Olympus MC-20 teleconverter for Micro 4/3

Some professional photographers openly express a strong dislike for teleconverters, and seem to regard them as gadgets that only an amateur would use. Other professional photographers do use teleconverters, albeit sometimes without openly disclosing this fact to their customers. One of the reasons for the bad name of teleconverters is that, in the past, most of these accessories were cheaply produced gadgets of questionable optical quality. Some of the most famous camera makers, like Nikon and Canon, also made teleconverters, albeit of better quality and accordingly priced, and optimized for use with their premium telephoto lenses.

I have owned in the past Vivitar, Nikon, Kenko and Sigma teleconverters, and found them of variable quality. Sometimes, a given teleconverter seemed to perform better with certain lenses, an another teleconverter with a different set of lenses. The quality of the lenses I used with teleconverters, in general, had an even greater impact on image quality than the teleconverters themselves. Even a well-designed teleconverter does magnify the optical aberrations of a lens by the same amount it magnifies the center of its image circle, and starting out with a cheap consumer-level lens is not a reasonable way to guarantee excellent results.

Another reason for the bad name of teleconverters is that many amateur photographers in the past used to buy a third-party teleconverter and mounted it on a 50 mm lens, or at most a 100 or 135 mm short telephoto. Such a combination is not likely to work as well as with a good telephoto lens of longer focal length, and the resulting focal length becomes barely equivalent to a medium telephoto lens, despite the (often excessive) hopes of these photographers.

The loss of effective lens speed implicit in a teleconverter (1-2 stops) was also unexpected or poorly understood by many amateurs, and often blamed as a fault of their particular teleconverter. It is instead an unavoidable limitation of all teleconverters, regardless of their individual design and quality.

A few 3x teleconverters were introduced in the film era. Even when coupled with the best super-telephoto lenses, results were typically mediocre. They did make sense as the only practical way to magnify an image beyond the limitation of existing focal lengths, but the unavoidable loss in image quality and lens speed today makes electronic zoom and AI image enhancement a better solution. 1.4x and 2x teleconverters of good quality, however, are still very useful with digital cameras.

Olympus MC-20 (left) and MC-14 (right), lens side.

After the Olympus MC-14, the MC-20 is the second native teleconverter for the Micro 4/3 lens system introduced by Olympus. Like every 2x teleconverter, the MC-20 doubles the effective focal length of the lens it is mounted on, and reduces its speed by two stops. Thus, for example, it turns the Olympus 300 mm f/4 lens into a 600 mm f/8. Modern Micro 4/3 cameras recognize this teleconverter and automatically adjust to the effective focal length and effective aperture, which are displayed on the LCD screen and in the EXIF data. This is required, among other things, for sensor-based IS (image stabilization) to work correctly. Lens-based IS works the same even when a teleconverter is used.

According to asia.olympus-imaging.com, image stabilization on the 300 mm with MC-20 is equivalent to 5 aperture stops, while the lens alone is rated at 6 stops. This means that there is a minor drop in IS performance with the teleconverter. What Olympus calls 5-axis image stabilization remains available also with the MC-20.

Other teleconverters for Micro 4/3 and 4/3 lenses

I earlier reviewed the Olympus MC-14 1.4x Micro 4/3 teleconverter here.

Panasonic has 1.4x and 2x Micro 4/3 teleconverters, i.e. the DMW-TC14 and DMW-TC20, specified for use with the H-ES200 & H-ES50200 lenses and particularly expensive. Their front elements project approximately as much as the Olympus counterparts, but the clear diameter of the DMW-TC20 is larger than the Olympus MC-20. They also seem to have the same extra front contacts as the Olympus ones. I do not own either of them, have not tested them, and have no idea whether they might be compatible with Olympus lenses.

The legacy Olympus EC-14 1.4x teleconverter works well with certain 4/3 telephoto lenses, including the Olympus Zuiko Digital 50-200 mm f/2.8-3.5 SWD, and its use on Micro 4/3 cameras requires a 4/3 to Micro 4/3 adapter. In my experience, autofocus with 4/3 lenses, and especially with the EC-14, works well with high-end Micro 4/3 Olympus cameras (E-M1, E-M1 II, E-M1 III and E-M1X). I do not use current consumer-class Olympus cameras or any Panasonic Micro 4/3 cameras, and I do not know how well their AF works with 4/3 lenses. AF with the 50-200 SWD was far too slow to be usable on the original E-M5.

