Olympus 300 mm f/4 Pro
The Olympus 300 mm f/4 Pro is one of the largest (227 mm long, 92.5 mm wide not counting the tripod shoe) and heaviest (1.48 kg including the tripod shoe) native lenses for Micro 4/3. It was released in 2016 after some delay from the initial schedule and a design change to add in-lens image stabilization (IS). Prior to its release, the Micro 4/3 system contained only an Olympus 75-300 mm f/4.8-6.7 and a Panasonic 100-300 mm f/4–5.6 zoom reaching 300 mm. These two zooms are compact and lightweight, but neither of these two lenses provided a really good image quality at 300 mm.
Nikon has a 300 mm f/4 that uses an internal Fresnel lens surface to correct chromatic aberration and allows substantial savings in lens physical length and weight, albeit at the price of introducing a novel type of flare. Fresnel lenses have been used as collimators for almost two centuries. Canon's "refractive" optics in, e.g., their 300 mm f/4 provide an apochromatic correction, totally unrelated to Fresnel lenses. Canon's choice of the "refractive" name for this technology is possibly a way to avoid the old "apo" or "apochromatic" denomination, much abused in the past by brands like Sigma (Sigma Apo lenses are not apochromatically corrected). It is nonetheless remarkable that the Canon marketing people failed to make up a catchy new term, and used an exceedingly old one (the phenomenon of refraction has been used for 27 centuries, and mathematically understood for 10 centuries). If it is correct that the Canon "refractive" lens technology (also called, more informatively, "optimized refractive-index distribution" in Canon's patents) is a type of radial gradient of refractive index, then the technology is sophisticated, but not novel because it was patented earlier, e.g., in the 1980s by Xerox (US patent 4373780 A) and 1990s by Minolta (US patent 6166862 A), and its optical theory understood since much earlier. Olympus does not claim the use of "new" technologies in the 300 mm f/4 Pro, other than the use of three special types of optical glass in addition to more common ones.
It should be remembered that the Olympus 300 mm is designed specifically for Micro 4/3 sensors, while Canon and Nikon 300 mm lenses cover full-frame sensors and "waste" much of their image circle on APS-C cameras. Therefore, testing these Canon or Nikon lenses on APS-C cameras is not really fair. Even taking this into account, the Olympus 300 mm seems nonetheless to have an edge over the Canon and Nikon offerings in terms of image quality, at the expense of lens size, weight and price.
Roughly at the same time as the Olympus 300 mm, Panasonic relased a 100-400 mm f/4.0-6.3. The 100-400 is significantly lighter, smaller (albeit extends by another 76 mm when zoomed to 400 mm) and much cheaper. In fact, you could buy two 100-400 for about the price of one 300 mm and MC-14 teleconverter.
Having decided to get a long telephoto lens, or a long telephoto zoom, of top quality for Micro 4/3, my only reasonable choices were the Olympus 300 and Panasonic 100-400. Already owning the Olympus 50-200 for 4/3 and Panasonic 100-300, I was not particularly interested in the 100-200 mm range. In the past, I used for years two long telephoto zooms on APS-C DSLRs (Sigma 100-300 f/4, with internal focus and zoom, and Sigma "Bigma" 50-500 f/4-6.3, which grows out like Pinocchio's nose when zooming). I was not impressed by the image quality of these Sigma and Panasonic zooms (the Olympus 50-200 is far better). While a zoom is faster and easier to use than a prime lens with teleconverter, it is a well-known fact that telephoto zooms are best near the low end of their zoom range, while the overwhelming majority of photographers (me included) use them at the opposite end of the zoom range. Unless the ease of use of a zoom is more important than image quality, I would bet on a prime lens. Heck, even the Olympus 500 mm f/8 catadioptric lens produces a better resolution than the Sigma 50-500 at 500 mm.
