Nomad Z
Well-known
Brian, can a pre-war 50 f2 collapsible CZJ Sonnar for Contax be readily fitted into a J-8 mount for LTM?
Pre-war Sonnar into J-8?
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Yes, I have done several of these. The Jupiter Aperture ring must be used on the pre-war Sonnar. The Wartime Sonnar "T" can keep it's aperture ring, seems to be smaller diameter.
After the switch- the collapsible mount can be used for an Industar-61, but the taper of the J-8 prevents it from mounting into the collapsible mount.
Wartime Sonnar (~1941) in J-8 mount. The pre-war uncoated lens must use the aperture ring from the J-8. ANY J-8 mount will work, I have used from 1954 through to 1986 mounts.
After the switch- the collapsible mount can be used for an Industar-61, but the taper of the J-8 prevents it from mounting into the collapsible mount.
Wartime Sonnar (~1941) in J-8 mount. The pre-war uncoated lens must use the aperture ring from the J-8. ANY J-8 mount will work, I have used from 1954 through to 1986 mounts.
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roadmouse
Member
I'm kinda new to this. But is this conversion easy to do?
I would love to have an Sonnar with LTM!
I would love to have an Sonnar with LTM!
The worst part is collimating the lens, ie setting the shim correctly for focus to agree with the RF. After that, you need to "re-index" the aperture ring to it lines up again.
Instructions for converting the 5cm F1.5 are here:
http://www.rangefinderforum.com/forums/showthread.php?t=79975&highlight=conversion
The F2 lens is similar, except the aperture ring will probably have to be switched.
http://www.rangefinderforum.com/forums/showthread.php?t=79975&highlight=conversion
The F2 lens is similar, except the aperture ring will probably have to be switched.
roadmouse
Member
I think I'll give it a try. Thanks for the info Brian!
Nomad Z
Well-known
Thanks Brian. Am I right in thinking that the smaller screw with the red arrow pointing to it in the attached photo is the one that needs to be removed to allow the optics module to be unscrewed?
Also, why does the J-8 aperture ring need to be used? Does part of the J-8 barrel foul the Sonnar ring?
Also, why does the J-8 aperture ring need to be used? Does part of the J-8 barrel foul the Sonnar ring?
The single set screw holds the optics module in place, it should come out once it is out. The Sonnar aperture ring is too high in diameter to fit in the J-8 mount.
Nomad Z
Well-known
I take it the larger screw nearby has something to do with holding the bits for the collapsible bayonet in place. I just realised you already mentioned the diameter (oops). I'm wondering of there's scope for removing material from the J-8 mount instead. Inside diameter measures 43.6mm, and the ouside dia of the Sonnar ring is 43.75mm, so it should be possible to bore out the mount a little on a lathe. It's then a case of whether the ears on the Sonnar foul the edge (more lathe). I'll look into this at the weekend.
Nomad Z
Well-known
Nearly there, but stuck at one bit. How do I separate the chromed part of the aperture ring from the bronze coloured part? I have removed the three set screws.
Answer: Brute force - it unscrews towards the back of the lens.
Answer: Brute force - it unscrews towards the back of the lens.
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Ron (Netherlands)
Well-known
Very interesting, since I also have a nice old pre war sonnar lying around, would like to try also. Could you please put up some pictures of your work?
thanks
Nomad Z
Well-known
A-a-a-a-nd....... ..........breathe.
Just finished - photos soon.
Just finished - photos soon.
Nomad Z
Well-known
Here's what I did to fit a pre-war Contax mount 50mm f2 Sonnar fit into a Black Jupiter-8 LTM mount. I wanted to retain the Sonnar's aperture ring. The problem with this was the diameter of the Sonnar's ring is larger than the inside diameter of the J-8's focus ring (which extends over part of the aperture ring). The solution is to take a hammer and chisel to the J-8, and hack big lumps out of it to make clearance.
Okay, not a hammer and chisel, but a lathe. 🙂
First thing to do is get the focus ring off and chuck it up on the lathe. With this done, I used a dial guage to check that any runout was within an acceptable limit. With the lathe switched off, the chuck is rotated, and deviation noted on the dial guage. It spanned about 50um (microns - thousandths of a millimeter) - deviated +/-25um (1 thou in old money). Good enough for me, since I was looking to make the inside diameter bigger by at least 200um.
Next, I put the boring bar into the lathe's tool holder, and brought it up to the job. The boring bar is a lathe cutting tool that works 'backwards' - the cutting edge is towards you and it's drawn outwards to cut on the inside surface of a cylinder.
The third photo shows the focus ring with the material cut away from the inside. The eventual diameter was 43.9mm - 0.1 larger than the outside diameter of the Sonnar's aperture ring.
Okay, not a hammer and chisel, but a lathe. 🙂
First thing to do is get the focus ring off and chuck it up on the lathe. With this done, I used a dial guage to check that any runout was within an acceptable limit. With the lathe switched off, the chuck is rotated, and deviation noted on the dial guage. It spanned about 50um (microns - thousandths of a millimeter) - deviated +/-25um (1 thou in old money). Good enough for me, since I was looking to make the inside diameter bigger by at least 200um.
Next, I put the boring bar into the lathe's tool holder, and brought it up to the job. The boring bar is a lathe cutting tool that works 'backwards' - the cutting edge is towards you and it's drawn outwards to cut on the inside surface of a cylinder.
