[quote name='miro' timestamp='1301098141' post='7098']
Hello Wim,
How do you come to this numbers 1,5 and 1 2/3 stops?
According to my cacluations.
1,5 crop must have 2,25 times higher DOF - in terms of stops it is 1,17 Stops
1,6 crop must have 2,56 times higher DOF - 1,35 Stops.
With Kind Regards,
Miro
PS Finally I fond Wim to say something wrong. :-)
[/quote]
It is a little more complex that that. I don't particularly feel inclined right now to look up the formulas, but it is related to FL, distance and AoV in a reasonably complex way. It is certainly not linear, but also not quadratic. All in all, a direct conversion of linear magnification to f-stop comes very close, however, hence my indication of roughly 1.5 stops for Nikon 1.5 APS-C sensors (slightly more actually) and roughly 1 2/3 stops for Canon (slightly less actually). <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />
Since this is a very usable rule-of-thumb, this is what I tell people most of the time <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='' />.
Warm regards, Wim
Hello Wim,
How do you come to this numbers 1,5 and 1 2/3 stops?
According to my cacluations.
1,5 crop must have 2,25 times higher DOF - in terms of stops it is 1,17 Stops
1,6 crop must have 2,56 times higher DOF - 1,35 Stops.
With Kind Regards,
Miro
PS Finally I fond Wim to say something wrong. :-)
[/quote]
It is a little more complex that that. I don't particularly feel inclined right now to look up the formulas, but it is related to FL, distance and AoV in a reasonably complex way. It is certainly not linear, but also not quadratic. All in all, a direct conversion of linear magnification to f-stop comes very close, however, hence my indication of roughly 1.5 stops for Nikon 1.5 APS-C sensors (slightly more actually) and roughly 1 2/3 stops for Canon (slightly less actually). <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />Since this is a very usable rule-of-thumb, this is what I tell people most of the time <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />.Warm regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....
