A question about 50mm 1.5 LTM Summarit

[Wayne]

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This may be a hard question to answer, given the fact that it involves a purely tactile aspect of the lens.

 

Should one expect that the force required to rotate the the focus ring of one of these lenses will be significantly greater than that which is needed to rotate a new/newer Leica lens? I have had the lens serviced (Lapped) and it is now much smoother in rotation, but is not significantly easier to rotate.

 

While I am at it, I also have a comment and question on the common practice of lapping lens helical elements:

 

I spent nine years in the engine rooms of navy ships and am more than familiar with the theory and practice of "lapping." As used in the mechanical spaces, it involved the use of an abrasive paste to perfect the mating surfaces of metal elements- such as valve seats and discs- in order to allow them to better seal when brought together. As I understand, lapping of camera lens focus helical is routinely performed to remedy stiff or uneven focus ring rotation. It seems, to me, that problems associated with focus ring rotation would be largely related to stiff, dirty, or insufficient lubrication; and, the cure would be cleaning off old lubricant and applying new. I cannot understand how applying an abrasive, i.e. lapping compound, would not be, ultimately, destructive in the long haul. Am I missing something important? Is lapping the ideal means of correcting stiff or uneven focus ring rotation on old lenses,? or is it simply the fastest and most economical way to address such problems?

 

Thanks for the benefit or your knowledge and/or experience.

Edited December 1, 2015 by Wayne

[TomB_tx]

I agree - the stiffness on old lenses is normally just old dry grease, and cleaning and re-lubing properly should cure it. Lapping would be more to smooth a newly machined thread, but should not be needed on well machined parts. The last new Summicron 50 I bought was stiff and a bit rough on focus when new, but wore-in on its own with use, and now is perfect.

I've often found just a tiny drop of very light oil on a focus helical, or on the aperture ring and barrel joint, will free up old lenses. (Not a cure to avoid a CLA, but a stop-gap solution.)

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[jaapv]

I agree - the stiffness on old lenses is normally just old dry grease, and cleaning and re-lubing properly should cure it. Lapping would be more to smooth a newly machined thread, but should not be needed on well machined parts. The last new Summicron 50 I bought was stiff and a bit rough on focus when new, but wore-in on its own with use, and now is perfect.

I've often found just a tiny drop of very light oil on a focus helical, or on the aperture ring and barrel joint, will free up old lenses. (Not a cure to avoid a CLA, but a stop-gap solution.)

If one uses thin silicon oil, the solution is not all that stop-gap.

[250swb]

 Am I missing something important?

 

Yes, lapping is done when there are other compensating adjustments that can be made, so lapping a valve removes metal and that is compensated for in adjusting the valve clearances. If you lap a lens helical you are removing metal without any way to mechanically compensate, you then rely on the grease for fine adjustment, not very accurate or dependable.

 

Old lenses are not by default stiff even if the grease has dried. But try enough old and modern lenses and you'll find that the focus weight is variable on all fully adjusted and fettled lenses of widely different designs, so it's down to the design of the lens more than servicing if one is stiffer than another. So I think lapping is a barbaric way to loosen up the helical, it's two pieces of brass after all, they would 'self lubricate' and lap each other in anyway, the grease is as much to stop dirt and water getting all the way through and inside the lens as it is needed as a lube.

[Wayne]

Thanks for the responses.

 

What brought the question is the fact that, inquiring two reputable, i.e. listed, repair/service providers, all stated that lapping would be the means of addressing the stiffness and my LTM Summarit. This, before ever seeing the lens.

 

@250swb:

"Yes, lapping is done when there are other compensating adjustments that can be made, so lapping a valve removes metal and that is compensated for in adjusting the valve clearances."

 

Yes, that is  my understanding of lapping.....and the reason for my concern regarding its use in lens repair.

 

Best regards,

[jc_braconi]

As I make my own CLA I can assume 99% that your lens need only cleaning and new adapted grease, after that there are lapping and lapping.

Speaking about precise mechanical element in the lenses or jewellery, watches mechanism have no thing in common with engine pieces  so there are lot of lapping compound with different shape grinding element. For example the fine mechanism need round structural grindind element so there are not embedding soft material like the large variety of copper alloyes.

[pico]

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it's two pieces of brass after all, they would 'self lubricate' and lap each other in anyway,

 

Don't you mean sintered bronze rather than brass?

Edited December 1, 2015 by pico

[spydrxx]

I have to wonder if the originl stiffness may have been due to some minor impact which might have slightly deformed a helical thread. I had that occur several years ago, and DAG brought it back to butter smoothness and ease of use...although I don't know if he lapped it.

[menos I M6]

Wayne, with the brass helical in these Leica lenses the means of how much force is needed to adjust focus is mainly a means of different types of lubrication and different techniques on how to properly lubricate them.

 

The 50/1.5 Summarit is a fairly old lens, designed back in the late 1940's, when entirely different lubricants where widely used than are available today (there has been a revolution in lubricant technology over the past few decades).

 

Nowadays seldomly will be the same lubricant be used to re-lube such a vintage lens, but a replacement.

Not always the choice of lubricant and lubrication technique results in the perfect feel you expect (and different people do also have different preferences on how their lens should "feel" - some like it light, focus by the pinky, some like it smooth but squishy and heavy to rotate, some like it fast yet still well dampened, …

 

It is best to get in touch with the person who serviced your lens and talk about you wanting to have it "lighter".

A different lower viscosity lubricant can be used - maybe it was also excessively lubed (which leads to very heavy dampening).

 

If this fails, I agree that Don Goldberg from DAG camera in the US is reputed to be able to get difficult lenses to "feel" just right when others have failed.

 

When I do CLAs on vintage lenses it does take with certain lenses several tries with different types of grease to get the feeling just right. Mostly this is all that is needed.

 

Normally a "lapping" on the helical of a vintage lens is exclusively needed when said lens has been deformed (damage through shock, taking a hit when falling, etc).