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Old Sep 24, 2003, 12:52 AM   #1
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Default 10D and 550EX question

I actually posted the question to the flash area, but it dawned on my that maybe I should have posted it here because its kinda specific to canon flashes.

If you know anything about ETTL and using the flash not as fill but as the main light source, could you look at this question? I'm really stumped and annoyed and could use the help!

http://www.stevesforums.com/phpBB2/v...ic.php?t=14495

Eric
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Old Sep 24, 2003, 6:59 AM   #2
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See here

Why do you need to be in the high-speed sync mode? This mode is only useful if you want to balance the fill-in flash with ambient light (ie bright sun).

-> In your case, there's not enough light... even 1/60s will do since the flash burst is normally super fast 1/10,000s or faster and will freeze anything in its track! 8)

With normal E-TTL the flash emits a series of pulses (too quick for you to see) before the main flash, but allows the camera/flash a much better controlled metering environment. In high-speed sync this pre-flash sequence is usually disabled and works more like the previous A-TTL mode with less flexibility (even though this is only supported in E-TTL mode), but allow you a faster sync speed... which will not help you in this case since you're not trying to balance the ambient light. A 'faster' flash burst alone (with slower shutter speed) will do the trick!
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Old Sep 24, 2003, 8:19 AM   #3
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I attempt to answer your post but then I saw NHLís post pop up, everything he said is very true and practical. High synch speed will work if you have the favorable lighting condition in the combination with high-speed lenses. If you set the camera for high speed synch and the lighting condition is worst than average, and your maximum aperture of your lens is not large enough to cover the situation, the camera will automatically adjust the shutter speed to lower speed to accommodate the maximum aperture of your lens. Like NHL pointed out, one of the advantage of using flash is the flash duration will freeze any movement of the subject, you donít really need to use the high synch feature unless you really want to control depth of field in the fill-in flash shooting (set your lens wide open to blur the background)

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Old Sep 24, 2003, 9:01 AM   #4
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(Bing, light goes on over Eric's head. Or is it a flash pulse? )

Oh, now that is a way of describing it that I hadn't heard before.

So you both are saying that the lower shutter speed should not be a problem for camera shake because the flash pulse is so fast?

Here is what I do, tell/teach/correct me to the right way.

I was getting a tight shot at a close range. Normally, without the flash, I'd want to use 1/500 - 1/1000 (hand held) if I could. That was completely out, so I though of the flash.

Now with a flash, this logic goes out the window. In lower light, I can depend on the flash being so quick that 1/200 (or even 1/60th, as in this case?) would be fast enough so that minor camera shake won't be an issue?

That just seems really so wrong to me, but I'll do some experiments and see what happens. Of course, being completely ignorant in the way of the force... ah, flash, I have no grounds for saying what is and isn't wrong!

Thanks both for your help!

Eric
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Old Sep 24, 2003, 9:04 AM   #5
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Yeap, the flash pulse is several order of magnitude faster that the camera shutter!
... Remember the stroboscope effect in Physics class?

The slower shutter speed will balance the fill-in with available light, the easiest example is how light(slow shutter) or dark(fast shutter) of a background do you want!

If it's very dark... even 1/30s won't be an issue (it's all depends on the ambient light) -> Close down that aperture and get more DOF (in case that bird decide to move)!!! :lol: :lol: :lol:
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