Exposure triangle explanation please.

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

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.

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.

Second, not all cameras are created equal.  I want to be able to compare cameras based on their ability to light into images as measured under controlled conditions. That control is the gain. It's got to set somehow, why not ISO?

Somewhere in the chain you need to establish the relationship between Hv hitting the sensor and the image brightness. Historically that's been measured as ISO. Sure, it's an historical artifact from the world of film, but it does the job and everyone 'gets it'.  It's not going away anytime soon.

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You don't make a photograph just with a camera. You bring to the act of photography all the pictures you have seen, the books you have read, the music you have heard, the people you have loved.” -- Ansel Adams

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