high resolution modes (80 Mpixel mode shoots 8 images with 1/4 pixel shifts), 50 Mpixel hand-held high resolution mode (shoots 12 pictures and compensates for camera movement).	50 and 80 Mpixel tripod high resolution modes.
Pro Capture: 20 fps with CAF on Micro 4/3 lenses (not 4/3). Pro Capture SH1: 120 fps with SAF (single AF). Pro Capture SH2: 50 fps with CAF on certain Micro 4/3 lenses.	Pro Capture L: 18 fps with CAF. Pro Capture H: 60 fps without AF.
Electromechanical shutter rating: 400,000 actuations, 60 s to 1/8,000 s, 1/250 s flash x-sync. Electronic shutter 60s to 1/32,000 s, flash sync speed: 1/100 s.	Electromechanical shutter rating: 200,000 actuations, 60 s to 1/8,000 s, 1/250 s flash x-sync. Electronic shutter 60s to 1/32,000 s, flash sync speed: 1/50 s.
IS range: 7 stops (CIPA). 8 stops with in-sync compatible lens.	IS range: 5.5 stops (CIPA). 6.5 stops with in-sync compatible lens.

Sensor

The sensor consists in practice of two chips separately manufactured, attached on top of each other and communicating directly with each other through multiple, physically very short and very fast pipelines. The top layer converts photons to electrons and stores the latter in electron wells, while the bottom layer quickly reads the electrons at the end of the exposure, strongly reducing the rolling-shutter problems, and does additional data processing before sending the picture data to the image processors on the motherboard.

The top layer of the sensor is rear-illuminated. Although the advantages of rear- versus front-illuminated sensors are not as big as camera makers would us believe, there is a small advantage in photon-collecting capabilities, and it is nice to know it is available in the OM-1. Another advantage of rear-illuminated sensors is that the photodiodes are closer to the chip surface, which among other things reduces the amount of corner darkening (or vignetting) with fast wideangle lenses. Most Olympus lenses, particularly wideangles, are designed to reduce the amount of corner darkening. Their optical design is sometimes described, somewhat loosely, as telecentric, although this term has a strict definition that often is not properly applicable to these lenses.

Some testers have reported that, with the same Olympus wideangle lens at the same aperture, the amount of darkening in the corners is much lower in the OM-1, compared with the E-M1 III. Note that we are talking about a reduced amount of corner darkening before the camera applies a software correction to images taken by lenses that the camera can identify in its internal database, not after this correction. Likely you will not see a significant difference if you compare images shot with different camera models, since the camera firmware or the raw converter apply a correction by default. To see a difference, you must either use one of the very few raw image converters that allows you to switch off the compensation it automatically applies, or use a legacy lens not recognized by the camera firmware. As a whole, the less the image needs to be changed in postprocessing (by firmware or external raw converter), the less the chance that compensating for dark corners will result in a higher image noise in these parts of the image. Thus, even this small advantage of the new sensor is welcome.

A simple, further reason for using a rear-illuminated sensor chip is that it is easier to design a stacked sensor if the chip carrying the photodiodes is rear-illuminated. Specifically, a rear-illuminated front sensor chip makes it easier to add the numerous electrical connections necessary between the two chips being assembled in a stacked configuration.

The four, individually readable sub-pixels of each pixel open up several interesting possibilities, besides aiding CAF during sequence shooting (the OM-1 AF system is said to use focus information from the imediately preceding shot to complement the information read from the AF sensors while sequence-shooting). Several mobile phones use partly similar sensors to switch between a low-noise, low-resolution mode and a high-resolution mode for high-illumination scenes. The OM-1 additionally is already capable of sensor-shift 50 and 80 Mpixel modes, which might be further enhanced by processing the individual outputs of the 80 million subpixels (we cannot properly call them 80 Mpixels because each microlens covers four adjacent photodiodes).

The sheer number of subpixels does not slow down the reading of image data from the top to the bottom layer of the sensor, thanks to the reading speed being much higher than in earlier cameras. In practice, reading the 80 million photodiodes in the OM-1 takes half the time required to read 20 million pixels in the fastest earlier Olympus cameras.

The fully electronic shutter, called (silent, with its various sub-modes) in the menu, is getting better and better in each new camera model. It is still not as good as a global electronic shutter, but the electromechanical shutter is not as good as a global electronic shutter, either, and has already been optimized to such an extent that further improvements become harder and harder to implement. The performance gap between electronic and electromechanical shutter is therefore getting smaller and smaller, and in the OM-1 we are not far from the difference becoming irrelevant in many practical situations. With the OM-1, I find myself successfully using the silent shutter in many situations in which, with older cameras, I was forced to use the electromechanical shutter.

