I-61 woes, now

[Murray Kelly]

Thanks for the help with the counter on the FED-2
I was using an I-61 L/D but decided to switch to an I-61 plain (no L/D marking) to see if there was any difference at all, as has been suggested. I noticed the lens was quite movable sideways and checked the other two I-61s here.
The L/D is fine except for a tiny sideways slide movement but both the 'vanilla' ones were able to be rocked a little, side to side.
The LTM is held underneath by a ring with 3 screws and is sandwiched between the focusing mount and this ring.
These 2 lenses allow in/out movement - one by 0.04mm and the other by 0.1mm, which is quite a lot I would say compared to the lens register having to be +- 0.02mm to be in range.
My question is - would one pack the lens? I can see a case for leaving well alone. The other alternative is to pack, but what with? Maybe just grease.
Then there is the question as to where put any packing - above or below the LTM element in the sandwich between the ring and the focusing mount? Either has the possibility of changing the focal length of the lens.
I have seen this with other FSU lenses and chosen to ignore it as 'too hard' but I am intrigued to know what others may think.
Thanks
Murray

 

[Sonnar Brian]

I recently packed one with heavy vacuum pump grease to ease this problem.

BUT: I end up taking the I61 optics module out and making it into Contax mount. That completely solves the problem of GREAT optics being in such a poor mount.

 

[Murray Kelly]

I recently packed one with heavy vacuum pump grease to ease this problem.

BUT: I end up taking the I61 optics module out and making it into Contax mount. That completely solves the problem of GREAT optics being in such a poor mount.

Blast! Don't tell me that! I was vaguely thinking the other way round - using the mount for a Helios-103. I just don't have the Leica adapter you used.
I will try the grease, then. Presumably the vacuum pump grease doesn't creep? I've got white lithium and boat trailer grease which is really gooey.
Probably what they used in Kiev (or wherever) 😛
Thanks
Murray

 

[wolves3012]

Personally I've re-lubed every I-26 and I-61 that I own (several!) since they always come with gunged-up helicals. My copies have some float as you mention but I've never worried over it and they work just fine.

I have some doubts about the oft-quoted +/- 0.02mm tolerance. That's an error of just under 0.07% and I really wonder if the depth of focus (not depth of field!) for a lens is THAT shallow! If it is, I'd want to sack the lens designer. I suspect the film transport couldn't keep a film within that flatness too. Not that I've ever tried to measure these things, so I may be talking out of my rear-end!

 

[Sonnar Brian]

> I have some doubts about the oft-quoted +/- 0.02mm tolerance.

For an F1.5 lens it is critical. For an F2 lens, it gets the "sweet Spot" dead-on. The range covered by DOF is "acceptable" focus based on some arbitrary sized enlargement. For that, 0.02mm is covered by DOF.

For an F2.8 lens, a shim within 0.02mm should be fine. But I have still shimmed several LTM I61's.

The I61 and I26 mount cannot be used for the Helios-103. The optics module is too big, even for a J-3 mount.

 

[Murray Kelly]

Thanks, all. I will give the grease trick a go. It's pretty easily done.
I have seen the same problem with J-8s and tried shimming but all I seemed to achieve was a very stiffly moving J-8. A greasy sheet of paper was probably all I needed.
Pity about the H-103 being too big. I had one apart to 'dull' the iris blades and never thought to measure it while it was there in my hand.
Murray

 

[wolves3012]

> I have some doubts about the oft-quoted +/- 0.02mm tolerance.

For an F1.5 lens it is critical. For an F2 lens, it gets the "sweet Spot" dead-on. The range covered by DOF is "acceptable" focus based on some arbitrary sized enlargement. For that, 0.02mm is covered by DOF.

I'll bow to your greater experience and knowledge then, I admit lenses are not my forte! Just seemed a mighty close tolerance in percentage terms...