How much light does CNTL flash "spill" into scene?

Started Jan 10, 2013 | Discussions thread
WaltKnapp
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Re: sybersitizen is right (again) — the ANSWER
In reply to William Porter, Jan 12, 2013

William Porter wrote:

sybersitizen wrote:

BTW, the 'huge' amount of light you're seeing from the flash controller is because you're shooting at f/2.8 and ISO 800/1600. Don't do that if you don't want so much extra light in the image. Use normal flash parameters by lowering the ISO and/or closing down the lens.

I would make a bad testing engineer, as this thread proves conclusively. I've been hearing these conflicting claims for a year or two and wanted to see for myself. I opened the aperture up precisely because I wanted to call as much of the "slop" as possible. Bart7D asked if this problem occurred in real life, and I tried to test that — but that test (with my dog) was done with wide aperture and high ISO. Anyway, I posted here hoping for correction. Seemed like the right thing to do. But not everything that seems like a good idea, actually is.

In short, YOU ARE RIGHT.

There is one reason why you might want to use a wide aperture in flash photography, and that is DOF control.  A limited use as in flash photography you are more likely trying to get things to be seen, including in focus.  More likely to want more rather than less DOF.

Can't see any reason to use higher ISO. But then that's true in nearly all photography.

Here's a shot taken in my office, with basically no light other than that supplied by the two flashes. Before I hit the shutter I was sitting in the dark. Aperture is wide (f/3.2) but the ISO is down to 200.

I don't see any light spillage or slop here from the control flash. I would expect to see some light on the near side of the chest of drawers on the right if the control were having an impact and I don't.

It does show how much light can reflect all around off surfaces. And those surfaces reflecting even more.  All part of the complexity of lighting control.

One last question: Why do people keep talking about using a piece of film to cover the triggering flash?

Shows that they are way out of date to still have film around? And probably engage in film thinking rather than digital. (BTW, you can buy synthetic filters that will do the same thing if you are paranoid.)  I have been DSLR digital since the early 90's when the RD-175 came out, no unexposed film or the chemicals around to develop it here. And I tossed all way overexposed shots in film long, long ago.

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