Why is flash sync speed so important?

twitch · 12-02-2010, 08:23 PM

Originally posted by amoringello

Although I'm sure I am misunderstanding your point. (at least I hope I have, apologies in that case)

I just re-read our posts and I think we misunderstood each other, sorry, that's a first on an internet forum

A ND filter will cut absolute flash power, that is true, my point is it cuts ambient more (if shutter goes from over sync to under). What I meant to disagree with was your conclusion "Thus you need even more flash power", that is the bit that isn't true. Because the ratio between flash/ambient swings back towards flash under sync speed, and even though flash power is cut, in fact you don't need more flash power because you compensate with aperture or iso. It's the ratio that matters, not absolute power.

In fact right on sync speed, the flash to ambient ratio is at the highest possible flash/ambient ratio. However you achieve sync speed is irrelevent; ND, aperture whatever. Any slower shutter and more ambient light gets in with no additional flash, any faster and the flash drops into HSS and power output drops like a stone.

Hope that makes sense.

Last edited by twitch; 12-02-2010 at 09:11 PM.

mlatour · 12-02-2010, 08:24 PM

In my firegrounds photos, a higher sync speed allows me to 'define' or 'freeze' the flames
in the dark background and light up my subjects in the foreground.

a few examples:

Fuji S9100 + Nikon SB-80 taken around 1/350 or so:
CODE ROUGE - Photos
CODE ROUGE - Photos

K-x / Sigma 18-50mm f2.8 / Nikon SB-80, taken at 1/125:
CODE ROUGE - Photos
and at 1/180
CODE ROUGE - Photos

yes different conditions but same principle applies.

Michel

openyourap · 12-02-2010, 08:36 PM

Originally posted by amoringello

If your ND filter cuts 1-stop of light, it cuts that from any available light; sun and/or flash. . . .

True! But shutter speed (below sync) affects exposure from ambient sources only. Exposure from flash remains unchanged. If you can independently control one variable, you can control them both.

Shooting in daylight, with lots of ambient light, dialling up the shutter speed darkens the sky. You can, however, only darken it so much at 1/180.

You can add an ND (or close the aperture) to darken the ambient lit parts of your shot sufficient for 1/180 or below, then blitz the flash-illuminated foreground subject to brighten it up/freeze the action.

The more you've dialled down the aperture or introduced ND filters, the more powerful your flash needs to be.

Aperture, also controls depth of field, which is one reason why many would prefer to control light with ND.

In terms of light control:

Shutter: Ambient only
Aperture: Ambient and Flash (with DoF trade-off)
ND: Ambient and Flash (with no DoF trade-off)

aleonx3 · 12-02-2010, 08:58 PM

Originally posted by amoringello

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. :-)

Thanks, amoringello, I don't follow it in detail exactly but I think I get a general idea - and will need definitely need to do more dd on HSS compare to max sync speed.

aleonx3 · 12-02-2010, 09:03 PM

Originally posted by noblepa

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.

Since I only have AF360 and AF540 both support HSS, so if I did not switch to HSS, I would not be able to get shutter higher than 1/180.

twitch · 12-02-2010, 09:17 PM

Originally posted by openyourap

In terms of light control:

Shutter: Ambient only
Aperture: Ambient and Flash (with DoF trade-off)
ND: Ambient and Flash (with no DoF trade-off)

Sorry to be pedantic, but shutter affects ambient up to sync speed, after which it affects both ambient and flash. That's why if you want max effect from fill flash you should shot at sync speed. Whether "max" is actually enough for the effect you are after is a different matter.

openyourap · 12-03-2010, 12:50 AM

Originally posted by twitch

Sorry to be pedantic, but shutter affects ambient up to sync speed, after which it affects both ambient and flash. That's why if you want max effect from fill flash you should shot at sync speed. Whether "max" is actually enough for the effect you are after is a different matter.

I'd consider this to be one of the semantic little idiosyncrasies of the HSS implementation, rather than the generality covered be the dot points

We might be better conceiving our exposures knowing that for speeds above sync, the output of the flash unit itself is throttled.

If we want to break it right down, we could argue that shutter speeds shorter than the flash blitz also affect the exposure, or that the flash could then be considered ambient.

amoringello · 12-03-2010, 03:11 AM

Quote:

I just re-read our posts and I think we misunderstood each other, sorry, that's a first on an internet forum

ha! so true! :-)

**Rondec** · 12-03-2010, 12:24 PM

Doesn't having iso 80 effectively increase sync speed by half a stop over cameras that only have iso 100 available?

twitch · 12-03-2010, 12:50 PM

Originally posted by Rondec

Doesn't having iso 80 effectively increase sync speed by half a stop over cameras that only have iso 100 available?

You have a good point, having ISO 80 on the K-5 certainly makes 1/180 more achievable.

amoringello · 12-03-2010, 01:33 PM

Except when talking about flash vs ambient light. ISO affects sensor sensitivity, so both flash and ambient light are affected. It will bring down the brightness of the sun, but will also affect flash. So lets say your flash was just not quite powerful enough to overpower the sun... adjusting ISO half a stop would not help to bring you half a stop closer to overpowering ambient light. A faster shutter speed would.

flyer · 12-04-2010, 03:26 AM

Originally posted by eddie1960

but one of the reasons a lot of people shooting went medium format as the ability to sync at any speed

Not all medium format can sync at any speed. Only the medium format with a leaf shutter in the lens can sync at any speed. If your medium format has only a focal plane shutter, the sync speed is actually often slower than APS-C DSLR.

tibbitts · 12-05-2010, 09:05 AM

I had never thought about this, but given that higher-end 35mm cameras had 1/250th sec flash sync, what's with the 1/180th? My 35mm cameras (spotmatic, a-1) had horizontal cloth/rubber shutters, but certainly higher-end cameras seemed to offer 1/250th with metal vertical shutters. Shouldn't we be at 1/350th or something with aps?

