Paul C. Buff, Inc. Technical Forum

Reflector coverage formula
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Author:  RNPhotog [ Fri May 19, 2017 3:52 am ]
Post subject:  Reflector coverage formula

Is there a formula for figuring out the coverage of the various reflectors? For example, the 11" reflectors coverage at 65 ft would be...?

Author:  Technical Support [ Fri May 19, 2017 9:15 am ]
Post subject:  Re: Reflector coverage formula

If you need the actual formula, I can get that for you. If you need a close ball park, you can visit this link:

This graph shows the beam spread of various grids when installed on a 7" reflector. The 11LTR is 28 degrees, so I would use the 30 degree zone for reference. As the distance doubles, so does the diameter.

Yes, an 11" reflector would have a slightly larger area than the 7", but at 65 feet it is irrelevant (it would be a 4" difference at any distance).

So at 65 feet, you are looking at a 40' spread.

incidentally, at ISO100 and 640Ws, you are looking at f/5.6.

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