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04-11-2008, 12:55 PM   #1
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How to Control Flash in long exposures?

During a longer exposure (1/2" and up) how do I control the built-in unit to flash only towards the end of the shutter opening?

I've tried playing with the flash settings, but it is flashing twice, probably once in the shutter opening and another right before shutting it down.



I am doing some shooting in a nightclub and I want to be able to control the flash in that way.



Anyone?


thanks in advance.

04-11-2008, 01:30 PM   #2
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Trailing curtain sync

The first flash is not when the curtains open but before the curtain opens. It is the exposure test flash.
04-11-2008, 01:37 PM   #3
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QuoteOriginally posted by Canada_Rockies Quote
The first flash is not when the curtains open but before the curtain opens. It is the exposure test flash.



Only thing that could screw up my photos is that having two flashes always cause people to move right after the 1st, because they think the picture is done.. Kinda similar with red-eye flashes...


Hmm... so you are saying that the camera is behaving accordingly? so basically there is no settings to change in this regard? The buit-in will always flash twice?


Thanks for the clarification!
04-11-2008, 01:43 PM   #4
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QuoteOriginally posted by BBear Quote
Only thing that could screw up my photos is that having two flashes always cause people to move right after the 1st, because they think the picture is done.. Kinda similar with red-eye flashes...


Hmm... so you are saying that the camera is behaving accordingly? so basically there is no settings to change in this regard? The buit-in will always flash twice?


Thanks for the clarification!
That's the big downside to P-TTL (Pentax' name for it). Occasionally a grumble will come up on other manufacturers' forums as well. I wish we could just tell the camera - I want manual flash! - and use that, but I have been unable to find a flash mode that uses anything else for metering.

The current solution seems to use an automatic flash (uses its own photocell to meter) and set the internal flash off, it I read the forums correctly.

04-11-2008, 07:42 PM   #5
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BBear, are you asking about Rear (or Trailing) Curtain Sync where, say during a 2 second exposure, the flash will fire at the very end? If so, I believe you need to use an external flash to control that aspect.

Unfortunately, there's no way to get around the 2 flashes of P-TTL using only the onboard flash.

(not to hijack this thread) but also on this subject: For some people, their reflexes are fast enough to blink very quickly right after the first flash, therefore getting caught with lazy eyes in the photo. On another forum, there was a guy who ran some timing test for the lag between the two flashes. Some camera systems are quick enough to beat even the fastest human reflexes, and others are so slow they give quick people time for a full blink. Pentax seems to fall somewhere in the middle I think. I was actually very suprised to only find limited Pentax-related discussion on this issue because me, my son, and both of my parents get caught greater than 98% of the time with our eyes half closed! The only work-around with onboard flash is using the 2-second delay with places the first flash at the begining and the final photo flash at the very end of the 2 seconds. Glad we are a minority. While it's called lazy eye....our eyes aren't actually lazy at all, quite the opposite in fact!

-jeff
04-12-2008, 08:27 PM   #6
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QuoteOriginally posted by tbone-ike Quote
BBear, are you asking about Rear (or Trailing) Curtain Sync where, say during a 2 second exposure, the flash will fire at the very end? If so, I believe you need to use an external flash to control that aspect.

Exactly what I wanted to do, and unfortunately is not possible with the built-in unit.


I had a blast yesterday with the camera, and after different approaches, I finally got the nightclub shooting to work pretty well. I have 200 pics.. still working on them, but i'll post some pictures soon.


And yes, I've lost dozens on photos due to the fact that people were moving right after the 1st flash, so I will be getting an external flash to have control over this feature.


Can someone clarify which type of flash I need to get? Or most of the external units (even TTL) will let me control the curtain and all? Are the pentax units capable of manual modes?


Thanks all... i had a great time with the camera!


04-14-2008, 09:59 AM   #7
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QuoteOriginally posted by BBear Quote
Can someone clarify which type of flash I need to get? Or most of the external units (even TTL) will let me control the curtain and all? Are the pentax units capable of manual modes?


Thanks all... i had a great time with the camera!


I just got the Pentax AF-540 2 weeks ago. It is capable of both leading and trailing curtains, and can be set to manual mode.
04-14-2008, 11:04 AM   #8
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QuoteOriginally posted by Zilla Quote
I just got the Pentax AF-540 2 weeks ago. It is capable of both leading and trailing curtains, and can be set to manual mode.


I had no idea this flash trailing thing was that complicated. Apparently, I only have two options:

1. Use a TTL pentax unit and have the camera/external unit do the work - and there will be a pre-flash.

2. Get a PocketWizard unit and set the shutter speed and set it for 2nd trailing.



I'll buy the 360 unit and see how it works in my next club shooting... hopefully it will work nice and i wont need the PW, because that thing is $$$.



