[Guest]

[quote name='Brightcolours' timestamp='1305777380' post='8574']

f2.8 to f2 is one stop... f2 to f 1.8 is 1/3rd stop.

For Canon, its f1.8 -> f2.88, a bit over 1 1/3rd.

For Nikon its f1.8 -> f2.7, a bit under 1 1/3rd. Actually... f2.726 for for instance a D300 (1.52x crop), f2.808 for a D3100.

[/quote]

Ok, thought so. I'm calculating from another end:



1 stop - 2x light loss.



1 1/3 stop - ~2.67x



Nikon crop - 1.52^2 = ~2.3x



Canon crop - 1.61^2 = ~2.6x



Both less than 1 1/3 stop. So it's either my calculation is wrong or yours <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/rolleyes.gif' class='bbc_emoticon' alt='' />

[Brightcolours]

[quote name='Lomskij' timestamp='1305790000' post='8585']

Ok, thought so. I'm calculating from another end:



1 stop - 2x light loss.



1 1/3 stop - ~2.67x



Nikon crop - 1.52^2 = ~2.3x



Canon crop - 1.61^2 = ~2.6x



Both less than 1 1/3 stop. So it's either my calculation is wrong or yours <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/rolleyes.gif' class='bbc_emoticon' alt='' />

[/quote]

Mine are right (they are not just mine, they are more or less "common knowledge"). <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/wink.gif' class='bbc_emoticon' alt='' />

Even though I did figure it out myself, only later finding out it is "common knowledge" (except on Olympus boards.. strange but true).



I did not sleep enough to think about why your approach is wrong (in other words: why it does not work), but follow my aperture (hole size) way of calculating (same hole, same captured field of view) and you bypass the whole crop factor thing, and still reach the exact same results as the crop factor multiplication way.



Maybe your way is suggesting holes are squares instead of circles.

[Guest]

[quote name='Brightcolours' timestamp='1305790699' post='8590']

Mine are right (they are not just mine, they are more or less "common knowledge"). <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/wink.gif' class='bbc_emoticon' alt='' />

Even though I did figure it out myself, only later finding out it is "common knowledge" (except on Olympus boards.. strange but true).



I did not sleep enough to think about why your approach is wrong (in other words: why it does not work), but follow my aperture (hole size) way of calculating (same hole, same captured field of view) and you bypass the whole crop factor thing, and still reach the exact same results as the crop factor multiplication way.



Maybe your way is suggesting holes are squares instead of circles.

[/quote]

Lol, that's why I'm trying to figure out the math behind the "common knowledge".



Ok, I think I get it. Looks like it depends whether you calculate 1/3 of stop linearly, i.e. like this: 1.4 - 1.6 - 1.8 - 2,



or you calculate by light loss, i.e. 1/3 is ~0.67x and corresponding aperture values would look like this: 1.41 - 1.63 - 1.83 - 2.



So in the former case canon's crop (1.61) is slightly over 1 1/3 stop and in the latter is slightly less <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='' />



Not that it makes much difference, but I had to get to the root of this.