How to re-work a Yashica/ Contax lens To fit a Pentax Camera

[bigdawg]

Sorry it took so long to get these up but I fell last night and all my weight hit on the back of my neck against a side table in the dinning room. Don't drop a screw and step on it if you are in sock feet on a slick hardwood floor. Just glad I've such a bull neck or I would have broken it again. Wife's poor table suffered damage.
Warning!!!!!
If you do this you accept all responsibility for any damage to your lens or camera. I am and will not be responsible for anything that happens...I do not know how well you can use tools or machines. So therefore you must accept all responsibility for your own actions here.
Caution!!
Another thing to be very careful with...Remove the Lens mount from the lens to do any of these things. Don't scratch the lens or get chips of metal in the focus ring or aperture ring.

ONLY remove what you have to...NO MORE!!!!

Any way lets look at how to do this. Really very simple to do. Both the Yashica and the Pentax lens have a tri-flange mounting system. The good thing is the inner barrel (the area between the Flanges and the lens base) is close to the same outside diameter (OD). Also the flange OD is almost the same. They are close enough to where no work is needed on them. There are some coupling levers that need to be cut off flush with the lens mount or removed. On some lens I cut them off on others I removed them. Which ever is easiest for you to do. They will not work on a Pentax or any other camera except a film Yashica/Contax so removing them harms nothing and may prevent bumping into something inside the camera.


Yashica/Contax lens mount



Pentax Lens Mount



Items to cut or remove



The next thing is to look at the distance between the bottom side of the tri-flanges and the lens base. This is the one thing that must be machined. I'm sure there are other ways to grind or file the material away but I found that a small parting tool on a small lathe does the best job...If you feel uncomfortable doing it..then take it to a small machine shop or tool and die shop and have them do it for you. I got the dimension of this distance from a 2X teleconverter and used it (the teleconverter) to test the fit. This prevents damage to the camera trying it out. When the distance was right for the teleconverter I then tried it on the camera. Wound up having to remove another 10 thousandths to get a good fit.
The place to remove some material.


After you've gotten a good fit with the machining, then you need to remount the lens mount to the camera. Try fitting it to the camera and see where the markings for the aperture and the focus and zoom wind up. I always try to get it on the top at least. This is accomplished by removing the screws that hold the base on and rotating it to the next set of screws. Try it again...If you need to repeat the process till the markings are somewhere on top of the camera.

Next remove the lens and then remount without turning the lens . The place that the lens will seat is the place you need to put a mark so the red dot on the camera and the mark you put on the lens will line up. I usually do this by marking the spot with a Sharpie the drilling a small depression in the side of the lens mount and filling it with red ink. A small center drill works for this or a 3/16 drill bit.


Dot for lens alignment



Next mount the lens and rotate it till it is firmly in place. This may happen a lot quicker than with a Pentax lens. It may only rotate a inch or so. Doesn't matter as you are not matching coupling levers or contacts anyway. Now go to the release pin on the camera and mark directly in line with it on the side of the lens mount again with a sharpie. Take the lens mount off the lens and where that mark is, either machine ( I use a 3/32 end mill ) or file or grind a slot in the lens base for the locking pin to mount in. Doesn't have to be too deep either as it is only there to prevent the lens from rotating and falling off when you focus, zoom or adjust the F/stop.


Slot for locking pin.


Hope you have fun doing this...Any questions please ask away!!
_________________
Dawg

[Hayward]

bigdawg wrote:

The next thing is to look at the distance between the bottom side of the tri-flanges and the lens base. This is the one thing that must be machined. I'm sure there are other ways to grind or file the material away but I found that a small parting tool on a small lathe does the best job...If you feel uncomfortable doing it..then take it to a small machine shop or tool and die shop and have them do it for you. I got the dimension of this distance from a 2X teleconverter and used it (the teleconverter) to test the fit.

Any idea what the actual gap should be.... vs grind a little, then a little more trial and error? Especially for those that might take it to a shop and need to tell them make it this.

[DMJJR]

I have three Contax Carl Zeiss lenses-mm style-these are in like new conditon-a 28mm 2.8, a 135mm 2.8, and a 50mm, 1.7. Think these are worth about $700.00 so I really don't want to mess them up-I know a few machine shops-might have them do all three-any idea if the MM version of the lens will affect your instructions? Read some reviews that state the 28mm is the best ever made by any mfg so I would really like to use it. Also have a few Tamron Adaptall 2 PKA mounts-are they of any use doing this?

Thanks

[bigdawg]

Hayward wrote:

bigdawg wrote:

Any idea what the actual gap should be.... vs grind a little, then a little more trial and error? Especially for those that might take it to a shop and need to tell them make it this.

I'll do that today sometime for you Hayward. A very good suggestion.

Dawg

[bigdawg]

DMJJR wrote:

I have three Contax Carl Zeiss lenses-mm style-these are in like new conditon-a 28mm 2.8, a 135mm 2.8, and a 50mm, 1.7. Think these are worth about $700.00 so I really don't want to mess them up-I know a few machine shops-might have them do all three-any idea if the MM version of the lens will affect your instructions? Read some reviews that state the 28mm is the best ever made by any mfg so I would really like to use it. Also have a few Tamron Adaptall 2 PKA mounts-are they of any use doing this?

Thanks

Shouldn't matter the lens focal length but I've only done a few and they are all of similar focal lengths. I cannot tell you to do this as it would be your decision. As for the adaptall 2's I don't have one to look at and measure so I cannot speak to that.
The Carl Zeiss Lens are collector items and may be worth quite a bit to a collector of them. If you were to try this I'd recommend buying a cheap lens on ebay and try it first then progress on to those Zeiss lens. When you do one of them pick the one you least like or you can do without the most and do it. If the first two trys succede then do the others. Think smart and safe, as with any conversion they can go South on you in a hurrry.

Have fun !!

Dawg

[DMJJR]

Thanks for the reply-will have to think about this a while-might be worth it to sell them and not take a chance on ruining them. Appreciate your input.

[bigdawg]

DMJJR wrote:

Thanks for the reply-will have to think about this a while-might be worth it to sell them and not take a chance on ruining them. Appreciate your input.

You are more than welcome....I believe the truth is always the best path.



Dawg