What makes exposure more important than DOF, diffraction, and the total amount of light projected on the sensor?
Because photography is the craft of exposing a piece of photosensitive material to an image projected by a lens/pinhole.
It is not the craft of measuring DOF (which, let's not forget, is a bit subjective), sharpness, or noise.
And what matters more, in terms of the visual properties of the photo, the total amount of light falling on the sensor or the density of the light falling on the sensor?
I would never describe the visual properties of an image by such crude measurement but yes, the density of the light falling on the sensor is more readily apparent than the total amount of light.
So, you are saying, for example, that a photo of a scene at 50mm f/2.8 1/100 ISO 400 on mFT will look more similar to a photo of the same scene from the same position using 100mm f/2.8 1/100 ISO 400 on FF than 100mm f/5.6 1/100 ISO 1600 on FF?
Obviously that's not what I'm saying. Your question was "what makes exposure more important than DOF, diffraction, and the total amount of light projected on the sensor" - and my answer is that a difference in exposure is much more visible than a difference in DOF (which, again, is a bit subjective), diffraction (which might be or might not be a problem at the set aperture) or noise (not an issue except in low light, for large sensor cameras)
Really? The exposures for 50mm f/2 1/100 ISO 400 and mFT and 100mm f/4 1/100 ISO 1600 are two stops apart (but the same total light). What makes this difference in exposure more visible than the differences that we would see if the FF photo were instead taken at 100mm f/2 1/100 ISO 400, which has the same exposure?
I see... I never said the ISO should be considered constant, thinking it would be obvious - and that was a mistake from my part.
Why would you set the ISO to anything other than what would give the desired brightness in the photo (aside from ISOless shooting with a camera that has an ISOless sensor)?
Why would you change the ISO in a scenario where this wasn't mentioned?
I would change the ISO as needed (or let the camera change the ISO for me in Auto ISO) to get the desired output brightness. I mean, isn't that painfully obvious?
Not in (virtual) tests which should be controlled. If we said that one factor (e.g. exposure) would be changed, the others are usually assumed constant.
But I already assumed responsibility for not explicitly mentioning this, and make the necessary clarifications. Which you don't seems to be willing to accept, instead going on with your convenient scenarios.
By differences in exposure I actually mean deviations from the "correct" (intended) exposure, not numeric differences between some EVs.
If f/2 1/100 gave the "correct exposure" on mFT, why wouldn't f/4 1/100 give the "correct exposure" on FF?
"Correct" (intended) exposure depends on the effective ISO;
And there we have it -- why many, if not most, of the anti-Equivalence crowd can't come to terms with Equivalence -- a complete and total misunderstanding of what exposure is and what role the ISO setting plays.
I wonder, why Equivalence? Is that some sort of religion?
The misunderstanding is yours, what I say is correct.
what you say could, or could not be true.
What I said is true, and what I said is that the ISO setting merely sets the output brightness of the photo.
If constant exposure. Or you could adjust the exposure to match the ISO.
However, the format is not included in the equation; only scene luminance, aperture (f-stop), shutter speed and ISO are.
What is correct about 50mm f/2 1/100 ISO 400 on mFT that is not "correct" about 100mm f/4 1/100 ISO 1600 on FF?
As I said, the exposure triangle does not depend on the format; it's designed to be independent of the format. Thus, "on mFT" and "on FF" is just useless information.
The focal length is useless information.
In a strict sense, exposure is indeed no more than light per area, that's not very meaningful by itself. But then, total light is exposure multiplied by area, not very meaningful either.
The total amount of light that falls on the sensor is indeed rather meaningful since, combined with sensor efficiency, it results in the same noise. In any case, the total amount of light falling on the sensor has far more to do with the visual properties of the photo than does the exposure, with regards to cross-format comparisons (for comparisons within a format, either measure works just as well).
But the exposure value, combined with sensitivity/ISO, is giving the image "brightness", variations of which are usually more apparent than noise differences.
If you only knew the total light you would not be able to take a properly exposed image. You might be able to approximate noise, though ;-)
What is the difference in brightness between 50mm f/2 1/100 ISO 400 on mFT and 100mm f/4 1/100 ISO 1600 on FF?
The question is unrelated to what I said.
However, it's components are important. Same exposure, or same total light can be obtained with very different settings - one can vary aperture, shutter speed and even scene luminosity.
You're quite skilled at pushing the conversation on a convenient track.
What you mean to say is that I'm quite skilled at pointing out that you do not understand how exposure and total light relate to the visual properties of the photo.
I wonder...
While you're wondering, if you could let us know how the exposures compare with total light as a measure for the visual properties of the following three photos of the same scene from the same position displayed at the same size:
- 50mm f/2 1/100 ISO 400 on mFT
- 100mm f/2 1/100 ISO 400 on FF
- 100mm f/4 1/100 ISO 1600 on FF
I find the way you're trying to "teach" me things instead of discussing them quite arrogant. You already have your answers, try not to ignore them.
More likely is that you find questions that reveal fundamental misconceptions you have about exposure, total light, ISO, and brightness to be uncomfortable.
You have nothing to teach me, except perhaps arrogance - thanks, but I'll pass.
Unfortunately, I am unable to teach you how to read.
The answer may just clear up some rather important fundamental misunderstandings.
Why, are you misunderstanding something?
It's pretty obvious who is misunderstanding here. So, I ask again:
Could you let us know how the exposures compare with total light, and how the brightness compares, as a measure for the visual properties of the following three photos of the same scene from the same position displayed at the same size:
- 50mm f/2 1/100 ISO 400 on mFT
- 100mm f/2 1/100 ISO 400 on FF
- 100mm f/4 1/100 ISO 1600 on FF
Of course, as always, answers are voluntary, not compulsory.
I'd rather not discuss red herrings. You already have the answers and more than enough clarifications; you have no excuse for refusing to understand.