Combining together these past experiences of mine, as well as the tests and sample images from both lenses available on the Internet, the Panasonic 100-400 left me the impression of a consumer lens designed as a compromise in which price and weight play a major role. Basically, I was afraid that with this lens I would get just a big brother of the Panasonic 100-300, and this was simply not good enough. This time, I wanted something decidedly better while still portable (which ruled out the Olympus 300 mm f/2.8 and 90-250 mm f/2.8 for 4/3), so I bit the bullet and went for the Olympus 300 mm f/4 Pro.
In published tests and reviews, the Olympus 300 mm f/4 has been called the finest Olympus lens so far, and one of the best ever among telephoto lenses for any system. With these credentials, I was left with no credible alternatives. The Olympus 300 mm, at last, was designed to be the best in its class, with cost and weight being subordinate factors. The Olympus 300 mm is more expensive than other comparable top-notch lenses, including the latest Nikon and Canon 300 mm f/4. Compared with refractor 600 mm telephoto lenses for full-frame like the traditional Canon and Nikon ones, which give similar images, the Olympus 300 mm is, however, much smaller, lighter and cheaper.
The Olympus 300 follows the same style as earlier Olympus Pro Micro 4/3 lenses, which means a finely machined metal focus ring sits roughly halfway on the barrel surface. The metal focus ring pulls back to disengage AF and display a distance scale for manual focusing. Three switches (focus limiter, IS on/off and the programmable L-Fn button present on all Pro lenses) are placed on the left side, near the tripod collar. The focus limiter provides 1.4-4 m, 1.4-∞ and 4-∞ intervals.
All external parts are metal, except for the lens shade, which telescopes back around the front of the lens for storage. Therefore, there is no need to remove the lens shade (and no way to do so that I can easily see). To fully extend the lens shade, pull it outward until it stops, then turn it clockwise (as seen from the rear of the lens) until it engages a thread hidden under the lens shade and stops after about half a turn. Now the lens shade is locked in position, and putting down the lens onto its lens shade will not cause the lens shade to collapse back onto the lens barrel. Repeat the procedure in reverse to put the lens cap in place and prepare the lens for storage.
The interior of the lens shade is coated with a synthetic felt-like layer, unlike the lens shade of the 40-150 (which is built like the optional lens shade of the 60 mm macro, i.e. with concentric plastic rigdes to block stray light and deep longitudinal grooves to slide on cams of a plastic ring attached to a bayonet mount at the lens front).
The filter mount accepts 77 mm filters. Before you are tempted to mount a protector or UV filter there, there are reports of third-party filters of known brands causing a detectable degradation of image quality on this lens. Perhaps the Olympus Nano 77 mm protector filter can be used on this lens, but it is quite expensive and I would like to see some evidence of good results before opening my wallet.
The lens collar/tripod shoe is solid and, as typical of telephoto lenses, rotates for shots in portrait orientation. Unlike other Olympus lenses, including the 70-150 f/2.8, the tripod shoe of the 300 mm has lengthwise machined slots that fit in an Arca-compatible clamp or tripod head. PerhapsOlympus got the idea late under development, since the 70-150 lacks this feature, and I think I saw pre-production specimens of the 300 mm lacking this feature. It is so useful that adding it to a revised version of the 40-150 would be a significant enhancement at a low cost for Olympus, now that virtually all top-quality tripod heads are Arca-compatible.
The tripod collar can be removed by releasing its locking knob and rotating it almost (not exactly) half a turn. A smooth metal ring, quite lightweight, is enclosed with the lens and can be mounted in place of the tripod collar to protect the cams holding the tripod shoe onto the barrel and to give the hands a smoother surface for holding the lens. This ring also gives a better esthetic impression of the lens, if you like this sort of things, but you need to remove the ring before putting the tripod shoe back. Of course, it is entirely possible to use the 300 mm hand-held without removing the tripod collar (you can rotate the tripod collar so that the shoe is out of the way), and you can attach an extra neck strap to the tripod shoe. I do this with all my long lenses, since it avoids putting unnecessary mechanical stress on the lens mount and camera body by forcing the latter to carry all weight. The lens strap also lets me switch lenses more easily by leaving the telephoto lens hanging around my neck instead of having to put it back in the bag.
