Wireless High Speed Sync
Posted 05/11/2007 - 13:08
Link
Article here:
http://www.photozone.de/3Technology/flashtec5.htm
If I had the time... I'd setup the storage 'scope and some measurement equipment and measure it.
Matt
http://www.photozone.de/3Technology/flashtec5.htm
If I had the time... I'd setup the storage 'scope and some measurement equipment and measure it.
Matt
http://www.mattmatic.co.uk
(For gallery, tips and links)
(For gallery, tips and links)
Posted 05/11/2007 - 13:09
Link
Quote:
but this lowest power flash duration of 1/20000 would require 5 pulses to cover 1/4000 seconds, correct? A higher power flash from the AF360FGZ would result in a longer flash duration and therefore require even fewer pulses.
It's remarkable that it's so easy to forget that a 'shutter speed' 1/4000s is really nothing of the kind. Each part of the frame may only see light for that length of time, but of course the whole exposure presumably takes much the same time as the sync speed.but this lowest power flash duration of 1/20000 would require 5 pulses to cover 1/4000 seconds, correct? A higher power flash from the AF360FGZ would result in a longer flash duration and therefore require even fewer pulses.
I wrote this:
Quote:
The more I think about HSS, the more it boggles my mind.
The K10D has a flash sync speed of 1/180, and with HSS it can sync all the way up to 1/4000, AIUI. At a shutter speed of 1/4000, presumably the gap between the curtains is only about 1/20 of the frame as it crosses the sensor.
So does that really mean that the flash must flash about 20 times during the exposure? Presumably the exposure itself must last about 1/180s in total, but even so.
And how accurate must the timing of the flashes be, so as not to miss bits, or expose parts more than once?
and subsequently this:The more I think about HSS, the more it boggles my mind.
The K10D has a flash sync speed of 1/180, and with HSS it can sync all the way up to 1/4000, AIUI. At a shutter speed of 1/4000, presumably the gap between the curtains is only about 1/20 of the frame as it crosses the sensor.
So does that really mean that the flash must flash about 20 times during the exposure? Presumably the exposure itself must last about 1/180s in total, but even so.
And how accurate must the timing of the flashes be, so as not to miss bits, or expose parts more than once?
Quote:
I was assuming that the curtains themselves travel across the frame at about the same speed irrespective of exposure, once it's shorter than the sync speed.
So they'll travel at the same speed, thus taking the same total time to get across, at 1/4000 as they do at 1/180.
Of course, at 1/4000s they'll be much closer together, as I said, so each part of the frame will only get the 1/4000.
If my estimate of 20 flashes is right, then it's 20 flashes in 1/180s or thereabouts, not 20 flashes in 1/4000s, but the precise timing still amazes me.
As you say, it does seem amazing. I'd be interested to know where my assumptions or calculations are wrong.
I was assuming that the curtains themselves travel across the frame at about the same speed irrespective of exposure, once it's shorter than the sync speed.
So they'll travel at the same speed, thus taking the same total time to get across, at 1/4000 as they do at 1/180.
Of course, at 1/4000s they'll be much closer together, as I said, so each part of the frame will only get the 1/4000.
If my estimate of 20 flashes is right, then it's 20 flashes in 1/180s or thereabouts, not 20 flashes in 1/4000s, but the precise timing still amazes me.
Posted 05/11/2007 - 13:12
Link
Actually, it doesn't have to be precise... it's almost certainly providing a higher burst rate to effectively create a short continuous lighting
Matt
Matt
http://www.mattmatic.co.uk
(For gallery, tips and links)
(For gallery, tips and links)
Posted 05/11/2007 - 13:42
Link
Quote:
It's remarkable that it's so easy to forget that a 'shutter speed' 1/4000s is really nothing of the kind.
Argh! Well aware of that , but like I said, my head wasn't quite awake yet. At a flash duration of 1/20000 you would need 5 pulses for every 1/4000 second slit of which there are about 22 sections in each full frame at the 1/180sec sync speed. You would probably need 100+ pulses in a worst case scenario.It's remarkable that it's so easy to forget that a 'shutter speed' 1/4000s is really nothing of the kind.
Still at higher power, the longer flash duration should reduce that count.
Posted 05/11/2007 - 14:04
Link
Quote:
I never doubted it Quote:
It's remarkable that it's so easy to forget that a 'shutter speed' 1/4000s is really nothing of the kind.
Argh! Well aware of that It's remarkable that it's so easy to forget that a 'shutter speed' 1/4000s is really nothing of the kind.
I didn't just mean you, trust me..
Posted 05/11/2007 - 14:08
Link
Incidentally, from Matt's reference:
"Today most manufacturers use a series of high frequent flash bursts (say 50 kHz) with reduced single light emission to simulate a (theoretically) long single constant flash burst."
50kHz for 1/180s is 277 flashes
If correct, it explains why the timing doesn't have to be precise at all, since each part of the frame gets exposed more than 10 times at 1/4000s.
"Today most manufacturers use a series of high frequent flash bursts (say 50 kHz) with reduced single light emission to simulate a (theoretically) long single constant flash burst."
50kHz for 1/180s is 277 flashes
If correct, it explains why the timing doesn't have to be precise at all, since each part of the frame gets exposed more than 10 times at 1/4000s.
Add Comment
To leave a comment - Log in to Pentax User or create a new account.
967 posts
20 years
Virginia,
USA
20 pulses would require extremely low output. Probably too low to be of much use.
The flash duration must be considered. The manual states that the lowest output of the AF360FGZ, for example, has a flash duration of about 1/20000 sec. Full power flash duration is about 1/1000 sec.
My brain ain't quite awake yet (it is still early for me out this way), but this lowest power flash duration of 1/20000 would require 5 pulses to cover 1/4000 seconds, correct? A higher power flash from the AF360FGZ would result in a longer flash duration and therefore require even fewer pulses.