Contax lens register?

[Grytpype]

It always surprised me that there seems to be a lot of uncertainty about the exact lens register for the Contax mount. Some say that the distance to the film plane from the front of the outer bayonet should be 35mm. Peter Tooke's repair book for the Contax II/III states that the Contax IIa/IIIa manual gives the figure from the front of the INNER bayonet as 35mm, which is completely wrong (by about 3mm), and he has redrawn the original Zeiss Ikon diagram to support this thesis!

Now that I have seen a copy of the Contax IIa/IIIa manual, I am certain that the 35mm figure is based on a misunderstanding of the diagram in the manual.

First I have attached a picture from the manual showing the tools used for setting the register.

 

[Grytpype]

I have attached another picture showing the set-up used for checking the register, and here is a rough translation of the instructions in the manual:

Alignment of the lens surfaces on the inner and outer bayonet must be made with extreme care. To adjust, a surface table with Fühluhr [dial gauge?] (1/100 mm reading) is required.

Before beginning the adjustment, put the gauge block 563/24 M/715-3 on one of the longitudinal cut surfaces of the support for the film plane 563/24 M/715-1 and set the dial indicator to 0.

Place the camera with open shutter (set to T) on the support 563/24 M715-1, put the bayonet to infinity and place the insert 563/24 M715-2 into the inner bayonet.

By placing shims 39 371 or 39 372 under the screw holes of the outer bayonet the lens support is to be adjusted so that when the screws are tightened well the indicator shows again at 0 (maximum deviation permitted +0.01 / -0.03 mm).

The original text gives a second series of tool numbers which applied pre- December '52, that I have omitted for simplicity.

 

[Grytpype]

So from this, the method would work as follows:

1/ You place the first tool 563/24 M/715-1 on the surface table, stand the gauge-block 563/24 M/715-3 on the precision-ground surface of this tool and zero the dial-gauge on its top surface (from what follows you can deduce that the height of this gauge-block must be exactly 35mm).

2/ The camera is placed on the support 563/24 M/715-1 so that the rectangular section screwed to the tool locates in the film gate, and the film rails lie on the ground surface of the tool.

3/ You place the circular piece 563/24 M/715-2 so that it rests on the front of the inner bayonet, and set the pointer of the dial-gauge on to the front (top) surface of the circular piece. If the register is correct the dial-gauge will read zero, and if it isn't, you correct with shims as you would expect.

Thus the register is set from the front of the inner bayonet, and is equal to 35mm MINUS the thickness of the disc 563/24 M/715-2.

The attachment shows the diagram that illustrates this, and you can clearly see that the 35mm dimension is to the surface of the disc 563/24 M/715-2, not to the front of the outer bayonet. It is possible that the surface of the disc should, in fact, be at the same level as the outer bayonet, though there is nothing to confirm this. The diagram actually shows the outer bayonet as being slightly forward of the 35mm mark, though I suspect it should be slightly below it.

 

[Grytpype]

Unless there is some other Zeiss Ikon literature which gives an actual figure for either bayonet (or unless someone finds they have a 563/24 M715-2 disc lying around in their junk box!) there doesn't seem to me to be any way of finding a definitive figure. The Kiev Survival Site quotes the Peter Tooke book, though unlike the book he does give the 35mm figure as being to the outer bayonet. I found a list of mounts here that gives a figure of 34.85mm to the outer bayonet (which I suspect may actually be near the mark).

The only camera I have measured accurately so far is a 1975 Kiev, which was 34.90mm to the outer bayonet (plus/minus about .02mm), but perhaps a late Kiev is not the best guide.

Does anyone have any other information, or accurately measured figures?

Steve.

 

[bowieknife]

34.85mm:
http://www.graphics.cornell.edu/~westin/misc/mounts-by-register.html

 

[Grytpype]

The link in my previous post is the same site. I'm just not sure how reliable their figures are: for example for Exakta they give 44.7mm, whereas the correct figure is 44.72mm. Not a huge difference, but outside the official Ihagee tolerance which is plus/minus .01mm.

If they use an inaccurate figure for a register which is easy to find elsewhere online, can we be sure their Contax figure is correct? Their figure is fairly close to my Kiev measurements, though, which is why I think it could be in the right ball-park.

 

[Grytpype]

More support for 34.85mm. On the Zenit Camera page for the Jupiter-12 there is a cutaway diagram of the lens in Kiev mount showing the 34.85mm dimension to the front of the outer bayonet.

In the absence of any reliable information to the contrary, I think 34.85 is the number to go for.

Edit 07/05/12:
It looks as though the zenitcamera.com site may have closed, but the diagram on the page I linked to is availble on Wayback Machine at:
http://web.archive.org/web/20081204114839/http://www.zenitcamera.com/archive/lenses/jupiter-12.html

Edit 16/11/12:
Possibly worth mentioning that I have checked one Contax II since last edit, which measured exactly 34.85mm to the front of the outer bayonet. I'd reckon my measurement method accurate to .02mm, so there is no doubt that 34.85mm is the correct figure.