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75 summilux back focus question


lawman

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I have obtained a late manufacture 75 Lux in lovely condition. It was supposedly 6 bit coded and cla'd by Leica. At 2 meters at 1.4 it is backfocussing 1-2". Is this something I have to live with, with this lens or should it go back to mother for adjustment? My m240 focuses right on with most of my other lenses and I use a 1.4 magnifier. Thanks for opinions.

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I have obtained a late manufacture 75 Lux in lovely condition. It was supposedly 6 bit coded and cla'd by Leica. At 2 meters at 1.4 it is backfocussing 1-2". Is this something I have to live with, with this lens or should it go back to mother for adjustment? My m240 focuses right on with most of my other lenses and I use a 1.4 magnifier. Thanks for opinions.

 

 

I had the same problem with my 75 'lux, including the 6-bit coding and CLA by Leica. For a couple of years I attributed my hit or miss focussing with the lens at close focus to my error, but sent it to DAG this winter for focus adjustment, it's now spot on.

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When I first obtained my 75mm Summilux in the M8 days, it was off focus.  I sent it in to DAG and it's been spot on with subsequent M9 and M240 cameras.

 

So what did DAG do to correct it? That is what I want to know. Was the helix cut incorrectly (unlikely) or was the thrust surface incorrect? That is the most important issue!

 

Rick, pay attention.

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Edited by pico
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So what did DAG do to correct it? That is what I want to know. Was the helix cut incorrectly (unlikely) or was the thrust surface incorrect? That is the most important issue! ....

Im not familiar with the 75mm Summilux, but I have sent in a 90mm Elmarit-M to Leica (Switzerland) for coding. When they sent it back, they stated that they had adjusted focus for infinity. I did not like the new behaviour and re-sent it, asking to improve focus for the close range. This they did and it was off at infinity. They said they couldn't adjust the lens for the whole range as they had run out of some parts.

 

This would suggest that the helix was off; I wonder whether different copies of that model varied by such an amount that they needed different helices.

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A really good independent repairer could file the helix, maybe.
BTW. the placement of the shims depends on the lens design. Sometimes between the optical cell and the barrel. I once had a 21/2;.8 ZM that shifted an element and Will told me each individual eement was shimmed. FWIW.

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I don't think filing would work. You'd have to turn a helix with a different steepness (if that's the term). I don't see how filing can turn a too steep helix into a flatter one, for instance.

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