Archived posting to the Leica Users Group, 2012/02/02

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Subject: [Leica] 90mm APO Summicron M Asph Price Range
From: benedenia at gmail.com (Marty Deveney)
Date: Fri, 3 Feb 2012 15:31:46 +1030
References: <mailman.2071.1328205042.33714.lug@leica-users.org> <0F11FD49-66C3-4A6F-833E-E26D4C178AD5@netvigator.com> <CABmfTOXzuiHmK8y27LMt-NOvaksFQNg3PBsrn=vMARZ_NCwaPw@mail.gmail.com> <EE63531F-E3A2-4774-9989-A8408E75F6BD@archiphoto.com>

Hi Henning,

Oh.  The 90AA I trialled showed quite a bit of focus shift when I
measured it, but it could have been due to the kind of issue you've
described here.  I didn't put it on an optical bench.

Yes, I have a table I calculated for the 75 Summilux somewhere about
how to proportionally compensate at each aperture where focus shift is
an issue.  I never liked the 90AA enough to buy one so I never
characterised this - thanks for making me aware of that - I'll be on
the lookout for it.

Thanks,

Marty





On Fri, Feb 3, 2012 at 12:41 PM, Henning Wulff <henningw at archiphoto.com> 
wrote:
> Marty,
>
> This is not a focus shift issue as in - it shifts plane of focus as it is 
> stopped down. This is an issue as in - it focusses accurately at one 
> distance, but not at another, all at the same aperture. The 90AA exhibits 
> very little focus shift, as stopping it down doesn't change the plane of 
> focus much at all, at any distance.
>
> The problem with mine, and I believe Howard's, was that the cam did not 
> follow the focus properly. If the lens focussed properly at infinity, it 
> was off at 10m and then on again at 3m. Not very user friendly. I too now 
> have some other 90 options which work better.
>
> In a related vein, the 75 Summilux exhibits focus shift in the traditional 
> manner, but at f/2.8 it is off the intended focus plane by the same 
> proportional amount at every distance, and I have learned to compensate. I 
> can use it very well, and have a high degree of confidence in it.
>
> Henning
>
>
>
> On 2012-02-02, at 4:56 PM, Marty Deveney wrote:
>
>>> Another consideration about the 90 APO Summicron Asph is that some of 
>>> them do not focus accurately on the M8 or, by extension, the M9.
>>
>> This is not an issue with "some" of them. ?The 90AA has substantial
>> focus shift - it's an atrefact of the design. ?The lens gets
>> calibrated for optimum focus at a specific aperture and object
>> distance. ?Focus shift means that even a properly calibrated lens will
>> focus incorrectly at some apertures and object distances. ?In a
>> rangefinder camera, the mechanism assumes a linear focus arrangement,
>> but this isn't the case and there is no engineering solution to make
>> the cam shape change with aperture.
>>
>> This problem also occurs with SLRs because they focus wide open and
>> then stop down before shooting without re-focusing. ?In autofocus SLRs
>> where there is lens-camera communication I've never understood why
>> manufacturers didn't characterise the shift and make camera bodies
>> that compensate for it, or have a menu selection that enables the
>> camera to focus then stop down and re-focus then shoot. ?The former
>> may not exist because autofocus is less accurate than manufacturers
>> like to admit, the latter might attract more complaints than praise
>> because it would be slower.
>>
>> Marty
>>
>> _______________________________________________
>> Leica Users Group.
>> See http://leica-users.org/mailman/listinfo/lug for more information
>>
>
>
> Henning Wulff
> henningw at archiphoto.com
>
>
>
>
>
> _______________________________________________
> Leica Users Group.
> See http://leica-users.org/mailman/listinfo/lug for more information


Replies: Reply from richard at richardmanphoto.com (Richard Man) ([Leica] 90mm APO Summicron M Asph Price Range)
Reply from tgray at 125px.com (Tim Gray) ([Leica] 90mm APO Summicron M Asph Price Range)
In reply to: Message from cummer at netvigator.com (H&ECummer) ([Leica] 90mm APO Summicron M Asph Price Range)
Message from benedenia at gmail.com (Marty Deveney) ([Leica] 90mm APO Summicron M Asph Price Range)
Message from henningw at archiphoto.com (Henning Wulff) ([Leica] 90mm APO Summicron M Asph Price Range)