The OM-1 continues the Olympus tradition of allowing the use of the electronic shutter with electronic flash, and improves it by halving the sync exposure time with electronic shutter with respect to the Mark II. This is one of the several advantages of increasing by eight times the data reading speed from the sensor, in part thanks to the stacked sensor architecture. Several current and recent cameras of other brands, especially the Sony Alpha, still don't allow flash with the electronic shutter. This makes life easier for the camera designers, but restricts the photographer's choices.

The statement, sometimes found on the web, that silent shutter still produces an audible mechanical sound (of low intensity) is fully correct, and applies to the OM‑1 as well. There are two sources of sound when using the silent shutter.

The first is the lens iris closing at the beginning of the exposure and re-opening at the end of the exposure. Different lenses, different apertures and different exposure times may generate a slightly different sound (this is perfectly normal). The mass of the iris and its motor is so small that the vibrations generated by their movement, while not being zero, are negligible in practice, especially with a physically large and heavy lens.

IS is the second source of sound, and is heard as a low-level hiss during long exposures. Even switching off IS still produces the same sound. Apparently, the IS electromagnets always need to be active during the exposure to keep the sensor centered at the correct position. Keeping the sensor centered in its bearings likely requires actively compensating for camera movements. The sensor's inertia would otherwise result in its de-centering when the camera moves, since the sensor is suspended in a system of electromagnetic fields that, without active compensation, allows some inertial drift with respect to the camera body.

When this electromechanical system is powered off, the sensor "falls" within its bearings, under the effect of gravity, to its lowermost position, which is not the best position for recording images. You can see the sensor "falling down" a fraction of a mm if you look at it through the lens mount while powering off the camera.

The sound generated by the lens aperture can be minimized (if you really must) by shooting with the lens aperture fully open. Using a lens with manual mechanical aperture or manually closing the iris before the exposure also eliminates this sound source. As far as I know, there is no practical way to eliminate the sound produced by the IS system.

If you think that the inertia of the sensor subassembly is negligible, think again. If you have access to a Sony Alpha camera (most of these models use the IS system to shake dust off the sensor), you can physically experience the effects of the sensor's inertia by activating the sensor-cleaning function while holding the camera in your hands. Just make sure that the surprising vibrations (for someone who has never experienced them) don't make you drop the camera.

Image processor

The image processor is version 10, or in full a TruePic X Quad Core Processor (where X is the Roman numeral for 10). The OM-1 uses two processors (like all E-M1 models after the Mark I), but each flagship camera model has used a newer generation of processors, and each generation has been substantially more powerful than the preceding one. Note that the processors of the E-M1X are two generations older than those of the OM-1. We should expect to see new, creative camera functions added in future firmware releases, just in the same way as Olympus was releasing new functions in the free firmware updates of current cameras, that subsequently were incorporated and improved in new cameras once extensively field-tested on the current cameras.

AF

Additional AF information is derived from normal sensor pixels (apparently by processing the differential information from the 4 photodiodes composing each pixel) in a region of the sensor surrounding each active AF point. This increases the reliability of subject tracking and other AF-related functions.

AF is much faster and more accurate than in earlier camera models, including the E-M1X.

Starry sky AF can be useful to correctly focus on the night sky in landscape photography, besides obviously in astrophotography.

Computational imaging and Subject Tracking

Up to ND64 (6 stops) electronic neutral density filter. Several other enhancements of the computational imaging methods and AF processing, e.g. the use of image stabilization while shooting live composites, and Subject-Tracking AF on trains, cars, planes, helicopters, birds and pets (the subject category, however, must be manually chosen). Face and Eye AF are also improved, but cannot be used simultaneously with Subject Tracking (naturally, since Face ane Eye AF look for human faces, while Subject Tracking does not). Although most of these capabilities were introduced in the E-M1X or E-M1 III, they are faster and more reliable in the OM-1.

Live Composite has a Lighten Composite sub-mode, which uses multiple-exposure sequences to increase the brightness of bright subject areas (e.g. individual stars), while not washing-out dark backgrounds (the surrounding sky). This is usable also hand-held.

Subject Tracking on birds is discussed here.

In-camera focus stacking is faster than in earlier camera models.

Auto ISO

This subject is discussed here.

