EV Difference and Camera Raw

[Samotano]

This question might seem elementary...
How do I calculate the difference in exposure values between two given exposure times? 
For example, I have two identical shots (same ISO, f/) bracketed so that

shot1 is 1/50'' and
shot2 is 1/10''

I want to adjust shot2 to the same exposure as shot1 in CameraRaw/Lightroom or any other software with Exposure adjustment.  How do I calculate what the adjustment factor is?

[bjanes]

This question might seem elementary...
How do I calculate the difference in exposure values between two given exposure times? 
For example, I have two identical shots (same ISO, f/) bracketed so that

shot1 is 1/50'' and
shot2 is 1/10''

I want to adjust shot2 to the same exposure as shot1 in CameraRaw/Lightroom or any other software with Exposure adjustment.  How do I calculate what the adjustment factor is?

The EV units are log base 2. The ratio in your example is 5:1, so the answer is log (base 2) of 5 = 2.32 stops. If you have Microsoft Excel the calculation is easy.

[Bart_van_der_Wolf]

The EV units are log base 2. The ratio in your example is 5:1, so the answer is log (base 2) of 5 = 2.32 stops. If you have Microsoft Excel the calculation is easy.

Or just use a calculator log(5) / log(2) = 2.32

Same procedure.

Cheers,
Bart

[Johnny_Johnson]

Or, enter log(5)/log(2) into Google Search.

Later,
Johnny

[Samotano]

Thanks.  Just to clarify, what if the ratio was, say, 5:3.

[Bart_van_der_Wolf]

Thanks.  Just to clarify, what if the ratio was, say, 5:3.

Log(5/3) / log(2) = 0.74, so 2/3rd (or 1) stop difference.

Cheers,
Bart

[RFPhotography]

If you need it to be exact, use the log math provided.

If you want it to be close use simple math.  Each halving or doubling of the shutter speed is 1 stop.  1 sec to 2 sec is 1 stop.  2 sec to 4 sec is one stop.  1/125 to 1/60 is 1 stop.  Got it?

In your case you're going from 1/10 to 1/50.  1/10 to 1/20 is 1 stop.  1/20 to 1/40 is 2 stops.  You've got 1/10 left.  1/40 to 1/80 is one stop which is a 1/40 difference.  10 is 1/4 of 40 so your total EV is about 2 1/4 stops (not too far different from the 2.32 calculated by the more difficult math) and much easier to do on the fly in the field or in the editing room without having to fire up a spreadsheet.

[Samotano]

I need to be exact... 
Thanks so much!

[RFPhotography]

I need to be exact... 

On this forum, I should have figured.