# Dynamic Range -- what it is, what it's good for, and how much you 'need'

Started Oct 17, 2011 | Discussions thread
Relative significance

boggis the cat wrote:

Then consider that the relative size difference between FourThirds and APS-C is considerably less than that between APS-C and 135.

From 24x36 to 15.8x23.6 is about 1.2 stops.
From 15.8x23.6 to 13x17.3 is about 0.73 stops.

(Using "stops" to denote "noise equalisation through ISO change" and not exposure, obviously.)

That's for "1.5x" APS-C.

Canon APS-C is 14.8 x 22.2 mm, or 1.4 and 0.55 "stops" respectively.

These calculations ignore the additional aspect ratio efficiency of 4:3 over 3:2, which is roughly 4%. This changes e.g. the Canon APS-C to FT ratio from 0.55 to 0.49 "stops", and the 135 to FT ratio from 1.94 to 1.89 "stops".

Do you really think that calls for an adverb like 'considerably'?

Is 1.2 litres considerably more than 0.73 litres? It's not that far from double the amount, Rikke.

I would agree that a 0.5 stop difference in DR may be of limited significance in real terms. The Olympus cameras from the E-P1 through to the E-PL3, inclusive of the E-5, only appear to have a DR spread of about 2/3 stop. This is of little significance compared to the other differences present -- detail, contrast, relative brightness levels (presumably due to the tone curve) and so on.

How about 'APS-C is slightly closer to Four-Thirds than it is to full frame'?

How about "APS-C is twice as close to FourThirds as it is to 135"?

This is especially true if you want to factor in the 30% or so Canon APS-C sensor share, which is nearly three times as close to FT as 135.

For people not hung up on insignificant decimals it is roughly midway between FT and FF, roughly a stop from each.

You should ask Joe if that degree of "roughness" is acceptable. In practice a half-stop may not amount to much, but if you are trying to calculate things to a 0.1 stop resolution then the more accurate your starting measurements the more accurate your result will be.

By your own math, that's a 0.47 "stop" difference (or 0.85 "stop" for Canon APS-C). Hardly insignificant if we are to take DxO's 0.1 stop resolution DR numbers as meaningful.

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