pre-war Elmar 9cm / 4 : backfocus

[kawabata]

Hello,

I picked up a nice copie of a pre-war black Elmar 90/4.

Only problem, once mounted on my Canon 7, it shows a strong back focus, to the point it is hardly usable.

I am wondering whether I am missign some shim, or whether the focusing block has been put together in a wrong way. The backfocusing distance gets longer with subjects further away. So I could guess, the problem is just that the optical block is too close to the film, by some fixed distance.

Does anybody have some experience with this lens, or some documentation available ?

I was hoping that using Leitz gear instead of my usual soviet lenses, I would avoid these issues, for once 🙂

Thank you in advance for your help.

 

[Sonnar Brian]

The optics module of the Elmar unscrews from the focus mount, but there is no shim. Mine did this, a chrome 9cm F4 Elmar, early coated lens. I had to polish down the focus mount so the optics would screw in farther. That worked. It took some trial and error for the focus, and you need a way to check the actual focus. The Canon 7 at "T" will do it, with a negative strip at the film gate.

Look at the repair instructions for the Jupiter-3 for using the Canon 7 with "T" setting for testing focus.

http://pentax-manuals.com/repairs.htm

 

[kawabata]

Thank you Brien. Yes, I will do some trials.

But I must say that I find the focus error suspiciously important. One point is the front elements can be screwed out from the opitcal block themselves. And there is lateral screw which could be meant to hold these front elements in a position further front. I wonder whether this could be a calibration mean.

 

[kawabata]

I did the tests. The optics seem to be around 2mm too close to the film. Sharpness at infinity is obtained when the lens (and the RF) is focused at about 7m. Weird thing is that looking at pictures of other samples of black elmars, the focusing block seems to behave the same (judging from its position at infinity).

Screwing out the two front elements does not give enough adjusting room. I could try to find a shim to reposition the optical block at the right position. Still, there is some mystery here; I still do not understand what is wrong.

 

[Landshark]

helical assembled incorrectly would do it, presuming the lens was serviced at one time.

 

[kawabata]

I think it is indeed an incorrect assembly.

I would like to see the corresponding pages in Tomosy's book. Ironically, google books shows it up to page 66 and the elmar is described on page 68....

Should anybody have the two corresponding pages handy, it would be of great help.

Edit : I found the pages on http://www.isbnlib.com

Seems one has indeeed to start by removing the mounting flange. I will need good screwdrivers, the screws seem quite stuck on mine.