General notes on
Micro 4/3 lens adapters
Usefulness of lens adapters
The Micro 4/3 "standard" includes system cameras produced mainly by Olympus and Panasonic (but open to other camera and lens manufacturers, including e.g. Sigma and Samyang). It is a mirrorless camera type with a short registration distance of 19.25 mm. The registration distance, or flange focal distance, is the optical distance between seating flange of the lens and sensor surface (or, originally, film surface). Since the sensor is normally covered by a set of optical filters and glass sheets, the geometric distance between sensor surface and lens flange is slightly higher than the optical distance, and this has a practical importance when converting a camera to multispectral photography by removing some of these glass sheets.
The Micro 4/3 registration distance is significantly less than the registration distance in SLR and DSLR system cameras. In turn, this means that, at least in principle, it is possible to use an adapter to mount on a Micro 4/3 camera almost any camera lens ever made. For instance, the Nikon F lens mount, which is probably the oldest still in production, has a registration distance of 46.5 mm (which is a little more than average), and the M42 threaded system of 45.46 mm. This implies that it is not possible to mount an M42 lens on a Nikon F camera via an adapter and still focus to infinity. A possible solution is mounting a divergent optical group in the adapter, which shortens the optical distance and increases the physical distance, but these additional optics cannot be optimized for all possible M42 lenses (especially if implemented as a low-cost 2-element group), and end up lowering the image quality. The pages on Micro 4/3 adapters on this site deal only with lens adapters devoid of internal optics.
Focal length reducers, also called speed enhancers, are interesting adapters with built-in optics and reduce the effective focal length of a lens designed for a larger sensor, thus allowing, in practice, an increase of lens speed between 1/2 stop and 1 stop and the same shallow depth of field possible with the lens on a larger format sensor. Basically, a focal length reducer takes advantage of the larger image circle of lenses designed for full-frame or APS-C sensors and has the opposite effect of a focal length multiplier. Focal lengh multipliers are commonly used with larger sensors but not yet available for, and of scarce usefulness to, the Micro 4/3 format. Micro 4/3 focal lengths reducers are expensive if built with high-quality optics.
Since the time of the M42 format in SLRs and the earlier M39 format in rangefinder cameras, the Micro 4/3 format is the first type of lens mount that can be called universal, in the sense that it allows very large amounts of legacy camera lenses to be used (only in manual aperture and manual focus mode) on Micro 4/3 bodies. This is a dream come true for camera enthusiasts and tinkerers, and especially for practical use in macrophotography, photomacrography and photomicrography.
In practice, this potential for using legacy lenses has remained only a theoretical possibility as far as the Micro 4/3 camera manufacturers are involved. Except for adapters that allow the use of 4/3 lenses on Micro 4/3 cameras (in theory, with automatic aperture and autofocus, but the latter is essentially unusable in practice with most Micro 4/3 bodies), Olympus and Panasonic have not developed lens adapters for other brands. However, China Inc. has quickly come to the rescue of photographers by developing a broad variety of (usually) cheap adapters for almost any lens mounts to Micro 4/3 bodies. The varying quality and usefulness of these adapters is one of the main subjects of these pages.
Native Micro 4/3 lenses versus adapted legacy lenses
Historically, another factor that encourages the use of lens adapters with mirrorless cameras has been the scarce enthusiasm shown by the manufacturers of these cameras to market high-quality lenses. Commercial factors are certainly involved, but this lack of support is also due to the (probably mistaken) attitude of camera makers in regarding mirrorless system cameras as products for the amateur market, rather than semi-professional and professional photographers. With professional lenses, advanced users would be much more willing to abandon their bulky and heavy DSLRs for much lighter and smaller systems. Lately, Olympus and, to a lesser degree, Panasonic have shown an interest in producing professional Micro 4/3 lenses, but the range of these high-end bodies and lenses is growing slowly and must be substantially increased to cover professional needs. As far as I am concerned, I switched from Nikon DSLRs to Micro 4/3 in 2012. I have rarely used my Nikon bodies since then, and sold about half of them and their lenses, without regrets. The only reason I did not get rid of the other half is the lack of native Micro 4/3 long telephoto lenses of good quality (with this lens type, I regard fast autofocus as essential, so I cannot use Nikon lenses with adapters).