The electronics are safely tucked away from sight inside the lens, so I can say nothing about them, except... that the lens mount has two extra electrical contacts. I have seen these contacts before only on the Olympus 40-150 mm f/2.8 Pro for Micro 4/3. I found no online explanation of these contacts, so I can only offer my educated guess that they are used with the MC-14 teleconverter and one or more "mystery" accessories (so far not announced by Olympus) that will also mount between camera and lens. These future accessories may be as straighforward as a 2x teleconverter (Olympus already has 1.4x and 2x teleconverters for 4/3), or something different, perhaps even surprising like a 2x teleconverter to use Micro 4/3 lenses on a future Olympus full-frame mirrorless body. Two contacts in combination with two logical states (grounded and no connection) allow for recognizing up to three different accessories (plus the "no accessory" state), and with three states (grounded, + voltage, no connection), or a serial communication protocol, more accessories can be recognized. The lenses can be made compatible with future accessories through a firmware upgrade.
At f/4, which already provides the best image resolution, enough light is captured to allow reasonably short exposures without pumping up the ISO to extreme values. As usual with Micro 4/3 lenses (of any focal length), diffraction sets in at f/8, and the rest of the narrower apertures are mainly available as a cultural throwback to a long-gone time when there were good reasons for shooting at f/22 and f/32 on medium and large film formats, or as a compromise when DoF is more important than fine resolution.
The minimum focus distance is about 1.3 m, which produces a magnification on-sensor of 0.48x, i.e. a field of view of less than 36 x 27 mm (45 mm diagonal). This is as good as many legacy macro lenses, which typically reached only 0.5x. So this is clearly a good lens for close-up, almost macro work. In practice, this requires a solid tripod or an exceptionally steady hand to have any chance of success. Before anyone starts complaining that DoF (depth of field) of this lens is too shallow for close-up work, this is a common error among photographers (but a glaring error nonetheless). The DoF of a lens does not depend on its focal length, only on magnification and on the acceptable CoC (circle of confusion), so this 300 mm gives you exactly the same DoF as a 30 mm macro lens at the same magnification and on the same camera. The only thing that changes is perspective. A telephoto lens "magnifies" a distant, out-of-focus background with respect to the subject, compared with a lens of short focal length shooting the same area of the subject.
The rear optical element is deeply recessed within the lens mount. This allows the use of the Olympus MC-14 teleconverter, which has a projecting front element. The MC-14 provides a 1.4x multiplier factor of the lens focal length, i.e., the 300 mm becomes a 420 mm f/5.6, still of exceptionally good image quality. With this teleconverter, the 300 mm effectively removes the focal-length advantage of the Panasonic 100-400 and keeps a half-stop speed advantage over the latter.
On the Olympus E-M1, S-AF (single-AF) uses only contrast AF, while C-AF (continuous-AF) uses a combination of contrast and phase AF. In S-AF mode, autofocus can be a bit slow with this lens. It is faster in C-AF, so there is no real reason to use S-AF unless it is necessary to shoot sequences faster than allowed by C-AF. It is possible that earlier firmware versions of the E-M1 used phase AF also in S-AF (see Dpreview), or that the reported behavior was a different type of AF bug in earlier firmware.
The E-M1 switches contrast AF off and uses only phase AF when it detects a 4/3 lens. It never does this with a Micro 4/3 lens.
On cameras capable only of contrast AF (which means at present all except the E-M1), use S-AF for fast sequences, C-AF for subjects that can move in and out of focus, and your preference of S-AF or C-AF in all other cases.
