Poll: should we lie to beginners? II

Started Sep 26, 2013 | Discussions thread
bobn2 Forum Pro • Posts: 60,919
Re: Higher ISO = more noise.

Steen Bay wrote:

bobn2 wrote:

Andre Affleck wrote:

EDIT: I think we also put to rest the misnomer (that people were claiming), that there is some unseen advantage to using the traditional method of exposure, as opposed to the brightness triangle. It doesn't seem to be true.

There is an advantage. When you know what exposure is, and its relationship with noise then you are in a better position to manage exposure to maximise image quality. Of course, first you have to ditch the motion that the goal of manipulating exposure is to set your image brightness. The best goal, when you set your exposure, is to minimise noise.

The goal is to get a 'properly expose'

Which means?

image with the preferred compromise between DoF/diffraction, shake/blur and noise,


and to get there you choose the combination of f-stop, shutter speed and ISO that represents that compromise.

ISO isn't really a part of the compromise. All it is, is fixing up the final brightness. It doesn't change any of the substantive elements of the compromise, which are the exposure, and the two controllable parts of it, the f-number and exposure time.

If you want to minimise the noise, then just keep the ISO as low as possible.

Rather, keep the exposure as high as possible. 'ISO' is just one route to doing that, and not the most direct.

In practice that's the same thing as optimizing the 'exposure' (in its 'strict' definition).

In practice, it isn't, because it is not direct and confuses the real goal. So, in the direct route, you would set the maximum exposure (subject to shake and the rest) and then set the brightening to match, whereas the other way you guess at the maximum exposure (via setting a guesstimate on the ISO dial). What most people will do, who don't know that it is exposure which matters, is centre the meter (or let the camera do it) and that will usually result in a lower exposure than had they set the maximum in the first place. No matter how you argue, that is how it really is. People using the ISO first technique will vary rarely set the maximum exposure, for the simple reason that that is not their goal, their goal is to 'nail' exposure, which means setting a final brightness with respect to the target exposure that they guessed in the first place. It is rarely best to choose an abstraction that obscures rather than reveals what is really happening.

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