ISO-less underexposure vs. ETTR and why it’s all hokum

2 Oct

For several years now, there’s been vivid discussion over how to correctly expose digital images. If allowed to set aperture, film speed, and/or shutter speed, your camera will attempt to produce an exposure that gives a JPEG image with good tonality and contrast. It’s implied that colour rendition is also pretty good with the automatically chosen settings in most scenarios.

Then for a while, internet-oriented photographers were caught up in ETTR (expose to the right) practice, which meant slightly over-exposing relative to the metering of the camera in order to produce a histogram that’s shifted to the right of the middle. This was intended to produce less noise and, so the proponents claimed, richer colour differentiation than the canonical exposure produced by the camera. The idea was essentially that the bit-space was more densely mapped onto the raw sensor measurement at higher light intensities and pixels with that higher exposure.

Then came along the folks who claimed that if you were going to over-expose, you might as well switch to a slower film speed, and get the same or better amount of noise. In fact, if you were going to have to correct your exposure in post-processing anyway, as you do with ETTR, you may as well shoot two or three steps slower with your film, and correct later. It was claimed, in essence, that noise does not increase linearly with higher film speeds, but at some function above that.

It is worth noting that the original argument in favour of ETTR came from landscape photographers, who typically have a reasonable amount of time available for setting up their shots. The risk with doing things this way is that you may be tempted to use exposure compensation to change the setting, and if you forget to set it back to zero, you may come across the once-in-a-lifetime fleeting shot and severely over- or under-expose it. In fact, the same thing may happen if you make settings manually rather than using exposure compensation. And let’s face it, as serious photographers, that scenario happens to us all the time, if not in reality, then at least mentally. The biggest fish is the one that got away, and the best shot was the one you couldn’t take. Isn’t that right?

Even as a Pentax shooter, you may be too overwhelmed with the moment to remember to press the green button (that’s the one that makes everything wonderful, or that’s the idea).

So, hard as it may be, rely on your camera to make settings that are approximately correct, and fix things in PP. And if you really have to intervene with the exposure (some of us believe in getting things right in the field rather than at the desk), remember damn well to set exposure compensation back to zero!


One Response to “ISO-less underexposure vs. ETTR and why it’s all hokum”

  1. Desmond February 20, 2015 at 8:08 pm #

    On my blog using samples from my D90 I prove that a well exposed high iso image has less noise than an under-exposed low iso image when shooting with jpegs. However it seems that some modern sensors allow for adjustment of iso after taking photos when shooting in RAW – so things are changing.

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