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What is microcontrast

Charcoal Happy , Mar 17, 2012; 08:53 a.m.

What is microcontrast exactly?

Responses


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William Kahn , Mar 17, 2012; 10:51 a.m.

Google is your friend:

http://www.luminous-landscape.com/tutorials/understanding-series/lens-contrast.shtml

Several other articles as well...

Michael Axel , Mar 17, 2012; 12:02 p.m.

I wouldn't know where to start, and wherever I ended, someone else would propose more. My personal view is micro contrast is the ability to capture fine detail such that a distinction exists between various tonal values. With film, where I spend most of my time refining micro contrast, three (primary) factors are most important to me in achieving micro contrast: the resolution of the lens, the capability of the film (there are many components to this one), and the processing procedure.

That is why I've spent a good amount of time experimenting with stand development, various lenses, and various films. I am constantly looking for ways to bring out specular details from shadows and highlights. Good lenses are not hard to find (but are expensive to acquire): Leica, Zeiss, Nikon, Canon, etc. Film has gotten much better, including T-Max, Delta's, and Acros. Development has been the most lengthy journey for me, but I believe I can maximize specular details (micro-contrast---and I realize some will take exception to my lumping them together) by using a developer that exhausts linearly (temporaly), such that highlights are not over developed, and shadows are coerced into yielding more information.

There are pitfalls in these methods. For lenses, the most obvious case to me is a lens that resolves very fine details, but produces too much contrast. Some Zeiss lenses come to mind (particularly for LF). Films can have similar problems. Development is the one area where I believe I have the most immediate control over micro contrast. Where a developer falls short, I can add or subtract chemical components to get what I need. That's not the case with film and lenses (even with filtration).

Ingemar Lampa , Mar 17, 2012; 04:28 p.m.

Microcontrast=fairy dust collected on the stroke of midnight in midnight sunlight. This stuff was also used by Peter Pan and enables children to fly, as documented by Disney. It is used in the final coating stages of Zeiss optics and lenses, but that is a closely guarded proprietary secret. :)

Michael Axel , Mar 17, 2012; 11:08 p.m.

That's certainly a theory Ingemar.

Arthur Plumpton , Mar 18, 2012; 02:11 p.m.

Contrast has generally been described by the difference between the overall deepest black and the brightest highlight of a scene that a lens can faithfully transmit, while microcontrast concerns that of two adjoining and extremely small yet potentially visible subject areas, and relates in particular to very fine details of texture that the lens can resolve. If some small detail is recorded, but the microcontrast is too low, it will show up only as a sort of image noise that will simply degrade the definition of the image. If the lens is not able to record microcontrast, little variation in film or paper exposure and development will help, although, as Michael infers I think, they are also important links in the overalll chain.

Charcoal Happy , Mar 18, 2012; 04:14 p.m.

How do you measure LP/mm for the lens and for the sensor?

Tom Mann , Mar 18, 2012; 04:37 p.m.

Charcoal, there are entire books devoted to optical system characterization and major sections of them are typically devoted to such measurements. Typically, a grad level course in this subject is given over two semesters and carries about 6 credit hours.

Although you will likely receive some replies which will attempt to compress all of the theoretical background, concepts, techniques, etc. into a couple of paragraphs, if you are truly interested in this subject, I suggest you may be better served by a less superficial approach either via textbooks on optical engineering or Google "measurement of MTF". There are also many folks on the web who attempt to make such measurements on their own, but often they don't get the nuances right and hence, endless / pointless discussion follows.

Tom M

PS - We've already seen some of the latter in this thread, specifically, the attempt to distinguish differences in small tonal values without reference to the spatial scale on which these changes occur. If folks would understand that MTF is essentially a Fourier domain characterization of an optical system, the relation between the amplitude changes and the length scales would be much clearer. OTOH, if you aren't familiar with Fourier concepts, this is going to be hard to do.

Charcoal Happy , Mar 18, 2012; 04:46 p.m.

Charcoal, there are entire books devoted to optical system characterization and major sections of them are typically devoted to such measurements.

What I'm looking for is the point where a lens or sensor outresolves the other.
LP/mm used to be common information but I don't see companies publishing these figures anymore.

What is the native resolution of slide, 35mm film, medium format etc?

Tom Mann , Mar 18, 2012; 04:50 p.m.

There is no sharp dividing line. The spatial resolution of an entire optical system is, to a decent approximation, the square root of the sum of the squares of the spatial resolution of the individual components. So, even if you had a lens and sensor, "perfectly matched" with the same resolution, and then you replaced one of the components with one that has perfect resolution, the overall system resolution would only be improved by a factor of about 1.4 (ie, sqrt(2)).

Tom M


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