Do I need FEC?

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Calzor Suzay

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Steve
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Scenario is taking shots outside in the sun, not crazy amounts we're talking 5pm onwards, I was going to put the camera into manual and expose the backround 1 stop under and run the flash (430EX II) on camera pointing forward in TTL HSS, a lot of what I've read implies it's best to dial in about -1 FEC.

I'll be using a 70-200 to capture candids so I'm guessing my biggest limit will be how bright it is and whether the flash can throw itself far enough before running out of oomph. Is the -1 FEC to compensate for me being 1 stop under on the background or people have just found it works better in practise :bonk:
 
If you do that, then in theory the background will be under by one stop and the foregound (flash) also one stop under. Result, under-exposure all round.

But in practise it doesn't work out like that and there are too many variables going on to be that prescriptive, not least of which is the kind of effect you want. But generally speaking, if you just want fill-in (as opposed to trying to over-power the sun and make the background deliberately dark) then the idea is to try and make the flash 'invisible' or at least not obvious unless you know, so a bit of under-exposure on the flash is a good starting point.

You can do it in a number of ways. On Av and the flash on E-TTL, the camera will attempt to balance the backrgound with shutter speed, and then the flash varies its output to match the f/number. In that situation, using +/- comp on the camera varies the background exposure (with shutter speed) and +/- comp on the flash (or in the camera menu) varies the flash output so you can get just the balance you want.

Another popular method is to meter the background and set that in manual, with the flash on E-TTL. Or you can have both in manual, or the camera on auto and the flash in manual. Any permuation you like really, depending on the conditions and whether or not they're likely to vary.

If you find youself running out of flash power, raise the ISO and/or lower the f/number. A two stops shift on either of those will effectively double the flash's range.

If the sun is low, you'll probably be okay with normal x-sync, but if it's bright and the shutter speed wants to run above 1/250sec, switch on high speed sync. Again you can juggle that will aperture and ISO, but HSS can be a get out of jail free card. Just be aware that simply switching it on cuts your maximum range in half (round numbers, could be more) and it halves again for every two stops you go above max x-sync (1/250sec on a 7D).

The LCD is the best way of judging flash/ambient balance. Take a test shot and tweak it, and keep checking it because exposure measurement with fll-in is always tricky and in addition flash exposure varies a lot with small distance changes. E-TTL will try and keep up with that, and usually does a decent job, but keep an eye on it.
 
Thanks for the useful info Richard :)
Indoors I tend to put the camera in manual for ambient about 1 stop under then bounce a flash on TTL with no FEC. All seems to work out well but obviously outside shutter speeds should be a lot higher and nothing to bounce off, there may be enough good light to just use ambient, that time of day the suns not blazing high in the sky but still plenty of light about.

To be honest a lot of it I won't know till it happens, hopefully it'll all work out and I'll be allowed to post some pics :)
 
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