Where is the full frame advantage?

Started Mar 31, 2008 | Discussions thread
bobn2
bobn2 Forum Pro • Posts: 61,123
Calculating the effect

I've done a spreadsheet to calculate the effect of diffraction on images from various cameras, making the following assumptions:
Perfect lens (diffraction limited only).

OLPF set to spread a point image by 0.75 pixel pitch (I suspect most manufacturers set them weak)
No resolution reduction for debayering (i.e. assume monochrome sensor)

Thus, at each aperture the maximum resolution in line pairs is 1/2*max(p, 0.75p+d) where p is pixel pitch and d is diffraction limit (this is a crude model, but given the assumptions that need to be made, there's not much point going for more accuracy). I've adjusted the units to lp/mm. Sensor parameters from http://www.digitaldingus.com/reference/general/sensorsizes.php (there are some oddnesses about them, for instance, the D3 is given as having a finer pitch than the 5D.) Obviously, any model can stand in for any other having the same pixel pitch and sensor size.
Here are the results.
Cam~ D40,20D,40D,D200,D300~1DII,5D,D3,1DIII,1DsII,1DsIII
f/1~ 64, 78, 89, 86, 94~ 61, 61, 61, 70, 71, 79
f/1.4 ~ 64, 78, 89, 86, 94~ 61, 61, 61, 70, 71, 79
f/2 ~ 64, 78, 89, 86, 94~ 61, 61, 61, 70, 71, 79
f/2.8 ~ 64, 77, 84, 82, 87~ 61, 61, 61, 70, 71, 78
f/4 ~ 60, 69, 75, 74, 78~ 58, 58, 58, 64, 64, 70
f/5.6 ~ 54, 61, 66, 64, 67~ 45, 45, 45, 49, 49, 62
f/8 ~ 47, 52, 55, 54, 56~ 45, 45, 45, 49, 49, 52
f/11 ~ 40, 43, 46, 45, 56~ 39, 39, 39, 41, 42, 44
f/16 ~ 32, 34, 36, 35, 36~ 31, 31, 31, 33, 33, 35
f/22 ~ 26, 27, 28, 28, 29~ 26, 26, 26, 26, 27
f/32~ 20, 21, 21, 21, 21~ 19, 19, 19, 19, 20
f/45~ 15, 16, 16, 16, 16~ 15, 15, 15, 15, 15

Things to note about this:

Finer pitch always means better resolution (even at f/45, it's just lost in the rounding)

The resolution advantage of fine pitches is increasingly small as f-number increases

Diffraction limiting begins to have an effect above f/2.8 (in reality, the resolution of most lenses is still increasing here, due to decreasing aberrations, but the resolution will never be better than the figure here.

What happens if we look at an A4 print? The same figures again, scaled to give a long sensor dimension of 297mm, now expressed in DPI (where 1 dot = 0.5 line pair).

Cam~D40,20D,40D,D200,D300~1DII,5D,D3,1DIII,1DsII,1DsIII
f/2.8 ~ 260, 301, 344, 347, 378~ 299, 372, 376, 343, 432, 477
f/4 ~ 245, 266, 290, 297, 313~ 286, 355, 359, 314, 395, 428
f/5.6 ~ 219, 234, 253, 260, 272~ 257, 319, 322, 279, 351, 377
f/8 ~ 189, 199, 212, 218, 227~ 223, 277, 279, 239, 300, 319
f/11 ~ 161, 167, 177, 182, 188~ 191, 237, 240, 203, 255, 268
f/16 ~ 129, 132, 138, 143, 147~ 154, 192, 194, 162, 203, 212
f/22 ~ 105, 105, 109, 113, 116~ 125, 156, 157, 130, 163, 169

Note here the clear advantage of 1.3x and FF, due to lower magnification. Once again, more pixels always gives some advantage.
--
Bob

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