Canon’s 1Ds series and 5D dSLRs triggered a new interest in classic 35mm manual focus lenses. Some photographers want to use their favorite lenses from years past, other photographers are experiencing these lenses for the first time. Whether you are searching for a hidden treasure at a bargain price or looking for ultimate wide-angle lens - don’t forget about finding a good adapter.

WHAT MAKES A “GOOD” LENS ADAPTER?

You probably already discovered that Ebay offers many lens adapters at varying prices points. Finding the right adapter requires some homework. ‘Google’ the seller’s Ebay ID and look for actual user reviews in photography forums such as Fred Miranda or the Manual Focus Forum. See what other users are saying. Most likely the results will be mixed with some people writing XYZ lens works perfectly with their adapter, while the next poster states the complete opposite. Why the conflicting reports? One plausible explanation is - not everybody has a critical enough eye to spot the flaws. Other possible technical explanations include:

Proper Flange Thickness - Adapter thickness is one of the most common quality control issue. In this case “thickness” refers to the adapter metal between Contax lens and Canon EF mount when the lens is mounted. This is the adapter’s “flange”.

Zeiss engineers designed the Contax C/Y for a specific distance between the rear exit pupil and the film plane. If this target distance is NOT maintained, then the design has been compromised. If the adapter flange is too thick then the lens may not focus all the way to infinity. If the adapter is too thin, then images may look out-of-focus. Matters can get even more complicated if the lens uses a floating element design. A floating element is used to provide superior near focus capabilities. If the proper distance to the film place (sensor plane) is not maintained, then we are not realizing all the lens’ potential. Aside from mis-focused images, other nasty things can happen - such as fringing (ie - chromatic aberrations commonly called “CA”) or halation (image looks blurred or smeared).

Some adapters are poorly designed. Others are well designed, but fabrication variances cause problems, such as poor quality control during plating process leading to increased thickness. For a Contax Carl Zeiss T* lens used Canon EF or EF-s dSLR, the correct adapter (flange) thickness is ~1.425mm. 1.425mm is NOT an absolute. In some cases a thicker or thinner may work better. There are many reasons why varying adapter thicknesses may work - some lenses aren’t as sensitive to adapter thickness, the Contax lens may not be in proper calibration due to age (use),  the Canon dSLR body may not have been assembled to strict enough tolerances (ie - the Canon 5D comes to mind) or maybe the Contax lens was not assembled to such tight tolerances.

Uniform Adapter Thickness - All adapters will have high and low spots in their flange thickness. Anything within +/- .005mm tolerance should not adversely effect performance. However, if an adapter’s thickness is already at the edge of acceptable thickness, then the plating may be the added bit of extra material needed to turn an otherwise acceptable adapter into a bad adapter.

If the plating is very poorly applied, then the adapter may sit crooked on the lens or camera mount. A crooked lens may result in one side of the image looking sharper than the opposite side. At smaller apertures such as F8, F11 and F16 depth of field (DOF) may hide the problem. Where as faster apertures such as F1.4 and F2 often reveal issues. If a lens does well at smaller apertures (ie - F8, F11, etc) and shows uneven sharpness across the frame (ie - pictures always look sharp on the left side, but soft on the opposite side) at faster apertures - then double check the adapter’s flange thickness along the entire circumference.

There is not much you can do to avoid this problem, though one would expect a $79.99 adapter would be better than a $14.99 adapter. Some of the better adapters include Kindai, Cameraquest (this is a relabeled Kindai adapter), HappyPageHK (Ebay seller ID) and Fotodiox Pro.

No Set Screws - Some older adapter designs use a set screw to lock the adapter in place. The set screw may push the lens away from the adapter, thus causing unevenness. If your adapter uses a set screw, carefully inspect the lens with the adapter mounted - make sure the screw does not push or cock the lens to one side. If the lens is sitting unevenly, then back out the screw slightly.

As of 2007 or so, set screws are no longer common. Some of the earlier adapters prior to 2006 used set screws such as the DSLR Exchange adapters (no longer made). If somebody is selling a lens WITH the adapter, you might want to ask beforehand what brand the adapter is. In my opinion do not use adapters with set screws. It is one more variable that can cause problems.

CANON LOCKING PIN

Some adapters have an over-sized hole cut in adapter flange for the spring-loaded locking pin on the Canon mount. Since the hole in the adapter flange over-sized, as a lens is focused the adapter may rotate slightly (a fraction of a degree) on the Canon mount. This movement produces a knocking sensation when the side wall of the hole strikes the Canon locking pin. In the picture below, the receiving hole for the Canon locking pin is at the 9:00 position (lens shown is a Zeiss 50mm F2 Makro-Planar ZF with a Nikon/EOS HappyPageHK Adapter).

Lenses with tighter or stiffer focus rings require more force, thus it is more likely the adapter will spin (slightly) on mount and hit against the locking pin. If the hole in the adapter flange is manufactured to a tight tolerance, then the rotational play is minimal and impact is slight at best. Even if the hole is oversized this can be a non-isse if the lens’ focus ring is light to the touch. In this scenario minimal force (torque) is exerted when focusing and the adapter does not rotate.  (Next Page)