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Multilens Backfocus Adjust Success!


JWW

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My M8 and all 5 of my Leica lenses were focusing fine until I tried out a 75mm Summilux. Thanks to Sam Shohan at Classic Connection, he mailed out two used 75mm's out to me on Maui and I found out that both backfocused, one more than the other but only at medium distances (8 ft and farther). I tried tripod tests at 3ft and 12 ft for the 75mm and all my other lenses. All focused fine at 3ft with varying centers of focus in the DOF field. All except the 75mms focused fine at 12 ft. At 12 ft distance one 75mm backfocused 1ft and the other about 1.5ft. By just barely moving the focus lever on the 75mm (and that's a long rotation focus ring!) to the nearside I can compensate and move the focus point closer by 1 ft. With such a small rotation required, imagine how small a movement that translates at the camera roller arm! I discussed this with DAG and they can adjust lenses but the shims are thicknesses of scotch tape. I believe we are at the limit with the 75mm 1.4 and the noctilux of what can be adjusted at the factory without custom matching.

 

To make a long story short, since looking at the DOF fields of all the non 75mm lenses, there was enough of a focus circle that if I could move the focus point forward on all of them, that might put the 75mm in focus also. So using the 2mm allen wrench, I moved it just slightly to get the 75mm in focus at 12ft and about 1in front focus at minimum distance. I now tried the other lenses and sure enough, they were all still in focus, just the focus point moved a little forward but since their DOF areas are so much larger it's ok.

 

So anyway this worked out well, so all six lenses seem ok now. I will do more comprehensive tests at all distances later today.

 

 

Jan

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I believe we are at the limit with the 75mm 1.4 and the noctilux of what can be adjusted at the factory without custom matching.

 

To make a long story short, since looking at the DOF fields of all the non 75mm lenses, there was enough of a focus circle that if I could move the focus point forward on all of them, that might put the 75mm in focus also. So using the 2mm allen wrench, I moved it just slightly to get the 75mm in focus at 12ft and about 1in front focus at minimum distance. I now tried the other lenses and sure enough, they were all still in focus, just the focus point moved a little forward but since their DOF areas are so much larger it's ok.

 

So anyway this worked out well, so all six lenses seem ok now. I will do more comprehensive tests at all distances later today.

 

 

Jan

I think your point is absolutely right. And this is a solution which is brilliant and realistic. Since I only have a 28mm 2.8 and a Noctilux, it could be THE solution for me (backfocusing Noctilux) and possibly for many other Leica users. Did your tests turn out OK? I will be away for one week, but I hope to read about your tests when I'll be back. Best Regards, Alex

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My M8 and all 5 of my Leica lenses were focusing fine until I tried out a 75mm Summilux. Thanks to Sam Shohan at Classic Connection, he mailed out two used 75mm's out to me on Maui and I found out that both backfocused, one more than the other but only at medium distances (8 ft and farther). I tried tripod tests at 3ft and 12 ft for the 75mm and all my other lenses. All focused fine at 3ft with varying centers of focus in the DOF field. All except the 75mms focused fine at 12 ft. At 12 ft distance one 75mm backfocused 1ft and the other about 1.5ft.

This exactly what I reported on this forum 2 weeks ago for my 75mm cron. I was advised to return the lens to Leica, and that is what I did.

 

By just barely moving the focus lever on the 75mm (and that's a long rotation focus ring!) to the nearside I can compensate and move the focus point closer by 1 ft.

What exactly did you do. What is and how do you move the focus lever.

Could you show some pictures ?

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Alex: All the lenses are focusing fine including an used 50mm lux preAsph that I just bought. The only critical one was the 75mm lux since that has such a short DOF. The M8 was adjusted for the 75mm and all the others were still ok in their DOF range. I am waiting for the 30% coupon Noctilux and that's the one I'm worried. Hopefully it will match the 75mm lux. Otherwise, I'll have to send them in to get matched up.

 

 

Hans: Adjustments were made to the M8 infinity allen adjust- just do a search for backfocus and you'll get plenty of pictures.

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