Viewfinder and LCD screen

The OLED viewfinder has twice the resolution of earlier models and refreshes at 120 fps. The 1600 x 1200 pixel resolution (5.76 Mpixel) is better than HD, and the delay only 5 ms. Up to a 0.83x magnification is available, depending on the viewing mode.

The LCD touchscreen has a 1.62 Mpixel resolution (1.04 Mpixel in earlier models). In spite of the relatively low resolution, its active area of 63 x 42 mm provides all the detail one can actually see by naked eye. As a whole, if you use the viewfinder, the amount of visible detail is noticeably higher.

In the past, the LCD screen traditionally used to have a better resolution than the electronic viewfinder. This situation gradually improved over the years, with the viewfinder getting better and faster in the top camera models. With the OM-1, the viewfinder has now exceeded the LCD screen in all respects. As I mentioned above, this electronic viewfinder looks and feels like the "real image" provided by an optical viewfinder. It's that good.

Custom settings

As mentioned above, four banks of custom settings are available, and can be recalled by setting the mode dial to C1…C4. The OM-1 Quick Guide suggests the following uses, although you do not need to follow them, nor the specific settings suggested for each mode:

C1 - Birds in flight
C2 - Pro Capture
C3 - Macro
C4 - Landscape

On the other hand, there is no way that I know of to assign a displayable name, description, or comment to each of these modes. You just need to remember what each of them is for.

Battery and charger

In-camera battery charging is obligatory, unless you purchase a separate battery charger. The camera comes with one BLX-1 battery, but no external charger. On the other hand, the USB power brick supplied with the camera can simultaneously charge the battery while you use the camera. This USB brick is specified to provide 5 VDC 3 A and 9 VDC 3 A. An ordinary USB 5 V power bank cannot do both things simultaneously, although it does appear to be recharging the battery also when the camera is in use (most likely, not as fast as the battery is being depleted by using the camera, but still better than no charging at all). Carrying one or more spare BLX-1 would be optimal, but if the cost of a genuine BLX-1 gives you pause, and you prefer not to risk using a third-party cheapo BLX-1 lookalike in your OM-1, you might consider the power-bank solution, at least as a stop-gap measure.

If the OM-1 is connected to a USB 3 port on a computer, for example to use the OM Desktop or OM Capture apps, the battery still seems to recharge, albeit more slowly than with its power brick. Typically it cannot use the power supplied by a USB port to simultaneously operate the camera. However, the orange LED on the OM-1 is lighted (with both the camera off and on), and I do expect that even the limited charging current available through an ordinary USB port helps to increase the time the camera can be used before a full battery recharge is needed.

SBCX-1 kit of charger and battery (left), connected to a third-party USB 3 PD power supply (right).

If you do need a separate battery charger, there is a remarkably expensive SBCX-1 kit that contains one BLX-1 battery, plus an external BCX-1 charger that can take two batteries at a time and must be powered by the USB power brick of the camera (or a third-party PD-compatible USB 3 power supply that can output, at a minimum, 5V 3A and 9V 3A).

BCX-1 electronics, top and bottom of PC board.

The BCX-1 charger is relatively large (unsurprisingly, since it accepts two batteries) and feels heavier than comparable chargers. Out of curiosity, I opened the casing, which had no warranty seal and was held together by four special screws and two plastic tabs that must be pressed in, near the center of the long sides. The required screwdriver is a security (a.k.a. "hollow-stem", "with bore" and "tamper-proof") T8. The PC board is additionally fastened to the top of the plastic casing by two alignment tabs. Both sides of the PC board are rather densely populated with components. The explanation for the relatively high weight is a tin-plated sheet soldered at several points to the bottom of the PC board, which may work as a heat sink for eight SM power components (albeit there is a visible air gap between some of them and the heat sink, and no heat-conducting paste) and/or possibly as an EM shield supplementing the well-made ground planes of the PC board.

This PC board is at the high end, in complexity and number of components, among the battery chargers I have seen so far, especially since it does not contain an AC to DC power converter and must be powered by an external USB 3 PD power supply. Aside for the small IC and a few other components located close to the USB connector, which are dedicated to PD, most of the components have to do with voltage/current conversion and communication between charger and battery. This level of complexity and the relatively low number of units expected to sell (fewer than one for each sold OM-1) only partly explain the high price of this charger. The charger is made in China, but OM System must still be getting a significant profit from overcharging buyers of this item.

Unlike the earlier BCH-1 charger, which made do with just one status LED, each battery slot has three charge status LEDs. This provides a more readable display of the charging status (50%, 80% and 100%, respectively). Once the battery is fully charged, all LEDs turn off.

