Archived posting to the Leica Users Group, 2010/11/07

[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]

Subject: [Leica] Rangefinder error on M9
From: benedenia at gmail.com (Marty Deveney)
Date: Sun, 7 Nov 2010 21:53:09 +1030
References: <F20C55B2-2025-407F-A579-625D7943E2C5@bex.net> <C594B6AA-D163-47EB-A712-858ECF02BE75@btinternet.com>

The 90 APO has focus shift that is less that the depth of field.  What
Howard is seeing is not focus shift; something in his camera, or more
likely his lens, is out of spec.

Marty

On Sun, Nov 7, 2010 at 9:32 PM, Frank Dernie
<Frank.Dernie at btinternet.com> wrote:
> Hi Howard,
> I think what you are seeing here is the effect of "focus shift". It seems 
> many lenses have a shift in focus with aperture which is normally masked 
> by the increasing depth of field with aperture closing, and, on film 
> bodies, by the effectively thick sensitive layer, since film emulsion is 
> fairly thick, and the film rarely flat anyway, the focus will fall 
> -somewhere- within the sensitive volume (it is not that much). A digital 
> sensor is flat and therefore less tolerant of focus shift, the 90mm f2 apo 
> has a tiny depth of field and at some apertures the plane of focus falls 
> outside the depth of field due to focus shift.
> It is also difficult to get perfectly in focus anyway, I use mine with a 
> viewfinder magnifier.
> A quick search on the internet will turn up quite a lot of discussion on 
> this and the 90mm f2 apo-asph lens is one of the most sensitive lens out 
> there for this problem - sadly.
> The new 35mm f1.4 asph came out because focus shift on the existing lens 
> was being noticed on the M8 and M9 when it was not using film bodies.
> cheers,
> Frank Dernie
>
> On 6 Nov, 2010, at 22:26, Howard Ritter wrote:
>
>> I have just discovered that the RF on my M9 does not bring the 90 ASPH to 
>> focus in at least the middle range, specifically 7 meters, although it 
>> does so, as far as I've been able to tell, at infinity. I have not tested 
>> it thoroughly at closer range, but I'll do so tomorrow during daylight 
>> when I can use a low ISO.
>>
>> I had seen comments on LUG/MUG along these lines previously but not paid 
>> attention because I didn't yet have an M9. I recall seeing something 
>> about lenses needing modding in order to focus properly on the M8 or M9, 
>> but can't recall details.
>>
>> This is very counterintuitive and perplexing to me. Given that the 
>> flange-to-sensor distance on digital Ms is the same as the flange-to-film 
>> distance on analog Ms, how does the problem arise at all, and why does a 
>> modification of the lens or adjustment of the RF mechanism to accomodate 
>> one combination not affect the modified unit's performance with other 
>> combinations?
>>
>> Any insight or advice would be highly appreciated.
>>
>> ?howard
>>
>> _______________________________________________
>> Leica Users Group.
>> See http://leica-users.org/mailman/listinfo/lug for more information
>
> _______________________________________________
> Leica Users Group.
> See http://leica-users.org/mailman/listinfo/lug for more information
>


Replies: Reply from Frank.Dernie at btinternet.com (Frank Dernie) ([Leica] Rangefinder error on M9)
In reply to: Message from hlritter at bex.net (Howard Ritter) ([Leica] Rangefinder error on M9)
Message from Frank.Dernie at btinternet.com (Frank Dernie) ([Leica] Rangefinder error on M9)