Close-Focus Mod for J-3

[Brian]

I picked up another J-3 that had issues, and did a rebuild on it.

The J-3 uses a double helical focus mechanism, and in my opinion, is a simplification and improvement of the LTM Sonnar. Like the Sonnar, it uses two guide slots with guide pins to prevent the second helical from rotating, and to make it move forward and back as you focus. The LTM Sonnar and J-3 use a set screw in a groove for the near stop at 1M and infinity.

I took that screw out, and am using just the guide rail for close-up and infinity stops.

[Brian]

That was the easy part: taking something off the lens. Getting to it: not bad, remove the optics module from the mount, take off the focus ring, the groove with the stop screw is visible: then remove it.

That allows the lens to be focussed ~6" closer.

But, the threads of the mount will block the RF follower of the camera from keeping up with it.

SO: take out the set screws that hold the helical into the mount, take the helical out. You now have the lens mount without any moving parts in it that you can mess up because of the filing that you have to do. Find out exactly how the lens aligns on your camera, mark it, and file down about 1mm or so: about to the first thread.

[Brian]

I found that my Canon III and Bessa R2 could both follow the focus to ~2.5ft, rather than the usual 3ft. That extra 6" is nice in a portrait, I've often leaned back just a little to get the near focus on my J-3. This extra 6" should be quite nice.

Another close-up of the modified mount.

[Brian]

I got the first two rolls with the modified lens back yesterday, and scanned them in.

Overall, I believe this mod is worthwhile. J-3's are inexpensive, fast, and decent Sonnar lenses. Getting it to focus "just a bit closer" adds to its qualities.

Wide-Open at F1.5, at its new close-focus of ~2.5ft.



Stopped down a little.



And mid-range.





Focus at infinity is also good.

[Brian]

I ended up swapping the optics module on this lens with a known good 1956 KMZ.

Some of the photo's showed that one edge had much more field curvature than the other. Made shooting wide-open "risky". That was the original reason of why the lens was sent to me. I reseated the front element before, but went ahead and reseated all of them today. I'll try this module as a Nikon mount lens, see how it does.

[raid]

Originally Posted by Brian

I ended up swapping the optics module on this lens with a known good 1956 KMZ.

Some of the photo's showed that one edge had much more field curvature than the other. Made shooting wide-open "risky". That was the original reason of why the lens was sent to me. I reseated the front element before, but went ahead and reseated all of them today. I'll try this module as a Nikon mount lens, see how it does.

So the posted images are with the original module that was unsharp across the images?

[Brian]

Yes- this is with the original module. One edge seemed to have more field curvature than normal, made it hard to get a tight focus at F1.5 when holding the camera vertically. Then, turn the camera on its other side and they were fine. Drove me crazy.

The focus mount is SO SMOOTH, I wanted a really good module in it. I'll mount this one for the Nikon and shoot more tests as I reseated all of the optics. The KMZ 1956 module is perfect.

[raid]

I have a non-KMZ 1956 in Contax mount.

[Brian]

As far as I know, KMZ started the J-3 line, evolved from the German Sonnar's after WW-II. The other manufacturers started in the mid to late 50s. My 1959 J-3 is not a KMZ, and is a great performer.

The 56 lens that I started with was sent to me with problems, I took it and some cash for a perfect J-3. I tried just reseating the front element, which helped but still left it with "anomalies". Try, try again!

[LeicaTom]

Nice Work Brian, it really moves in perfect for portrait`s........now I need one of these too, hmmmm have to find a Postwar Russian Army one with WW2 CZJ glass in it and have you carry out the CU mod - ANY SUGGESTIONS?

Tom