580 EX II as a fill in flash

I am using the flash 90% of the time as a fill in flash during races. Most of the shots are done against the sun. I noticed other photographers use the plastic diffusers.
Would it make any diffrence when shooting against the sun? Will it decrease the power of flash if I use the diffuser?

aliengin wrote in post #12714192
Would it make any diffrence when shooting against the sun? Will it decrease the power of flash if I use the diffuser?

Not really and yes. You are likely too far away for an on camera diffuser to make any difference.

see post #3 by Wilt here https://photography-on-the.net …/showthread.php​?t=1060717
the links only show you the posts, but you should try to read the entire thread where those links are located.

but i hope Wilt comes in this thread and perhaps give you direct answer(s).
i know not much about lighting

digital paradise's answer is the short/sweet answer. Those little, plastic diffuser devices only work (at all) when there are surfaces to bounce off of...out it the open they just send light off into spaces that don't matter and reduce the amount of light reaching your subject.

jobv2 wrote in post #12714264
see post #3 by Wilt here https://photography-on-the.net …/showthread.php​?t=1060717
the links only show you the posts, but you should try to read the entire thread where those links are located.

but i hope Wilt comes in this thread and perhaps give you direct answer(s).
i know not much about lighting

Thanks a lot that was the answer I was looking for.

My testing indicates that a plastic diffuser gives the 580EX flash a guide number of about 22 feet.

That means at f/10 it will have an effective range of about 2.2 feet for complete exposure, or about 3.1 feet for fill.

Snydremark wrote in post #12714296
digital paradise's answer is the short/sweet answer. Those little, plastic diffuser devices only work (at all) when there are surfaces to bounce off of...out it the open they just send light off into spaces that don't matter and reduce the amount of light reaching your subject.

For some reason I pictured the small softbox type of diffuser, not one that requires for something to bounce off when I responded the question. Gotta make sure not to make assumptions. Thanks for picking that up for me.

The only way to soften light is to make the light source bigger. Stofen omnibounce type domes do not make the light source bigger. The simply direct light out to the sides more. Works well if you have nearby surfaces to bounce off, but out in the open it isn't likely.

If you are using an on-camera flash for fill outside, you aren't likely to get it any softer. About your best bet would be to have a guy holding a reflector so you could bounce the flash off that, but you could do that with the sun just as easily, eliminating the need for a flash.