Alley in Pisa, Italy

by Lars Kotthoff

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2
votes
1answer
136 views

What flash guide number do I need to underexpose a “sunny” background?

I'm familiar with the maths behind flash usage (guide numbers, etc.). Here's a more practical question that doesn't yet seem to have an answer on photo.se: Consider a subject, outdoors, on a regular ...
4
votes
1answer
592 views

How can I calculate the effect of non-TTL flash on exposure?

I recently got an old Canon AE-1 film camera back in working order. I'd like to use my modern 430EXII Speedlight flash with it, however since there is no TTL metering, I have no idea how much the ...
2
votes
1answer
533 views

What is the relationship between Guide Number and flash power level?

From this post, I understand that the flash guide number (GN) is given by the following formula: Guide Number = Shooting Distance × f-number ÷ ISO factor I'm assuming that the GN calculated via the ...
8
votes
4answers
3k views

What is the quantative relation between flash guide number and ISO?

I found that formula on the Internet: Guide Number = (Shooting Distance * Aperture) ÷ ISO Sensitivity Is it correct? If it is could someone please explain why ISO is related to guide number in this ...
6
votes
4answers
840 views

Does adding additional strobes cumulatively add to the flash power?

I've been reading articles that talk about using multiple strobes next to each other, all pointing in the same direction: as a means to add more light over what one flash can do. Does the addition of ...