The higher lens speed of the 300 mm over the Panasonic 100-400 is significant for a faster and more precise AF performance, especially if phase AF is used. The phase sensels need to receive light from two sufficiently separate, oblique directions, and do not record light hitting them straight-on. If the cone of light focused onto a phase sensel is too narrow, as typically produced by a slow lens, the phase sensel is blind. This happens regardless of the amount of subject illumination. Contrast AF, on the other hand, gradually deteriorates when the overall illumination level decreases, but is not sensitive to intrinsic lens speed to the same extent as phase AF. Therefore, even a slow lens can still use contrast AF if subject illumination is bright and DoF is not extremely high.
The f/5.6 speed of the 300 mm + MC-14 is probably at the limit of the phase AF of the E-M1, while the f/6.3 of the Panasonic 100-400 at its telephoto end may be too slow for phase AF, so the E-M1 may be forced to use only contrast AF with this lens at 400 mm FL.
Of course, also phase AF works better and faster in abundant illumination. For good measure, if you need fast and accurate C-AF, don't use the MC-14 with the 300 mm and E-M1 unless really necessary.
The 300 mm f/4 is Olympus' first lens to use in-lens IS (image stabilization). This does not mean that you can use this lens like earlier Panasonic lenses, which provide IS to cameras devoid of in-camera IS. Instead, the 300 mm has a special in-lens IS designed to work together with the in-camera stabilization of Olympus high-end cameras (only E-M1 and E-M5 Mark II, plus of course the coming E-M1 Mark II) to provide an enhanced stabilisation over the one already provided by the in-camera IS. In practical use, exposure times with the Olympus E-M1 and this lens can be as low as 1/10 s. The coming E-M1 Mark II is said to do even better.
It has been stated that rotation of the Earth, rather than the IS system of the E-M1 Mark II, places a limit on the performance of IS with this lens and camera. I assume this means that rotation of the Earth is detected by the camera's accelerometers, but the fact that the subject is moving together with the camera and Earth surface is not compensated for by IS, which assumes that the subject is simply stationary in space. Improving IS beyond this point would require the camera to factor into the IS computation also the exact latitude and the exact direction the camera is pointed to. At this point, altitude and the difference in latitude between camera and subject would start to play a role, and then the Earth's orbit around the sun, etc. Everything was simpler in the good old times when the Earth was immobile at the center of the universe, and that was the end of the discussion. Now even our cameras are reminding us that things are more complicated than that.
Switching off IS with the switch on the lens also switches off IS in the camera. You cannot have one on an the other off.
IS only compensates for camera motion, not subject motion. Therefore, a moving subject will require a suitably short exposure. Nonetheless, exposure times that used to be restricted to a 28 mm or shorter hand-held lens when IS did not exist are now possible with a hand-held super telephoto lens.
IS does not work equally well with subjects in the close-up or macro range. Camera movements in the sensor plane cause a change in perspective, and there is no way to compensate for that by moving the camera sensor (the lens would have to be moved as a whole, together with the sensor). Therefore, successful close-up photography requires shorter exposure times than possible with distant subjects. On the other hand, electronic flash can often be used in close-up photography, greatly lessening the effects of camera shake. Incidentally, the E-M1 in silent shutter mode does not trigger the flash (except in combination with special modes like focus stacking), so you must shoot in normal (mechanic) shutter mode with a flash. It is probably just as good to switch off IS with a flash, since IS probably is not able to respond effectively in the millisecond or less of flash duration.
Even with IS enabled, achieving the maximum sharpness of which this lens is capable requires the use of silent shutter mode, i.e., electronic-only shutter (see also the tests on imaging-resource.com). This applies to tripod as well as hand-held shooting. So, once more, to fully take advantage of the quality of this lens, you need a camera body capable (among other things) of electronic shutter operation.
Silent shutter mode is not completely silent or free from mechanical movements, except at f/4. At slower apertures, the lens diaphragm still has to close at the beginning of the exposure, and re-open at the end. The noise is audible only close to the camera, and the amount of vibration must be minimal. Still, it is not zero.
Silent mode has a configurable delay from 0 to 30 s. Even with IS off, the characteristic white-noise hiss of IS is still audible, not only during the actual exposure but also during the programmable delay that precedes the silent exposure.
