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 . Others tried to overcome this problem by modifying the camera mount to accept the Zeiss (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 . 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?

Re: Lens mount conversion: CZ 50/1.7 to P/K

This might come in pretty useful. Cheers!

Mostly in my bag ATM: Fuji X-T1, X-E2, X-E1, Leica M8, Nikon1 V1 and several lenses...
Things ON SALE!

Re: Lens mount conversion: CZ 50/1.7 to P/K

Nice guide as usual, xtriky.Unfortunately, the design of my Distagon 28 is definitely different from the Planar 50. There is no screw underneath the focus rubber grip. Is this planar AE or MM? This method is simpler than my way of adjusting the IF.

As for the mount conversion, i would love to hear from others who would convert their Planar 85 or Sonnar 135.

C/Y Modded Pentax K10D
Prime Lens: Olympus Zuiko 21/3.5, Contax Distagon 28/2.8, Pentax FA 31/1.8 Limited, Zeiss Flektogon 35/2.4, Pentax SMC-M 50/1.4, Contax Planar AEG 85/1.4, Pentax FA* 85/1.4, Tokina AT-X 90/2.5 Macro, Vivitar Series 1 105/2.5 Macro, Tamron SP 300/5.6
Zoom Lens: Tamron MF SP 70-210/3.5, Pentax DA 12-24/4

Re: Lens mount conversion: CZ 50/1.7 to P/K

Thanks xtriky for posting this!

I did recently convert a Planar 1.7/50 just like you described it. I think this was described in lesser detail by magicmud on this forum before.

I placed some soft aluminium sheet in two pieces (supporting one and two screws) under the bayonet ring, and I would say the distance needs to be 0.2mm or less. My lens sits on a K100D in a 4 o'clock position.

There is a Planar 1.4/50 waiting in the queue. This should be basically the same procedure, but I am planning to produce a decent spacer ring and also a new bayonet ring as well as a hole for the lock to snap in. All these are non-MM and 'made in Japan'.

About the softness of the 1.7/50, confirmed. Stopped down it gets quite good though, but which lens doesn't ? I've put a very basic lens test here and it confirms the softness at full open - I doubted the infinity position because it is so soft, but it is definitely infinity.


Re: Lens mount conversion: CZ 50/1.7 to P/K


I know that every lens needs to be stopped down a bit to improve the sharpness. The point is that my Zeiss sharpness is not as good as other 50mm at any f-stop (strange !!!). For sure, it does not hold the legendary reputation of Zeiss. Orio in mflenses told me that the step of adjusting infinity focus could affect to the sharpness of the lens. Can you compare the Zeiss to other 50mm if you have some? I just want to find out why my Zeiss is not as good as I expected. Is it due to my modification or I just got a bad copy? Thanks

Re: Lens mount conversion: CZ 50/1.7 to P/K

Hi xtriky,

from my little lens test and the pics I have made so far with the 1.7/50 I gather:
- Stopped down it is quite good
- into the light it is quite good (should be with a T* coating on all air to air surfaces)
- this may be a diva lens, because you carefully have to postprocess the resolution from the pics - this is more speculation, but it's said that the planars trade resolution for contrast (which is usually considered as 'sharpness').

As I've mentioned, the M42 SMC Tak 1.4/50 is an all around very good lens and seems to be better than the 1.7/50 Planars that we hold in our hands. The 1.4/50 Planar though looks to be even better, which I've yet to prove in real world pics.
Greetings, Georg
PS: Please have a look at my flickr-site, the whole bunch of latest pics is with that 1.7/50, very moderately postprocessed (shades, little unsharp mask and gradual filter)
PPS: I did not change the infinity setting like you. If the whole lens unit moves with it, I can't see any relation to IQ change.

Last edited by georgweb (2007-12-27 16:54:13)