The BCX-1 breaks with the Olympus tradition of battery chargers directly connected to mains power by just a power cable. The BCX-1, as mentioned above, requires a USB 3 PD power supply or power bank.

A large number of third-party batteries and chargers purports to be compatible with the OM-1. Some are very cheap, others only moderately cheaper than the genuine BLX-1. Prices for apparently identical third-party batteries vary by almost one order of magnitude among end-sellers. I am somewhat skeptical of many of these claims of compatibility, given my past experience with third-party camera batteries leaking, overheating, swelling up and/or rapidly losing their charge if left unused.

In particular, I strongly recommend against recharging third-party batteries in the camera.

If you have no choice but using third-party batteries, charge them in their own external chargers, and discard them at the first sign of changes in behavior and/or swelling. Most often, a slightly swollen battery is already leaking inside its plastic envelope, and is a ticking time bomb that may ruin your camera at any time.

I found a statement on the web, repeated by a few sources, that the OM-1 can also use the BLH-1 battery from the E-M1 II/III/X. This is not true. The BLH-1 simply does not fit in the OM-1, and the BLX-1 does not fit in any of the earlier cameras. The OM System designers have made sure of it. The battery contacts may look similar, but all three dimensions of the battery envelope differ between the two battery types.

WiFi connectivity

I recently wished to connect my E-M1 II to the home WiFi in order to make use of the OM Capture and OM Workspace software to immediately transfer images from the camera to a PC without a physical tether between camera and PC and without swapping SD cards. No luck, the E-M1 II cannot do the simple task of connecting by WiFi to a home network. It only allows a one-to-one private WiFi network with a phone or tablet running a special Olympus app, and the OM Capture app for Windows complains loudly that it cannot pair with this camera by WiFi - only by USB.

This limitation, and the promise of a less restricted WiFi connectivity on the OM-1, became an additional reason to purchase this camera a few months earlier than I was planning. In fact, configuring the OM-1 to use my WiFi access point was easy and problem-free. When you need to connect the camera to your PC via WiFi, you need first to start the WiFi on the camera ( > 6.WiFi/Bluetooth > WiFi Connection > PC Connection), then start OM Capture on the PC. The rest is pretty much automatic after the initial configuration.

As mentioned above, the OM-1 automatically identifies itself to a WiFi router as buildroot. Why not OM-1, which would seem far more logical? Probably a developer forgot to update the host name before releasing the final version of the firmware. The camera gets an IP address assigned from the router's DHCP pool. In virtually all home routers, it is of course possible to manually assign a name and a permanent IP address to the OM-1.

Even the OM-1 cannot do everything I wish in terms of WiFi networking. For example, the camera can transfer images to my PC via WiFi if I shoot with the camera connected via OM Capture or OM Workspace, but that is about all all it does. In particular, pictures I shot without the camera connected to either OM app are not automatically transferred to the PC once I connect the camera and PC. Remotely accessing Live View and controlling the OM-1 from a PC still only works via USB.

I already had a 10 m long USB 2 active cable extension installed between my PC desk and my lab bench, and installed a second, 10 m USB 3 active extension for remotely operating the OM-1 via OM Capture (which also works with the E-M1 II). This setup allows my PC to simultaneously display the Live View, remotely control the camera, and automatically transfer the pictures (with OM Capture via USB 3), and operate the Stackshot controller (with Zerene Stacker via USB 2). Importantly, the double USB cable avoids using an external USB hub, or a USB to WiFi media converter, which often is fraught with problems.

Price, availability and competition

At a recommended EU price of 2,199 € (body only), this is not a cheap camera. On the other hand, it is only about 15% more expensive than the E-M1 Mark II was at the time of its release in 2016. The OM-1 is a few hundred € cheaper than the E-M1X at the time of its release in 2019.

Getting hold of an OM-1, on the other hand, may not be a given. According to 4/3 Rumors, in April 2022 OM System announced that the unanticipated high demand for the OM-1 was causing a shortage of parts, in turn forcing a production speed insufficient to satisfy the demand. In late August 2022, I decided to jump the gun for a number of reasons (among them, only one OM-1 body-only was left available on Amazon in the EU at the list price), and managed to snag it. In early September, more body-only OM-1 became available, but their number is not high, and they seem to sell like hot cakes. Predictably, some Amazon sellers are taking advantage of this by marking up their OM-1 prices by 20-25% above the list price.