Anti-Shock mode is second-best to silent shutter, and superior to normal shutter operation in this respect, but uses electronic front shutter curtain only at exposure times of 1/320 s or shorter, and even then it is not as good as silent mode. The mechanical shutter works as usual at longer exposure times, even with Anti-Shock enabled.
A telephoto lens can be used in two ways: mounted on a tripod, or hand-held. Super-telephoto lenses, on full-frame and APS-C cameras, are lenses with focal lengths starting at 500 or 600 mm. They are designed to be used on a tripod, and if you want to try hand-holding them, the lens maker will not even suggest a way to do that. Somewhat shorter focal lengths (300-400 mm, or possibly even 200 mm) qualify as a long telephoto on these formats. Some of them can be hand-held, especially the f/4 and slower ones, but almost all have a lens collar for mounting on a tripod. 135-150 mm lenses are regarded as medium telephoto, and are designed to be hand-held. Many don't even have a lens collar.
The Olympus 300 mm lens, in this context, is a super-telehoto lens for what concerns the field of view (equivalent to a 600 mm on full frame), but only a long telephoto lens for what concerns its physical size and weight. Since only the final pictures count for me, and I have no customers to impress with the size of my gear (the "my lens is longer than yours", or "real photographers don't use small format cameras" attitude), I regard this lens as a super-telephoto. The f/4 aperture places the Olympus 300 mm among other lenses that can be hand-held for rather lengthy sessions. My arms are not especially strong, and I find no joy in physical exertions, but I can manage 20 minutes holding this lens in shooting position without breaks, if I have to. I also find that lowering the lens and letting its weight rest on a neck strap for a few seconds now and then greatly helps to avoid fatigue. Compared to this lens, I find a front-heavy zoom like the Sigma 50-500 far less manageable in spite of being only about 300 g heavier, and I can track a subject by hand with a 300 mm f/2.8 (about twice as heavy) for only a couple of minutes before needing an armchair and a cold drink.
The main problem with hand-holding the Olympus 300 mm f/4 is not muscle fatigue, but finding the subject while looking through the viewfinder, especially with subjects like flying birds. This is where the 300 mm behaves exactly like a super-telephoto lens for larger formats. If you are new to super-telephoto lenses, this problem will be an unpleasant surprise. You see a bird gliding by steady and on a predictable landing path. Following the (good) advice you read on a web site while preparing for your first outing with the 300 mm, you point the lens along the line of sight, then lift the camera to eye level while keeping your eyes on the bird until the last instant. As you peer through the viewfinder, you see... an empty patch of sky. You panic and swing the lens around to find the bird, and still find nothing but a cloud and a couple of tree branches. Meanwhile, the bird has landed on a perch against an un-photographable background and looks at you disapprovingly. You try again with the next five passing birds, and manage to take home a picture of a bird's left wing, sticking out from the edge of the frame. You start thinking that maybe bird-in-flight photography is not your thing after all, and wondering how much your just-out-of-the-box Olympus 300 mm will fetch on eBay.
Fortunately, Olympus has an innovative solution for this problem: the red-dot-sight EE-1.
Inexperienced long-telephoto lens users are also confronted with another common problem: the inability to obtain sharp pictures, no matter what tripod and tripod head they use. It is especially common for first-time purchasers of a 500 mm f/4 or 600 mm f/5.6 lens to fail in this respect, and to blame the problem on poor lens quality. Many of these first-time users end up returning or selling the lens after a while. Most often, the problem is shutter (and, in DSLRs, mirror) vibration. The solution with the Olympus 300 mm and E-M1 is discussed in the next two sections.
Useful E-M1 settings with EE-1
E-M1 settings that help the use of the EE-1 (in addition to silent shutter and other settings discussed elsewhere on this page):
And finally, don't forget to use the focus limiter and the IS On switch on the 300 mm.
