Down sides of rear curtain sync?

[joe_lacy]

I shot a recpetion last week, 40th, Rear curtain and it came out great! Why

would I not use RC all the time even outdoors?

[rainer_t]

Some pictures look better with sync set on first curtain ... others look better with sync on rear curtain. The difference become more visible with longer exposures. See the three links in thread ...

 

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00Mjlh

[bob_osullivan]

Rainer: Come to think of it Joe has a point. Can you give us an example of pictures that would look better with first curtain? I'm always either using a fast shutter (so it doesnt' matter) or using 2nd curtain to get the trailing effect. When would someone want a leading effect? (making things look like they're moving backwards) I'm genuinely curiouse, I can't think of anyting.

[picturesque]

Another reason is if you are using multiple flashes, and the off camera flash is not rear curtain capable, you may get double or multiple images (ghosting) if the shutter speed is long enough.

 

At receptions, if you are photographing dancing, most of it is back and forth motion, not leading/trailing, so it doesn't matter if the shutter is rear curtain. Only if your subject motion is strongly across the plane of the frame and you want trailing blur lines does it matter.

[mark u]

Bear in mind that rear curtain is actually disabled at shutter speeds faster than about 1/25th anyway and the camera will default to 1st curtain. You can test with your camera using e.g. a tennis ball to see what is the fastest 2nd curtain sync shutter speed it manages.

 

One reason for limiting the shutter speed at which 2nd curtain sync operates is that flash duration at full(ish) power starts to last into the travel of the second curtain unless the flash is fired sufficiently ahead of the start of its travel - which results in little difference compared with first curtain sync. Second curtain sync is of course incompatible with high speed sync, which provides continuous flash output while the exposure is in progress.

[rainer_t]

-- "Can you give us an example of pictures that would look better with first curtain?"

 

Well, obviously personal preferences are involved here as well. But imagine a long time exposure of a street (nighttimes), when a car passes by.

 

Sync on first curtain will flash the car at one spot, and from there eventually only the headlights will be seen. The result is a car, with kind of beams coming out of the headlights pointing forwards.

 

Sync on second curtain results in a car, with the beams going backwards.

 

I personally prefer the first curtain sync here. But YMMV.

[bueh]

*Blink, blink*

[fourfa]

"Can you give us an example of pictures that would look better with first curtain?"

 

Imagine you're using the flash to freeze expressions, with a long exposure of dim ambient to burn in some motion and flow. I love this kind of still/blur shot for reception dancing late in the night, and live band photography. With front curtain you know the flash will fire right when you press the shutter (or near enough). With rear curtain, the expression you want may be long gone by the time the flash fires.

 

Rainer's example works the other way too - headlights or taillights trailing where the car has been makes more sense to me. the other way looks to me like the car is driving backward. purely psychological and YMMV.

[greg_segallis]

I had been thinking the same thing - use rear curtain as a default.

 

Probably the biggest reason I could see NOT to use it is you are more likely to get someone blinking since the preflash will be early. For example, suppose you are at an evening party or a beach sunset and you want a long exposure (maybe 1/4 to 1 second) to bring out some of the background. That long of an exposure will give a person plenty of time to blink before the rear curtain flash.

 

The example given of a dance where you want to get the perfect expression or subject position is another great case of where first curtain will give better control over timing.

 

The car headlights beaming out are another interesting possibility - I think I'm going to try that one.

 

I'm confused about the example of multiple flashes. I don't believe the flash has any concept of front or rear curtain sync - that is controlled by the camera. Even an optical slave will work with rear curtain provided it can ignore the preflash (not sure how long a delay they can tolerate inbetween). I suppose it's possible that the slave could add enough delay so that a long slave flash duration could get clipped by the falling shutter.

 

-Greg

[peter_popp1]

Of the cameras I've owned (and own) that have had rear curtain sync, the max rear sync

shutter speed was one stop slower than the front sync speed. So balancing flash with

ambient light outdoors is usually easier with the faster shutter speed that front sync allows.

[picturesque]

Greg--I don't know for sure about multiple flash and rear curtain, but I got a ghosted shot when using a shutter speed of around 1/30th and using a manual, off camera flash and the on-camera with rear curtain activated. The off camera was triggered by one of those cheap e-bay wireless transmitters off the camera's PC socket.

[dave_holland]

Google BEETTL syndrome for anecdotes about blinking subjects when exposed to rear curtain sync. It's enough for me to avoid rear curtain sync, except when I need it.

 

Dave

[greg_segallis]

Nadine,

 

Was the subject moving fairly fast? I don't have actual specs, but I would expect the delay of a wirless trigger to be on the order of milliseconds worst case. So an indoor sporting event could probably have a ghost image with a second slave unit (similar to the blur at 1/250 to 1/500 shutter speed but with two well defined images). This would be identical for a first curtain shot, since it is casued by the lag between two strobes on a fast subject. For a slow subject, the ghost could be casued by someone else's flash going off during the 1/30 second exposure (random chance). Again, this is risk with slow shutter flash (rather than which curtain it occurrs on, although first curtain usually means fast shutter speed).

 

-Greg