What makes a good Canon EOS / Contax adapter for Canon dSLRs



  1. 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.

  2. 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 the 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. Some adapters prior to 2006 used set screws such as the DSLR Exchange adapters (no longer made). I am not a fan of set screws and these adapters have gone the way of the dinosaurs anyways.

  3. 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 is over-sized, as the lens is focused the adapter may rotate slightly on the Canon mount. This movement produces a knocking sensation when the side wall of the hole strikes the Canon locking pin. Lenses with a smaller locking pin holes can be trickier to mount because the tolerance for the pin to snap in is smaller. So there is a trade-off - large hole makes it easier to lock the lens in place, but allows for some rotational play. Too small of a hole, and mounting the lens can be a fiddly exercise. It is important to note that the rotational play does NOT cause performance issues, it is just an annoyance. Even Canon lenses have some rotational play when mounted. A number of my Canon lens shifted on the Canon 5D, but were very tight on the Canon 1Ds Mark II.

  4. Aside from knocking sensation, the other ill effect is a slight lag time between when the focus ring is turned and when focus actually begins to move (this may happen if a lens has a very stiff focus ring). The first bit of rotation is “used up” by the adapter rotating until it presses against the locking pin. Once the adapter has come to rest against the locking, then there is enough resistance for the focus ring to begin to move. Again, this is just an annoying side effect. There is no “fix”, nor any way to know beforehand if an adapter’s locking pin hole (or groove in the case of some adapters) is over-sized or not. Also, this added rotational play may not bother some photographers. In my experience the adapters purchased from Leitax have been outstanding in their particular area. The lens lock into place easily, securely with less play than my Canon lenses.


The focus confirmation chip basically completes a circuit, thus enabling focus confirmation on the Canon dSLR. This chips are simply glued in place at the appropriate location. As the focus ring is turned, the AF light in the Canon viewfinder blinks and the dSLR beeps when focus is achieved. With an focus confirmation chip attached, Canon’s ETTL II will function also (with some chips). The are a number of difference focus confirmation chips on the market. The Optix v5 and Dandelion are the two most common. I prefer the Optix v5 because it is easier to program; however, in use both chips perform the same in my opinion. Both of these chips are fully programmable, allowing the end-user to set focal length and widest aperture value - this data populates EXIF info.

Focus confirmation works better with primes (fixed focal length lens) than zooms. I think this is because the adapter PRAM is coded to a specific focal length. Using the Contax 35-135 Sonnar-Vario zoom as an example, the DOF is different at 35mm vs 135mm. Using 50mm to calculate the DOF at 135mm is not a tight enough tolerance. Also, primes tend to have faster aperture, thus more incoming light which improves the auto-focus system performance (or in this case - focus confirmation).

Lastly, the Canon 1-series has a tiny micro switch at about the 11:00 position on the lens mount (see pictures #2 and #3). When a Canon auto focus lens is mounted, it trips this switch and the auto focus system is turned on. Most adapters have a tiny screw on the side of the adapter wall - when mounted on the Canon dSLR, this screw “turns on” the auto focus loop. Not all adapters brands include this micro switch - make sure you buy an adapter that does. It appears Canon has changed their design and the 1Ds Mark III and 1D Mark III no longer have this micro switch set-up, so this could be a non-issue in coming years.