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High Speed Flash sync
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May 16, 2019 11:42:32   #
The Woodpecker
 
Can anyone give me a valid explanation why I cannot use a flash faster than 1/180 second?
And if it is not an "available technology" issue, then why don't I have it?

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May 16, 2019 11:45:27   #
CHG_CANON Loc: the Windy City
 
What camera? What flash?

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May 16, 2019 11:47:52   #
BebuLamar
 
The Woodpecker wrote:
Can anyone give me a valid explanation why I cannot use a flash faster than 1/180 second?
And if it is not an "available technology" issue, then why don't I have it?


Cameras with focal plane shutter have a limit of how fast it will sync with the flash. Many of such cameras have high speed sync mode but the flash must strobe many flashes to do that. How fast is the fastest sync speed depends on which camera you're talking about.

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May 16, 2019 11:58:00   #
jdubu Loc: San Jose, CA
 
Focal plane shutters close too quickly above flash sync speed to allow light from flash to expose onto the sensor completely. It's a physical law, not a technology problem. Sync speed on a camera only means the whole sensor is exposed before the shutter closes. (comprised of 2 physical curtains, one opens and the other follows to close) One pulse of flash will light the sensor fully.

High speed sync pulses the flash many times to expose to the sensor as the shutter curtains are travelling partially open and closed in front of the sensor. How wide this "slit" is depends on how fast a shutter speed you set. The faster the shutter speed, the narrower the slit.

Of course, you can use a flash above sync speed without HSS, you will just get an uneven exposure or underexposed portion.

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May 16, 2019 12:01:55   #
pquiggle Loc: Monterey Bay California
 
The duration of the flash is very short, often less than 1/1000 of a second. The flash sync speed is the fastest shutter speed where the entire frame is exposed at one time. To get faster shutter speeds the shutter starts closing before it is completely open and a slit of open shutter moves across the frame. So if the sync speed is 1/200 s then at 1/1000 s only 1/5 of the frame is being exposed at a time and the flash would fire and expose only 1/5 of the frame, the rest would be underexposed. At 1/2000 s shutter duration only 1/10 of the frame is exposed at one time, etc.

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May 16, 2019 12:49:34   #
PHRubin Loc: Nashville TN USA
 
Focal plane shutters consist of 2 curtains. The 1st starts to scan across the sensor, exposing it to ight. After the "shutter speed", the second starts to follow, closing off the light path. Thus any part of the sensor is exposed to the subject for the "shutter speed", but not all at the same time.

Regardless of selected shutter speed, the speed at which these cross the sensor path, the flash sync speed, ranges from less than 1/200 of a second (such as 1/250) to greater than 1/200 sec (such as 1/180), depending on camera.

If the selected shutter speed is faster (say 1/400) sec, only about half the sensor is seeing the subject at any moment and, at most, only 1/2 the sensor sees the flash, there is never a moment when the entire sensor is seeing the subject, only a traveling slit of light.

You want the flash to happen when the entire sensor is seeing the subject. This only happens if the shutter speed is equal to or slower than the sync speed.

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May 16, 2019 14:17:04   #
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May 17, 2019 06:47:13   #
Nikonnorm Loc: East Gwillimbury Ont.
 
I have a Voeloon 331EX flash on my D7000.
It will let me use a shutter speed of 1/ 8000
of a second and works perfect.
I also have a Fugi bridge camera that will allow the
same with built in flash.It works perfect too.

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May 17, 2019 07:03:31   #
CO
 
What camera do you have? I was using high speed sync just recently with my Nikon D750 and SB-700 speedlight. I shot with a shutter speed that's faster than the sync speed of the camera. With Nikon cameras you go into the menus and select Auto FP mode.
Nikon Auto FP mode is high speed sync
Nikon Auto FP mode is high speed sync...
(Download)

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May 17, 2019 07:16:46   #
cschonwalder
 
There are a few "Tricks" that allow flash up to 1/8000 sec. One was posted on you-tube a while back. One needs to fire the remote flash (set at full power as a slave) with an on-camera flash (using a cable to get closer to the slave, if necessary).

