Topic: Lens mount conversion: CZ 50/1.7 to P/K
In several threads, members mentioned about the difficulty in mounting the Zeiss C/Y lenses to Pentax DSLR http://forum.manualfocus.org/viewtopic.php?id=7869 . Others tried to overcome this problem by modifying the camera mount to accept the Zeiss http://forum.manualfocus.org/viewtopic.php?id=8854 (I am not a big fan of this approach). At that time, I only have Yashica ML lenses to play with and they could be easily converted to P/K lenses by using the M42-P/K adapter. Here is the process for OM lenses but it is very similar for Yashica ML http://forum.manualfocus.org/viewtopic.php?id=8570 . However, I did not have any Zeiss lens in my hands to see how the mount is designed and what kind of modification is needed.
Yesterday, I got a Carl Zeiss Planar T* 50/1.7 from a friend by trading it for a Super-Tak 50/1.4. Surely, I would like to fit it into my K10D. After some efforts of directly mounting it into my K10D, I could not make it stay snuggly as I want. Then I took a close look to the lens mount of the Zeiss and my A 50/1.7. My observation is that the distance from the bayonet to the base of the lens is different between the two systems. The gap of Zeiss is smaller than that of P/K. That's why we can not rotate the Zeiss in the K body. I have no tool to measure exactly the difference but I know it is very small. Please see the following picture to clear what I mean (sorry I can't have them in the same scale, so just ignore the scale):
Luckily, the design of the CZ 50/1.7 allows me to adjust that distance. All we have to do is just loosen the three screws (red circles) that hold the bayonet to the lens flange
The next step is to put a thin shim/spacer into the opening gap to get the desired distance (same as P/K).
You also need to file off the aperture lever and the protruding tap on the lens mount. They are a bit too long and will touch the camera mount. Therefore, it may damage the camera and does not allow you to adjust the aperture setting. Sorry I did not take pics of the original lens mount but this is what it looks like after the mod. Please see you lens and know what I am talking about. I really don't want to (but have to) do this because it is permanent. As long as you don't plan to use this lens on Contax camera, it should be fine.
The Zeiss can not focus to infinity on my K10D. So I need to adjust the focusing ring a bit. To anh Hiep (hiepphan), the process is quite easy. I will post a brief instruction here in case someone needs it.
1. Set the lens to infinity first. Then peel off the rubber cover on the focusing ring and loosen the three screws on that.
2. Then, rotate the focusing ring clockwise to make the indication mark point closer than infinity (10 or 5m).
3. Tighten all three screws. Checking: set the focus to infinity and look through the vewfinder for some far away subject.
4. Do it untill you have a perfect match. I used both split screen and focus confirmation on K10D to verify my infinity focus adjustment, so it should be ok.
To mount the modified lens into your K10D, you will align the lens around 10-11 o'clock and rotate clockwise until it close to 12 o'clcok position. Then you have the Zeiss stay firmly on your Pentax as a P/K lens (just not being locked). If all Zeiss lenses have the same design as this 50/17, I think this process can be applied. (Please report us about other Zeiss lenses if you have any. Thanks)
Some of my initial opinion about the Zeiss 50/1.7: Many people talks about the greatness of this lens. This is my first Zeiss and IMHO, I was not impressed by it at all. After quick sharpness test, I found out that it is less sharp than any of my 50mm (A 50/1.7, Yashica ML 50/1.4, Zuiko MC 50/1.8, and SMC Tak 55/2.0) at any f-stop from center to corner. My Zeiss has a very good and clear glass (only slightly sticky blades). Maybe, I need more time to use it in order to evaluate it more precisely. Note that my lens is made in Japan. Is there any other version (made in Germany) of this lens or I just got a lemon?