Archived posting to the Leica Users Group, 2002/01/31

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Subject: Re: [Leica] microcontrast
From: "B.Entus" <brutus@mda.ca>
Date: Thu, 31 Jan 2002 17:58:31 -0800

At 06:16 AM 31/01/02 -0800, you wrote:
> > From: "Joseph Codispoti" <joecodi@clearsightusa.com>
> >
> > There has not been a Leica thread in a while.
> > Some time ago a member asked what "microcontrast" is. No one responded (at
> > least I don't recall a reply), I wanted to respond but, like the 
> inquirer, I
> > don't have the faintest idea what microcontrast stands for.
> > So let me ask the same question, what is microcontrast?

Following sescription found at 
http://www.imx.nl/photosite/leica/mseries/testm/M10-50.html

Overall contrast.
Macro contrast is the difference between the deepest black and the lightest 
highlight of a scene, that the lens is able to record faithfully. An ideal 
lens would only transmit all the light from the subject and bring it to 
sharp focus in the focal plane. In real life a quantity of non-imaging 
forming light ( for instance reflections between surfaces of two lens 
elements) will spread uniformly over the whole negative area. When we are 
taking pictures of a scene that has deep shadows, the light energy hitting 
the emulsion can be so low that no latent image will be formed. After 
development this negative area will be transparant. A lens with a high 
flare factor however will 'illuminate' the shadow areas and after 
development the negative will now have a certain density, but of course no 
details of the subject will be recorded. When comparing two lenses with the 
same nominal aperture (say f/1,4) we might think that the one that gives a 
slightly higher shadow density is actually a bit 'faster' as more light 
seems to be transmitted. In fact this lens may be just more flare prone and 
the other one could be more highly corrected for optical aberrations.
Micro contrast.
Microcontrast refers to the relative luminances of two adjacent very small 
subject areas. It has special relevance to very fine textural details. If 
some object detail is just recorded, but the contrast is below the visual 
threshold, we are not able to see it. What we will see however is a kind of 
image noise, that reduces the clarity of the picture. It will be 
appreciated that good microcontrast is needed when the higher spatial 
frequencies must be clearly separated. Flare eradicates marginally resolved 
textural details.

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