Exposure Value calculation

Started by blue-j, February 02, 2023, 10:17:31 PM

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blue-j

February 02, 2023, 10:17:31 PM
Any reason this calculation would not work?

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EV = log2(composite:aperture/composite:shutterspeed)
Thinking of making EV a composite tag over here.

- J

Phil Harvey

#1
February 03, 2023, 06:49:35 AM
The ExifTool LightValue tag does this already (including the effect of ISO).

- Phil
...where DIR is the name of a directory/folder containing the images.  On Mac/Linux/PowerShell, use single quotes (') instead of double quotes (") around arguments containing a dollar sign ($).

blue-j

#2
February 03, 2023, 12:54:06 PM Last Edit: February 03, 2023, 05:34:00 PM by blue-j Reason: Formula needed correction
EV = log2(F Number^2/Shutter Speed)

LV = 2 x log2(F Number) - log2(Shutter Speed) - log2(ISO / 100)

EV is a common metric now for people I think?  I was thinking of presenting both.

It seems EV is also normalized to a 100 ISO.

I am no expert (I'll probably say this for the rest of my life)!  I don't claim to understand this distinction in practical terms.

- J

Phil Harvey

#4
February 04, 2023, 07:30:22 AM
Just FYI:  (basic math)

log2(F Number^2/Shutter Speed) =  2 x log2(F Number) - log2(Shutter Speed)

EV is not very useful because it only represents part of the picture.  It was more useful with film cameras where the ISO was fixed, and is equivalent to LV for ISO 100 as you mentioned.

- Phil
...where DIR is the name of a directory/folder containing the images.  On Mac/Linux/PowerShell, use single quotes (') instead of double quotes (") around arguments containing a dollar sign ($).

blue-j

#5
February 05, 2023, 12:32:44 AM
Yes, understood.  Thank you!

- J
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