The legacy Olympus EC-20 is a 2x teleconverter for 4/3 (not Micro 4/3) lenses. I have no experience with the EC-20. It is said to be mechanically compatible with all 4/3 lenses.

Naturally, the EC-14 and EC-20 are physically incompatible with Micro 4/3 lenses.

A few modern high-end supertelephoto lenses have a dedicated teleconverter permanently built-in the lens barrel, that can be inserted into the optical path of the lens with a mechanical slider. The Olympus M. Zuiko Digital ED 150-400mm f/4.5 TC1.25X is currently the only such lens I am aware of in the Micro 4/3 system.


At present, the MC-20 is only compatible with the Olympus 40-150 mm f/2.8 Pro, 300 mm f/4 Pro and 100-400 mm f/5-6.3 IS. The first two of these lenses may need a firmware update to work correctly with the MC-20. The Olympus M. Zuiko Digital ED 150-400 mm f/4.5 TC1.25X is also said to be compatible with the MC-20. These compatible lenses have additional electrical contacts on their mounts that match a corresponding contact on the front of the teleconverter. This contact is located at different positions on the MC-14 and MC-20, allowing the lens to detect which of the teleconverters is being used.

The MC-20 and MC-14 have no updatable firmware, and they are invisible to the Olympus Digital Camera Updater app.

The projecting front optics of the MC-14 and MC-20 physically prevent mounting either teleconverter on other Olympus lenses than those mentioned above. For the same reason, it is also physically impossible to stack two Olympus Micro 4/3 teleconverters on top of each other. Although the rearmost element of the MC-20 is perhaps sufficiently recessed not to collide with the front of the MC-14, the projecting barrel at the front of the latter is too wide to enter the rear of the MC-20.

A few photographers specializing in macrophotography have reported that it is possible to mount an Olympus 60 mm f/2.8 macro lens on the MC-14 or MC-20 via one or two extension tubes equipped with electrical contacts, in order to achieve magnifications significantly higher than 1x with this lens. Some extension rings do not allow this because their inner diameter is too low. Naturally, this use of extension rings prevents the lens from focusing at infinity. This arrangement may also introduce curvature of field, spherical aberration and other optical problems, because it forces the lens to operate well outside its design parameters.

The MC-20 is physically (and often optically) compatible with most or all SLR and DSLR lenses mounted on Micro 4/3 cameras via a lens adapter. See for example my test of four legacy macro lenses in Nikon F mounts with the MC-20 and Olympus E-M1 II.

Mechanical and optical build

The MC-20 is relatively lightweight (150 g without caps) and adds 25.9 mm to the physical lens length. In comparison, the MC-17 adds 14.7 mm to the lens physical length. The exterior of the MC-20 is metal, with the exception of the plastic lens release button and other small details. The projecting front optics are surrounded by a synthetic rubber guard that prevents the optics from directly touching the rear parts of the lens, e.g. when attempting to mount an incompatible lens on the teleconverter.

The MC-20 contains 9 elements in 4 groups and is therefore optically more complex than the MC-14 (6 elements in 3 groups). The MC-20 has weather-proof seals, but relies on the lens to provide a rubber seal "skirt" around its rear mount. The front cap of the MC-20 is the proprietary BC-3 also used on the MC-14. A normal camera body cap does not fit on these teleconverters.

The diameter of the front optical element is narrower than in the MC-14, which is reasonable considering that the MC-20 enlarges a smaller portion of the image circle produced by the lens. A smaller front element also helps to reduce flare and loss of contrast that could be caused by strong light sources within the lens' field of view. The front element projects from the front mount by a similar amount as in the MC-14. The rear element of the MC-20, on the other hand, is much more recessed than in the MC-14, in which it is flush with the lens mount. This, together with the higher number of optical elements, explains the significantly higher length of the MC-20. Both converters feel heavy for their size, the MC-20 more so than the MC-14.


