87 — Rear curtain sync — front curtain sync in flash photography

Pho­tog­ra­phy pod­cast #87‚ talks about the dif­fer­ence between rear cur­tain sync and front cur­tain sync when using flash with your cam­era. Basi­cally when using rear cur­tain sync, the flash fires toward the end of the expo­sure instead of toward the begin­ning of the expo­sure as it nor­mally does. This allows the blur that results from using slow shut­ter speeds to trail behind the sub­ject where it looks nat­ural. When using slow shut­ter speeds, you’ll gen­er­ally need to use a tri­pod. We also go over some basics on com­bin­ing flash with ambi­ent light.

Front curtain sync

Front cur­tain sync — Notice the move­ment trail in front of my hand, it looks unnatural

Rear curtain sync

Rear cur­tain sync — Notice the move­ment trail behind my hand, it looks more natural

Photography mixing flash and ambient light

Wed­ding cen­ter­piece by Dominic Fuiz­zotto — Dominic skill­fully bounces flash to add detail to the flow­ers in this lovely bright image

Links /resources men­tioned in this pod­cast:
Dominic Fuiz­zotto pho­tog­ra­phy — Wed­ding pho­tog­ra­phy in Mon­treal

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  1. Robertv in Edinburgh. says:

    Thanks for the men­tion on the pod­cast #88.

    I’ve shot quite a bit of studio/model work over time and always man­ual flash con­trol from the 580ex2’s or the stu­dio lights. Even when out­door light bal­anc­ing I always use man­ual flash. I guess this is the rea­son I’ve not had a prob­lem with blinkers(from the pre-flash.)

    I don’t really agree with the “Front cur­tain sync lets you freeze the action as it hap­pens with LESS delay.…” part though. The flash dura­tions and the cam­era expo­sure time will remain the same regard­less or FC or RC sync.The cam­era still has to sense the pre-flash and the flash, regard­less of the tim­ing. If things are mov­ing and tim­ing is crit­i­cal then the shut­ter time becomes the crit­i­cal ele­ment. Also, I’d feel this is exactly the instance where you do want SC Sync. “Mis­sion crit­i­cal” tim­ing issues really need man­ual flash any­way, as the pre-flash sys­tems all intro­duce delays.

    Hope­fully this doesn’t sound like I’m argu­ing. I love a good debate on tech­ni­cal mat­ters as my daily job depends on this. They don’t call me “Dr No” for noth­ing! :-) Closely analysing things many peo­ple only give a cur­sory view is my job, as is say­ing “No, I don’t agree, because …”

    • admin says:

      Thanks for the com­ments RobertV and SeanG.

      RobertV — I too like a good debate so no wor­ries at all. :)

      The LESS delay (for mis­sion crit­i­cal tim­ing) I was talk­ing about refers to the delay related to the flash fir­ing toward the end of the expo­sure which of course does not affect over­all expo­sure, or flash dura­tion. I’d have to set up a test to prove this for fast shut­ter speeds and the effect might not be eas­ily notice­able but imo, you’ll MISS more shots with rear sync than with front sync for your aver­age shot where the sub­ject is mov­ing in a lin­ear fash­ion. Why? Sim­ply because most of us are not used to cap­tur­ing images in this way. Per­haps you may be, but I dare say most peo­ple are not. When the expo­sure is one sec­ond, we nat­u­rally expect to see the flash burst at the begin­ning of the expo­sure (closer to the moment we click the shut­ter). The delay throws peo­ple off to a degree, the longer the delay, the more the degree.

      So, if you buy that, given that it’s harder for most peo­ple to pre­cisely freeze a moment with flash with a slow shut­ter speed on rear cur­tain sync (even on my own exper­i­ment when I ran my hand though the frame, it was harder to freeze the shot with­out miss­ing it on rear cur­tain sync), to my mind it only stands to rea­son that the same effect will hap­pen with a faster shut­ter­speed though it may be less notice­able. Please note we are only talk­ing about mov­ing sub­jects here.

      Do you feel this logic holds?

      In terms of man­ual ver­sus TTL, for out­door shoot­ing, there too we dif­fer. I almost never shoot man­ual (I shoot mostly por­traits) out­doors because I don’t want to have to think about the ambi­ent light chang­ing slightly and my not notic­ing it. Also rarely is my flash the main light, it’s usu­ally fill.

      I nor­mally only use man­ual when I am in full con­trol of the light­ing as in a stu­dio, or my on cam­era flash is the pri­mary light source. But every­one shoots dif­fer­ently and it also depends the sub­ject mat­ter you shoot, flow­ers are always more for­giv­ing of an improp­erly exposed photo than a bride and groom for example.…but now I digress.

      Thx again for the food for thought! Marko

  2. Glenn Euloth says:

    Thanks for the review, Marko. One extra com­ment from me, Robertv. Marko’s already cov­ered the best rea­sons for front cur­tain sync but there is a style rea­son too some­times. I’ve seen shots where you want the sub­ject to look like they’ve left the frame and the front cur­tain synh was done to freeze the sub­ject and then pro­vide streaks as they move out of the frame.

  3. admin says:

    Thanks for the com­ments every­one!
    Robertv, Front cur­tain sync lets you freeze the action as it hap­pens with LESS delay. In mis­sion crit­i­cal tim­ing sit­u­a­tions, you want the flash to fire as you see the action hap­pen­ing, which is at the begin­ning of the exposure.

    Also when shoot­ing peo­ple in TTL mode, Rear sync intro­duces a PRE FLASH that you never see (it’s there but you don’t see it because it hap­pens too close to the actual flash burst) in front sync flash. This pre­flash can be damn annoy­ing to your sub­ject and cause your sub­ject to instinc­tively blink between the expo­sures. You will clearly notice this pre­flash as your expo­sure gets longer. This pre­flash will NOT hap­pen if the flash is in man­ual mode, just as an FYI.

    Yise­haq — You are cor­rect, for sta­tion­ary objects, no dif­fer­ence imo.

  4. Robertv in Edinburgh. says:

    I’ve never really under­stood the need for front cur­tain sync, other than his­toric value. If some­thing is mov­ing and the shut­ter speed is slow enough for this to be noticed, then I want the flash at the end of the expo­sure so it “looks natural.”

    I can­not think of any rea­son for it to be the other way. With that in mind, I always set Sec­ond Cur­tain on my cam­eras and flashes.

    As for the wed­ding flow­ers, It really wants a 1/4 or 1/2 CTO to match bet­ter. Nice shot all the same.

  5. Jack Label says:

    Marko, thats a explen­did pod­cast, slow shut­ter speed with rear cur­tain works alot on wed­ding and event pho­tog­ra­phy, it also works for long shut­ter posed pic­tures, because peo­ple tend to start move after the flash pops, and some­times its bad if youre using first cur­tain.
    The main prob­lem mix­ing lights is color of lights, you may want to do a pod­cast about colour­ing your flash with gels to get closer to ambi­ent light, usu­ally on wed­dings your flash will be white light and ambi­ent indoors will be yel­low­ish, some­times it is not a prob­lem, but if you want to go for a bal­anced light like archite­cural pho­tog­ra­phy white and yel­low light will cer­tainly be a problem.

  6. Yisehaq says:

    Thanks Marko,
    Once again a nice pod­cast.
    One thing though, if we are talk­ing about sta­tion­ary sub­jects, am I right to assume there is no dif­fer­ence among the two syncs?

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