Archived posting to the Leica Users Group, 2008/12/14

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Subject: [Leica] M8 upgrade - 90 Cron APO focusing problems now Question????
From: len-001 at verizon.net (Leonard Taupier)
Date: Sun Dec 14 17:12:15 2008
References: <20081215001455.1ACE41059C@ws1-3.us4.outblaze.com>

Marty,

I run resolution tests on my lenses after I buy them. When I ran the  
tests on the Noctilux I found a similar result to what Erwin  
describes in his testing. It was a pretty screwy test result. I was  
able to slightly change the focus to get very good resolution numbers  
at the stops between f2 and f5.6.  I then did some research and found  
Erwins test results on the Noctilux. I actually lived with the lens  
on film cameras shooting at f1.0 only. When I got the M8 the focusing  
errors became much worse and I decided to try the rangefinder  
adjustment procedure that was floating around the Leica Camera Forum.  
It seemed to fix the Noctilux and 75 Summilux focus issues by  
slightly setting the rangefinder to front focus wide open. However I  
also found that the focus from around 50 feet to infinity was way off  
on my 90mm Summicron AA and my two 135mm lenses. I eventually sent my  
Noctilux and 75 Summilux to Don Goldberg to get adjusted. I got a 2nd  
M8 and aligned my original M8 rangefinder to be as original. Now my  
lenses are fine. As far as older lenses go I have the 50mm f1.5  
Summarit and Xenon and 85mm f1.5 Summarex. These older lenses don't  
back focus. Actually most of the older lenses have a fairly centered  
DOF. I also have not seen any focus issues with the 50mm f2 Summar,  
Summitar or any version Summicron up to the most recent version. It  
has been my feeling that the older lenses were either built to  
tighter tolerances or tested to more stringent standards. I have no  
way to verify this except for my own experience and testing.

Len


On Dec 14, 2008, at 7:14 PM, Marty Deveney wrote:

>
> Len wrote:
>> The two lenses that I have that have a definite focus shift are
>> the Noctilux and the 75mm Summilux.
>
> Apologies if I jumped too fast, but there is some incredible  
> garbage being promulgated on the web about focus shift.
>
> The f1 Noctilux and the 75 Summilux definitely display the most  
> focus shift of the Leica lenses designed after 1970 or so (I  
> haven't tested many earlier lenses, but they tend to be more  
> conservative designs so they may not show much shift).  As they  
> left the factory, the 75s were adjusted to have a tiny amount of  
> front focus at f/1.4.  As you stop down, the focus shifts backward  
> but within the depth of field.  If you adjust for perfect focus at  
> f/1.4, your lens will focus incorrectly until depth of field  
> catches up at f/8.  Erwin describes the behaviour of the Noctilux  
> and its focus shift here: http://www.imx.nl/photo/leica/lenses/ 
> lenses/page56.html
>
> Dante Stella gives a good explanation about why adjusting the  
> rangefinder in your camera to 'fix' focus shift is hazardous:
> http://www.dantestella.com/technical/leicadjust.html if you have a  
> range of fast lenses, don't even think about it.
>
> My 35/1.4 ASPH tended to focus behind the point of focus when I  
> first put it on my M8.  A trip to Leica fixed that.  It displays  
> remarkably little focus shift considering the design - perhaps  
> Leica will redesign all their lenses to include a floating element  
> at some stage.
>
> Marty
>
> Gallery: http://gallery.leica-users.org/v/freakscene
>
>
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In reply to: Message from freakscene at weirdness.com (Marty Deveney) ([Leica] M8 upgrade - 90 Cron APO focusing problems now Question????)