Olympus recommends mounting the MC-20 on the camera first, then adding the lens on the MC-20. I usually do the opposite because I find it more practical. When I use a teleconverter, it usually sits on the 300 mm f/4 for the whole session, but I may need to alternate between this lens and a medium- or wideangle zoom once in a while. I do recognize that Olympus' suggestion is meant to place a lesser strain on the lens mount of the camera body, but with reasonable care (e.g. by holding the lens + teleconverter still with one hand and "screwing" the camera body onto the rear of the teleconverter with the other hand) the same goal can be achieved.

The 300 mm lens handles pretty well with or without a teleconverter attached. However, the change in lens balance with the MC-20 is more noticeable than with the MC-14. With the 300 mm alone, holding the lens with the left hand under the tripod shoe places virtually all the weight on this hand. With the MC-20, the right hand feels the weight of the camera body, which in itself results in a better weight distribution. On a gimbal head, on the other hand, the lens with MC-20 is rear-heavy, and must be mounted in a more forward position to be fully balanced.

A focal length of 600 mm on Micro 4/3 is equivalent in field of view to 1,200 mm on full-frame. This means that hand-holding requires image stabilization to be configured to run whenever you half-press the shutter button. The image in the viewfinder jumps around uncontrollably without IS. In most cases, atmospheric turbulence (in particular, rising air heated by contact with the ground) is the factor that limits image resolution, rather than the camera optics. With subjects located at more than roughly 50 m from the camera, shooting above cold water, as well as shooting early in the morning before or at sunrise, generally gives better results than shooting over land and in the middle of the day.

Olympus 300 mm f/4 and MC-20, hand-held, not cropped.

The extremely long focal length can also make it infuriatingly difficult to find the intended subject in the viewfinder. When no reference points around the subject are available, the generic "trick" of fixing your gaze on the subject, then (without averting your sight) lifting the camera and lens to your eye can help, especially with stationary subjects. This is how I repeatedly framed the moon in a cloudless sky, e.g. in the above shot, with good repeatability and relatively litle "hunting" for the subject. In the field, when reference points are available, I frequently locate a static subject in the field by initially pointing the lens by panning horizontally to an easily located reference like an object on the horizon, then alternately panning and tilting the lens to locate the subject. I intentionally avoid panning and tilting at the same time, because this makes it twice as difficult to find the subject.

Example of locating the subject with 300 mm f/4 and MC-20. See the text for details.

In the above example, the mainland on the horizon is easily located in the viewfinder. Afterwards, the clearing among trees shown in frame 1 is distinctive enough to be located quite easily by panning along the horizon. At this point, I tilted the lens downward until I met the birds in frame 2. Finally, I panned left to frame 3, which is my intended subject. Of course, a red-dot finder like the EE-1 (see below) would make the process much faster.

The Olympus EE-1 red-dot optical finder is the only practical way to shoot a moving subject with the 300 mm f/4 and MC-20. With the EE-1 and this lens mounted on a tripod via a gimbal head, I am occasionally able to shoot a flying bird, but more than 95% of my shots are unusable. The main problem is that, even with the "right" combination of AF settings and focus limiter, AF drifts away from the subject soon after the subject leaves the field of view of the camera, and once the subject is centered again it takes too long to re-acquire correct focus. By that time, the subject is usually out of the field of view again. Nonetheless, with perseverance and a large SD card, one can hope to bring home a few keepers. If at all possible, however, the best way to improve your keep ratio is by getting closer to the subject and use no teleconverter - it is hard enough to use the 300 mm even without one.

The instruction manual of the MC-20 does mention some useful information, including a warning not to leave the camera pointed at the sun without a lens cap. In a mirrorless camera, the sensor is typically exposed at all times to the light entering through the lens, and the lens is typically fully open. This can concentrate the image of the sun on a small enough area to permanently burn a blind spot in the sensor. Depending on the lens and geographic location, this may take as little as 10-20 seconds with the camera immobile (e.g. left on a table or a car seat). The problem does exist also with cameras that close the mechanical shutter when powered down. In this case, the sun can easily melt a pinhole in the shutter front curtain. This type of accident effectively ends the camera's life or requires a repair likely too expensive to be realistic, and is far from unique. A photographer should always remain aware of this risk. Many children, at one time or another, experiment by burning paper or insects with a magnifier in sunlight. I recommend you don't do the same with your camera.