Don't know why this works to avoid the shutter shadow problem. My guess is long flash duration. Can anyone remember and post that video?

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May 17, 2019 07:59:04   #
Notorious T.O.D. Loc: Harrisburg, North Carolina
 
Any flash with high speed sync should allow you to shoot above the normal flash sync speed up to the limit of your maximum shutter speed. Without high speed sync you are limited to the flash sync speed which is usually 1/160 to 1/250 second. The flash can be on or off camera.

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May 17, 2019 08:07:49   #
Low Budget Dave
 
Remember that at high speeds the whole shutter is not open at once. (So, for example, the bottom of the shutter is not "opened" until the top is already "closed".)

If the flash fires in the middle, then you will have a bright band in the middle, with dark bands at the top and bottom.

HSS flashes overcome this by firing three (or more) flashes rapidly. The little flash built in to the camera doesn't have enough power to fire three times that quickly.

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May 17, 2019 08:18:23   #
GoofyNewfie Loc: Kansas City
 
Low Budget Dave wrote:
Remember that at high speeds the whole shutter is not open at once. (So, for example, the bottom of the shutter is not "opened" until the top is already "closed".)

If the flash fires in the middle, then you will have a bright band in the middle, with dark bands at the top and bottom.

HSS flashes overcome this by firing three (or more) flashes rapidly. The little flash built in to the camera doesn't have enough power to fire three times that quickly.


I think it’s a lot more than three- a lot of pulses to keep the gasses in
the flash tube lit to imitate a brief contuous light source.

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May 17, 2019 08:19:58   #
bkyser Loc: Fly over country in Indiana
 
There are good explanations above, but the main thing to know is that it's not a limitation of the camera, the shutter speed is whatever you or the camera sets it at. The limitation is in the duration of the flash itself. In the trick mentioned above with setting the flash to full power, it's because the flash duration is at it's longest, so the flash is basically firing from the beginning to the end of the 2 curtains moving across keeping the sensor "open" If you reduce power, the flash doesn't stay "burning as long" so before the second curtain closes, the flash is "done" that's why there is a black band at the bottom of the photo... the flash just fizzled out before the shutter was done doing it's thing.

HSS works, basically by telling the flash to lower power, but stay "burning" much longer. Auto FP (Nikon) will lose a few stops of flash power in Auto FP, but thankfully, with the higher shutter speed, which controls ambient light allowed to hit the sensor, is different than the aperture, which controls how much of the flash effects the exposure. That's how we (wedding photographers) can get nice blue, non blown out skies at noon, while using a flash to fill in the shadows on the faces, so the couples don't look like raccoons. It's also useful for making noon look more like 6:00pm, but the couple is still properly lit.

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May 17, 2019 08:21:46   #
bkyser Loc: Fly over country in Indiana
 
bkyser wrote:
There are good explanations above, but the main thing to know is that it's not a limitation of the camera, the shutter speed is whatever you or the camera sets it at. The limitation is in the duration of the flash itself. In the trick mentioned above with setting the flash to full power, it's because the flash duration is at it's longest, so the flash is basically firing from the beginning to the end of the 2 curtains moving across keeping the sensor "open" If you reduce power, the flash doesn't stay "burning as long" so before the second curtain closes, the flash is "done" that's why there is a black band at the bottom of the photo... the flash just fizzled out before the shutter was done doing it's thing.

HSS works, basically by telling the flash to lower power, but stay "burning" much longer. Auto FP (Nikon) will lose a few stops of flash power in Auto FP, but thankfully, with the higher shutter speed, which controls ambient light allowed to hit the sensor, is different than the aperture, which controls how much of the flash effects the exposure. That's how we (wedding photographers) can get nice blue, non blown out skies at noon, while using a flash to fill in the shadows on the faces, so the couples don't look like raccoons. It's also useful for making noon look more like 6:00pm, but the couple is still properly lit.
There are good explanations above, but the main th... (show quote)


Even if you aren't a wedding photographer, you could check out the wedding section (no trolls allowed) and read up on Ed's many educational posts, where he gets in to detail, and examples.

Who knows, we may even convince others that we aren't quite as crazy as people think we are for loving what we do.

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