Six Kinds Of Contrast
How Each Affects Image Quality

Six Kinds Of Contrast

Margate Sands. The brightness range is enormous: dark hair under a beach umbrella is probably 1/1000 as bright as a white shirt in full sun. But because the individual areas of deep black and bright white are tiny, the overall shot doesn't look very contrasty. I used a Zenith Fotosniper (300mm f/4.5 Tair-3 lens) and Ilford XP2 Super for this shot, printed on Ilford Multigrade Warmtone RC and sepia toned with sulfide.
Photos © 2002, Roger W. Hicks, All Rights Reserved

"Contrast" means a surprising number of things in photography: at least six. Made to do so many jobs, it is not surprising that confusion reigns, plenty of contrast is a Good Thing in some contexts, and a Bad Thing in others; so let's try to sort it out.

Subject Contrast
First, the subject can be contrasty or not. Obviously this isn't a Good Thing or a Bad Thing: it just is. But a transparency or print can only record a limited range of brightness, so too much contrast can make it hard to record a faithful representation of the scene. Most photographers therefore regard it as a Bad Thing. In a transparency, all you can do is sacrifice the shadows; in a print, you can dodge or burn to recover them.

Church, Minas Santos Domingos, Portugal. This shot appears very contrasty because two big areas of widely differing tone are right next to one another: the bright white of the church and the (heavily filtered) sky. In reality, the contrast range is well within the recording ability of a "straight" print. Frances Schultz used a Nikkormat and 35mm f/2.8 PC Nikkor, with Ilford SFX and a true IR filter (T50 = 715nm), printed on Ilford Multigrade IV.

Contrariwise, a misty day reduces contrast. A faithful representation of the scene is easy enough, but often, a faithful representation is not what you want: you want more contrast than really existed. In this context, too little contrast is a Bad Thing. You can, however, restore contrast in a subject that is "flat" because of atmospheric haze by using a "sky" filter (yellow, orange, or red, in ascending order of power).

It's not immediately obvious, but a long brightness range does not always equate to a subject that looks contrasty. A landscape with deep shadows may have an enormous brightness range, as much as 1000:1, but if the darkest shadows occupy only a tiny part of the image and aren't important, you can ignore them, and the picture still won't look contrasty. But if there are large dark areas next to large light areas, even a subject with a small brightness range can look contrasty.

Print Contrast
Second, there's print contrast. A black and white print that is too contrasty has plenty of blacks and whites, but not too many subtle grays in the mid tones: it is what our ancestors used to call "soot and whitewash." A print that is not contrasty enough is flat, dull, and gray, like shades of cigarette ash. Similar effects can be seen in color, with the rider that in an overly contrasty print the colors are likely to be garish, while in an insufficiently contrasty print they will be flat, dull, and degraded. In this context, too much contrast is definitely a Bad Thing. So is too little.

Aljezur, Portugal. This was a very hazy scene. If it had been shot with a lens that lacked contrast, and no filter, it would have been no picture at all. But a contrasty lens and a red (Wratten 29) filter, plus Ilford SFX, restored all the contrast you could ask for without looking unnatural: it printed very well on Grade 2.

Film & Paper Contrast
Overall print contrast isn't the same as either film contrast or paper contrast, which are our third and fourth uses. Even if you start out with a film of optimum contrast, you can make a print that is too contrasty or too flat by using the wrong paper grade; and conversely, if you stick with a middling grade of paper, your prints can be too contrasty or too flat if your negative is less than ideal.

Let's start with black and white film. More development means more contrast: less development means less contrast. A film that is developed to the optimum contrast should print on average on a middling paper contrast grade, usually 2 or 3.

If there are mixed subjects on the film, the contrastier ones may require a softer grade of paper, and the less contrasty ones may require a harder grade. The simple rule is this: negatives with more contrast require paper with less contrast (Grades 2-1-0) and negatives with less contrast require paper with more contrast (Grades 3-4-5).

If your films regularly require hard grades more often than soft, you are underdeveloping them, and you should increase your development times in one-minute or half-minute increments until you get films that print on average on 2 and 3. If your films regularly require soft grades more often than hard, you are overdeveloping them, and you should decrease your development times in one-minute or half-minute decrements until you get films that print on average on 2 and 3.

Barn roof, Touraine. Deficiencies in negative contrast can be remedied by appropriate paper choice. This was part of a series of experiments in "gamma infinity" development coupled with grievous underexposure: I rated Ilford Pan F Plus (ISO 50) at EI 200 and tripled the development time. On Grade 2 Ilford Multigrade IV, the print was hopelessly flat; on Grade 4 (as here), there is plenty of subtlety and "sparkle." I shot the 200-year-old roof of my barn with a Nikon F and 200mm f/3 Vivitar Series 1 plus orange filter.