The third photo shows the focus ring with the material cut away from the inside. The eventual diameter was 43.9mm - 0.1 larger than the outside diameter of the Sonnar's aperture ring.
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Ron (Netherlands)
Well-known
Nomad Z
Well-known
I then disassembled the rest of the J-8 mount, cleaned up and regreased the helical, and refitted the focus ring...
At this point, I stuck the mount on my M2 to check the infinity end-stop in the rangefinder. I was lucky - it was near enough spot on, and no adjustment of the focus ring was needed. I then adjusted the close focus to get it to match the rangefinder, using an old SLR focussing screen to look through the lens with the back removed from the M2. It took nearly two turns of the end-stop ring on the Sonnar to get a match.
The next bit was to reposition the aperture ring so that it lined up with the index mark on the barrel. After removing the set screws, it took a bit of 'confidence' to get it to turn - it was pretty stiff. The aperture ring is threaded into the tapered bronzey part, so, once it was moving, it was pretty easy to get it into a suitable position. The next photo shows the lens after reassembly has been completed...
As you can see, the Sonnar aperture ring fits nicely inside the J-8 focussing ring. Note that the tapered shape of the focussing ring has not resulted in a sharp edge - if it had been neccessary to remove more material than I did, I would have had to clean that up on the lathe with a quick perpendicular cut.
Can't do one of these without a fire-for-effect shot, so here it is attached to my IIIf...
Rather cool, even if I do say so myself, and I'd like to thank Brian again for his advice and tips - certainly helped the conversion to go smoothly.
At this point, I stuck the mount on my M2 to check the infinity end-stop in the rangefinder. I was lucky - it was near enough spot on, and no adjustment of the focus ring was needed. I then adjusted the close focus to get it to match the rangefinder, using an old SLR focussing screen to look through the lens with the back removed from the M2. It took nearly two turns of the end-stop ring on the Sonnar to get a match.
The next bit was to reposition the aperture ring so that it lined up with the index mark on the barrel. After removing the set screws, it took a bit of 'confidence' to get it to turn - it was pretty stiff. The aperture ring is threaded into the tapered bronzey part, so, once it was moving, it was pretty easy to get it into a suitable position. The next photo shows the lens after reassembly has been completed...
As you can see, the Sonnar aperture ring fits nicely inside the J-8 focussing ring. Note that the tapered shape of the focussing ring has not resulted in a sharp edge - if it had been neccessary to remove more material than I did, I would have had to clean that up on the lathe with a quick perpendicular cut.
Can't do one of these without a fire-for-effect shot, so here it is attached to my IIIf...
Rather cool, even if I do say so myself, and I'd like to thank Brian again for his advice and tips - certainly helped the conversion to go smoothly.
Nomad Z
Well-known
Pictures should be fixed now. (I can't seem to insert full size images, however - my uploads were 800 pixels wide, but they got resized and turned into thumbnails.)
Ron (Netherlands)
Well-known
THanks Nomad, pictures are ok now! Great work! Lovely to see that black Jupiter/Sonnar at the Barnack
Nomad Z
Well-known
Thanks, Ron. Turning one's spare room into a machine shop definitely has its advantages. 😉
Ideally, I'd rather have a silver mount because the front of the black J-8 mount rotates with focus - the aperture index mark goes off-centre. As it was, a black one was what I had lying around. It was actually earmarked for my FED 1C (also pre-war), assuming I can get its non-standard lens registration sorted out (going to see what I can do with a FED 2 mount that somebody is sending me). However, the unexpected arrival of the Sonnar meant that the J-8 was sacrificed for the cause.
I have a silver J-3, but I didn't want to use that because I recently calibrated it for Leica (and its coated, and faster). I can keep my eyes open for a silver mount at a good price, and move the Sonnar into that later. In the meantime, this will let me use it.
Ideally, I'd rather have a silver mount because the front of the black J-8 mount rotates with focus - the aperture index mark goes off-centre. As it was, a black one was what I had lying around. It was actually earmarked for my FED 1C (also pre-war), assuming I can get its non-standard lens registration sorted out (going to see what I can do with a FED 2 mount that somebody is sending me). However, the unexpected arrival of the Sonnar meant that the J-8 was sacrificed for the cause.
I have a silver J-3, but I didn't want to use that because I recently calibrated it for Leica (and its coated, and faster). I can keep my eyes open for a silver mount at a good price, and move the Sonnar into that later. In the meantime, this will let me use it.
Looks great. Increasing the diameter of the J-8 mount is a great solution for retaining the "winged" aperture rings, a step oddly enough - not required for the wartime "T" 5cm f2.
On the chrome mount: the Tabbed version is usually the best. The chrome mount without the Tab- made later, and I have found the tolerances are not as good as the early ones. I have found more slop in the helical. I have my Wartime lens in Tabbed mount, as shown. I also moved my pre-war lens to a Tabbed mount from a Black mount.
The Jupiter-3 mount fits the 5cm F1.5 Sonnar.
On the chrome mount: the Tabbed version is usually the best. The chrome mount without the Tab- made later, and I have found the tolerances are not as good as the early ones. I have found more slop in the helical. I have my Wartime lens in Tabbed mount, as shown. I also moved my pre-war lens to a Tabbed mount from a Black mount.
The Jupiter-3 mount fits the 5cm F1.5 Sonnar.