Luminous Landscape Forum

Equipment & Techniques => Digital Cameras & Shooting Techniques => Topic started by: Samotano on September 02, 2010, 04:27:15 pm

Title: EV Difference and Camera Raw
Post by: Samotano on September 02, 2010, 04:27:15 pm

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?

Title: Re: EV Difference and Camera Raw
Post by: bjanes on September 02, 2010, 05:18:55 pm

Quote from: Samotano on September 02, 2010, 04:27:15 pm

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.

Title: Re: EV Difference and Camera Raw
Post by: Bart_van_der_Wolf on September 02, 2010, 06:15:16 pm

Quote from: bjanes on September 02, 2010, 05:18:55 pm

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

Title: Re: EV Difference and Camera Raw
Post by: Johnny_Johnson on September 02, 2010, 09:48:55 pm

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

Later,
Johnny

Title: Re: EV Difference and Camera Raw
Post by: Samotano on September 02, 2010, 10:37:29 pm

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

Title: Re: EV Difference and Camera Raw
Post by: Bart_van_der_Wolf on September 03, 2010, 03:19:18 am

Quote from: Samotano on September 02, 2010, 10:37:29 pm

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

Title: Re: EV Difference and Camera Raw
Post by: RFPhotography on September 03, 2010, 07:32:04 am

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.

Title: Re: EV Difference and Camera Raw
Post by: Samotano on September 03, 2010, 07:34:29 pm

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

Title: Re: EV Difference and Camera Raw
Post by: RFPhotography on September 05, 2010, 07:24:18 am

Quote from: Samotano on September 03, 2010, 07:34:29 pm

I need to be exact...  ;)

On this forum, I should have figured.  ;D