300 mm f/4 + MC-20 as a close-up lens

While researching the MC-20 on the web prior to purchasing it, I came across a number of incorrect statements about the maximum magnification attained with the 300 mm f/4 and MC-20. The most repeated of these erroneous statements is that the maximum magnification with this combination is 0.96x, or practically 1x. Before I discuss using the 300 mm f/4 and MC-20 for close-up photography, let me set a few things straight:

  • The 300 mm f/4 has a minimum focus distance of 1.4 m. This records a subject area of 72.1 by 54.2 mm, at a magnification of 0.24x.
  • Adding the MC-14 to this lens yields a minimum subject area of 51.5 by 38.7 mm and a magnification of 0.34x. The minimum focus distance does not change.
  • Adding instead the MC-20 to this lens yields a minimum subject area of 35.6 by 27.1 mm and a magnification of 0.48x. The minimum focus distance does not change.
  • The magnification of 0.96x found online among the specifications of the MC-20 is an error, as explained below.

The definition of magnification is

M = L' / L
where M is magnification, L' the linear image size and L the linear subject size. M is a dimensionless number, and its value is often accompanied by "x", read as times. Note that the sensor size does not appear in this formula. A lens set at 1x always yields 1x, regardless of sensor size. The lens knows nothing and cares nothing about the sensor located at its back. As an example, many macro lenses can be used on full-frame as well as APS-C cameras. These lenses reach the 1x magnification regardless of the sensor format. What changes with sensor size, at a given magnification, is the subject area. If we want to record the same subject area on two sensors of different sizes, then we need to use different magnifications.

As mentioned above, the 300 mm f/4 at closest focus with MC-20 covers a subject area of 35.6 by 27.1 mm, and yields a magnification of 0.48x. To cover a similar subject area on full-frame (36 x 24 mm because of the different aspect ratio), one needs to shoot at 1x, and this is where the confusion about "0.96x magnification" started. Olympus accompanied this specification with "35 mm equivalent" on their web site, then at some point the specification was copied but the equivalence information was left out, and from then onward everybody repeated the 0.96x figure without this essential context, sometimes even adding erroneous explanations. For example, slashgear.com erroneously adds that, with the 300mm f/4.0 and MC-20, "photographers will be able to shoot near actual size at 0.96x", with no mention of 35 mm equivalence. The same omission is repeated over and over again, e.g. on Olympus Malaysia Facebook page, bhphotovideo.com, tecobuy.com, aseanpriceblog.com, and dozens more. Camera-warehouse.com and others further muddy the water with explanations like "can actually shoot near the actual size at 0.96x (w/ a max magnification of 0.48x.)".

<rant warning>
The above is just an example of how the use of "35 mm equivalents" frequently leads to mistakes and misunderstandings. In addition, 35 mm film and 35 mm film cameras are long gone, so we should trust digital camera owners to understand simple concepts like magnification and focal length and how they apply to their cameras, without converting digital specifications to equivalents on a defunct medium.

No one today uses VHS, LPs or Compact Cassettes as terms of comparison for digital media, so why this insistance on "35 mm equivalence"? Seriously, any photographer younger than 30 years has probably never touched a 35 mm film roll or a plastic 35 mm film canister. Old photographers who cannot come to terms with digital cameras without continuously referring to "35 mm equivalents" might just as well hang their cameras in a closet and call it a day (take this from an old photographer who used 35 mm cameras for nearly 40 years, then switched to four different formats of digital cameras, but needs no "35 mm equivalents").

Full-frame digital cameras are also often used as "equivalents", because their sensor size is similar to 35 mm film. These cameras are a minority among all digital cameras on the market, and this format deserves no preferential treatment as a "standard" of sorts.
</rant warning>

Let me also clear up the difference between a macro lens and a close-up lens. Modern macro lenses typically allow continuous focusing between infinity (where M = 0) and a close distance where M = 1. Many legacy macro lenses only reach 0.5x with their focusing helicoids, and require an extension tube to reach 1x. In the past decade or so, we have seen quite a few macro lenses that focus between infinity and slightly more than 1x, in a few cases reaching 2x. By and large, however, we can continue to state that a typical macro lens provides a maximum magnification of 1x. I am not discussing here the "super-macro lenses" that provide a magnification range starting at 1x or higher but cannot focus at infinity, and the numerous copy/repro/enlarger/bellows lenses that lack a built-in focusing helicoid.