Tripod, head and supports
A solid tripod and a tripod head suitable for both static and panning shots with a super-telephoto lens are necessary to take full advantage of this lens. I do not make specific recommendations of a head for this lens, because there are many different types, suited to different subjects and different ways of shooting. See for example the Sunwayfoto XB-52 for a general-purpose, sufficiently large ballhead. Large dampened video heads like the Manfrotto 501 are also useful with long telephoto lenses. Bird photographers often use gimbal heads, which normally are not locked because they are designed to provide a perfectly balanced lens regardless of its tilt angle.
A tripod simply needs to be stiff and heavy. The best tripod for a telephoto lens is usually the heaviest professional tripod that you can manage to carry to the field location. This usually means one of the largest carbon-fiber tripods like the Gitzo series 5, because large aluminium tripods are generally too heavy for field use.
In general, you should choose a tripod with at most 2- or 3-section legs. If you have a tripod with 4- or 5-section legs, extend only one or two of the thickest sections of each leg (of course, this means that you will have no use for the additional leg sections, but still have to carry their weight in the field). The Gitzo series 4 is next best. Gitzo series 3 tripods are a bit too slim and lightweight, but you can use them (or even a Gitzo series 2) if you do not extend the legs at all.
If the tripod has a central column, replace it with a low-profile plate if possible, or at a minimum, never extend the column. Be prepared for a suitable tripod and head being as heavy as the rest of your field kit, including backpack and all.
If you are satisfied with the idea of shooting from near ground level and lying belly-down on the ground, a mini tripod, if sturdily built and equipped with a professional head, can be as steady as a much larger professional tripod. In this context, tripods (of any size) that allow their legs to be splayed wide become very stable ground-level platforms, and are far more versatile than those with a restricted amount of leg opening.
Tripods equipped with a central column, as well as video tripods with the legs mechanically joined to each other by a "stabilizer", are of course unusable in this context.
Wildlife photographers often suggest placing the left hand on top of the lens barrel, directly above the tripod shoe. The reason is that a hand in this position may help to absorb shutter vibration before it has a chance to travel to the front of the lens and back. A hand is often regarded as superior to a sand-bag for this use. If the E-M1 is used in silent shutter mode, there is no shutter vibration, and this reason does not exist. Still, the weight of a hand or sand-bag on the lens barrel may help to reduce lens movement induced by wind, which is another important disturbance. This is still a problem with the 300 mm. 600 or 800 mm super-telephoto lenses make larger sails that catch more wind, but a ligher lens is more sensitive to wind than a heavy one. Hanging a camera bag, backpack or sand-bag from a hook attached under the tripod, where the three legs meet, usually helps somewhat.
With a tripod-mounted E-M1 and 300 mm, it may be a good idea to use a wired remote control to trip the shutter. When using a dampened video head to track the subject, leave the camera and lens alone, and touch only the handle or lever that operates the video head. The remote control can be operated by the same hand, or by the other hand (which usually has nothing else to do).
A monopod is also useful for lengthy hand-held sessions where the subject does not move much, or only slowly. The advantage of a monopod is relieving your arms from the need to hold up the camera and lens, rather than steadying them. In fact, a monopod does almost nothing to prevent uncontrolled side-to side swinging movements, while it makes intentional changes in tilting difficult. A monopod can be equipped with a monopod head (i.e., a head that only allows tilting and no other movement) and the head can be unlocked to allow tilt changes. Lock the head afterwards, because leaving it unlocked adds one more degree of freedom of movement to the already unstable monopod. Some monopod heads can be partially locked to allow intentional changes in tilt with a moderate effort, while preventing accidental changes.
Improvised long-lens supports like thick tree branches, fences and rolled-down car windows (as long as the car engine is not running) are often more stable than a monopod. Use these supports when available. You can even improve stability by leaning a monopod against a vertical tree trunk. Even resting a hand-held long lens against a vertical tree trunk is preferable than bare hand-holding. A sand-bag or bean-bag placed between the lens and an improvised support makes it easier to support the lens at the correct orientation.
