I have recently purchased a 20D, having used Contax and T* lenses for 20 years, and am using the Cameraquest adapter to enable my Zeiss lenses to be utilised.
The results are variable, from slightly difficult to absolutely stunning.
I have the 21mm f2.8, 25mm f2.8, 50mm f1.7, 100mm f2.8 Makro Planar, 28-85mm f3.3-4 and the 100-300mm f4-5.6.
Firstly I would say that the quality of engineering and ease of the use of the Cameraquest adapter are excellent. No tools required and no slack or wobble experienced. It's expensive at US$175, but worth the money.
The problems I have found are mainly difficulty in focussing accurately at distance. The screeen on the 20D is obviously designed primarily for autofocus so there are no focussing aids like split screen etc. The screen is also a little dark, which adds difficulty when using the 100-300mm at the long end at f5.6.
The aperture stop down is not automatic, so stopping down to f11 gives a very dark screen. You have to focus wide open and then stop down to take the picture (if required).
I seems that the slight thickness of the adapter means that infinity focus is not actually at the infinity mark on the lens (you're moving the lens a couple of mm away from the sensor plane), so the scale becomes less useful. I'm sure with tests one could find out the exact focus point and place a new mark (removable of course!) on the lens barrel.
The results though are worth the effort as quality digital cameras tend to reveal flaws in lenses, and the quality of Zeiss really shows through.
The results with the 100mm Makro Planar in particular are nothing short of amazing. I was genuinely astonished after interpolating a 1:1 image up to 30"x20". Just stunning quality, sharpness and detail like you wouldn't believe, and of course that undefinable richness that only seems to come with Zeiss T* lenses. It is better than with any film I have used.
I have come to the conclusion that I shall keep certain lenses, notably the 21mm, 50mm and 100mm Makro, but use canon at the telephoto end.
Canon's telephoto lenses are excellent (I have the 70-200mm f2.8 IS USM and is it superb, I have also ordered a 300mm f2.8 IS which is also reputed to be extraordinarily good). You get quality lenses with the benefit of very fast autofocus and wide apertures.
However, Canon's wide angle lenses are nothing in comparison with Zeiss and this is why I shall keep the 21mm T* along with an RTS body and use film when I want the full 21mm (the 1.6 crop factor on the 20D makes it about a 33mm), but the quality is so much better than the Canon 17-40mm f4(which has shown some chromatic aberration and is nowhere near as sharp).
The Makro Planar could not be beaten by anything from what I've seen, and autofocus is not really required for macro work as I tend to move the camera in and out to focus, so this is a definite keeper and will probably be the most used combination (if you don't have one get one, you will not be disappointed).
Anyway I've rambled. Feel free to ask if there is anything specific you want to know.
Cheers,
Matt
