Ah, exposure. Every photographer’s favourite topic—or, in my case, a small mental gymnastics event.

After more than sixty years with cameras, I can still get myself tied in knots explaining underexposure and overexposure, particularly when I switch between negatives, slides and digital pictures. Put a negative in front of me and I know what I’m looking at. Ask me to explain it off the cuff, and suddenly I need a pencil, a quiet room and possibly a lie-down.

The trouble isn’t that light has changed its behaviour. It’s that we keep looking at different stages of the process and using the same words. So let’s sort it out in writing, where I have a fighting chance.

First, which exposure?

Exposure is the light received by the film, sensor or photographic paper. Underexposure means too little for the result we intend; overexposure means too much.

That last part matters. A deliberately dark photograph isn’t automatically underexposed, any more than a pale, high-key portrait is automatically overexposed. The question is whether we recorded the tones and detail we wanted.

And when we make a darkroom print, there are two exposures to think about: the one that made the negative in the camera, and the one that makes the print under the enlarger. My brain has been known to change trains between those two without telling me.

Negatives: more light, more density

With ordinary negative film, more exposure produces more density after development. The bright parts of the scene become the dark parts of the negative. The shadows become its clearer areas.

Assuming normal processing, an overexposed negative tends to look unusually dense or dark. An underexposed negative tends to look thin or pale, often with little useful shadow detail.

But a dark negative is not proof of overexposure on its own. Development and fogging can also affect density. As usual, photography supplies a straightforward rule and then quietly puts a few qualifications in the small print.

Now for the bit that used to send my explanation sideways: a dense negative does not inevitably give you a pale print.

It blocks more of the enlarger’s light. If you leave the printing time and everything else unchanged, less light reaches the paper and the print will tend to be lighter. A thin negative lets more light through, so the same printing exposure tends to produce a darker print.

However, we don’t have to leave the settings unchanged. We adjust the printing exposure and, where necessary, the contrast. Many dense negatives can produce perfectly good prints. What we cannot do is print detail that was never recorded in the first place.

So “dark negative equals light print” needs an important addition: at the same enlarger settings. Leave that out and the explanation becomes rather more confident than correct. I have now written it down, partly for my own benefit.

Slides and digital: the more familiar way round

With normally processed colour slides, too much camera exposure makes the image too light; too little makes it too dark. We view the positive image directly, so there is no negative-to-print reversal to negotiate.

A digital photograph generally behaves in the same familiar direction: more camera exposure makes the image brighter, and less makes it darker, if the processing stays the same. Too much can clip the highlights to featureless white; too little can leave shadows noisy or without usable detail.

But the screen isn’t a courtroom witness. Its brightness, the processing and the look we’ve chosen all affect what we see. A bright-looking picture alone doesn’t prove that the original capture was overexposed.

Nor does “there’s no detail” settle the argument. Detail can disappear at either end: in blown highlights or in deep shadows. I have to ask where it has gone before announcing a verdict.

Then the darkroom turns things around again

Ordinary negative-to-positive photographic printing paper darkens with more exposure after development. Give it too much enlarger light and the print comes out too dark. Give it too little and it comes out too light—assuming normal processing.

That describes the paper’s exposure. It does not, by itself, tell us whether the original negative was underexposed or overexposed.

A perfectly good negative can produce a dreadful print if I get the enlarger exposure wrong. No need to blame the camera; I am quite capable of introducing a fresh mistake further down the production line.

A small crib sheet for the easily tangled

  • Negative film, normally processed: more camera exposure means a denser negative; less means a thinner one.
  • Printing through that negative: denser areas block more enlarger light; clearer areas let more through. We adjust printing time and contrast to make the print.
  • Ordinary photographic paper: more enlarger exposure makes the developed print darker; less makes it lighter.
  • Slides and digital: more camera exposure generally makes the viewed image lighter; less makes it darker, with processing held constant.

Those rules cover the ordinary processes I’m talking about here. Special materials, such as direct-positive paper, can behave differently. Naturally. We wouldn’t want to become too comfortable.

Sixty years, and still checking

What ties me in knots is moving between the negative, the finished image and the exposure that produced each one. Once I stop and name the stage, it makes sense. Usually.

Photography has taught me plenty, including the usefulness of checking something I think I already know. Experience doesn’t make us immune to muddling an explanation. Sometimes it just gives us a much longer history of doing it.

So if you ever get confused about exposure, you’re in good company. Just don’t ask me to run through all of this verbally while you’re holding a negative up to the light.

I’ll send you the link.

For the technical background, see ILFORD’s explanation of negative density and compensation in printing and its guide to common film-processing problems.