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12-02-2010, 05:13 PM   #1
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Why is flash sync speed so important?

I've been doing research and some reviewers were not enthused that the k-5 had a 1/180 flash sync speed...some others were like 1/250...and the sony a 580 has only a 1/160.

I dont know anything about this and would like some experienced input on why this is that important.

Thanks all

12-02-2010, 05:17 PM   #2
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given that i lived a good chunk of my life with 1/60 i am slightly baffled, but one of the reasons a lot of people shooting went medium format as the ability to sync at any speed i would have to guess it has to do with DOF control
I'm not a big flash user but i could be wrong
(ie fast moving models and high aperture due to flash/shutter combination)
someone please enlighten us (1/180 would stop almost anything i'd use flash for)
12-02-2010, 05:39 PM   #3
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Sync speed is important for shooting with flash in bright conditions (like fill flash). Up to the sync speed you get max flash power, go above it and flash power drops off very steeply. Thing is for many shots in such a situation, you want a wide aperture. This resulting fast shutter speed cripples flash output once above sync speed.

So you are faced with a choice: shoot with this reduced flash power, employ additional flashes to make up for this loss of power, use a ND filter to bring the shutter speed down below sync speed, or stop down the aperture to bring down the shutter speed. All of these options though are less desirable than simply having a faster sync speed.

Keep in mind though that 1/180 and 1/250 is just 1/2 a stop, so yes it would be nice if Pentax was 1/250, but we're only losing half a stop here so it's not like it's only a problem for us Pentax shooters.
12-02-2010, 06:18 PM   #4
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Sync speed is also important for freezing motion. Actually the flash does most of the work, but if ambient light is high enough you will get some of that movement to expose on the sensor.

When doing martial arts photos for example (with permission to use flash), the stadium or room lighting often cannot be turned off nor turned down. So you have to suck it up.
In this case, the higher shutter speed helps both to cut ambient light and helps freeze action should the ambient light be high enough to expose movement.

Although for the most part, 1/250s just isn't that big of a difference. I would like to see 1/500. Maybe some day electronic shutter speed of 1/1000 or faster might be implemented. ;-)

My bigger gripe is that I wish Pentax didn't cripple their cameras by completely disabling flash above the sync speed. Knowing the mechanics, I could use the higher shutter speed to good effect - keeping in mind that a portion of the frame would be affected.
In some cases that is acceptable or even desirable. Argh!

12-02-2010, 06:45 PM   #5
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QuoteOriginally posted by amoringello Quote
My bigger gripe is that I wish Pentax didn't cripple their cameras by completely disabling flash above the sync speed. Knowing the mechanics, I could use the higher shutter speed to good effect - keeping in mind that a portion of the frame would be affected.
In some cases that is acceptable or even desirable. Argh!
Are you referring to the built-in flash or the hot shoe mounted flash? How is this different from HSS from hot shoe mounted flash?
12-02-2010, 06:49 PM   #6
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When using built in flash you are not allowed to set shutter speed above 1/180.

When using HotShoe or PC-Sync socketed flash, the contacts are disabled when the shutter speed is set above 1/180.

High Speed Sync, is a special mode that requires compatible flash units to work. The flash is actually fired multiple times in order to handle the fact that only a portion of the sensor is being exposed at any given time when shutter speed is above 1/180.
12-02-2010, 06:55 PM   #7
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QuoteOriginally posted by amoringello Quote
When using built in flash you are not allowed to set shutter speed above 1/180.

When using HotShoe or PC-Sync socketed flash, the contacts are disabled when the shutter speed is set above 1/180.

High Speed Sync, is a special mode that requires compatible flash units to work. The flash is actually fired multiple times in order to handle the fact that only a portion of the sensor is being exposed at any given time when shutter speed is above 1/180.
What I am saying is that... so, if you use hotshoe mounted flash, why is higher sync speed important since you can still use set shutter higher than the sync speed? How is multiple flashes differ from a single burst where the sensor gets exposed at the same time - not saying that you are wrong, just trying to understand it better. Thanks..
12-02-2010, 07:12 PM   #8
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HSS uses multiple flashes to work. This requires each flash pulse to be significantly reduced.
If the flash requires four pulses, each pulse can be no more than 1/4 power.
Often in sunlight, for example HSS requires you be as close as three feet in order to get any significant fill light.

