Exposure triangle explanation please.

Started Jul 9, 2013 | Questions thread
Jeff Veteran Member • Posts: 5,087
Not yet an ISOless world!

texinwien wrote:

Jeff wrote:

texinwien wrote:

There is confusion, no doubt. But just replacing ISO with gain is rather minor tweak. It'd be nice, sure. But recasting it all in terms of what's happening at the sensor plane might not be the best way to resolve the confusion for most people.

What I really care about are the image attributes, like image brightness relative to scene brightness, depth of field, motion blur, perspective, dynamic range, color. That we control them in terms ISO, sensor size, saturation, sensor efficiency, f-stop, focal length, etc., are all artifacts of the equipment and medium.

One of these things is not like the others. On an ISOless sensor, ISO has no effect on anything but the image brightness relative to scene brightness. That is, it's simply gain, and it's something that you should be able to simply adjust after the fact.

Being able to adjust gain after the fact allows you to focus on the only parameters that really matter, shutter speed, aperture and scene luminance. ISO just muddies the water on an ISOless camera.

If only that were actually true.

With today's sensors, {gain|ISO} does have an effect on the final image which is the introduction of noise. If I expose an image such that very high gain is required in PP, then that may not be a good result. I may prefer to accept creative constraints on aperture and shutter in order to keep noise under control.

As you've noted, highlighting in live view allows you to avoid blowing highlights. So that's a situation where you accept creative constraints on aperture and shutter to avoid problems in the final image. The other problem is losing shadow detail or noise due to underexposure. For that I accept a cap on ISO, and therefore need to manage ISO at time of exposure.

Perhaps I'm more cautious about this because I've been trying to work with iPhones for the last few months where both extremes are present in almost every scene.

Here's a shot from two nights ago -- http://www.flickr.com/photos/jck_photos/9242469199/in/set-72157633967193553 Believe me, with small sensors we are definitely not in anISOless world!

If you're going to restructure the camera interface, why not do it terms of final image attributes. Sort of a stripped down version of the Lightroom Develop panel where I can set brightness, shadows, highlights, color and tint, clarity, etc. Now that would be truly useful, imho.

Sure - it's already possible in some cameras. Still, my point is that you shouldn't have to choose your gain BEFORE you take the picture. It's an extra, unnecessary variable that you shouldn't have to keep in mind when choosing settings. Given static scene luminance, the only variables you should think about are shutter speed (freeze motion) and aperture (DOF). Why throw the third variable into the mix, when it can just as easily be changed after the fact? Let the camera choose the gain automatically, for all I care, and allow the user to adjust it easily after the fact.

No need to force the user to choose the gain before he takes the picture.

But I want to, because I want at least some control *at the time of exposure* over noise and shadow detail in the final image.

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