Can Rear Curtain Sync (Second) Cause Soft Portraits To Be Soft?

Can Rear Curtain Sync (Second) Cause Portraits To Be Soft?

I photographed a wedding yesterday and for half the time, I used my 50mm 1.8G @ f1.8 - 2.2. I used rear Curtain sync TTL for my sb700 and bounced off the ceiling. I was about 10ft or so away from my subjects. A lot of the photos have come out soft with this lens while some came out pretty sharp. All the photos from my Tamron 70-300 came out sharp. What would explain the softness in some of my photos? Could it be subject movement? I was shooting at 1/200 pretty much all the time indoors with the 50mm. Or could rear Curtain sync be the cause? Should I have used front curtain?

No, rear curtain sync cannot cause images to be soft.

Except, rear curtain sync will allow slow shutter speeds in dim light, and slow shutter speed could hurt sharpness, but you said 1/200 second, so no, there is no effect from rear curtain sync.

Rear curtain sync is pointless except at very slow shutter speeds, when you want the intentional slow blur to trail the motion instead of leading it. But it will have no effect at faster shutter speeds, and won't hurt.

See Four Flash Photography Basics - Rear Curtain Sync, color filters

hmmm, ok. So rear sync is used if you want to allow ambient light to come through in low lit areas while freezing the subject with flash? Ok I will have to investigate this issue with my lens then, it's odd.

Rear curtain sync just fires the flash duration at the end of the shutter duration, instead of at the beginning. (and, it allows slow shutter for ambient in camera A and P mode, since Rear Curtain is about a slow shutter).

If the flash and shutter speed (for ambient light) are fast enough to stop all blur, it does nothing.

If the shutter speed is slow (we're usually talking well slower than say the 1/60 second Minimum shutter speed with flash), so that the ambient causes a long blur trail, then firing the flash at the end of long blur makes stopped image lead the blur, so it looks natural. If you fired the flash at the start of the blur, the stopped image trails the blur, does not look natural. If you have no blur trail, it really does not matter when you fire the flash.

Just saying, Rear Curtain sync will not affect the presence of any blur (which is determined by shutter speed and ambient light). Rear Sync merely positions the stopped flash image at the end of this blur, instead of at the start of it.

You realize at those apertures you're talking about a depth of field about 1', right? And if you have more than one subject, there's a good chance they're not in the same focal plane. Is that what you mean by soft?

Triedntru, I am aware at those apertures that there is a shallow depth of field. When doing groups of 4, I used f5.6. With pairs, I did use f2.0 and 2.2 a few times which came out great as they were on the same focal plane. However, in some photo , even many single portrait shots, everything was soft like out of focus. I don't think it was back or front focusing as some photos came out good with the same setup. Also when I inspect the photos, there isn't any area that is sharper than my focus point (the eye). It's all pretty soft. Should I post some examples?

Perhaps the subjects sometimes moved their while taking those shots. But at 1/200 I should think they should be frozen still. Perhaps my distance of 10 feet with a 50mm also meant that the face will never be that sharp.