HSS @ 1/8000 A700 and A900

[Javelin]

Gaby over on DPR posted instructions he used to get his sflash setup to sync at very high speeds. Ither than for freezing very very fast motion i'm not sure the use of this but I heard some people ask for higher sync speeds in wish lists

http://forums.dpreview.com/forums/read. ... e=30873172" onclick="window.open(this.href);return false;

[gbloncourt]

LOL I was going to post it here, anyway thanks Javelin for letting other people know. Since I shoot models and sometimes, I want nice Bokeh while overpowering daylight and darken the sky, so High Speed with Strobes is a must. So let me know what do you think.


Gaby

[Javelin]

studio work is a subject that comes up here a lot .. i'm interested but it's beyond what I would do. I'm inpressed that you got all that to work with a minimum of adaptors

[Dr. Harout]

Nice one, Gaby, and welcome to the forum.

[David Kilpatrick]

Your setup depends on the T=0.5 time for the studio flash heads. I would guess the Interfit models you are using have a pretty long duration, in the order of T=0.5 1/300th - the best way to find flash heads like this is to buy vintage Bowens Monolites, Courtenay Sola 4, Multiblitz Vario 500 (T=0.5 1/250th). If you buy certain modern flash types, the T=0.5 duration can be as low as 1/1800th and I think you would have more issues with sync.

T=0.5 is a measure of how long an output duration delivers 50% of the total light. T=1 is the total light output duration, and could be as long as 1/30th, but with most of the light concentrated in a much short time, then a long fading tailoff. T=0.1 is sometimes used to express how rapidly the flash creates its peak output, but most flash makers quote only T=0.5.

The wireless high speed sync is working because unlike regular sync, the wireless mode starts the flash burst (from the camera flash) before the shutter opens, and keeps it going until it closes - at 1/8000th, that means a slit travelling across the sensor height which is less than 2mm wide. With your studio flash, the duration is so long that you have accidentally found a way of using this like a burst mode. With normal sync, the flash only triggers when the shutter has started to open (or slit started to move). It might will not even achieve T=0.1 before the shutter has closed at 1/8000th. But you are using the premature start of the burst mode flash to trigger your studio heads early, a similar principle to FP sync (focal plane synchronisation) with FP flash bulbs, which burned steadily for a duration of around 1/30th and therefore allowed any shutter speed even with focal plane shutters.

Your 1/1000th or 1/8000th exposures are being made, by luck, within the peak of the T=0.5 measurement of your particular flash heads. If you try this with Elinchrom, Alien Bee, or a dozen other makes it won't work as well. You absolutely need these dirt cheap, very old-style electronics, slow duration Interfit 150 (or similar) flash units to make this work. You do not need the Pocket Wizard stuff at all, a slave cell in the flash head or plugged in should work, but once again you may just be lucky in the latency of the rig-up you have devised just happening to match the curve of the studio head output.

Back in the days of using big, slow firing studio flash (Multiblitz Vario) we used to use the shutter speeds of leaf shutter lenses to reduce exposure. You had to use 1/60th to get full flash exposure but the 650w/300w halogen modelling lamps then made the shot very warm (looked great usually). Cutting down to 1/125 meant losing half a stop and some warmth, to 1/250th a full f-stop. They were T=0.5 1/250th heads, that is, the flash had given out half its total energy by 1/250th after triggering, and I used that as an extra control. It was never possible to try focal plane shutters because the X-sync was wrongly timed, I guess we never had an SLR at that date (1981) with FP sync which might even have worked. Probably too early.

Your solution - to use HSS on minimal triggering power to fire long duration slave flash heads early - is as far as I know original, and has never been done before. Good work! But the complexity of the setup should not be needed in theory.

David

[Dusty]

How is the setup for consistent results? Does the flash fire when the shutter is fully open, or is it that the flash is of long enough duration to give even results over a traveling slit of a shutter.

I remember that in the film days, the challenge was to get a shutter that would actuate fast enough be fully open when the shutter was wide open. On faster speeds, the shutter never fully opened, it was a traveling slit. This meant you couldn't get even illumination with electronic flash, as it was of too short a duration. Flash bulbs could actually work better in that regards. I haven't looked into the construction of DSLR shutters, but it's kind of hard to believe they could now be fast enough to do 1/8000 sec by opening one blade fully then closing another behind it!

