New to the LL forums but have been lurking for a while.
After weighing the input from William and Theodoros here and other forums, I bit on purchasing the JAS adapter last May. Yes, $849 is quite a chunk of change for such an item but the rationale was based partially on the current investment I had in both camera systems and in the future ability to use the best of both worlds in my work. I actually have a digital back for my Contax 645 (as well as film), am happy with it but as a realist I know the Camera itself has a finite lifespan. In the worst case future, being able to port my beloved Zeiss glass to a more modern camera platform (even 35mm) appealed to me.
So I contacted Steel Chen via email, and he initially put me off from making the purchase - his explanation was that critical parts that he outsourced were not meeting his specs and that he was waiting for the next batch before accepting any orders. He asked for my patience and would contact me when he was again up and running. A few weeks later, he did so and we worked out the details via email using paypal for fund transfer. Shipping via EMS to the USA was included in the price and final receipt took about a week from the point of purchase - cleared US customs without additional charge. Pretty smooth process. However - no manual, only instructions on how to fine tune focus adjust in English at this time. The adapter was shipped inside a cocoon of semi rigid antishock plastic, overwrapped in clear plastic and inside a small shipping box with peanuts. The adapter did not come with any caps - I spent the extra to buy a generic Nikon back cap and Contax body cap as a safeguard for storage in my case.
1) Fit and finish are very nice, with a heftiness that belies all metal construction. The initial fit to my Nikon bodies upon receipt was very tight but repeated use over the last few months has eased the coupling process to a smooth action. The lineup dot is a dimple on the body and should have been marked in white or red to be able to be seen in less than optimal light situations. The adapter couples just like a Nikon lens with that noticeable attachment click at the end of the movement. Again, the attachment is tight and feels like it isn't going anywhere (no wobble or gaps). As the dimple now lines up at the 12 o'clock position on the camera, attaching the Contax 645 lens involves lining up the red dot on the lens mount to the dimple on the adapter and twisting the lens in the opposite direction as that of the adapter (takes getting use to) until it clicks in attachment. I did have an initial bit of trouble finagling all of the lens mount bits into the adapter, but realized this was my fault, as I found myself rotating the lens while looking to ensure that all of the lens was lined up properly. Trusting the line up markers seems to be enough now to make a good coupling with all of my lenses. But lets just repeat and say tolerances are "tight" - to me a good thing.
2) Once the lens is attached - the camera body is now in control. However there is one important exception (and hence the need for a manual someday), the attached Lens' aperture ring by default becomes an additional "M/AF switch" (perhaps as a safeguard) once attached. When the lens ring is at minimum aperture (say f-22 on the 80mm) AF contact to the lens is off. Any other f-value allows the AF command to the lens focus motor to electronically engage - this switch has no effect on the lens aperture motor. The Nikon body M/AF switch still works independently as it should. Otherwise, the camera body controls the lens' focus and aperture actions via electronic connections - the Lens aperture ring has no control (outside that noted above). Manual focus over-ride works the same with the Nikon body as it does on the Contax body. Focus, metering and aperture indicators work well in the finder and on the camera body LCD's. All aperture stops from the lens are listed on the camera body when turning the body function wheel. Using the DoF preview on the camera body visibly drives the aperture motor (and lens blades ) to the supposed f-stop. Some of the details I've listed here can be seen on Steel Chen's YouTube video.
3) All of the lenses I have operate well with the adapter 35mm, 45mm, 80mm, 120mm (manual focus only), 140mm and 210mm, much like the Youtube video. However, while my 45mm and 140 are sharp with AF, the 80mm isn't. I have to yet go through the process of fine tuning the AF on all of the lenses, but at least the instructions were available in English. AF performance of the Contax 645 lenses using the Nikon bodies is a night and day experience over that of the Contax body. The Nikon bodies tested (D800 and D810) appear to be able to drive the larger Contax 645 lens focus motor more effectively and without the focus hunting that the Contax body produced. This may just be due to the advance AF system (i.e. feedback) that the Nikon has over the older Contax system. I have no way to measure speed between the two. Using driving the focus on the Contax 645 lenses via the Nikon body feels solid. Metering feedback via changes to the DoF, shutter speed or ISO appear unhampered with the Contax lenses being attached.
4) Disconnecting the set up is a matter of taste. My experience with using extension tubes, other adapters and teleconverters has been to take the lens + adapter off from the camera as one unit (decouple at the adapter/camera) and then disassemble the lens from the adapter. The Nikon body's release button does this first step easily. To then remove the lens from the adapter, a metal tab on the adapter is toggled which releases the coupling lock, allowing the lens and adapter to be uncoupled. This can be done while the adapter is still on the body for quicker lens changes, but the initial stiffness of the release tab made sticking to old habits an easy choice. Of course the camera should be turned off prior to uncoupling anything. I have not seen so far any negative usage issues stemming from using the Nikon body and Contax lenses together, or when using them within each exclusive system afterwards.
5) Other tidbits learned from communicating with Steel Chen. A) Cannot use the adapter on the D3/D3S/D3X in its current state of manufacture (dont know why as yet as I own one), B) adapter contains proprietary firmware so if it is to be updated the adapter would need to be sent back to Steel to do so, C) he has ideas on other adapters to try.
So far, I am a happy camper with this set up. Its not something most of us would want or need - but that its available and brings a different angle to using my equipment is a good thing.