With color negatives, film development times are fixed, which means that contrast is fixed. Also, there are far fewer paper grades to choose from: often just "normal" and "contrasty" and sometimes not even that. Even so, contrast problems in conventional silver halide photography are rarer in color than in black and white--not least because people are much more willing simply to sacrifice the shadows in color, and let them block up to a featureless black.

In digital photography, print contrast is simply a question of turning the color and contrast up or down at the postproduction stage until it looks right to you.

Lens & Camera Effects
Although you can have too much or too little contrast in conventional prints or negatives and in ink jet or other digital prints, contrast is pretty much a one-way bet when it comes to lenses and cameras: you can't have too much of it.

This is our fifth use of the term "contrast." All scenes lose contrast when they are projected by a lens onto the film (or image sensor) inside a camera, because of non-image forming light bouncing around inside the lens and indeed the camera itself: that is why contrast depends on both the camera and the lens together, not just on the lens.

Door, Loches (Touraine). The importance of film acutance can be overestimated: lens contrast and sharpness are at least as important. This was shot on Ilford XP2, which is not as sharp as (say) Ilford Delta 100, and which cannot be developed in trick developers to increase acutance. But the staggeringly sharp lens (90mm f/3.5 Voigtländer Apo Lanthar, with B+W 2x orange filter, on a Bessa-R) gives all the microcontrast you need.

Some of this non-image forming light is reflected back out of the front of the lens, reducing the amount of light available to take the picture; some is absorbed by the various light baffles; and some ends up on the film, where it "fills" the shadows and reduces the contrast range.

The way that this sort of contrast is measured is as a "flare factor." If the brightness range of the original scene is (say) 128:1, seven stops, and the brightness range of the projected image is 64:1, six stops, then the flare factor is 2. This would not be unusual for a modern 35mm SLR, but a box camera with an uncoated lens might have a flare factor of 4, so that 128:1, seven stops, becomes 32:1, five stops at the image plane. A view camera with a top-flight multi-coated lens might have a flare factor of little more than 1, implying no significant degradation of the brightness range: the 128:1, seven stops, of the subject would be projected with effectively the same brightness range.

Old, flary lenses can however be useful when you are trying to reproduce the effects of the past, when lenses were uncoated. For example, I use an uncoated 21" (533mm) f/7.7 Ross for shooting 8x10" Hollywood style portraits. The low contrast of the lens means that I have to develop the film longer in order to regain contrast. This gives a different tonality from using a modern, contrasty lens and developing the film for less time.

Then there is a sixth use of the word "contrast," this time in a compound: "microcontrast." Also known as "acutance" and "sharpness," microcontrast is a measure of the rapidity of the transition between light and dark in an image.

Imagine an image of a backlit razor blade. The dark side is black: around it is light. In a perfect imaging system, there would be an immediate transition between dark and light. In the real world, there is literally a "gray area," a transition zone between the two. The smaller the gray area, the better the microcontrast--and as with lens/camera contrast, more microcontrast is better, unless you are specifically trying for an
old-fashioned effect.

For obvious reasons, microcontrast is more important with 35mm than with roll film, and more important with roll film than with large formats.

Microcontrast is affected by the lens (including flare); by the film; by exposure; and by development. It's not the same as resolution, incidentally. A lens can have high resolution and low contrast: you'll be able to see the finest lines on a resolution chart, but only as faint shades of gray. A lens with lower resolution and higher contrast will often look "sharper": you won't be able to see the finest lines at all, but the ones you can see will be crisper and contrastier.

Much the same is true of film. Increased exposure will always reduce microcontrast, principally because of light diffused by the thickness of the emulsion: for maximum microcontrast, keep exposure to a minimum.

High Acutance Developer
The effect of development on microcontrast is particularly interesting, though principally relevant to black and white. "Acutance" developers are specifically designed to increase microcontrast, always at the expense of fine grain: that is to say, fine-grained developers show lower acutance, one of many tradeoffs that exist in photography. And with most developers, more agitation means lower acutance, so for maximum acutance, keep agitation to the minimum necessary for even development: typically, 5-10 seconds agitation every minute, on the minute. Minimum agitation will however reduce film speed for a given contrast level: another tradeoff.

At the beginning, I said that "contrast" can mean at least six things. Some of the others include color contrast, contrast of scale, and even contrast of subject matter (old and new, young and old, that sort of thing). But the six mentioned here are all related.