There is no formal definition of a close-up lens. It is generally understood that, to qualify as a close-up lens, it should be able to focus down to a distance somewhat closer than normal for a general-purpose (i.e., non-macro) lens. 0.1x is common enough among general-purpose lenses, and a bit too little to call "close-up", while 0.2x might be enough to qualify as such, especially considering it records a subject area of only 110 mm diagonal on Micro 4/3. In the present discussion, I use the ill-defined close-up lens denomination to describe lenses that focus close enough to record small subjects, but don't reach the 1x or 0.5x magnifications that would make them "true" macro lenses. The Olympus 300 mm f/4 does qualify as a close-up lens because, unaided, it can focus continuously from infinity to approximately 0.25x.

Things have been made even more confusing since the late 20th century by dozens of consumer-grade zoom lenses with close-up focusing capabilities marketed as macro zooms. Googling this term yields half a million hits. With one or two exceptions, none of these lenses continuously focuses down to 1x or 0.5x unaided, and they should instead be called close-up lenses. Additionally, many of these "macro zooms" switch to close-up mode with a mechanical control, so they do not satisfy the criterion of continuous focusing from infinity to close-up.

The MC-20 turns the 300 mm f/4 Pro into a close-up lens capable of maximum magnification close to 0.5x (which in this discussion I approximate to 0.5x for simplicity), with an unsurpassed working distance around 1.2 m. This combination may be the ultimate way to shoot exceptionally shy or dangerous small animals, as well as small subjects that for some reason cannot be approached closer than about 1-2 m. An example of such a situation is shooting close-ups of plants and flowers from the walking planks for visitors of natural preserves and hydrothermal fields, where you are not allowed to step onto the ground for your own safety, as well as for protecting the fauna and flora.

The E-M1 and E-M1 II display the effective aperture at infinity with the MC-20, i.e. the aperture range displayed on the LCD screen is f/8 to f/22. If you wonder why f/22 instead of the expected f/44, the E-M1 II with 300 mm and MC-20 refuses to stop down past f/22, probably to avoid calls to Olympus support by inexperienced photographers complaining that their MC-20 is defective beyond f/22 (which is instead an unavoidable result of diffraction at these apertures). These cameras, however, do not compensate for the increase in effective aperture caused by focusing at close range. For example, after setting the lens aperture on the camera to f/8 with the lens focused at infinity, refocusing to 0.5x still displays the aperture as f/8, although the effective aperture closes by one stop (f/11). I believe this is the general behavior of Olympus cameras, but cannot directly verify this on other cameras than those I currently own.

A tripod, or at least a monopod, is often necessary with the 300 mm + MC-20. Electronic shutter (or at least front electronic shutter curtain) and a remote shutter control are also highly desirable. Parallax is too high to use the EE-1 red-dot sight in close-up photography. It is possible to calibrate the EE-1 for parallax in advance, but the distance between camera and subject must remain strictly constant afterwards. AF can be problematic if the background is cluttered and "distracts" the camera's AF system, in which case a fixed, small 1 by 1 AF area may work better than a larger and/or "floating" group of AF areas.

Contrary to common belief, the DOF (depth of field) of a 600 mm lens in macrophotography is exactly the same as any other lens of any focal length, at the same subject magnification and effective aperture. You cannot get a higher DOF by using a lens with a shorter focal length, all other factors remaining the same. The only thing that changes with focal length is the perspective rendering (i.e., the relative size of foreground vs. background objects). In macrophotography, most lenses behave like telephoto lenses, so there is very little difference among lenses in this respect. In addition, the background is so much out of focus in macrophotography that its perspective rendering becomes irrelevant in most cases.

Diffraction affects image resolution as a function of effective aperture. On a 20 Mpixel Olympus Micro 4/3 sensor, the optimal range of effective apertures of the 300 mm f/4 lens (without teleconverter) with regard to diffraction is limited to effective f/4-f/11. At 0.5x, effective f/11 corresponds to f/8 displayed on the camera (regardless of whether this magnification is obtained with the lens alone, or with an added teleconverter).

