Does rear-curtain sync increase background exposure in low light?

Question

I understand rear-curtain (rear sync) flash means the flash fires at the end of the exposure instead of the beginning, mainly so motion blur trails appear behind the subject. But I’ve seen it claimed that rear sync also helps the camera expose more of the background ambient light in a dark room before the flash freezes the subject.

Does the timing of the flash itself actually change how much background exposure you get? Or would the ambient background exposure be the same with front-curtain and rear-curtain sync if shutter speed, aperture, and ISO are unchanged?

user1943 · Accepted Answer

I'm pretty sure that Scott Kelby means slow sync in general as opposed to the normal flash modes, not first curtain vs. trailing curtain slow sync. From the context (see excerpt in google books), although he talks about the timing of the shutter, he really only contrasts to normal operation.

I searched the rest of the book too, and he never talks about first curtain slow sync as a possible option at all. Possibly the thinking is that rear curtain is likely to be the only slow sync flash mode available on some cameras – although in my much more limited experience with point & shoots it's generally the other way. (And I've never seen a DSLR that doesn't have both.) Or, perhaps Scott thinks that the other reasons you mention are good strong enough that people should get in the habit of using second curtain sync instead of first curtain sync, and doesn't want to confuse people by contrasting the two at this point. That's one of the risks of "no nonsense" beginner photography books — sometimes they unintentionally mislead through oversimplification.

Does rear-curtain sync increase background exposure in low light?

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