Inverse Square Law for Photographers

Started Jan 21, 2010 | Discussions thread
UKphotographers Veteran Member • Posts: 4,321
Re: Easier to think in terms of f-stop ratios for distance and light

calson wrote:

You really do not understand the basics which is fine but why not keep an open mind and learn something.

Me ?!!

Whether the light is reflected from an umbrella or softbox or goes directly to the subject, moving a light source that is 4 feet away to a point 5.6 feet away reduces the light reaching the subject by 1/2 the same as leaving the light source where it is and using an aperture of f5.6 instead of f4.

It doesn't. You may have read this in a book or on a blog entitled something like 'Inverse Square Law – A Photographers Take' but UNLESS you state the size of the umbrella or softbox (and type) and then quote the distance you are taking your readings from and then include the word 'approximate' then you are wrong.

And I would just like to add that even previously when WFulton was illustrating his results which worked for him - AT LEAST he made some attempt at trying out these things rather than quoting the ISL verbatim. On the blog which started this thread the author can't be BOTHERED to EVEN TRY IT. might wonder why this could be so annoying and people go around regurgitating false information.

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Samples of work:

Theres only one sun. Why do I need more than one light to get a natural result?

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