Olympus OM 600 mm f/6.5

The Olympus OM series of 35 mm SLR cameras and lenses (the latter branded Olympus Zuiko) was introduced in 1972 and discontinued only in 2002. The cameras were characterized by very small sizes for the time, and most of the lenses were designed to complement the camera sizes without compromising on optical quality. As typical of lenses of the time, they have manual focus and aperture, albeit with focus and exposure fully open and stopped down to the preset aperture by the camera body.

The original Zuiko lens series introduced a large number of prime lenses and a few zooms. Focal length varied from fisheye to supertelephoto. Among the latter, 300, 350, 400, 600 and 1,000 mm refractors were available, as well as a 500 mm catadioptric. Most of these supertelephoto lenses have a modest speed, compared with lenses of similar focal lengths offered by Canon, Nikon and other "big names". The idea with the Zuiko supertelephoto lenses was apparently to avoid lenses so heavy that they required very sturdy tripods and a troupe of Sherpas to carry in the field. Among these Zuiko lenses are a 400 mm f/6.3 and a 600 mm f/6.5 refractors, which I still remember salivating about in my teens (although they were far above my finances at the time, and for decades afterwards).

For several reasons, over the past decade I have assembled a moderately sized collection of legacy lenses of various brands. One of the reasons is that several of these lenses are usable in UV imaging, because the number of optical elements is lower and the anti-reflection coatings less effective in rejecting UV than modern lenses. The Zuiko 400 mm and 600 mm are candidates with these characteristics, and it would be nice to have a reasonably suitable supertelephoto for UV imaging. The Olympus 500 mm catadioptric is not quite good enough for this use (reasonable UV transmission but poor UV image resolution). Both the Zuiko 400 mm and 600 mm use relatively simple optical schemes that make them potentially interesting for this use, while being known for their rather good image quality in VIS.

I chanced on a Zuiko 600 mm at a lower-than-usual price on eBay, and got it. I might or might not get a 400 mm in the future. It does not have a high priority, because I already have a few legacy 300 mm primes.

The Zuiko 600 mm was initially made with single-coated lens elements. This lens was introduced, or at least planned, at the outset of the Olympus OM series. A multicoated version (identified by "MC" on the front fascia) was introduced after 1984. The specimen tested on this page is the MC version.

General characteristics

Little information is available on the Internet about this lens, with Malaysian Internet Resources (mir.com.my) being the best source. The Zuiko 600 mm is one of the physically shortest (337 mm) and lightest (2.9 kg) 600 mm refractors ever made. It is obviously meant to be used on a tripod, although when coupled to modern mirrorless bodies with built-in IS (image stabilization) one can get away with less of a rock-steady support than it did in the film era. It uses 6 optical elements in four groups.

By no means is the Zuiko 600 mm a small lens. It only looks a little smaller when compared with other 600 mm refractors (in fact, it is comparable in physical size to most 500 mm f/4.5-f/5.6 refractors, see above figure). The non-removable lens collar sits slightly offset toward the rear of the lens, and its tripod platform is small and very close to the surface of the lens barrel, compared to the oversized lens collars typical of modern supertelephoto lenses. In the above picture, a long Arca-compatible plate is partially visible, attached at the bottom of the lens collar.

The aperture ring has a high diameter and is placed next to the lens collar. It has full-stop clicks at f/6.5, 8, 11, 16 and 22.

The focusing mechanism by rack-and-pinion is surprising, and present only in a few supertelephoto lenses, none of them modern. Even the older Tele-Votar in the above picture has a conventional focusing helicoid. One focusing knob is present on each side. With mirrorless cameras, however, there is a workaround to add a focus ring.

The rear (not the front) of the lens barrel extends by almost 41 mm at the closest focus distance of 11 m. This is obviously not a lens for close-up photography, although the field of view on full frame is 55 by 37 cm at closest focus.

The main reasons why this particular lens specimen came at a relatively low price are that the lens storage trunk and front cap are missing, and that the lens itself has a few defects, some declared by the seller, others not. The seller declared very faint remains of molds on one of the rear elements, but they turned out to be nothing to worry about. A small dent at the front margin of the lens shade, also declared, was easy to fix, and is now almost imperceptible. The focus rack was blocked, which was not declared by the seller (perhaps it was knocked hard during transportation), and this was of course a serious concern. Fortunately, after 15-20 minutes of inspection and disassembly I was able to completely realign it, and now it works very smoothly. Kudos to the Olympus designers for mechanisms meant for a long usage life and relatively easy maintenance. A very small backlash of the focusing knobs has remained, which I might fix if it turns out to be troublesome (so far it does not seem so). The 1/4-20 threaded socket in the aluminium alloy at the bottom of the tripod shoe was ruined (also a fault not declared by the seller), but I fixed it in another 10 minutes with a Heli-coil steel insert, and it is now stronger than it ever was.