It is easier to find OM-1 kits with the 12-40 mm f/2.8 Pro II than body-only. However, I already have the first version of this lens, and the only difference is that the new version has a slightly updated weather sealing, not because it needed improvement, but just to obtain a better weather sealing certification for the camera itself.

As for alternatives, Olympus has always had an edge on Panasonic Micro 4/3 in still imaging, and the OM-1 is no exception. Against Olympus-branded Micro 4/3 cameras, the OM-1 wins hands down. If you want to find real competitors to the OM-1, you need to consider the flagship full-frame mirrorless models of Nikon, Canon and Sony. They actually belong in a different class than the OM-1, and their prices are substantially higher (not to speak of the price of a full-frame super-telephoto lens with the same reach of the OM System 300 mm f/4 Pro or 150-400 f/4.5 Pro).

How practical is it to use an OM-1 and an E-M1 Mark II together?

Using the E-M1 Mark II as a second body, together with an OM-1, requires a double set of certain accessories, not compatible with both cameras:

E-M1 Mark II charger and battery (left) and OM-1 USB power brick and battery (right).

Different batteries. The OM-1 and E-M1 II batteries are differently shaped, so you need to keep, and pack in your luggage when traveling, two sets of spare batteries, the E-M1 II external charger, and the OM-1 charging USB brick (or external charger). You may (slowly) recharge the OM-1 battery in-camera from the USB port of a laptop or a USB power bank, but in most cases you cannot use the OM-1 simultaneously. In case you wonder, you cannot use the E-M1 II charger to recharge the OM-1 battery (reports that this is possible are erroneous).

Most modern laptops are powered and recharged with a USB C AC adapter. There seem to be multiple, incompatible types of USB C chargers, so before attempting to recharge your OM-1 with your laptop AC adapter, make sure you know for a fact that the latter is not going to destroy the camera. Just because the laptop AC adapter has the same USB C connector as the OM-1 power brick, it is no guarantee that the voltages are also the same.

The USB power brick supplied with the OM-1 is fairly large, about twice the volume and weight of the (non-PD) USB bricks provided with Sony Alpha cameras, and the almost identical USB power bricks supplied with Olympus Tough cameras.

Same USB connectors. The OM-1 and E-M1 II use a type C USB connector, so you need only one USB cable. However, the OM-1 USB brick has a USB C connector (i.e., it needs a C-to-C cable), while many laptops still have USB A connectors, so you may need to carry two different USB cables, or one C-to-C cable and an A-to-C adapter.
Same remote control port. Both cameras use a 2.5 mm 3-pole jack for a wired shutter trigger (same as used by most Canon DSLRs, but not the 4-pole jack used by Panasonic).
Same bundled flash. The FL-LM3 speedlight (bundled with the E-M1 II) works on both cameras.
Different Arca plates. As mentioned above, the two cameras need different L-shaped brackets (or base plates). At the time of writing, no sensibly designed brackets/plates are available for the OM-1.
The add-on vertical battery grips differ.
No AC power supplies can be connected directly to the E-M1 II for studio work. At most, you could get a third-party dummy battery with an attached DC cable, which prevents you from closing the door of the battery compartment and may eventually break off the tiny plastic clip that holds the dummy battery in place, if you happen to snag the power cable somewhere. The battery grip for the E-M1 II does accept an AC power adapter with a proprietary connector. The OM-1 can be happily powered in the studio by its USB brick power supply, but this occupies the OM-1 USB port and prevents it from being used for tethering to a computer. The USB ports of most desktop PCs and several laptops can either power the tethered OM-1, or recharge it when it is switched off, but not do both things simultaneously.

Should you sell your E-M1 Mark II/III?

For a professional photographer, having two identical camera bodies makes perfect sense, and in this case the most reasonable decision is buying two OM-1 bodies and selling older cameras. Quite a few advanced amateur photographers are likely to buy an OM-1, and in their case the question presents itself of what to do with one's older Micro 4/3 camera(s). For amateur photographers who don't need to sell an older camera in order to finance a new OM-1, buying a single OM-1 and keeping an older camera as a second body can be a reasonable choice.

If you are an amateur photographer with a newly-purchased OM-1, find the idea of having two bodies desirable, and already own an E-M1 Mark II/III, then I believe it is not immediately necessary for you to replace the latter with a second OM-1. The E-M1 II and III are capable cameras even by current standards, and unless you absolutely must use some of the new OM-1 features on both bodies, an E-M1 II/III as a second body will give you, in most "normal" photography situations, essentially the same image quality. Eventually, you might decide that you need a second OM-1, or perhaps a new camera will come out that makes an even better sense to upgrade to, but you don't need to decide in a hurry.

