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Discussion in 'Leica M and LTM Lenses' started by KS11, Jun 6, 2013.
saving bandwidth on photobucket.
looks like a nice lens.
I found my old write-up on this, and uploaded the How-To images.
A quick-fix now, will edit later.
The J-3 is based on the pre-war Carl Zeiss Jena Sonnar, and is available in Contax/Kiev mount and in 39mm thread mount.
Both versions are built to the Contax 52.4mm standard, according to the specification sheet that came with
the "new-old-stock" 39mm thread mount versions that I bought. This typically means that the lens must be
"shimmed" to work more accurately with a camera built to the Leica 51.6mm standard.
I've also found that the RF coupling in some lenses needs to be adjusted, as was necessary with this
1) the optics module unscrews from the focus mount;
2) Set the focus to infinity. The Focus Ring is held on by three set screws, undo them with a small jewelers screwdriver
and carefully put them somewhere safe. I use an ice-cube tray.
My Kitchen Table (when home alone!)
3) Keep the helical positioned at infinity. The Helical is held in the mount by 3 set screws. Loosen them, if too loose, place them somewhere safe. You can now move the helical
in the mount. If the lens could not drive the RF to infinity, it needs to be screwed in a bit more. If it drove the RF past infinity,
it needs to to come out a bit. You have to tighten the helical down to get an accurate reading from the camera. So, leave the helical in the infinity position, screw it in or
back it out of the mount, tighten the screws, and test it on the camera.
If the helical can't be screwed in far enough to get the RF to infinity, you need an extra step. You need to grind the mount down a little bit. Take out the three set screws
and store them safely. Take the helical out of the mount. The idea is to polish a little bit of the mount down so that the helical can be screwed in closer to the camera body.
I use some coarse sand paper for this, placing it on a hard flat surface. Move the mount over it in smooth, circular motions. Take off a little bit at a time. Thoroughly clean the
filings off of the mount and then Re-insert the helical into the mount, tighten the set screws, and check the RF alignment on the camera.
The Helical set to infinity should now couple with the camera, and show infinity for a distant object.
Now you need to get the focus ring back on, and have the distance scale read infinity. You need to
tap out three new holes for the set screws. This is a pain.
The Helical set to infinity should now couple with the camera, and show infinity for
a distant object. Now you need to get the focus ring back on, and have the distance scale read infinity. You need to tap out three new holes for the set screws. This is a pain.
I start by putting the focus ring over the helical and positioning the Infinity mark to the "thin red line". Scribe it, and ever-so-carefully begin to drill it out with a '000' drill bit.
Once the first one is done, I put in a set screw to hold the ring on and proceed to the next two screw holes.
Jason Howe hosts my PDF versions of working on the Jupiter-3.
50mm Jupiter 3 f/1.5 Information
I ended up taking a J-3 apart and tried to get an approximate measure of the focal lengths of the front section and of the back section. The math to change the focal length for the complete lens requires knowing the individual focal lengths. Some trial and error is required, but you need to move the rear triplet in ~1mm to get the lens close enough to the Leica standard for full range focus. I have one 1950 J-3 that is accurate at F1.5 from 0.75m to infinity.