MTF tests of the 300 mm (without teleconverter and focused at near-infinity) available online show it to perform better at f/5.6 than f/4. With the MC-20 at 0.5x, a simple extrapolation would suggest that the lens performs better at displayed f/11 than displayed f/8. The MC-20 magnifies diffraction blur, as well as the center of the image circle, by the same amount. This can magnify a diffraction blur unnoticeable with the lens alone into one already noticeable in tests with the MC-20. Displayed f/11 corresponds to effective f/16 at 0.5x, which is in diffraction territory and detectable by eye in 1:1 pixel crops. The 300 mm + MC-20 at 0.5x should therefore be used fully open to minimize diffraction blur. On the other hand, the better correction of lens aberrations provided at displayed f/11 and the slightly higher DOF give a better overall visual impression than at displayed f/8, in spite of increased diffraction. In the tests discussed below, f/11 does indeed give the best image resolution and contrast with a subject 9 m away.

The combination of 300 mm f/4 and MC-20 at 0.5x cannot give the same image resolution of a very good f/2.8 macro lens shot fully open at 0.5x, simply because diffraction at effective f/4 is lower than at effective f/11. The 300 mm + MC-20 is therefore best used when the very high working distance is really necessary, or when the aperture can be stopped down beyond the optimal resolution in order to increase DOF. When there are no restrictions to working distance and maximum image detail is desired (at the expense of DOF), a faster lens should instead be used.

In-camera focus stacking and focus bracketing are possible with the 300 mm, MC-20 and a camera that supports these functions.


In earlier use of the 300 mm f/4 with MC-14, I consistently noticed that images shot with this teleconverter look less sharp than without. However, the amount of detail with the teleconverter is higher than without, i.e., using the teleconverter records more information than shooting without teleconverter and subsequently cropping the image. I expected the same to be true with the MC-20, i.e., that images shot with the 300 mm f/4 and MC-20 show more detail than images shot with the 300 mm and MC-14.

Another of my reasons to test the 300 mm with MC-20 is that I own a legacy Olympus Zuiko 600 mm f/6.5 for the OM system. This lens is relatively small for a 600 mm full-frame refractor lens, but still much larger and twice as heavy as the 300 mm. In earlier tests, I found that, on Micro 4/3, the 600 mm lens does record a little more detail than the 300 mm alone, but the 300 mm produces significantly better contrast and color. Adding the MC-20 to the 300 mm, it is possible to directly compare images produced by the two lenses, while my earlier tests made comparing the two lenses difficult.

The following test results place pairs of images side-by-side to allow a direct comparison. All test images were shot with E-M1 II at ISO 400 (chosen as representative of real-world shooting conditions), a solid tripod, the lens setup and aperture indicated below, wired remote shutter control, electronic (i.e. fully silent) shutter and Godox AD200 flash in TTL mode, controlled by a Godox radio master on the camera. The target is a positive 1951 USAF target metal-evaporated on glass and etched (target quality is quite poor for macrophotography, but more than adequate for this particular test) placed at 9 m from the camera and transilluminated by the electronic flash via a diffuser and ground glass. This distance is too little to focus only with the built-in focusing rack of the legacy Olympus 600 mm f/6.5, so I used also an OM to Micro 4/3 adapter with built-in focusing helicoid to achieve the extra distance and precise focusing.

Test images with the 300 mm without teleconverter were up-sampled to 200% by bicubic interpolation to allow comparison with the 2x teleconverter. these images display some processing artefacts, and are therefore only indicative. They are added as proof of whether images shot with the MC-20 do contain more detail than without.

In all cases, focusing was done manually with the lenses fully open at the maximum magnification provided by live view of the camera.

The three sets of tests were shot at all available apertures with the 300 mm alone, then with the 300 mm + MC-20, and finally with the legacy 600mm. Side-by-side comparisons are provided below for the 300 mm (upscaled) vs. 300 mm + MC-20, and 600 mm vs. 300 mm + MC-20. For apertures not available in a given setup, a blank image is displayed. All pictures are 1:1 pixel crops near the center of the original image.