My situation is probably not typical among amateur photographers. I use digital cameras for generic nature photography, some birding and field macro, quite a lot of photomacrography and focus stacking in the lab, as well as photomicrography with a compound microscope. For these reasons, a single camera, or even two cameras, are not quite enough. Physically switching a camera between different devices is time-consuming, and even with separate banks of custom settings the process of reconfiguring a camera for each device is time-consuming and error-prone.

I use both Micro 4/3 and full frame cameras, of course with different lenses. In addition, one camera of each format is converted to full-spectrum imaging. For these reasons, my new OM-1 is not going to immediately replace any of my present cameras. If I had to choose, my E-M1 Mark I would be the first camera to get rid of, but at present it sits permanently mounted and ready-to-use onto a lab microscope, where it is perfectly adequate (not to mention that the second-hand value of a Mark I is quite too low to go through the hassle of selling it).

Should you buy an E-M1 Mark III or an OM-1?

This section discusses my recommendations if you:

Do not currently own an E-M1 Mark III, and
You are considering whether to buy an E-M1 III or an OM-1.

This discussion assumes primarily that you have an older Micro 4/3 camera (especially Olympus, since I am not familiar with Panasoníc models) than the E-M1 III. I also assume that you have a large enough set of modern Olympus (preferably Pro) Micro 4/3 lenses to serve your current and planned needs. Several advanced features of both camera models are only available with a subset of Olympus lenses, mostly Pro ones. If you are new to Micro 4/3, or if you additionally need to purchase multiple lenses in order to use some of the capabilities of the new camera that are important to you, the decision becomes a lot more complex.

As discussed above, there is no question that the OM-1 is a better, more modern and more capable camera than the E-M1 Mark III. However, the latter camera is also much cheaper than the OM-1, especially now and in the immediate future while both camera models are still available but the E-M1 III is scheduled to be discontinued.

That said, neither of these two camera models is a magic bullet. For example, improvements in dynamic range and high-ISO noise with respect to earlier models are only incremental. Don't expect either camera model to magically eliminate high-ISO noise. At best, it will only reduce it by 1-2 stops (depending on how old your current camera is).

First of all, you need to decide whether there are features available in the OM-1, but not in the E-M1 III, that are a deal breaker. For example, if you shoot birds or types of motor sports where subject tracking is paramount, then the OM-1 will, very likely, allow you to reliably take shots that are problematic (i.e. will depend on sheer luck) with the E-M1 III. If the OM-1 does not have any such advantage that is significant for you today, or likely to become significant in the next 2-3 years, then an E-M1 III may be a more reasonable choice. You might be able, for example, to use the saved money to buy a new Pro lens that, together with your new E-M1 III, significantly extends the range of photography you can perform today.

If you currently own an E-M1 Mark II: I do not recommend that you upgrade to an E-M1 III. The differences are just too small to justify the cost. If you can afford the upgrade to the OM-1, and you can justify the OM-1 based on your photography needs and plans, then go for it. Otherwise, you could wait a while and see what else OM System will come up with next.
If you currently own an original E-M1 "Mark I": The E-M1 III is so much better than the Mark I, that if you are currently struggling with AF and other technical limitations, this upgrade is likely to improve your photography. At the same time, the OM-1 is such a step up from the Mark III that it constitutes a far better long-term strategy. Again, the choice depends largely on how much you can afford to spend today and on whether you really need some OM-1 capabilities not available in the E-M1 III.
If you currently own an E-M5-series or E-M10-series camera: Either the E-M1 III or the OM-1 are a large step upwards in every technical respect. If you are struggling with technical limitations of your current camera, it is likely that an upgrade will do you good. However, you need to take an informed decision. In particular, since these camera series were usually sold with non-Pro lenses, you must make sure of whether the technical issues you are struggling with also require better, more expensive lenses.

Summary

The OM-1 is a substantial improvement on the E-M1 II/III and X. In particular, the OM-1 substantially improves on the E-M1X, in a package of practically the same size and weight as the E-M1 II/III, and a price just 150 € higher than the E-M1X current price. At times it can be difficult to find an OM-1 at a non-inflated price, in part because of the much higher demand than anticipated by OM System. The price of the OM-1 is relatively high in a Micro 4/3 context, but definitely low when compared with full-frame flagship mirrorless cameras of other brands.

Olympus E-M1 Mark II versus OM System OM-1