High Speed Sync - using Studio Lights

Interesting read, looks like I have found my Sunday afternoon play around.
 
I don't think you are getting high speed sync, not as we normally understand it. Not in a useful manner anyway.

You cannot achieve High Speed Sync (as Canon call it) or FP Sync (Nikon) with a studio flash. They work differently. It is possible with hot-shoe guns by strobing the flash rapidly, at around 50,000 per sec, just long enough for the focal plane shutter to complete its cycle. That way you can get flash sync right up to the max 1/8000sec and even beyond (with certain drawbacks).

The Hypersync feature of Pocket Wizards varies the timing of the normal flash pulse to exploit the small amount of leeway that exists beyond the camera's normal x-sync speed timing window. That way they can push 1/250sec up to 1/400sec or so, depending on the camera.

What you appear to be doing here is exploiting the long flash duration that is common with studio flash units. The total flash duration is much longer than the quoted time. If you look at an oscilloscope trace, the flash peaks at a high level almost immediately, then falls away also very quickly to a much lower level but retains a long 'tail' of light that goes on for quite a long time, but at that very low light level. That's the bit of the flash that you are recording here - the long, low, flat tail. And it is not quite flat, just falling slowly, as shown by your test images being darker at the top. As a rough guess, I would say it's about a tenth of the brightness of the peak, something of that order, and uneven over the frame. Cameras with slower cycling shutters than your pro-spec D700 wil show this more.

You are able to make use of the tail in this way because the HSS/FP mode of the tiggering hot-shoe gun alters the sync timing away from the normal x-sync point, by which time the flash peak has passed and only the long, low, flat-ish tail is left.

It's interesting though :)

Edit: BTW, the slight reduction in x-sync speed you are getting with the Skyports is normal with lower end radio triggers. Only top end jobbies like Pocket Wizards have high speed processors that are fast enough to maintain the normal (optical) remote slave sync speed.
 
Hoppy, I knew you would write an essay on the subject.

I am still going to try it though.
 
tiler65 said:
Hoppy, I knew you would write an essay on the subject.

I am still going to try it though.
Click to expand...

Haha yes! :) Do try it. It works. And it's interesting, but not very useful.

The reason for the essay is that I think the OP is mixing up other aspects of flash operation that are actually quite different to what has been described in the link, eg reference to Pocket Wizards and Nikon/Canon high speed sync modes. Not the same thing at all. Misleading.

Sorry if I'm being picky. I like things to be right ;)
 
The reason it was darker at the top is because the head is pointing down ;)

The main point of the post was "here's a way of shooting 1/8000s with studio lights without any clipping of your frame"

An alternate methid would be to do it in a black environment, open the shutter on bulb and manually pop the flashes.
The way I mention in the blog blogged makes it possible to still achieve high shutterspeeds on location or areas that you can't obliterate the ambient. :thumbs:
 
callumw said:
The reason it was darker at the top is because the head is pointing down ;)
Click to expand...

It is darker at the top because the power of the flash 'tail' is dropping off. The top of the pic is the last section of the frame to be exposed. It's actually at the bottom of the camera, not the top, as the image is inverted on the sensor.

The main point of the post was "here's a way of shooting 1/8000s with studio lights without any clipping of your frame"

An alternate methid would be to do it in a black environment, open the shutter on bulb and manually pop the flashes.
The way I mention in the blog blogged makes it possible to still achieve high shutterspeeds on location or areas that you can't obliterate the ambient. :thumbs:
Click to expand...

That's the point of my post - you cannot obliterate the ambient with this technique. The power left in the tail of the flash is too low - it's a tiny fraction of the full light output.
 
HoppyUK said:
That's the point of my post - you cannot obliterate the ambient with this technique. The power left in the tail of the flash is too low - it's a tiny fraction of the full light output.
Click to expand...

I'm not disagreeing with you :bonk:
On location you wouldn't want to obliterate the ambient - you may as well be in a studio.

Picture(sic) the scene.
You're on location at midday in a parking lot and the sun is kicking thy butt. Your client likes your shots, but wants to see some more dramatic contrast. You don't have your ND filters or 10+ HSS speedlights in your bag.... but you did read this thing once which may work and it only takes 10 minutes to set up and do a rough test to check the results.