Left: 300 mm without teleconverter, upscaled to 200%. Right: 300 mm with MC-20.
Left: 300 mm without teleconverter, upscaled to 200%. Right: 300 mm with MC-20.

The above test is also useful as proof that the MC-20 does indeed double the focal length of the lens quite precisely, without "short-changing" the photographer.

I did not expect f/22 to still be quite good with the MC-20. It is much blurrier than at f/16 with the 300 mm alone, but not so much with the MC-20. The reason may be that it is easier to manually focus on fine detail with the MC-20 than without, so diffraction may be compounded by imprecise manual focusing in tests without the MC-20.

Focusing by wire is at its precision limits here. This focusing system works in discrete increments, and on the LCD screen, at the maximum magnification of live view, I can clearly see that just one focus increment makes the difference between sharp and unsharp. Finer manual focus increments would be necessary here to nail the focus with precision, but the lens does not provide them. I do not know whether autofocus uses smaller focus increments than manual focus. If it does not, then there are situations where the lens focus-by-wire mechanism cannot provide the full image resolution of which its optics are capable.

Left: legacy Olympus 600 mm f/6.5. Right: 300 mm with MC-20.
Left: legacy Olympus 600 mm f/6.5. Right: 300 mm with MC-20.

An unexpected result of the legacy 600 mm test is that the subject is magnified with respect to the 300 mm + MC-20, which in turns means that the actual focal length of the 300 mm + MC-20 is significantly shorter than the focal length of the legacy 600 mm lens.

As discussed above, the MC-20 does double the lens' focal length rather precisely, so the only explanation left is that the focal length of the 300 mm lens is actually shorter than half the one of the 600 mm lens. Assuming that the 600 mm is "honestly" rated, an approximate calculation yields about 246 mm as the actual focal length of the 300 mm focused at 9 m, which is 18% less than the nominal value. This difference is quite a bit, but not unique.

The difference between nominal and actual focal length may not be as bad as this. The different ways these two lenses focus can be partly responsible for the observed results. The 300 mm has internal focus, which usually works by reducing the focal length when focusing close. The legacy 600 mm has an optical assembly that moves as a single piece, away from the camera when focusing close (over 100 mm for focus at 9 m). This results in the cone of light entering the lens to become narrower as the lens moves outward when focused closer, achieving the opposite effect. So it is possible that the 300 mm and 600 mm lenses at infinity have actual focal lengths not too different from their nominal values, but their focusing behavior may cause the size of their respective fields of view to diverge in opposite directions at close focus distance.

Test conclusions

In terms of recorded details, the 300 mm + MC-20 clearly beats the 300 mm alone at all available apertures. The former is best at displayed f/11 (group 2 element 6 is resolved), while the 300 mm alone is best at f/8 to f/11 (group 2 element 2 is barely resolved). There is no question that the 300 mm + MC-20 resolves a lot more real detail (not just a little more) than the 300 mm alone.

Tests with the 300 mm + MC-14 (not shown) give results intermediate between the 300 mm alone and 300 mm + MC-20. In other words, the MC-20 adds more detail than the MC-14, not just empty magnification.

The legacy 600 mm is already good fully open in the center (less so in the corners, not shown). The two lenses are pretty much similar at f/8 (group 2 element 6 clearly resolved by both lenses) and f/11 (group 3 element 1 barely resolved by both lenses). The 600 mm is helped in this by its higher effective focal length at the test-subject distance, which magnifies detail to a larger extent, and the 300 mm + MC-20 by its higher contrast and lower axial chromatic aberration. At f/16, the 300 mm + MC-20 looks sharper because of its lower effective focal length and higher contrast, but the amount of resolved detail is the same in the two lenses and only slightly worse than at f/11. At f/22, both lenses are clearly affected by diffraction, to the same amount (group 2 element 3 resolved). As expected, f/32 on the 600 mm is unusable, unless one needs to trade lots of resolution for a higher DOF. This test set shows that the legacy 600 mm is a really good lens, even when used slightly outside its design parameters, and only penalized by the lower contrast of its antiquated lens coatings. It is, however, made more difficult to use by its size, weight, and manual focusing.