Almost half of the length of the lens barrel is covered by the built-in sliding lens shade, one of the best in photographic industry to avoid direct sunlight from striking the front optical element. Many supertelephoto lenses, even very good ones, are instead handicapped by too short and/or too wide a lens shade.

Tests

The following tests only deal with performance of this lens in the visible range. I will carry out NUV and NIR tests separately.

This lens is designed to cover full-frame, so it makes sense to test it on a full-frame body. In this case, I used a Sony Alpha 7R II with 42 Mpixel sensor. As it quickly turned out, the Tele-Votar 500 mm shown above, compared with the Zuiko 600 mm, is only a little better than using the bottom of a wine bottle as a lens. Thus, the Tele-Votar will not be discussed further. The Zuiko Reflex 500 mm f/8 is not a bad lens as catadioptrics go, but not a competitor in the same class as the 600 mm. I am not showing comparisons between the 600 mm and these two lenses, because there would not be much point to it.

My best modern supertelephoto lens is the Olympus 300 mm f/4 for Micro 4/3. This lens is extremely sharp, but it covers only Micro 4/3 and is therefore problematic to compare with the 600 mm on Sony 7R II, because my Micro 4/3 cameras only go up to 20 Mpixel (with the Olympus E-M1 II). Using the 50 Mpixel pixel-shifted mode of the E-M1-II would further complicate the test, because of the way the added resolution is obtained. As a compromise, I also tested the 600 mm on the E-M1 II. This involves resizing images in different ways, as discussed below, which adds uncertainties to the process. Also, to keep things relatively simple, I only show detailed comparisons among center crops.

I did not test the 300 mm with the Olympus 1.4x focal length extender, because the 20 Mpixel sensor already slightly out-resolves this combination.

I used electronic first curtain shutter and the infrared remote on the Sony 7R II at ISO 100, and the normal electromechanical shutter and wired remote on the Olympus E-M1 II at ISO 200. With both cameras, the magnified image in the viewfinder was visibly vibrating and bouncing with traffic and my steps on the plastic-covered wooden floor while IS was inactive, but the images do not show obvious motion blur. IS was active on both cameras while shooting, and likely improved the results. Focal length for IS was manually set to 600 mm on both cameras for the test with this lens. IS with the 300 mm on E-M1 II automatically reads the lens focal length.

About performance in the image corners, I will say, qualitatively, that the 300 mm fully open on Micro 4/3 has a significantly better corner performance than the 600 mm fully open on full frame. Corner quality with the 600 mm fully open on Micro 4/3 is far better than on full frame (naturally, since Micro 4/3 uses a diameter of the image circle just slightly more than half that of full frame). Image quality in the corners with the 600 mm improves dramatically when stopping down (much more than in the center).

On both full frame and Micro 4/3, green-and-purple transversal chromatic aberration is visible, especially in peripheral and high-contrast areas and especially if these areas are strongly out of focus. I don't regard this as a serious fault, because transversal chromatic aberration is easily corrected in post-processing.

The subject of the test is a group of houses at a distance of about 40 m, as displayed on the focusing scale of the 600 mm. Focus was set as precisely as I could on the brick wall in the center crop, and not changed during the test. This brick wall was illuminated only by diffuse daylight, not direct sunlight. This makes it a "difficult" subject, likely to be affected by lens flare and loss of contrast. In the center crops, out-of-focus white pieces of wind-borne fluff change position in each shot (aspens are having a good time releasing their seeds right now), so ignore them and concentrate only on features that repeat from image to image.

The relatively high distance from camera to subject means that air turbulence may play a part in reducing the image resolution. This is unavoidable with super-telephoto lenses. All test images were collected within one hour, and the temperature and weather conditions remained the same, so there is little reason to suspect that air turbulence changed substantially during the test.

Test with 600 mm on Sony A7R II

And the center crops:

Best center resolution is clearly obtained at f/11. Corner resolution is also clearly best at f/11.

Test with 300 mm on E-M1 II

As a first comparison, the corresponding center crop with the 300 mm at f/5.6 (the optimal aperture with this lens and format) on E-M1 II. This lens and camera has approximately the same field of view of the subject as the 600 mm on Sony 7R II. The lower pixel count of the E-M1 II results in a center crop that, at the same pixel number, covers a moderately larger field of view. This was equalized by slightly enlarging the following image in post-processing. The color rendering of the E-M1 II is darker and warmer than the A7R II.

