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: kididdoc at cox.net (Steve Barbour)
Date: Sun Dec 14 16:22:54 2008
References: <20081215001455.1ACE41059C@ws1-3.us4.outblaze.com>

On Dec 14, 2008, at 5:14 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

Marty,

is this simply due to the fact that with their potentially very narrow  
dof  they will show any focus shift  most readily  ?

Steve


> 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????)