Thank you Photozone for starting to include "Equiv. max. fstops" in the reviews.
It brings attention to the fact that it is misleading to specify equivalent focal length along with nonequivalent relative apertures (thus breaking simple proportion: ApertureDiameter = FocalLength / FNumber). It is great that you specify both.
In recent Nikon 1855vr review:
[indent]Equiv. focal length: 2782.5 mm (full format equivalent)
Equiv. max. fstops: f/5.08.0 (full format equivalent, in terms of depthoffield  not speed)
[/indent]
Only slight detail: values should be f/5.38.5 since crop factor for Nikon DX cameras is 1.52, not 1.4.
It could be also improved by linking to this excellent article (or write some shorter explanation on your site): http://www.josephjamesphotography.com/equivalence/
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Yes, technically you're, of course, correct.
It's already a difficult topic so we decided to do it the simple way because it is more widely known that you loose about a stop.
cheers
Klaus
[quote name='jtra' timestamp='1300989287' post='7079']
Thank you Photozone for starting to include "Equiv. max. fstops" in the reviews.
It brings attention to the fact that it is misleading to specify equivalent focal length along with nonequivalent relative apertures (thus breaking simple proportion: ApertureDiameter = FocalLength / FNumber). It is great that you specify both.
In recent Nikon 1855vr review:
[indent]Equiv. focal length: 2782.5 mm (full format equivalent)
Equiv. max. fstops: f/5.08.0 (full format equivalent, in terms of depthoffield  not speed)
[/indent]
Only slight detail: values should be f/5.38.5 since crop factor for Nikon DX cameras is 1.52, not 1.4.
It could be also improved by linking to this excellent article (or write some shorter explanation on your site): [url="http://www.josephjamesphotography.com/equivalence/"]http://www.josephjam...om/equivalence/[/url]
[/quote]
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Actually, you lose 1.5 stops approximately with Nikon, and almost 1 2/3 stops with Canon, on APSC.... So 1 stop is a little optimistic IMO. <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 EFR adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OMD 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EFMFT adapters ....
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 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]
Hold on, the DOF difference between FF and 1.5x crop is exactly 1.5x, or at least online DOF calculators show that. One aperture stop is 1.4, which affects DOF exactly in the same way  1.4x. So 1.5 crop is slower by 1.5/1.4 = 1.07 stop, not a huge difference.
For nitpickers  I know that Nikon's crop is nearly 1.52x, however one aperture stop (sqrt 2) is not exactly 1.4 either <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/cool.gif' class='bbc_emoticon' alt='B)' />
[quote name='Lomskij' timestamp='1301136339' post='7102']
Hold on, the DOF difference between FF and 1.5x crop is exactly 1.5x, or at least online DOF calculators show that. One aperture stop is 1.4, which affects DOF exactly in the same way  1.4x. So 1.5 crop is slower by 1.5/1.4 = 1.07 stop, not a huge difference.
For nitpickers  I know that Nikon's crop is nearly 1.52x, however one aperture stop (sqrt 2) is not exactly 1.4 either <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/cool.gif' class='bbc_emoticon' alt='B)' />
[/quote]
Well,
I don't agree with your calculation.
The DOF function on Squire of Distance
While Aperture affect DOF linearly.
Mathemathical writen is
DOF = f(D^2, A)
while
D  distance to subject
A  apeture number
for example if you shoot subject from 5 meters and you have DOF 1m.
If you shoot the same subject from 10m at the same focal length and aperture you will have DOF 4m.
For simplicity I assume that we work with fixed focal length lens.
What does it mean?
It remembers me one of my first photographic lessons. The master explain us how to change the DOF.
If you want shallow DOF
 first you have to go as close as possible to the subject.
 secondary you have to choose the appropriate aperture.
As technical aware person I ask the teacher about how DOF is affected by camera formats.
He answer  well the larger the format the shallower the DOF you acheve, BUT you have to remember first you have to be as close as possible.
That is the answer of artist. Later on I found the mathematical equation and I understood what did he said.
greetings,
miro
[quote name='miro' timestamp='1301138788' post='7103']
Well,
I don't agree with your calculation.
The DOF function on Squire of Distance
While Aperture affect DOF linearly.
Mathemathical writen is
DOF = f(D^2, A)
while
D  distance to subject
A  apeture number
for example if you shoot subject from 5 meters and you have DOF 1m.
If you shoot the same subject from 10m at the same focal length and aperture you will have DOF 4m.
For simplicity I assume that we work with fixed focal length lens.
What does it mean?
It remembers me one of my first photographic lessons. The master explain us how to change the DOF.
If you want shallow DOF
 first you have to go as close as possible to the subject.
 secondary you have to choose the appropriate aperture.
As technical aware person I ask the teacher about how DOF is affected by camera formats.
He answer  well the larger the format the shallower the DOF you acheve, BUT you have to remember first you have to be as close as possible.
That is the answer of artist. Later on I found the mathematical equation and I understood what did he said.
greetings,
miro
[/quote]
I didn't do the maths, I've just used online DOF calculators:
http://www.dofmaster.com/dofjs.html
http://www.cambridgeincolour.com/tutoria...ulator.htm
And both of them show that dependance of DOF against the crop factor is linear <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/wink.gif' class='bbc_emoticon' alt=' ' />
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[quote name='Lomskij' timestamp='1301136339' post='7102']
Hold on, the DOF difference between FF and 1.5x crop is exactly 1.5x, or at least online DOF calculators show that. One aperture stop is 1.4, which affects DOF exactly in the same way  1.4x. So 1.5 crop is slower by 1.5/1.4 = 1.07 stop, not a huge difference.
For nitpickers  I know that Nikon's crop is nearly 1.52x, however one aperture stop (sqrt 2) is not exactly 1.4 either <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/cool.gif' class='bbc_emoticon' alt='B)' />
[/quote]
Not all Nikon APSC cameras have the same crop factor (And not all Canon APSC cameras have the same crop factor either). So 1.52x might be a bit too precise? The D3100, for instance, has a crop factor of 1.56x.
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03262011, 10:27 PM
(This post was last modified: 03262011, 10:28 PM by wim.)
[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 fstop comes very close, however, hence my indication of roughly 1.5 stops for Nikon 1.5 APSC 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 ruleofthumb, 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 EFR adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OMD 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EFMFT adapters ....
