j8 tuning

[rolleistef]

Hello,
could somebody please help me tuning my J8? 🙂
I've transplanted the optical part of a LTM J8, 1963 vintage, into a Kiev mount, the original J8 being near blind.
I've got slight difficulties to adjusting it correctly. I've put a focusing screen on the film rails and "focus" the lens using a loupe.
Now, the problem is (not new) that when it's properly collimated at infinity (using the chimney of a building in the distance) it isn't at 1 or 2m etc.
How then?
Thanks a lot!

 

[Valkir1987]

Did you measure the distance using the rangefinder of the camera, or did you measure it by hand? (or with the use of another camera). Maybe you need to readjust the rangefinder for this, not easy done on a Kiev.
A J8 in kiev mount is quite easy to get, and a lot cheaper then the ones found in LTM.

 

[xayraa33]

Try collimating it at the largest f stop opening at a distance of 1.5 metres or so.
Brian Sweeney did that on the J-3's he worked on.
at infinity the smaller apertures are usually used, so DOF can take care of some of the problems sometimes.

 

[rolleistef]

Hello, thanks for the tips!
if the focusing screen used is too thick ( from my Rolleiflex in this case) does it affect the result?
I measured the distance using a meter, at 2m. I've put a film in the camera today. Will give the results soon!
Luv,

 

[xayraa33]

Hello, thanks for the tips!
if the focusing screen used is too thick ( from my Rolleiflex in this case) does it affect the result?
I measured the distance using a meter, at 2m. I've put a film in the camera today. Will give the results soon!
Luv,

It can, I use a thin sheet semi opaque plasticized paper that looks like wax paper but thinner and less opaque and a loupe to focus accurately.
Brian S. liked using a piece of non exposed developed colour film scotch taped on the film plane of the camera.

 

[Ed S.]

Can you set up a set of distance tests using a measuring tape? An indoor test on a table or hallway floor, with a playing card (a face card, to focus on the pattern) set at 0.9m, 2m, and the marked ranges in between, should be simple to create.

An outdoor test is also a good idea; Select objects at measured distances of 3, 4, 5, 10 and 20m.

There is a small advantage to changing from a 8x loupe to a 15x loupe, and there are inexpensive sets on eB.

Perform your original tests again, preferably with a known-good 50mm lens. This is a sanity check, to make sure that you do not have a camera issue, and it is also a chance to collect data. At each measured distance, record the indicated range.

Do your tests again with your new J8, and note the indicated range.

Compare the collected data. How close are the results to the measured ranges? Close enough? Is one lens off a lot?

I’m guessing that you simply need a shim. If you have to compromise, getting focussing right at 1m, 3m and 5m might be the best choice.


I’ve found that using a translucent plastic shopping bag (the very thin ones) makes a reasonable replacement for ground glass. It isn’t quite as translucent, but it stretches, so getting it very flat is possible. It is also essentially free.

 

[rolleistef]

Ok I'll order a proper loupe and use translucent paper, "papier calque" we say in French 🙂.
Will do everything you said! RFF definitely is the most Dr-Frankenstein-photographer friendly place!
Are the LTM J8 and the Contax J8 different then, in spite of their looking essentially identical?