There is a little more detail visible in the image taken with the 600 mm on 7R II at f/11, than with the 300 mm on E-M1 II. This is in part due to the latter image having been enlarged to compensate for the lower pixel count. Unfortunately, this is unavoidable if we are to make a same-size comparison.

Test with 600 mm on Olympus E-M1 II

In this case, best resolution is obtained at f/8. This is not a surprise, because the smaller Micro 4/3 pixels are more affected by diffraction than the larger full-frame pixels. As a whole, resolution is poorer with the 600 mm on Micro 4/3, than on full frame. This is not a surprise either, since the Micro 4/3 pixels are smaller (about half the surface area) than full-frame ones, and therefore place more stringent requirements on lens resolution.

An interesting question is whether the 600 mm produces better real detail, on Micro 4/3, than the 300 mm on the same format. In other words, does the 600 mm produce more detail, or only empty magnification?

When the image taken with the 600 mm is reduced to half its size, the image taken with the 300 mm seems to show slightly more detail, but this looks mainly a result of the higher contrast of the 300 mm, rather than a really higher resolution. But what if we compare the image taken with the 600 mm at its original size with the image taken with the 300 mm magnified 2x in post-processing?

In this case, the image shot with the 600 mm displays sharper lines and a little more of the finest detail. With the provision that magnifying an image is software-dependent and may change its perceived sharpness, this result seems to confirm that the 600 mm has a moderate edge on the 300 mm in terms of real resolution of subject detail, while the 300 mm has better contrast. There is therefore a moderate resolution advantage in using the 600 mm on Micro 4/3, as opposed to the 300 mm. The actual detail is not twice as good, but the difference is there. Contrast has not been adjusted in this test, but it can be done without introducing visible artifacts, and results in an even better detail in the 600 mm image.

Reflections

Tests of a legacy full-frame lens on a 42 Mpixel full-frame sensor, or a 20 Mpixel Micro 4/3 sensor, are both extremely demanding. On full-frame, for example, 24 Mpixel is a far more common resolution, and the Zuiko 600 mm performs far better at this resolution (although it is still capable of resolving details between 1-2 pixels at f/11 on 42 Mpixel). Testing this lens on Micro 4/3 only uses one-quarter of the film/sensor area this lens is designed to cover, and on this format it is limited to f/8 for best performance. Keeping this in mind, the overall results of the Olympus 600 mm are excellent.

A practical difference between the Zuiko 600 mm and the Olympus 300 mm is that the 600 mm weighs almost 3 Kg and requires a time-consuming manual focusing on a tripod, while the 300 mm weighs about 1.3 Kg and works very well hand-held with autofocus. I have read anecdotal reports of a photographer using the 600 mm hand-held, but I have occasionally shot with a 300 mm f/2.8 hand-held (before IS became available), and it was far from satisfactory. It should also be remembered that, at current prices, the 300 mm costs roughly 4 times the 600 mm.

I did not directly compare the Zuiko 600 mm with equivalent Sigma or Tamron lenses. My experience with a few telephoto and zoom telephoto lenses of these brands (Sigma 100-300 mm f/4, Sigma 50-500 mm "Bigma", Tamron SP AF LD 300 mm f/2.8) was with 6 to 12 Mpixel APS-C cameras. These lenses were regarded as good at their time, but I suspect that anything more than 16-20 Mpixel sensor resolution would clearly show the limitations of these lenses. For example, the Tamron 300 mm lens looked good on a Nikon D300, but was not satisfactory on a 16 Mpixel Olympus Micro 4/3 E-M1. The Zuiko 600 mm at its best aperture, on the other hand, is a good match for the 42 Mpixel sensor of the Sony A7R II, and still usable on the 20 Mpixel Olympus Micro 4/3 E-M1 II.

Another factor to consider is that use of a 600 mm lens in the field, with subjects farther than the minimum focus distance of 11 m, is limited by image degradation caused by air turbulence, especially when shooting horizontally from a low height over land, and especially if the land is heated by sun (which, unfortunately, is the typical scenario in which these lenses are used in nature photography). Shooting over open water is better, as well as shooting from an elevated position, early in the morning, and stopping down the lens while avoiding long exposure times (by increasing ISO), but the problem still exists. Therefore, no matter how good lens and camera are, in real-world conditions they will often not provide the expected image quality. This, together with unfamiliarity of the photographer with the technique of shooting with supertelephoto lenses, may negatively bias some of the reviews of this lens I have seen on the web.

