Exposure triangle explanation please.

Started Jul 9, 2013 | Questions thread
Jeff Veteran Member • Posts: 5,087
Re: All fine and good, but ...

texinwien wrote:

Jeff wrote:

There certainly is an elegance to the Hv = Ev * t formulation, but I don't think we'll be seeing an iso-less world for a very long time.

Physics is often quite elegant, and I think (and hope) you're wrong about ISO.

First off, few shooters want to wait until PP to set image brightness. Most want an image now, out of the camera and straight to facebook. So somewhere the captured light has to be translated into an image. The camera might set the gain automatically assuming the user wants a 'middle grey', or the user might do it him or herself. But either way, there's a gain knob that has to be calibrated and set. Historically the gain knob is calibrated in ISO units. You prefer to do it PP, which is fine and actually quite logical, but you're still turning a knob, too. Call it whatever you like, it's just a proxy for ISO.

Actually, I'd say ISO is a proxy for gain, and I think it's a confusing proxy for most beginners, and even for many advanced photographers (including a few professionals) who think that adjusting ISO has some effect on their camera's photosensitivity.

The point is that we are moving from ISOful sensors to ISOless sensors. When all sensors are ISOless, I think we should start talking about the saturation sensitivity of a camera's sensor and the gain we wish to apply to a specific exposure. Just call it gain or brightening. Allow the user to set it before they record the photo (or have it set automatically by the camera) and allow the user to adjust it (in-camera) after the exposure has been recorded.

The main point, for me, is that the topic of ISO always seems to be surrounded by a good deal of confusion, including this infernal exposure triangle. Get rid of it and replace it with an easier-to-understand and physically correct concept rather than the flawed conceit of ISO.

See here for more discussion of the matter. There have been other discussions here about how to relabel and redesign the 'gain knob' on ISOless cameras. I think it'll happen, one of these days.

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.

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.

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