Archived posting to the Leica Users Group, 2007/09/01

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Subject: [Leica] Re: do it yourself back-focus adjustment..."
From: hoppyman at bigpond.net.au (G Hopkinson)
Date: Sat Sep 1 23:20:34 2007
References: <98A0D67D-CE25-48F3-84D2-A34BBA5BEC1C@mac.com><002001c7ec8b$e5295910$6400a8c0@corp.nortel.com><5DDF2A59-8784-410E-9C7C-C56C8073DAB1@mac.com><001701c7eced$f924a0c0$6401a8c0@asus930> <A5BF3089-C334-4065-87FF-7BA589E05B00@comcast.net>

Len, understood. You are describing a focus shift as you stop down slightly, 
rather than a global  focus error requiring individual
lens adjustment. Focus presumably correct wide open, shifts as you stop down 
owing to residual aberration. Error not apparent as you
get to smaller apertures with greater DOF. Evidently your method works for 
you guys and that's what is important. Worth reading the
article in the August LFI on the subject, if you get a chance. Thanks for 
the information.
Cheers
Hoppy

-----Original Message-----
Subject: Re: [Leica] Re: do it yourself back-focus adjustment..."

Hoppy,

The adjustment is the infinity adjustment cam just inside the camera  
mount. The close focus adjustment is actually behind the Red leica  
dot on the front of the camera. It's not a case of just adjusting DOF  
to be favoring in front or in the rear of the focus point. In the  
case of the Noctilux and the 75mm Summilux, from wide open to a stop  
or two closed all the photos are just plain out of focus. Between  
about 5 to 10 feet from the target, the only thing in focus was  
behind the target. I own 19 M lenses that I can use on my M8 and 5  
LTM lenses I use with adapters. After my adjustment every lens  
focuses perfectly on the M8 except the 135mm at infinity. So I am not  
matching 1 lens to 1 body. I don't think the 24 lenses needed  
adjustment and the M8 didn't. BTW leica does not recommend using a  
135mm on the M8.

Len


On Sep 1, 2007, at 7:15 PM, G Hopkinson wrote:

> Guys can someone be explicit there regarding what you are  
> correcting? Focus wide open at practical infinity or a close position?
> Focus at a particular f stop?  Someone said that they are adjusting  
> so that there is more apparent DOF in front than usual. Since
> the acceptably sharp zone will always be deeper behind, I read this  
> as actually moving the sharpest point forward.
> There is a difference between a global back focus (lens adjustment  
> error) and a focus shift visible near wide open as you stop down.
>
> I can certainly understand that you may end up with an adjustment  
> that works in practice for your own circumstance (lens and use),
> I'm just really interested as it seems to me that you are  
> introducing new errors, especially with other lenses for example.  
> It may
> be that DOF masks the error with other lenses. Just guessing, I  
> imagine that Leica is checking/adjusting the individual lens focus
> mechanism, which is not the same as adjusting the camera body  
> roller arm naturally.
>
> The inquiring Hoppy wants to know.
>
> -----Original Message-----
> Subject: [Leica] Re: do it yourself back-focus adjustment..."
>
> Vick,
>
> The original idea to do this came from the Leica Forum.  Look there
> if you want to find a more rigorous approach to the problem.
>
> Bob
>
> On Sep 1, 2007, at 4:33 AM, Vick Ko wrote:
>
>> Okay, now I understand.
>>
>> You are adjusting the RF arm.  I anticipate that it only takes a
>> very very
>> small amount of adjustment.  If the adjustment is large, then you
>> will end
>> up affecting the infinity alignment of the RF image.
>>
>> Congratulations on discovering this method.
>>
>> regards
>> Vick
>>
>> -----Original Message-----
>> From: Robert Rose [mailto:robert.rose@mac.com]
>> Sent: Saturday, September 01, 2007 2:33 AM
>> To: Leica Users Group
>> Cc: vick.ko@sympatico.ca; Leonard J Kapner
>> Subject: do it yourself back-focus adjustment..."
>>
>> Vick,
>>
>> We had a thread on this around March or so.  I had posted some
>> samples and
>> how to do it at:
>>
>> http://gallery.leica-users.org/v/rjrose/focus/
>>
>> Bob Rose
>>
>
>
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> See http://leica-users.org/mailman/listinfo/lug for more information
>
>
>
> _______________________________________________
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Replies: Reply from len-1 at comcast.net (Leonard Taupier) ([Leica] Re: do it yourself back-focus adjustment...")
In reply to: Message from robert.rose at mac.com (Robert Rose) ([Leica] do it yourself back-focus adjustment...")
Message from vick.ko at sympatico.ca (Vick Ko) ([Leica] RE: do it yourself back-focus adjustment...")
Message from robert.rose at mac.com (Robert Rose) ([Leica] Re: do it yourself back-focus adjustment...")
Message from hoppyman at bigpond.net.au (G Hopkinson) ([Leica] Re: do it yourself back-focus adjustment...")
Message from len-1 at comcast.net (Leonard Taupier) ([Leica] Re: do it yourself back-focus adjustment...")