I only recently started to use this lens for wildlife photography. The following samples are in fact from my first and third day in the field with this lens. All samples were shot hand-held with the 300 mm at f/9.5 on an Olympus E-M1 Mark II at ISO 200 and S-AF on one AF target (usually located in the center of the image). Each pair of pictures shows (1) the whole frame, reduced, and (2) a 1:1 crop near the center of the image. The MC-14 was used in some of the samples as indicated in the captions.
In short, the 300 mm f/4 Pro, judging from these early images, is one of the best lenses I ever used, and quite likely the best long telephoto lens I used. There is a moderately visible loss of resolution with the MC-14 teleconverter, but I still would rate these pictures as good to very good.
There are already plenty of sample images shot with this lens on the web. However, I did not see many illustrative samples at or near the minimum focus distance. The following samples are shot in the studio with illumination by a Trond LED panel and the camera mounted on a sufficiently sturdy tripod and head (although the head did sag slightly but visibly in the course of a few minutes). The focus distance is just shy of minimum (1.4 m), in order to allow manual focusing on the detail of interest (the head of the fossil, slightly right- and top-of center in the image). Manual focus with the E-M1 is greatly helped by using maximum magnification on the LCD screen and focus peaking on the area of interest (in this case, the head of the fossil).
Although image quality is still quite good even at f/16, images between f/4 and f/8 have the highest resolution, as expected of a diffraction-limited lens. Since this is a lens with internal focus, it does not keep its 300 mm focal length at close-up focusing distances, although it does not seem to be as bad an offender, in this respect, as other lenses I have tested. It is also quite possible that internal focusing makes the effective aperture slightly faster than expected from a lens of constant focal length at the same magnification (e.g., nominal f/4 at 0.5x should become effective f/5.6, but if the focal length changes, the effective aperture may instead remain somewhere between f/4-f/5).
In close-up photography and macro photography, the photographer is usually free to frame and compose, without resorting to extensive cropping in post-processing. Therefore, in this type of photography, a sufficient DoF is often more important than a high resolution on a pixel-peeping level. Therefore, I would not exclude shooting at f/11, or even f/16, with this lens in the close-up range.
One limitation of the 300 mm in this application is the fact that manual focusing is by-wire, not by mechanically coupling the focus ring to the internal focus helicoids. This means that manual focus takes place not continuously, but by discrete increments. These discrete increments are small and unnoticeable with distant subjects, but near the minimum focus distance just one focus step, corresponding to turning the focus ring by a fraction of a mm, already makes the difference between a perfectly focused image and a significantly unfocused one (as seen in magnified live view).
If perfect focus is necessary, it may be necessary to do the same as recommended with macro lenses:
A coarse-focus microscope focusing rack is good enough for this application, but the large majority of photographic focusing racks are not.
For advanced macrophotographers, there is the additional possibility of using in-camera focus bracketing to collect a series of images while varying the focus plane, and post-processing the series with focus-stacking software. As implemented in Olympus cameras, focus bracketing starts at the chosen focus position and proceeds outwards, allowing a programmable number (up to 999) of images, but the process always stops if focus reaches infinity before the chosen number of images is reached.
In-camera focus stacking is not available with this lens.
The Olympus 300 mm f/4 is an uncompromisingly excellent super-telephoto lens bringing wildlife photography (and other types of photography that require such a lens, including close-up photography at a high physical distance) available at a professional level to Micro 4/3 users. However, only owners of one of the top-level Olympus camera bodies who take the time to learn using this lens will achieve this lens' full potential. With consumer or semi-pro cameras, you may not see a significant difference from other, cheaper lenses. If you need the speed of changing focal lengths that only a zoom can provide, and don't mind a somewhat lower image quality, then the Panasonic 100-400 may be the right alternative. If you need the very best image quality and IS, and are willing to pay the higher price, this lens has no real competition.
The EE-1 red-dot-sight and MC-14 teleconverter are extremely useful, in fact almost indispensable, for use with this lens, in addition to a solid tripod and head.