Dusty

[David Kilpatrick]

How is the setup for consistent results? Does the flash fire when the shutter is fully open, or is it that the flash is of long enough duration to give even results over a traveling slit of a shutter.

I remember that in the film days, the challenge was to get a shutter that would actuate fast enough be fully open when the shutter was wide open. On faster speeds, the shutter never fully opened, it was a traveling slit. This meant you couldn't get even illumination with electronic flash, as it was of too short a duration. Flash bulbs could actually work better in that regards. I haven't looked into the construction of DSLR shutters, but it's kind of hard to believe they could now be fast enough to do 1/8000 sec by opening one blade fully then closing another behind it!

Dusty

Read my post, Dusty - Gaby has got the FP shutter duration timed to fit within a long, relatively constant part of the studio flash's overall output. He's managing to trigger the flash early, before the shutter uncovers the sensor, so that his 1/1000th or 1/8000th fits within the studio flash's period of maybe 1/500th or even 1/250th stable, nearly level output.

David

[gbloncourt]

I would like to thank you David for the clever explanation I was looking for. I was also thinking about the long duration of the Interfit and I'm afraid, it maybe won't work with other flash systems. So far from 1/250 to 1/8000 with the interfit, I can use the trick.

I've used the interfit's optical cell too, It works when I'm close to them and outside under bright sunlight the slave cell behind the studio light just doesn't work, that's why I have tried it with the PW.

Thanks again for your input.

Gaby

[David Kilpatrick]

Gaby feel free to link to my post, or copy it your dPreview thread - as you probably know, I am not able to post there and have decided not to, as right now I would be doing stuff in six different forums and wasting LOADS of time!

David

[douglasf13]

Here's to hoping this works with Alien Bees, although David's posts don't sound to positive in that regard. This would be game changing for me, if it does work.

[douglasf13]

The Interfit website says the EX150 flashes have a duration of "1 ~ 3 m/secs" whatever that means?? The ABR 800 has 1/3200th second at t=.5

[David Kilpatrick]

1 to 3 millisecs means 1/1000th to 1/330th - presumably 1/330th at full power. That probably means 1/250th and even 1/200th would still look even. The Alien Bees are a different sort of insect entirely and I would guess their triggering sequence as a whole is faster - so it might not be possible to fit even 1/8000th 'into' the duration, and the timing accuracy needed would be extreme.

But this has given me an idea, I have a Metz CT60 which at full power must be close to 1/250th. With a slave cell placed near the onboard flash of the A700, maybe the Metz could deliver a boost to HSS enabling workable apertures at really high speeds.

David

[gbloncourt]

David,

I have just tested it with 2 Elinchrom 600RX and it works like a charm from 1/250 to 1/8000

Pict at 1/8000

[Dusty]

Read my post, Dusty - Gaby has got the FP shutter duration timed to fit within a long, relatively constant part of the studio flash's overall output. He's managing to trigger the flash early, before the shutter uncovers the sensor, so that his 1/1000th or 1/8000th fits within the studio flash's period of maybe 1/500th or even 1/250th stable, nearly level output.

David

I was composing while holding a fussy baby, so your post slipped in under mine. I didn't get the chance to read it when I saw it post first, I just hit the submit again. Your explanation maps it out in my mind. This appears to be a case where you actually get a better chance of good exposure at higher shutter speeds, if the initiation timing is right!

Dusty

[David Kilpatrick]

David,
I have just tested it with 2 Elinchrom 600RX and it works like a charm from 1/250 to 1/8000

So much for Elinchrom's claims for high speed flash duration!

I have a Style 600/300/300 set up and at the moment, testing a twin BXri 300 kit. I'll try to make some similar tests using the slave cells in the heads. I agree, your shot shows a perfect result.

Mr Friedman is too busy writing his A900 book to be around here, but I think he needs to know. It is not very often that someone stumbles on a new, repeatable, technique for using existing equipment. I'll send you a pm.

David