Front and Rear Curtain Sync

[TimG]

For folks who are new to Waterpixels or, more importantly maybe, underwater photography more generally, would anyone like to have a crack at explaining the difference (other than the obvious one!) between front and rear curtain sync? The pros and cons? The why bothers?

 

It'd make for an interesting read and perhaps shine some light on a slightly obscure avenue.

 

 

[Guest]

Old school mechanical shutters have two curtains: the first opens and the second closes the shutter

Front and rear curtain sync refers to how the flash will sync

The default setting is to sync the flash with front curtain and therefore at the beginning of the exposure. Rear curtain means the flash will fire when the second curtain closes the exposure

 

https://westcottu.com/flash-photography-front-vs-rear-curtain-sync

 

When the exposure time is fast it makes no difference between rear and front curtain

However when the exposure is long this makes a huge difference

With front curtain the flash will strike but the subject will move in the frame which means any motion blur will be ahead of the subject

With rear curtain the subject will move in the frame and the flash will freeze it at the end motion blur will look more natural and behind the subject motion

In general terms I set my flash to rear curtain as default and move it to front only for panning shots (which I do very rarely)

Edited April 25 by Interceptor121

[Kamaros]

Rear-curtain sync:

- Good to have as a default setting when NOT deliberately trying to do blur shots because fast moving subjects might still result in some motion blur, in which case rear-curtain will result in a more natural trail behind the subject

- Also good for deliberately blurred shots where there isn't necessarily a single direction of motion, such as schools of fish that aren't moving together, or something like a juvenile sweetlips with erratic motion

- The downside of using rear-curtain sync is that you're at the mercy of the subjects' movement, so you don't have much control over where the final image of the subjects frozen by your strobes will be in the frame

 

Front-curtain sync:

- Generally preferred for shots where you're deliberately trying to introduce blur by panning your camera in the same direction the subject is moving, but at a higher speed than the subject (sometimes referred to as "accelerated panning" shots). This is because your strobes freeze the subject in the position they were in when you initially press the shutter button, giving you more control over the final composition.

- The downside of front-curtain sync is that you'll end up with unnatural looking motion trails ahead of the subject if you don't pan fast enough, or if you forget to switch back to rear-curtain sync for non-panning shots

[dentrock]

There is an interesting article on this very topic, with underwater examples, in the current UWP.

[Adventurer]

It is worthwhile pointing out that not all underwater camera configurations are able to do a rear curtain sync ( 2nd curtain sync ).

 

Especially many compact camera setups which utilize the cameras internal strobe and sTTL offered by INON, SEA&SEA and others will not work reliable via optical cable, when 2nd curtain sync is set inside the cameras strobe menu.

 

Very often this missing auto-exposure motivates to purchase an additional optical TTL trigger or TTL converter which can overcome this shortcoming. 

Usually this demand only rises when the photographer wants to experiment with the first light trailing effects behind subjects, to create a more artful image.

 

In 95% of everyday underwater photography the difference between 1st and 2nd curtain strobe sync stays unnoticed and only issues during a misconfiguration of the camera or interest raised in forum topics like this one. 😉