confused about exif information
Posted 05/05/2014 - 23:22
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That should have read "gallery photos".
Posted 05/05/2014 - 23:59
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I'm assuming that aperture value might refer to the open aperture, which will vary with a zoom lens. The f/stop will be the actual aperture set.
So an f/2 lens perhaps set at f/8.
Do the actual figures confirm this possibility?
So an f/2 lens perhaps set at f/8.
Do the actual figures confirm this possibility?
Best regards, John
Posted 06/05/2014 - 00:34
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Don't think that is the case: Look at the recent images of the Yellow Wagtails.
Both at 300mm - the picture of the male has F-stop f/7.1 and Aperture Value of f/5.6, whereas the picture of the female has f/8 and f/6.
If JRs assertion was correct then the Aperture Value would be the same and given that the lens was a DA*300 it would be f/4.
If I look at teh EXIF data for teh first externally it gives:
F Number F7.1
Aperture 5.66 Av (F7.1)
So is the Aperture value at 5.6 actually an actual aperture? or not, possibly not.
Both at 300mm - the picture of the male has F-stop f/7.1 and Aperture Value of f/5.6, whereas the picture of the female has f/8 and f/6.
If JRs assertion was correct then the Aperture Value would be the same and given that the lens was a DA*300 it would be f/4.
If I look at teh EXIF data for teh first externally it gives:
F Number F7.1
Aperture 5.66 Av (F7.1)
So is the Aperture value at 5.6 actually an actual aperture? or not, possibly not.
Posted 06/05/2014 - 01:19
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Aperture Value(Av) is indeed different to the f stop number
I had an article about it somewhere but lost it. here' aa post on DPReview which might help
http://www.dpreview.com/forums/post/10984603
I had an article about it somewhere but lost it. here' aa post on DPReview which might help
http://www.dpreview.com/forums/post/10984603
Quote:
The camera information in this standard conforms to the APEX (Additive System of Photographic Exposure ) unit system. APEX is a convenient unit for expressing exposure (Ev). The relation of APEX to other units is essentially as follows.
· ApertureValue (Av) = 2 log 2 (F number)
· ShutterSpeedValue (Tv) = - log 2 (exposure time)
· BrightnessValue (Bv) = log2 (B/NK) Note that:B:cd/cm2,N,K:constant Film sensitivity (not used in this standard) is expressed as follows.
· Film sensitivity (Sv) = log2 (ASA / 3.125)
Using these values, exposure (Ev) is calculated as follows.
· Ev = Av + Tv = Bv + Sv
The table below gives examples of values actually used as camera information.
ApertureValue_ F-Number
0_1
1_ 1.4
2_ 2
3_ 2.8
4_ 4
5_ 5.6
6_ 8
7_ 11
8_ 16
9_ 22
10_ 32
The camera information in this standard conforms to the APEX (Additive System of Photographic Exposure ) unit system. APEX is a convenient unit for expressing exposure (Ev). The relation of APEX to other units is essentially as follows.
· ApertureValue (Av) = 2 log 2 (F number)
· ShutterSpeedValue (Tv) = - log 2 (exposure time)
· BrightnessValue (Bv) = log2 (B/NK) Note that:B:cd/cm2,N,K:constant Film sensitivity (not used in this standard) is expressed as follows.
· Film sensitivity (Sv) = log2 (ASA / 3.125)
Using these values, exposure (Ev) is calculated as follows.
· Ev = Av + Tv = Bv + Sv
The table below gives examples of values actually used as camera information.
ApertureValue_ F-Number
0_1
1_ 1.4
2_ 2
3_ 2.8
4_ 4
5_ 5.6
6_ 8
7_ 11
8_ 16
9_ 22
10_ 32
[i]Bodies: 1x K-5IIs, 2x K-5, Sony TX-5, Nokia 808
Lenses: Pentax DA 10-17mm ED(IF) Fish Eye, Pentax DA 14mm f/2.8, Sigma 17-70mm f/2.8, Pentax-A 28mm f/2.8, Sigma 30mm F1.4 EX DC, Pentax-A 50mm f/1.2, Pentax-A 50mm f/1.4, Pentax-FA 50mm f/1.4, Pentax-A 50mm f/1.7, Pentax DA* 50-135mm f/2.8, Sigma 135-400mm APO DG, and more ..
Flash: AF-540FGZ, Vivitar 283
Lenses: Pentax DA 10-17mm ED(IF) Fish Eye, Pentax DA 14mm f/2.8, Sigma 17-70mm f/2.8, Pentax-A 28mm f/2.8, Sigma 30mm F1.4 EX DC, Pentax-A 50mm f/1.2, Pentax-A 50mm f/1.4, Pentax-FA 50mm f/1.4, Pentax-A 50mm f/1.7, Pentax DA* 50-135mm f/2.8, Sigma 135-400mm APO DG, and more ..
Flash: AF-540FGZ, Vivitar 283
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321 posts
14 years
durham
I like to look at the "your photos" section of the forum, and i normally look at the exif info.
Im a bit confused why the f/stop may be for example f16, but the aperture value may be f/8.
Why the two different values?
Excuse my ignorance if im missing something obvious here.
Cheers,