Better to know it and not need it rather than need it and not know it :thumbs:
 
callumw said:
I'm not disagreeing with you :bonk:
On location you wouldn't want to obliterate the ambient - you may as well be in a studio.

Picture(sic) the scene.
You're on location at midday in a parking lot and the sun is kicking thy butt. Your client likes your shots, but wants to see some more dramatic contrast. You don't have your ND filters or 10+ HSS speedlights in your bag.... but you did read this thing once which may work and it only takes 10 minutes to set up and do a rough test to check the results.

Better to know it and not need it rather than need it and not know it :thumbs:
Click to expand...

Callum, my whole point is not that the technique doesn't work in theory (albeit with uneven light across the frame) just that it is of no use in practise because the power left in the tail of the flash is so weak.

Since I have my Elinchrom lights set up next door, I've just tried it to see how much light you can actually get. They are D-Lite 2 so not the most powerful and maybe with a 400ws head these numbers might be one stop better, but firing on full power this is what I got.

Normal sync at 1/200sec on a 5D2, correct exposure was f/11 with ISO200. Switching to triggering with a 580EX in HSS mode and 1/128th power, that goes down to 1/200sec at f/4 with ISO800. That is a difference of five stops, even with a shutter speed of 1/200sec. Increasing the shutter speed obviously reduces that further, so at 1/1000sec which might be the case in the situation you outlined, the difference would then take it to over seven stops, which of course is no use at all.

Putting that another way, I could match the output of the studio flash synched in this way by firing my 580EX gun direct in HSS mode at 1/16th power. And that also gives even light copverage across the frame.
 
Volume is key.
D-Lights won't cut it. Even the BXRi500's are a bight light(sic) for the job

*sigh* I give up. I try to be helpful and share something .... :bang:
 
callumw said:
Volume is key.
D-Lights won't cut it. Even the BXRi500's are a bight light(sic) for the job

*sigh* I give up. I try to be helpful and share something .... :bang:
Click to expand...

callumw said:
How did you get on?
Click to expand...

More to the point Callum, how did you get on? It's a sunny Sunday, give it a try. Your BXRi500s will only be about a stop better than my D-Lites.

" *sigh* I give up. I try to be helpful and share something ...." I explain why it doesn't work, go to the trouble of actually testing and measuring it... You get more light just using the HSS mode of the normal hot-shoe flash, which is about as useful as a torch in bright light.
 
I'm waiting for my inverters to arrive before I do some outside testing, but a friend of mine did some last week to see the range/depth available.
His initial results with his setup showed best results at f4@1/1000 using 2 Profoto heads and it gave him an even spread 20ft deep.

http://www.facebook.com/callum.wint...lobal&view=global&subj=862755524&id=862755524

FYI - I have D-Light2's too and the BXRi500's are 2 stops brighter

Max f/stop@1m@ISO100
DLite2: 45
DLite4: 64

BXRi250: 64
BXRi500: 90

RX300: 64
RX600: 90
RX1200: 128


Did some tests with speedlights at @1/1 and my lightmeter set to read flash 1/1000 @ISO200:
SB-800@105: f/29
SB-900@200: f/36
SB-800@24: f/20
SB-900@24: f/20
Which is phenominal for the size of them - only 2 stops down from the DLite2 at the center of the beam

Put the SB-900 on camera so [FP] was active and got the following at 1m @1/1000@ISO200:
200mm: f/13
70mm: f/11
24mm: f/7.1
Which is about 2-3 stops down from it's full 1/1

As well as the speedlights perform, they don't keep up with monoblocks.

Can it be done with speedlights? Absolutely, but you'll need to have have loads of them which can do HSS just to keep up and give you the volume and depth you may need.
Then you have 1s recycle times instead of 4s, speed/ease of setting up, less grip gear, quality of light and so-on.

Yes, you clip the tail of the monoblock's duration but surely it's worth noting?
I for one will be testing so I can use it if the situation arises
 
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