Zilla, can you do me a favor? Check how the 2nd trailing works when you use the Pentax 540 wireless off the camera? Your K10d should be able to normally "talk" to the unit off the camera, now I wonder how it does the 2nd curtain off the camera...


thanks in advance!

04-14-2008, 11:30 AM   #9
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You could use a 555 timer circuit to control the flash. Such that, on trigger, it delays a set period of time before trigging the flash. There are a number of intervalometers made for photgraphy such that they separately control a flash and camera at two different times once a trigger has been received (such as an IR motion detector). This is used a lot to make those "milk-splash" shots -- the drop of milk passes through the beam, triggers the camera to open in bulb mode; then a few MS later the flash fires (as the drop hits the fluid), and the shutter is closed on the camera.

While those units are expensive, with a little soldering skill and some ingenuity, you can kit a 555 timer kit for about $15 online, and have a programmable delay.

!c
04-14-2008, 11:39 AM   #10
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QuoteOriginally posted by shutterdrone Quote
You could use a 555 timer circuit to control the flash. Such that, on trigger, it delays a set period of time before trigging the flash.

Here are some nightclub photos and the reason why I am looking to control the flash:

https://www.pentaxforums.com/forums/post-your-photos/25128-nightclub-photogra...lp-needed.html




After reading a lot about this and exchanging some PM, I think I'll get the Pentax 360 unit and try it OFF the camera and see the results.


I can live with the TTL pre-flash, I only have to warn people to wait for the 2nd flash. The advantage to go with a Pentax unit is the wireless feature...

If the wireless 360 doesnt do for me, then I'll have to look for another solution: 555 timer circuit? Or maybe a PocketWizard?



Let's see... and thanks for the replies.


BB
04-15-2008, 04:23 PM   #11
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I e-mailed Pentax regarding this feature, and believe it or not, someone responded with the following...

(my question)
Is it possible to use trailing curtain sync with the AF 540 in wireless mode? It works just as expected when flash is on the shoe.

(from Pentax personnel)
I have tested this and in all sync modes (leading-curtain, High-Speed
and trailing-curtain)the AF-540FGZ when used off-camera in Wireless mode
fires as the shutter curtain opens. I have tested with the flash in both
SL1 and SL2 modes, and with the pop-up flash set to either Controller or
Master. I will forward this along to our Digital Products Manager as a
product enhancement suggestion.
04-16-2008, 03:12 PM   #12
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QuoteOriginally posted by Zilla Quote
(from Pentax personnel)
I have tested this and in all sync modes (leading-curtain, High-Speed
and trailing-curtain)the AF-540FGZ when used off-camera in Wireless mode
fires as the shutter curtain opens.
I have tested with the flash in both
SL1 and SL2 modes, and with the pop-up flash set to either Controller or
Master. I will forward this along to our Digital Products Manager as a
product enhancement suggestion.




Great.... at least I wont have to waste another 4hrs trying to figure how to set up the 360 for second curtain when wireless...


Crap crap crap...
04-16-2008, 05:57 PM   #13
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BBear,

Forgive me if this is a dumb question, but what effect are you trying to achieve/avoid by having the flash at the end of the exposure vs at the begining? If you want to capture some of the ambient / background lighting, you'll need a long exposure either way and the flash to light and feeze your subjects. True, with any longer exposure you may pick up thier motion, but I don't see any difference there whether it's front or rear sync for that. I would think you would want the flash at the begining of the exposure when they are posed and fully ready for the shot vs at the end.

With P-TTL, tru there are two flashes, but we are talking milleseconds here. Enough for some peoples eyelids to react, but not much more time than that for the P-TTL process.

I may be confused however or missing something
04-17-2008, 08:42 AM   #14
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QuoteOriginally posted by tbone-ike Quote
If you want to capture some of the ambient / background lighting, you'll need a long exposure either way and the flash to light and feeze your subjects. True, with any longer exposure you may pick up thier motion, but I don't see any difference there whether it's front or rear sync for that. I would think you would want the flash at the begining of the exposure when they are posed and fully ready for the shot vs at the end.

With P-TTL, tru there are two flashes, but we are talking milleseconds here. Enough for some peoples eyelids to react, but not much more time than that for the P-TTL process.

I may be confused however or missing something

Absolutely a valid question. And to be honest, I don't know the answer.

Basically I read posts and guides for nightclub photography and all of them mentioned trailing flash.


I then went to the club last friday, used the built-in flash in 2nd Trailing and I liked the results. Now I am trying to buy an external flash and have it still the 2nd Trailing. Thats when the problems started.



But you are right: I should try regular trailing in those pictures. I have no idea what kind results I'd get. maybe the results are the same. I dunno.


I'll have another club opportunity on the 25th. I will have received (hopefully) my Pentax 360.


I'll try different setups and see what works the best.



Thanks for the input!


BB
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