Loving this J3 - with help from Mr. Sweeney

[former member]

My best J-3's have been the KMZ 1950's J-3's. The second best are those from GOmZ through about 1960. The worst have been from the 1980s.

http://ziforums.com/album.php?albumid=97

 

[raid]

I stay away from any J-3 made after 1965.

 

[MXP]

How do you use the J3 on the Leica M. Via a 39mm to M adapter? .....or is the J3 converted so it is re-born as a pure M-lens?

 

[tbarker13]

LTM converter.

 

[MXP]

How big is the difference between a Leica LTM and a FSU LTM? .....is the distance the same teoretic.....but needs to be adjusted in practise?

 

[former member]

The difference in travel of the optics module between the FSU 52.4mm Optics and the Leica 51.6mm optics is 0.1mm. Typically, I need to add a 0.1mm shim to optimize the lens for close-up/wide-open performance. Most J-3's need to be stopped down a little to F2 or F2.8 for infinity, where the Sonnar focus shift helps correct the residual error.

 

[raid]

Brian,
Are Contax mount J-3 lenses somehow better shimmed for a Contax than a LTM J-3 is shimmed for a Leica?

 

[former member]

Yes- the Contax/Kiev focus throw matches the FSU lenses. The FSU lenses are made to the Contax standard.

 

[raid]

This is good!
Does this imply that with the Amedeo adapter I will also get better focus on a Leica? I think, you may have said one time that this is true.

The lens is better shimmed for Contax body,and the adapter simply uses fixed spaces for the LTM fit,and then accordingly, the lens should be also shimmed correctly for the LTM body.

 

[former member]

Amedeo does not use an "indexed Cam". To perfectly match the Adapter to the Leica RF, a small cut needs to be made in the Cam to correct for the 0.1mm difference. Roland did this with an Adapter, and it works well.

 

[raid]

So I need to also have such a modification done?
Why didn't Amedeo do it?

 

[former member]

The original Orion adapters did not do this either, they basically do what I do on the J-3: set it to a good compromise position.

 

[raid]

So the extra work is to optimize focusing at close distances, and then have us use a smaller aperture for infinity?

 

[Amedeo Muscelli]

Hello Brian,
Please explain to me about the modification on the adapters, I understand than the 0.1mm but be corrected in the pitch of the helical, so instead to have a 4.5mm the helical should be 4.6mm. But the original Contax helical is 4.5mm and I am making it with this pitch.

 

[former member]

Roland put a cut into the RF cam of his adapter to translate the motion of the 52.4mm focal length of the Contax to the motion expected by the RF pickup of the Leica. Basically, it looks like the cut-cam on the M-Mount Summicrons to correct for slight deviations in the focal length. The motion of the Contax Helical "overdrives" the RF pickup without this cut.

I'll get some close-ups of the cut, again it is very shallow.
Took some, posted here:

http://ziforums.com/album.php?albumid=176

 

[raid]

Thank you, Brian. We learn all the time here.

 

[former member]

I'd just like to point out,

Seeing beautiful images that the OP put up makes all of this technical stuff about shims and indexed cams worthwhile...

 

[raid]

I agree. These are wonderful images that contribute more to world peace than any shimming.😀😀😀😀😎

 

[tbarker13]

Heh. My contribution to world peace. I like that.

 

[raid]

Tim,
If all people would focus on the beauty around them, there wouldn't be much time for anything else.