In conclusion, for use on full frame up to about 40-45 Mpixel, if manual focusing is acceptable, the Olympus 600 mm is definitely a very good performer, at a price and weight only a fraction of the 600 mm lenses branded Canon, Nikon and other "big names".

Adding a focus ring

The helicoid adapters shown above extend by 26.5 mm (Micro 4/3) and 27.4 mm (Sony EF). This is more extension than usual, which may potentially invite problems with wobble and misalignments. In fact, the micro 4/3 adapter has a significant amount of wobble if used at full extension. If one limits the extension to 18-20 mm, however, the wobble is barely perceptible. On the other hand, the Pentax EF adapter has only a barely detectable wobble, and feels overall much better built.

The two adapters are evidently produced by the same factory, but they use no interchangeable parts except for the OM mount. In particular, the screws of the rear mounts are not placed in the same positions, so I cannot swap the rear mounts and make one good Micro 4/3 adapter by using the other's helicoid.

For fixed amounts of extension, e.g. for focusing with the built-in lens focuser at closer than the minimum focus distance, the original Olympus OM extension rings are probably the best choice. They are available in lengths of 7, 14 and 25 mm, distinctively heavy, and entirely made in metal with chrome-plated front and rear bayonets. At least in my specimens, the bayonets are extremely tight-fitting, with no play at all.

There are two series of Olympus OM extension rings: an earlier one without aperture transmission, and a subsequent "Auto" series with diaphragm transmission. For the purpose of using the 600 mm on mirrorless cameras, either series will do, but the non-Auto rings should be made light-proof as discussed below.

The Auto series is identified at the bottom of the rings with the labels "AUTO 7 JAPAN", "AUTO 14 JAPAN" and "AUTO 25 JAPAN", and is shielded by an internal sleeve against light leaking around the bayonet release button. The non-Auto rings, identified by "7 JAPAN", "14 JAPAN" and "25 JAPAN" labels, can be made light-proof with the addition of small pieces of adhesive flocking on the interior of the tubes. The above figure shows non-Auto rings with no internal sleeve.

Hard case or soft case?

As it turns out, this tripod case is exactly of the right size to contain the Zuiko 600 mm equipped with adapter for mirrorless camera and a flat Arca-compatible plate. This case is semi-rigid (it has no hard shell, but the padding is quite stiff), well built and abundantly padded, and weighs about 400 g including the detachable shoulder strap with non-slip pad. This case also has a zippered lid at one end, a permanently attached strap handle, a very small zippered external pocket, a transparent holder for address label hidden behind a discreet Velcro tag, and a 10 cm long, removable doughnut-shaped padded sleeve that fits inside the case and is meant to prevent the ends of the tripod legs from rattling around within the case. This sleeve fits around the rear of the lens and the focus rack, and holds them centered within the case. I find it easiest to put the lens into the case starting with its front end, and to insert the sleeve in place last, before zipping the lid of the case shut.

Front lens cap

So far I did not find a screw-in or clip-in replacement front cap to fit this lens. It seems the 100 mm diameter of the filter mount is a non-standard size. A 110 mm slide-on lens caps should fit over the end of the lens shade. Such a cap might be available, but this size has so far eluded me. So far I can make do with a 120 mm slide-on cap, which is big enough to semi-permanently fit at the bottom of the Marsace case, or in its lid.

 I serendipitously discovered a small stock of unused Olympus front lens caps with a diameter of 100 mm on eBay a few months after I purchased this lens. Since I still did not have a satisfactory front cap for this lens, I purchased one from the Canadian seller. This lens cap, made for the Olympus OM 600 mm f/6.7 and 1000 mm f/11, is machined out of a block of solid aluminium alloy, screws into the front filter mount of the lens, and prevents the lens shade from extending while handling the lens. It also provides a little protection against denting the edge of the lens shade.

My best guess for the existence of such a stock of 100 mm replacement caps is that an Olympus representative, decades ago, had to order one from Japan for the owner of one of these lenses who had happened to lose the original lens cap, and placed an order for a few more of these caps "just in case".

Summary

The Zuiko 600 mm f/6.5 from the legacy OM series is a good supertelephoto lens, usable on high-resolution (42 Mpixel) full-frame cameras. It performs well also on 20-Mpixel Micro 4/3, where it captures slightly more real detail than the Olympus 300 mm f/4.