PS-CS2 v.9.0.2 Exif Aperture Value

JC
Posted By
John_Cane
Sep 2, 2006
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427
Replies
2
Status
Closed
Please advise if CS2 is communicating correctly with the DNG and JPG file formats in retrieving Exif aperture values. I am getting some strange results.

First off, please confirm that the Exif property, "Aperture Value" is supposed to be the diameter of the aperture in mm.

As an example, with L=70, F=1/22 you expect aperture = 3.2. When I apply the depth of field lever, the aperture looks like about 3 mm diameter. However, Photoshop gives me "Aperture Value" of 8.9. I tried other values of L (28, 50, 90 mm) with F=1/8. The aperture value was consistently 6.0. See this link for results of testing to date.

Any ideas appreciated. <http://photo.enw-ltd.com/ApertureData.htm>
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aperture exif value

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MD
Michael_D_Sullivan
Sep 3, 2006
The EXIF standard 2.2 specifies that the ApertureValue property is stored as an APEX value. For apertures, the APEX value is 2 * log2(f), where f is the f-stop. The chart in Annex C to the standard indicates that f/22 is often represented as 9. In fact, it is between 9 and your 8.9. Because of how the APEX values are defined, each increase of 1 in the APEX value represents a single F-stop of difference — i.e., a doubling of the amount of light allowed through the lens. The chart gives the following equivalents:

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
JC
John_Cane
Sep 3, 2006
Thanks for clearing this up for me. Great help.

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