[Failed]Hacking early Opton Sonnar into J3 mount

[TenEleven]

I have tried and failed to mount a Carl Zeiss Opton 50/1.5 Sonnar with a frozen aperture mechanism, which common for those early silver-nose models, into a M39 Jupiter-3 lens tube and helical.

1. The front element has slightly different curvature and diameter, however this is so minimal that it will completely fit into the J3 mount.

2. The rear triplet in my particular Opton Sonnar was a press-fit with no threads. So I .. "liberated" it out of its mount using a metal file. The rear triplet is the exact same shape and dimensions as the J3 one. It can be mounted in either a KMZ element holder or straight into a later J3 lens tube, both fit.

3. The middle triplet is where the problems arise. Its diameter is identical, so it will slide right in for a tight fit. However the rear part, which faces the aperture mechanism has a different shape. When tightening down this ends up pressing against the aperture which does two things:

• renders the aperture mechanism inoperable

• prevents the lens from being fully seated in its mount changing the inter-element spacing. I've tested it as-is and while one can bring the focal length "back in" with the main shim and rear triplet adjustments there still is excessive curvature of field

I could try to remove the aperture mechanism and I'm nearly sure that it would work, but then I'd be stuck with the same problem that the lens already had in its original mount: No aperture mechanism.

I'm going to attach a picture of the rear elements side by side to this thread later.

 

[TenEleven]

Jupiter-3 glass on the left, Opton Sonnar front lens group still in its brass holder on the right.

The brass holder screws into three parts. The individual lens elements are now free.

The front lenses are similar, and the rear lenses while identical in diameter and height have a different rear protusion.

Better view of the Opton Sonnar middle triplet flat "brim" which pushes on the aperture actuator on the CZJ/J3 lenses. On the left is the J3 middle triplet which ends in a pointy shape.

Another view

 

[Sonnar Brian]

Many of the post-war West German Sonnars have bad glass from the cement failing. The glass on your lens looks good. It should be easier to find a donor barrel with working aperture mechanism to house the glass. Try a "want to buy" or "want to trade" here- it is free.

 

[Sonnar Brian]

As the shape of the middle triplet is the problem- have you tried using the middle triplet of the J-3 with the front and rear of the Sonnar?

 

[TenEleven]

As the shape of the middle triplet is the problem- have you tried using the middle triplet of the J-3 with the front and rear of the Sonnar?

Hey Brian,

Thank you for your input. I actually tried that but failed to report on it:

What happened was very strange - at least on my Nex 5 (APS sensor, which is my only digital camera) it had very strong field curvature but unlike the normal Sonnar curvature the sign was flipped; the corners reaching further away from the focus point. I first thought I had it in wrong way around, but nope.

I guess this is due to the Opton lens using different glasses which required altering the curvature of elements. That said the Russian donor was a Valdai lens, hardly ideal - but I was not going to "ruin" a perfectly good KMZ one.

As a "bonus" and more for a laugh, really, I put just the front element of the Opton into the Jupiter-3. Very little that I could see on the APS crop sensor changed. Sort-of confirming the hunch that in 50/1.5 Sonnars the front-most element is fairly uncritical.

I agree, that since it can't be transplanted and the glass is good with a crisp rendition typical of the Opton Sonnars, it should be moved into the housing of a beater. I'll keep an eye out.