Down to Brass Tacks Let's cut the crap.

Expose to the Right (and then some)

Following up on the previous post, where I was making the point that fully embracing the new photographic technologies meant more than shooting raw, I would like to point out to a recent post by Michael Reichmann. His text, from just a couple of weeks ago, was an open letter to Leica, explaining his ideas on how to improve their cameras.

The most interesting part of the letter, for me, wasn't so much Leica-related, but the part where he clearly stated how camera makers (and camera users, by extension) should fully come to terms with the actual behavior of the current technology:

All major digital camera makers seem to be stuck in the film era when it comes to exposure metering and setting. Part of the problem is that consumers want the image on the rear LCD or in the viewfinder to "look right", but looking right and being optimum from a raw image quality perspective are not the same thing. [...] In other words – let's leave the film exposure paradigm behind. Digital exposure is different than film exposure, and basing 21st Century cameras on 19th Century exposure rules has to end.

Well that's all good — we're all familiar with the "expose to the right" approach to optimizing exposure, and that understanding leads us to deliberately use generous exposures in the field, when gathering ambient light.

But what about when we're working in a controlled environment, when using strobes in a studio for example? There, it's as if we suddenly forget the "expose to the right" mantra and rather rely on our flash meters to calculate the exposure. If we want to push the reasoning all the way, shouldn't we reconsider our approach?

Let's consider this very simple experiment. Single Speedlight in a Lastolite EzyBox to camera left, ISO100 at f/5.6. This is what we get (as expected): a "correct" exposure.

I took an item on my desk that contained bright white, so that we can really see what's going on:

Whites are white — no doubt about it. Now let's double the flash power (f/8), but leave the aperture at f/5.6. This is what we get, straight out of the camera:

Overexposed! But of course, this is exactly what we would expect — exposing to the right is supposed to optimize the file, not get the best result straight out of the camera (or on the LCD display, or on the histogram). As a matter of fact, this is what the two histograms look like, without any adjustment:

According to this histogram, we were too enthusiastic and went too far to the right — we know that we shouldn't clip the highlights, because then we can't bring them back at all. To adjust the exposure so that we get (visually) the same result as the first file, I simply pull back the "Exposure" slider in Camera Raw — I'm not even messing around with the "Recovery" hack, there is no need, there is plenty of information in the highlights. Ta-dah! This is the result I get:

Well well. Nothing is clipped now, I get information everywhere from that same file, which was over-exposed by a full stop.

The question is, did this really have any effect on the quality of the image? Well yes it did indeed. Remember that this image was shot at ISO100, so the noise was already pretty low. But by taking a region from the blurred background and bringing up the exposure to get a middle gray (which, obviously, enhances the noise further) and removing any kind of noise reduction there was, we get this result:

I will grant you that, in practice, this would not be much to write home about. But certainly, even in an ideal situation, there is a difference — deeper shadows, in particular, would benefit even more from this 1-stop gain.

Now this is where it gets interesting. Because we know that the "expose to the right" approach has a more obvious impact on the quality of a file in the shadows, and especially when we're dealing with high ISOs, there is another situation where we should definitely apply it.

When we're working in a mixed "flash+ambient light" exposure! In these situations, we normally have large parts of the image in darker tones, and we're usually working with rather high ISOs to get acceptable shutter speeds. The typical exposure is usually somewhere around the -2 stops for the ambient, over which we add the flash. Well, I'll let you work out how you incorporate the lesson from situation to situation, but in the end it should probably look more like -1 stop for the ambient, +1 stop for the flash!