An additional reason why I am still hanging on to some of my Nikon-mount lenses is that I have not completely given up the hope that someone will develop a lens adapter that provides autofocus with these lenses on Micro 4/3 bodies (Canon adapters of this type for Sony mirrorless cameras have been developed, for instance). There may or may not be incompatibility problems that prevent this for Nikon lenses on Micro 4/3 cameras. However, nothing has happened so far, and at this point I would be ready to invest in Micro 4/3 long telephoto lenses of professional quality - if any were available, which will not be at least until 2015. Incidentally, the Panasonic and Olympus 100-300 mm Micro 4/3 zooms currently available are only amateur-level lenses, and the third-party 300 and 500 mm reflector lenses for Micro 4/3 are far poorer than even these 100-300 mm zooms.
Other mirrorless formats have the potential of using an equally broad variety of legacy lenses. However, these formats are proprietary and exclusive to a single camera brand, the range of their native lenses is severely limited even for amateur uses, and China Inc. is not yet offering a range of lens adapters comparable to those available for Micro 4/3 (probably because the much smaller market provided by these cameras, with respect to Micro 4/3, makes the development of new products riskier).
Problems with Micro 4/3 lens adapters
Some of the third-party implementations of lens adapters for Micro 4/3 cameras are highly questionable. For instance, adapters for some types of Canon lenses have a built-in diaphragm meant to replace the lens diaphragm (which in these lenses apparently can neither be operated by a manual mechanical ring nor controlled by the Micro 4/3 body). The position of this added aperture is non-optimal for most lenses, and likely to introduce strange optical aberrations.
The quality of bayonet mounts and their mechanical tolerances in these third-party adapters is especially variable, and ranges from very poor to very good. The average quality has been somewhat improved lately, but many questionable products are still sold.
The Micro 4/3 bayonet of most of these adapters, i.e., the part that connects the adapter to Micro 4/3 cameras, is a weak point of these adapters (in more than one sense). Typically, this bayonet is machined out of the aluminium body of the adapter (above figure, left) i.e., the bayonet mount is an integral part of the adapter body, not a separate part. I can see several problems with this cost-saving solution:
- An aluminium bayonet is mechanically weaker than a brass or steel one. This is why we don't see aluminium bayonets on camera lenses. Aluminium is not much stronger than the plastic used for the bayonets of particularly cheap camera lenses (which, however, are replaceable if they break).
- An aluminium bayonet is more difficult to manufacture to strict tolerances, and more likely to wobble and play in the camera mount.
- Aluminium wears down much more quickly than brass or steel. Wear produces aluminium particles that eventually work their way into the camera body and lens.
- A black-anodyzed aluminium bayonet is a particularly worrysome sign. Its surface is a film of aluminium oxide that wears off as fine dust. Aluminium oxide is industrially used as an abrasive, easily scratches glass and metal, and spreading it within the camera and lens is a sure way to damage the lens surfaces and the camera lens mount and internal mechanisms. Most cheap Micro 4/3 lens adapters have a rear bayonet of black-anodyzed aluminium. Non-colored anodyzed aluminium is just as dangerous, by the way. Blackened brass is sometimes used, but a chrome-plated brass bayonet or a stainless steel bayonet are more desirable.
Metabones markets expensive adapters with (as far as I am aware) the best Micro 4/3 bayonets among third-party Micro 4/3 lens adapters. This bayonet is machined from brass and chrome-plated. The bayonet on the lens side is also usually of good quality. However, most of the Metabones Micro 4/3 lens adapters in my possessions, purchased over the span of a few years, show that the chrome plating is uneven, and so thin that often it starts showing the underlying brass after mounting and dismounting the adapter on the camera body just a few times.
It appears that most manufacturers of these adapters with black-anodyzed aluminium bayonets have gotten the wrong idea about how photographers use these lens adapters. In fact, they generally suggest that the lens adapter be left permanently mounted on the camera body, and that lenses be mounted and dismounted on the adapter. In fact, they generally use a better-quality bayonet on the lens side than on the camera side of the adapter.
Time for these manufacturers to wake up, because this is not how lens adapters are used. The use they suggest is feasible only assuming that the owner of a Micro 4/3 camera owns no Micro 4/3 lenses, and instead uses only a set of legacy lenses with the same type of lens mount. The reality is just the opposite: virtually all Micro 4/3 camera owners do have and use Micro 4/3 lenses, and often also legacy lenses with multiple types of lens mounts. Therefore, the lens adapter is usually left attached to a specific lens, and the bayonet at the Micro 4/3 end of the adapter is the one that sees frequent use. Therefore, the bayonet at the camera end is the one where high quality and resistance to wear is essential. A well-made and wear-resistant bayonet is of course desirable also at the lens end, but in this position it is not as critical as the bayonet on the camera side of the adapter.
Links to the pages on Micro 4/3 adapters on this site are available on the main photography page.