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07-20-2013, 05:57 AM   #16
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It depends on the speed of the motion across the frame.
With HSS the flash actually strobes so you light up the subject several times during that time, with droplets it hard much better result with the normal flash.

Here is a good example and explaination.
HSS is not made to stop motion but to lower the shutterspeed, handy for fill flash on a sunny day but much more uses i can not think about.
With HSS you also lose a lot of flash power you see.

http://www.scantips.com/lights/flashbasics2b.html


Last edited by Anvh; 07-20-2013 at 06:02 AM.
07-20-2013, 07:15 AM   #17
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Folks- You can read several threads on HSS (and see some misconceptions debunked) over in the Flash sub-forum.

In a nutshell, the primary purpose of high speed sync flash is NOT to stop motion, but to balance the flash when there are high levels of ambient light. This is because the focal plane shutter ALWAYS takes 1/180 second for each curtain to travel across the sensor gate. Variable shutter timing is achieved by creating a slit of light between the leading and trailing curtains as they make their 1/180 second trip. A wider slit exposes some portion of the sensor to more light and a narrower slit exposes a portion of the sensor to less light. X-sync is the shortest time the entire sensor gate is open at once (the slit is exactly the size of the entire sensor).

To achieve a faster X-sync requires either more energy, lighter curtain materials, or a smaller travel distance. Doable? Certainly. And except in the case of a smaller travel distance (either a smaller sensor or switching to a leaf shutter built inside each lens instead of the camera body), it can significantly drive up the cost of the camera body.
07-20-2013, 08:15 AM   #18
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QuoteOriginally posted by Anvh Quote
It depends on the speed of the motion across the frame.
That's always the case.

QuoteOriginally posted by Anvh Quote
With HSS the flash actually strobes so you light up the subject several times during that time, with droplets it hard much better result with the normal flash.
I know perfectly well how HSS works and that it is usually used in bright conditions.

However, given a shutter speed of 1/2000 or even faster, there is no chance a lot of motion is going to be captured.
The strobing of the flash in HSS mode is not changing this.

BTW, flash manufacturers often provide T.5 times when quoting flash durations. These look good, but much more relevant are T.1 times. At full power, a typical flash needs around ~1/125 to dissipate its power, i.e., you are already cutting off some of its energy at 1/180 or even 1/250. In order to get a flash duration of 1/3000, you need to reduce the power to 1/8. That's not such a lot of light anymore. Or in other words, that's a lot of ambient light to get rid off at 1/180.
07-20-2013, 12:18 PM   #19
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Sure but we were talking about stopping movement right? with HSS you also have the rolling shutter with motion, it just isn't made for it.

Also HSS consumes about 3 stops of flash power it seems.

07-20-2013, 12:19 PM   #20
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QuoteOriginally posted by JimJohnson Quote
To achieve a faster X-sync requires either more energy, lighter curtain materials, or a smaller travel distance. Doable? Certainly. And except in the case of a smaller travel distance (either a smaller sensor or switching to a leaf shutter built inside each lens instead of the camera body), it can significantly drive up the cost of the camera body.
Electronic shutter is also an option The Nikon D70 had one i believe.
07-20-2013, 03:42 PM   #21
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Ok, I apologise guys because this is all fascinating stuff, but from a newbie's perspective, I have no idea what the hell you're talking about. Should I start a different thread about this issue in the appropriate forum? I just want to know what HSS is, and X-sync, and this business about leading and trailing curtains, and how it translates to getting really fast shots with lens setups and situations where appropriate light levels are hard to achieve eg. small aperture or extension tubes etc.

These sort of things are not particularly google friendly, but in the meantime, I'm gonna keep trying.
07-20-2013, 06:05 PM - 1 Like   #22
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QuoteOriginally posted by timbo Quote
I just want to know what HSS is, and X-sync, and this business about leading and trailing curtains ...
Ask and ye shall receive:
Flash synchronization - Wikipedia, the free encyclopedia

https://www.pentaxforums.com/forums/general-technical-troubleshooting/200030-...ml#post2364654
07-21-2013, 05:48 AM   #23
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X sync is the "max" normal shutter speed when using flash light. this is 1/180 for Pentax DSLR.

Some flash lights made for Pentax can do HSS, high speed synicing and what basicly happen is they emit aan almost constant light for the duration of the shutter speed. With this you can "flash" faster then x-sync, so 1/2000 for example.
But you lose about 1/4th of the power at the start and the faster the shutter speed the more flash power you lose.
You actually lose 1 stop of flash power with each shutter stop.

Now to stop motion.
HSS is continues light source so it depends on the shutterspeed. And expect to get rolling shutter effect.

If you use the normal flash mode you get one burst of flash light. So if you can get the majority of the light in the photo flash light then that is your stopping power.
The lower the flash output setting the faster the shutterspeed.
With the lowest setting most flashes will be faster then 1/10,000 if not a lot faster but at full setting they are around 1/250 so they don't stop much then...

07-21-2013, 10:17 AM - 1 Like   #24
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QuoteOriginally posted by timbo Quote
Ok, I apologise guys because this is all fascinating stuff, but from a newbie's perspective, I have no idea what the hell you're talking about. Should I start a different thread about this issue in the appropriate forum? I just want to know what HSS is, and X-sync, and this business about leading and trailing curtains, and how it translates to getting really fast shots with lens setups and situations where appropriate light levels are hard to achieve eg. small aperture or extension tubes etc.

These sort of things are not particularly google friendly, but in the meantime, I'm gonna keep trying.
Don't apologize - as what you requested and what this thread got hijacked into - are two almost entirely different things. From your perspective (and 99% of all shooting situations) HSS is irrelevant. In fact, for the vast majority of flash shooting situations your basic set up for multi-flash shooting will work fine and at least as reliably as the "sophisticated" pTTL set ups - which tend to get confused in multi-flash set ups. Certainly for macro work, you have what you need to do quality work - as you have already shown. Master what you have, and then look to see if you need more to fit your needs.

A lot of pros have abandoned preflash TTL and gone the simpler, more reliable route of auto and manual flash. We can't afford to miss shots. Even in situations where you might need HSS, PLs and NDs are the better way to go.
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