What is "microcontrast"?

[N Dhananjay]

I'm sorry to disagree but you are not having your cake and eating it too. You are still robbing Peter to pay Paul - Peter just doesn't realize it, for one reason or another....

I did not mean to suggest that you cannot make choices that let you get both overall luminance range without sacrificing micro contrast but these are small effects and usually involve a compromise elsewhere in the system. Tanning developers like pyro give you enahnced micro contrast due to adjacency effects and that is part of their appeal, although you give up other things there (speed, grain etc.). Masking can help, for sure - assuming you have some micro contrast to begin with on the negative - no masking technique is going to give you texture on a smooth surface (barring process artifacts). And to keep some semblance of visual logic within the picture plane, you cannot be heavy handed with it. In other words, it helps make those small adjustments that make such a large difference to an aesthetic response, but it does not change the logic of the system.

Within any given system you have adopted, there is always a ceiling your head will butt up against. Just for purpose of illustration, assume you have two large tonal areas - say Zone III and Zone IX, next to each other. You want these two areas to show up as zones III and VII. Each of these areas, obviously, also has texture, or micro contrast and getting that to look 'right' is important. So let us say the Zone III area has smaller regions of tone varying from Zone II to Zone IV. It really does not matter how you approach this - you can pull develop, you can process normally and dodge and burn, use masks etc. But there is simply no getting away from the fact that you have only a scale of paper base white to max black. If you do an N-- film development, we know you will compress the scene such that the zone IX area will appear as zone VII but micro contrast across the whole picture plane will be lowered. So, if you print this negative to get those areas at zone III and Zone VIII, local contrast or micro contrast across the whole scene will now be lower. So you could move to a higher grade paper and do some dodging and burning, or use masking techniques etc. But what is still going on here? Remember you have to get those areas to have an overall look of Zone III and Zone VIII (and all the other zones looking right) but with the appropriate local contrast. Take the Zone III area - you want this to have a micro-variation going from Zone II to Zone IV. Given the N-- processing, this is going to require a higher contrast paper coupled with dodging and burning or a contrast mask or something else. But whatever it is, when you increase the contrast in that region, you are increasing the amount of the scale used to render that region. It has to come from some other part of the scale. If you just bumped up the contrast here without thought for anything else, you get the contrast here looking right i.e., from Zones II - IV. But your original picture may have also had an area of Zone IV (with micro contrast ranging from Zone III-V), which got lowered in the N-- processing. So now you might have the internal visual logic of the picture fracturing because a part of you Zone III area has bits of it which are of higher value than the Zone IV area. If you keep pushing everything up the scale in an effort to keep the internal logic sound, eventually you run out of room at the other end. Your Zone VII area which had an upper micro contrast end of Zone VIII is pushed off the scale into and beyond paper base white.

Now all these techniques work. And that is usually because we have holes in the scale for the picture we are making. If your picture has only Zone III, IV, VI and VII - i.e., no Zone V - then you can steal from this unused region of the scale and use that in the other regions. And sometimes, this kind of stealing does not affect the internal visual logic of the picture. So, some of the light parts in the shadows may indeed look unrealistically brighter than the dark parts in the lights - but these may be separated enough by distance that it does not wreck the illusion.

The point is there are a huge number of interlocks and we make choices and trade offs, hopefully in a reasonably intelligent manner, that gets us what we want while giving up something we don't care about that much. But in order to make these choices intelligently, you need to think of things both at the level of detail and of the system as a whole.

Cheers, DJ

[Michael R]

Missing from your list is the tanning effects of some developing agents which can increase the micro contrast in areas of very fine detail,

There's also the effects of Iodide in the film or formerly in some high acutance developers, This may explain why Rodinal in particular gives very good micro-contrast with T0grain and similar films. It falls into your low sulphite, dilute category.

Ian

I more or less agree. Tanning developers would fall under my "low sulfite" category, but I didn't want go into any detail on the types of developers, developing agents, iodide content etc. I was just trying to give an illustrative example using some broad generalizations.

[LabRat]

I more or less agree. Tanning developers would fall under my "low sulfite" category, but I didn't want go into any detail on the types of developers, developing agents, iodide content etc. I was just trying to give an illustrative example using some broad generalizations.

Yea I agree, and there's different ways to skin a cat...

Seems to me that some one shot/diluted film developers (low sulfite), that go into partial exhaustion, gives me controlled highlights, and edge effects over the scale routinely... Nice grain/nice scale, day or night, easy to print/little dodging/burning without changing the paper grade much at all... And too many tones to start counting!!! And looks natural/organic...

One funny thing I have noticed while louping a neg for printing, is that sometimes there is a plain wall in the subject, that starts to have specks or shading on it... I think something is wrong with the neg, but looking closer, I see that the film/process picked-up microshadings of dirt or texture on the wall surface when using my sharp lenses... I realized that it is something with the high resolution, that I now call "the dirty layer"...

But no more details... The OP was asking "what", not "how"...

Steve K

[Drew Wiley]

All the tricks add up. Tanning developers, more responsive VC papers these days, paper developer tweaks, better enlarging lenses, supplementary masking in certain cases. In other words, microcontrast isn't such an abstract subject if you have means to make it visually obvious in relation to prints before you knew all
those tricks, which was certainly the case with me, though I do sometimes go back to negs from my D76, D23, and Dektol days and significantly improve the prints with at least portions of my newer tool kit, meaning what I switched to decades ago.

[Drew Wiley]

D - The Zone System is simply a shorthand tool for facilitating predictable printing results. It isn't sensitometry per se, but a practical application of it. Same goes
for what I say about having my cake and eating it to. I'm referring to the practical end result. What masking does, if one intelligently applies it, is to selectively
reconfigure the characteristic curve of the film in relation to the specific printing application. So the internal contrast of chosen "Zones" can indeed to expanded,
even when reining in overall contrast if necessary.

[Nodda Duma]

The disagreement between posts #25 and #26 and the reference to Zeiss in #25 got me to look at the Zeiss link posted in #16. As I understand it, microcontrast is a property of a lens, viz., high contrast at high spatial frequencies. This is inconsistent with my understanding of the relationship between contrast and spatial frequency, viz., that contrast (MTF value) falls with increasing spatial frequency. Back into the rabbit hole ...

Hi Dan,

No rabbit hole jumping:

One thing to keep in mind is that optical bandwidth is much greater than the typical sampling frequencies of film.

So really, "high" spatial frequencies for film (or a focal plane array) are moderate as far as the lens is concerned.

So consider this:

When I'm doing a lens design, given enough design variables I can "push up" the MTF at moderate spatial frequencies by trading off performance at higher spatial frequencies. This is all done under the diffraction limit. This type of trade-off will affect micro-contrast. Where and by how much depends on the requirements of the design.

Keep in mind an f/2.5 optic has a polychromatic diffraction limit MTF value of 0.9 or so at 70 lp/mm...up to 0.75 for a production lens after tolerances. That's a lot of design leeway and the high (for film) spatial frequencies won't necessarily be low contrast (i.e. 20% or less).

Many times I won't artificially manipulate the MTF, leaving it a monotonically descending curve since it's a simpler solution, but I have played those games in the past. Doing that currently, in fact, on high resolution imaging lens.


Veiling glare and control of stray light also plays a part.. I tend to reduce veiling glare to maximize contrast in my designs but using it as a design variable (opto-mechanics) can also soften high contrast transitions in an image.