[Leica] Vignetting in FF digital Ms

[tedgrant at shaw.ca (tedgrant at shaw.ca)]

Geoff Hopkinson OFFERED:

Gee Geoff I didn't know you were describing my ARGUS A2 1950 model! ;-) ;-)


" <hopsternew at gmail.com>
To: "Leica Users Group" <lug at leica-users.org>
Sent: Friday, March 21, 2014 6:40 AM
Subject: Re: [Leica] Vignetting in FF digital Ms


> Well now Howard that is quite a topic you have broached ;-) Before Dr Ted
> reminds me that only content matters ultimately (as is true of course) I
> shall dive in.
>
> For some attempt at clarity (post brevity not being my strength!) I will
> just talk about the specific hardware you mentioned, although the
> principles are more generally relevant.
> Wide open the lens you mentioned has 2.5 stops of vignetting. How much of
> that do you consider ought to be corrected out? There's no wrong answer of
> course just preference.That is what you got with positive film previously
> though.
> The camera corrections are also non-aperture dependent. That is to say 
> that
> a single (compromise aperture value I guess)  (less vignetting when 
> stopped
> down) is corrected for because neither the  M9 nor the M (typ 240) can
> reliably determine the exact aperture used due to the legacy designs. A 
> new
> system (S & X for example) and I guess T? is not so limited. By brightness
> sensor value comparison estimate the M full frames might be within say a
> stop/stop and a half or two at worst. If the (single) correction value per
> lens was set at that for the worst case (wide open) you would get
> over-correction at smaller apertures. Actually odd lighter corners and at
> the expense of increased noise/ more loss of dynamic range there to do so.
> All correction is a compromise with some loss of quality in those corners.
> That may or not matter at all or be noticed.
>
> The camera is also making significant correction for every image for basic
> homogeneity because the 1954 fundamentals were just never designed for
> optimum use with a sensor.That includes asymmetric colour shift which is 
> an
> optical reality with all systems more or less (Italian Flag) as well as so
> called red edge syndrome. That fundamental is why M digital sensors have
> their unique microlens arrangements in the first place and why the legacy
> wides in particular are compromised when adapted to other systems' sensor
> (Sony being the current prominent example).
>
> Phew, that ought to kick the discussion off, or get filtered out because 
> my
> name is on the top!  ;-)
>
>
>
>
>
>
> Cheers
> Geoff
> http://www.pbase.com/hoppyman
>
>
> On 21 March 2014 21:50, Howard Ritter <hlritter at bex.net> wrote:
>
>> In doing some preliminary exploratory shooting with my new M240 and the
>> previous-generation 35mm Summilux ASPH, I encountered the inevitable 
>> severe
>> fall-off of illumination at the corners, as I expected. What I did not
>> expect was that the M's built-in lens correction feature would reduce 
>> this
>> by only a subjective 50% or so, leaving a prominent and very 
>> disappointing
>> degree of vignetting still to be seen.
>>
>> I realize that this can be easily corrected in post-processing, e.g.
>> Lightroom, PS, and DxO, but my question is WHY? Why would Leica 
>> engineers,
>> after recognizing the problem, creating a software correction to it, and
>> deciding to incorporate that correction into the FF M digital camera, 
>> then
>> proceed to implement it in such a half-assed fashion? Clearly a full
>> correction is straightforwardly implementable in post-processing, so why
>> not write the firmware to accomplish it rather than hobble it to perform 
>> a
>> half-correction?
>>
>> Anybody know the reasoning behind this? Or am I missing some feature that
>> would actually give full correction? And when correcting for this in
>> Lightroom etc., what do most of you do? Let the camera do its bit and 
>> then
>> finish it, or simply dispense with the built-in correction and do
>> everything in LR? Will LR and the other software suites with built-in
>> corrections for various lens and body combinations even perform properly
>> with the M's built-in correction applied?
>>
>> Thanks for any suggestions.
>>
>> --howard
>>
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>>
>
> _______________________________________________
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