F stop difference calculation / normalization question

Started Oct 19, 2013 | Discussions thread
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Earthlight Veteran Member • Posts: 3,208
F stop difference calculation / normalization question

Hello everyone,

Am I correct in assuming the following:

We have two exposures:

  • Exposure 1: 298s, ISO 1600, f3.5


  • Exposure 2: 112s, ISO 1250, f2

What is the difference between them in f stops?

I started by inserting the f stops and exposure times here:


Unless I am mistaken the exposure 2 is 0.2029 stops (we'll round it to 0,2 stops) brighter based on the f stop and exposure time.

Then there is the ISO difference, meaning that the exposure 2 is 0,3 stops less than exposure 1.

So, if we want to normalize the exposure difference, we will need to increase the exposure 2 by 0,1 stops

Is this correct?

Thanks a lot!


ps. tried asking this in the astrophoto forum, but no answers.

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