The tests show that the MC-20 is a desirable addition to the 300 mm f/4 for times when the 300 mm focal length, or the 420 mm focal length when coupled with the MC-14, are not enough. However, the 300 mm with MC-20 is much harder to use hand-held than the 300 mm alone, and this combination works best on a tripod with a gimbal head. This is in no way a specific problem of the 300 mm with MC-20, which is equivalent in field of view to a 1,200 mm lens on full frame. Such a lens unavoidably requires an excellent tripod and head, as well as excellent long-lens technique and discipline. What is truly extraordinary is that I can carry the Micro 4/3 equipment equivalent to a 1,200 mm full-frame telephoto and camera for hours in a small backpack and, if necessary, even shoot hand-held with it for an extended time with reasonable chances of success. The equivalent full-frame equipment would require two or three strong persons to carry and set up, cost at least ten times more, and require the body-build of a Terminator to shoot hand-held.

The combined 300 mm f/4 and MC-20 provide advantages over using the legacy Olympus Zuiko 600 mm f/6.5 on Micro 4/3:

  • Better contrast, better color, and lower axial chromatic aberration.
  • Much smaller size and half the weight (1,420 g vs. 2,900 g). Even now that I am closer to 70 than 65 years old, I can carry the 300 mm + MC-20 in a small backpack, as part of the everyday kit of lenses, for a few hours without my back complaining. The 600 mm requires its own dedicated bag, is as inconspicuous as a shoulder-mounted rocket launcher, and I don't want to carry it in the field unless I have a very good reason.
  • If necessary, I can shoot the 300 mm + MC-20 hand-held in good light with reasonable chances of success. I have heard of a photographer shooting with the 600 mm hand-held, but this is nothing I look forward to emulate. For one thing, focusing while hand-holding the lens requires a third hand because of its peculiar focusing mechanism.
  • Higher flexibility of having two focal lengths available (300 and 600 mm). By adding the MC-14, one gets a third focal length (420 mm) while increasing the equipment weight by only 105 g.
  • Much shorter closest focus (1.4 m vs. 11 m).
  • Fast and accurate autofocus in good light, in addition to manual focus.

I can only think of one disadvantage of the 300 mm + MC-20, i.e. price. Together, they cost some 5 times the 600 mm, which puts them out of the reach of a sizable number of amateurs. However, to put things in perspective, the price of the 300 mm + MC-20 is only a small fraction of the price of current 600 mm telephoto lenses of brands like Canon, Nikon and Sony for full-frame cameras.

Prices and availability

The MC-20 is expensive, quite more so than the MC-14. Since the MC-20 is relatively new, it is not common to find second-hand specimens. As usual, prices for a new MC-20 are quite variable online, and thorough research can help you to find a relatively low price.

Like the MC-14, the MC-20 is sometimes packaged by Olympus as part of a kit with either the 40-150 mm f/2.8 or 300 mm f/4. These kits are sometimes broken apart by sellers, who find that they can fetch a higher total price by selling each item separately, while still offering them at prices competitive with items separately packaged by Olympus. An MC-14 or MC-20 from a broken-up kit is often sold without packaging and without the soft pouch that accompanies a separately packaged teleconverter, but these items are worth giving up in exchange for a lower price.

Like most Olympus lenses and accessories these days, the MC-20 is packaged in a recyclable cardboard box, padded by a cardboard cradle instead of a plastic foam one. The accompanying soft pouch, however, is still packaged in a plastic bag.


The MC-20 is a 2x teleconverter for Olympus telephoto lenses starting with the 40-150 mm f/2.8 and up. It is expensive but good. Coupled with the 300 mm f/4, it records more real detail than the 300 mm alone, or the 300 mm with MC-14 teleconverter. The 300 mm f/4 with MC-20 gives better contrast and color than the legacy manual-focus Zuiko 600 mm f/6.5 for the OM system, is much smaller and lighter than the latter, provides fast AF in addition to manual focus, and adds the versatility of carrying two (or three, by adding the MC-14) different focal lengths with a minimal increase in weight. However, this combination is much more expensive than the legacy 600 mm.

The 600 mm records roughly the same amount of detail as the 300 mm + MC-20, and has a moderately longer focal length than the latter when focused at close distances.