Exif Query...

[Darryn]

Ive just been looking at some of my photos and ive checked the Exif that is embedded in This shot exported from Aperture.

What i dont understand is when loaded into CS3, under Camera Data 1 it lists "F-Stop = f/4.5" and "Aperture Value = f/4.6"

Whats that all about?

To my limited knowledge they are one and the same, so i dont understand, firstly why it would list them seperately and secondly why they would be differant... Can anyone shed any light on this matter?

Thanks Darryn.

 

[chuckles]

Unless it's a constant aperture zoom lens (say, f2.8 at all focal lengths) then the aperture value will alter at different focal lengths even though the actual aperture setting on the lens remains the same. That's my take on it anyway :shrug:

 

[Darryn]

It was taken using the 300f2.8IS with a 1.4x TCII attached... So yup it is a constant aperture lens.

 

[chuckles]

Ok - well that's kept me busy for ages. And the answer goes back to the 1960's

My synopsis.....

It seems it stems from trying to make calculations when making and calibrating exposure meters, cameras (with built in meters) and the like. The reason for the differences, as I understand it, is to compensate for the inaccuracies when performing additions/transpositions using both logaritmic and/or linear calculations. So, some (well, quite a lot) bright sparks came up with the APEX system which supplies (supposedly) a more accurate set of definitions based around the Brightness and/or Luminance of the subject.

I tried to read all of it but it increased my soporific awareness to my surroundings.... the next stage would've been ....... :baby:

For your further edification.....


Wikipedia's take on it

What Douglas Kerr said......

"The Additive System of Photographic Exposure (APEX) provides for stating several factors involved in photographic exposure in logarithmic form. In this way, calculation of the "proper exposure" for a given situation may be done manually using only simple addition. Although changes in practice and technology have diminished the importance of that objective, it is today still common and convenient to express certain factors in APEX terms. This article explains APEX and the factors it describes, including the commonly-encountered "Ev" (exposure value). Some basic principles of basic photographic exposure metering are also discussed, including the concept of the "exposure meter calibration factor." "

His Article....

Best used at bed time if you ask me!