Is my thinking about equivalence right?

Started 5 months ago | Questions thread
bobn2 Forum Pro • Posts: 69,811
Re: Is my thinking about equivalence right?

RobBobW wrote:

bobn2 wrote:

RobBobW wrote:

What I meant by “it is a wash” is that more light is required to illuminate a full frame sensor to the desired light intensity. The only relevance of total light is in obtaining the desired intensity.

The 'desired intensity' is set by your requirements for image quality (noise), and for any given requirement will be different full-frame and mFT.

Actually, I was thinking about 'desired intensity' referring to the exposure to give a good Zone system type of overall tonal range. No ETTR or stuff like that. My film days are showing!

Film days were much like digital days. The 'overall tonal range' was determined mostly by processing, and, if you were making prints, but the printing. The zone system was about getting the most information into the negative, not about setting the tonal range. Remember, Adams would quite frequently reprint his negatives with completely different tonal ranges.

You have come to think that setting exposure is entirely about setting the output lightness, whilst on digital the ISO control is effectively the lightness control. If your exposure is not 'correct' according to lightness, you can just make it 'correct' by changing the ISO.

So, let's go back to the question of f-number and its effect on the image. If you're using f/4 at 200 ISO on mFT, you can get the same results with the same shutter speed by using f/8 and 800 ISO on FF. That's as much the 'same result' as you would get using two different mFT cameras at f/4 and 200ISO.

That's why your 'period' was a bit premature. It ignores the fact that what is the 'correct' exposure tonality wise is determined by the ISO setting, and with different format cameras you'll use different ISO settings, and different exposures, to get the same results.

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