Now what happens if you need a set of 1200ws heads to overcome the sunlight?
Thats would just about require my annual salary in hotshoe-mounted flashes to make up that much power. (will need to look up Joe McNally's attempt to do this in the desert... he had about 12 hot-shoe flashes on a rig using HSS and just could not get enough power to light his subject standing about five feet away)

Anyway, just no way HSS will work under all conditions.
Sometimes you need the camera to work *for you*, not being forced to make the universe work around your camera.
You cannot tell the sun to be less bright.
Yes, adding ND filters will cut the sun, but they will also cut the flash. Thus you need even more flash power. :-)

Dunno if that made things clearer or more confusing.
(sorry, just had Photoshop crash multiple times and got a job to finish... looking to debug and maybe re-install... so my heads not multi-tasking well at the moment)

12-02-2010, 07:13 PM   #9
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Less than sync speed and the entire flash power can be dumped in a single burst. This burst is much more powerful than what that flash is able to produce in multiple pulses. That's just how it is, same is true for every flash on the market regardless of brand.
12-02-2010, 07:15 PM   #10
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One more thing... the way HSS flash works can be confusing if you're not familiar with how things all works together.

I'd suggest to do some searches to see how HSS works in relation to Sync speed and how the shutter mechanism works. My apologies if you are familiar with that... if so, the above should make some sense. I hope. :-)
12-02-2010, 07:18 PM   #11
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QuoteOriginally posted by amoringello Quote
Yes, adding ND filters will cut the sun, but they will also cut the flash. Thus you need even more flash power. :-)
Sorry, but this is simply not true, what matters is the ratio of available light to flash power. Over sync speed and the ratio falls off a cliff for the flash. By getting the shutter speed down to sync speed the ratio is restored and flash can exert it's pressence in the scene. That strategy will obviously require a wider aperture (often disirable anyway), or a higher iso (so be it), but stating a ND filter requires more flash power is mistaken.

Here's an article that explains it far better than my attempt above
http://neilvn.com/tangents/2010/07/16/using-a-neutral-density-nd-filter-with-flash/

Last edited by twitch; 12-02-2010 at 07:24 PM.
12-02-2010, 07:54 PM   #12
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This is what happens if the flash is out of sync with the shutter.

12-02-2010, 08:12 PM   #13
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QuoteOriginally posted by twitch Quote
Sorry, but this is simply not true, what matters is the ratio of available light to flash power. Over sync speed and the ratio falls off a cliff for the flash. By getting the shutter speed down to sync speed the ratio is restored and flash can exert it's pressence in the scene. That strategy will obviously require a wider aperture (often disirable anyway), or a higher iso (so be it), but stating a ND filter requires more flash power is mistaken.

Here's an article that explains it far better than my attempt above
http://neilvn.com/tangents/2010/07/16/using-a-neutral-density-nd-filter-with-flash/
er, um, not sure what you're trying to say nor how the article relates, but ND filters will absolutely without a doubt cut both flash and ambient light!
Filters do not change physics. Light fall-off does not change.

If your ND filter cuts 1-stop of light, it cuts that from any available light; sun and/or flash. You cannot decrease the sun's brightness with a 100x filter and expect a 1/4 power hot-shoe flash to magically shine through and not be affected.

Although I'm sure I am misunderstanding your point. (at least I hope I have, apologies in that case)
12-02-2010, 08:16 PM   #14
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QuoteOriginally posted by mtroute Quote
This is what happens if the flash is out of sync with the shutter.
Extreme, but with lower shutter speed that black bar may only partially affect one edge. This can be acceptable, or you can even use it as a sort of ND-grad. (if placed correctly).
I didn't actually expect the near total black-out at 1/750. (Of course, my flashes' power duration are not very speedy, so that would have some effect as well).

Please tell me you figured out how to get a recent model Pentax camera to do that. :-)
12-02-2010, 08:17 PM   #15
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QuoteOriginally posted by aleonx3 Quote
What I am saying is that... so, if you use hotshoe mounted flash, why is higher sync speed important since you can still use set shutter higher than the sync speed? How is multiple flashes differ from a single burst where the sensor gets exposed at the same time - not saying that you are wrong, just trying to understand it better. Thanks..
Remember, not all flashes are capable of high-speed sync. Studio flashes, for example. Many non-Pentax or slightly older flashes can't do it, either.

I don't believe that, if the camera "sees" a hotshoe mounted flash, and it is not capable of HSS, the camera won't allow a shutter speed higher than 1/180.
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