Paul

omega leader · 12-08-2010, 04:36 PM

Sync speed isn't really important at all. Go look at strobist.

Though I've discovered that the best investment I've ever made is a used studio strobe and good quality ND filters.

amoringello · 12-08-2010, 05:31 PM

Originally posted by omega leader

Sync speed isn't really important at all. Go look at strobist.

Though I've discovered that the best investment I've ever made is a used studio strobe and good quality ND filters.

Can you point to the specific posting?

Note sure where that ever came up... I know he has a segment on how useful sync speed is, and how to over-clock your sync speed (or something similar).
Sadly that requires that your camera can fire a flash above its sync speed. Something which PENTAX crippled and you cannot make use of.

Without fast sync speed, ND filters does nothing but make matters worse -- unless you have strobes capable of overpowering the sun to begin with. But then you're just pulling everything down within proper exposure for an otherwise unattainable aperture.

TOTALLY different arena from what faster shutter speed allows.

12-02-2010, 08:24 PM	#17
mlatour Senior Member Join Date: May 2010 Location: Montreal Posts: 197	In my firegrounds photos, a higher sync speed allows me to 'define' or 'freeze' the flames in the dark background and light up my subjects in the foreground. a few examples: Fuji S9100 + Nikon SB-80 taken around 1/350 or so: CODE ROUGE - Photos CODE ROUGE - Photos K-x / Sigma 18-50mm f2.8 / Nikon SB-80, taken at 1/125: CODE ROUGE - Photos and at 1/180 CODE ROUGE - Photos yes different conditions but same principle applies. Michel Last edited by mlatour; 12-02-2010 at 08:38 PM.

12-02-2010, 08:36 PM	#18
openyourap Senior Member Join Date: Jun 2009 Location: Sydney Photos: Gallery \| Albums Posts: 171	Originally posted by amoringello If your ND filter cuts 1-stop of light, it cuts that from any available light; sun and/or flash. . . . True! But shutter speed (below sync) affects exposure from ambient sources only. Exposure from flash remains unchanged. If you can independently control one variable, you can control them both. Shooting in daylight, with lots of ambient light, dialling up the shutter speed darkens the sky. You can, however, only darken it so much at 1/180. You can add an ND (or close the aperture) to darken the ambient lit parts of your shot sufficient for 1/180 or below, then blitz the flash-illuminated foreground subject to brighten it up/freeze the action. The more you've dialled down the aperture or introduced ND filters, the more powerful your flash needs to be. Aperture, also controls depth of field, which is one reason why many would prefer to control light with ND. In terms of light control: Shutter: Ambient only Aperture: Ambient and Flash (with DoF trade-off) ND: Ambient and Flash (with no DoF trade-off) Last edited by openyourap; 12-03-2010 at 12:51 AM.

12-02-2010, 09:17 PM	#21
twitch Veteran Member Join Date: Nov 2009 Posts: 4,571	Originally posted by openyourap In terms of light control: Shutter: Ambient only Aperture: Ambient and Flash (with DoF trade-off) ND: Ambient and Flash (with no DoF trade-off) Sorry to be pedantic, but shutter affects ambient up to sync speed, after which it affects both ambient and flash. That's why if you want max effect from fill flash you should shot at sync speed. Whether "max" is actually enough for the effect you are after is a different matter.

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12-02-2010, 08:23 PM	#16
twitch Veteran Member Join Date: Nov 2009 Posts: 4,571	Originally posted by amoringello Although I'm sure I am misunderstanding your point. (at least I hope I have, apologies in that case) I just re-read our posts and I think we misunderstood each other, sorry, that's a first on an internet forum A ND filter will cut absolute flash power, that is true, my point is it cuts ambient more (if shutter goes from over sync to under). What I meant to disagree with was your conclusion "Thus you need even more flash power", that is the bit that isn't true. Because the ratio between flash/ambient swings back towards flash under sync speed, and even though flash power is cut, in fact you don't need more flash power because you compensate with aperture or iso. It's the ratio that matters, not absolute power. In fact right on sync speed, the flash to ambient ratio is at the highest possible flash/ambient ratio. However you achieve sync speed is irrelevent; ND, aperture whatever. Any slower shutter and more ambient light gets in with no additional flash, any faster and the flash drops into HSS and power output drops like a stone. Hope that makes sense. Last edited by twitch; 12-02-2010 at 09:11 PM.

12-02-2010, 08:58 PM	#19
aleonx3 Veteran Member Join Date: Jul 2007 Location: Brampton, Ontario Photos: Gallery \| Albums Posts: 3,996	Originally posted by amoringello 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. :-) Thanks, amoringello, I don't follow it in detail exactly but I think I get a general idea - and will need definitely need to do more dd on HSS compare to max sync speed.

12-02-2010, 09:03 PM	#20
aleonx3 Veteran Member Join Date: Jul 2007 Location: Brampton, Ontario Photos: Gallery \| Albums Posts: 3,996	Originally posted by noblepa 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. Since I only have AF360 and AF540 both support HSS, so if I did not switch to HSS, I would not be able to get shutter higher than 1/180.

12-03-2010, 12:50 AM	#22
openyourap Senior Member Join Date: Jun 2009 Location: Sydney Photos: Gallery \| Albums Posts: 171	Originally posted by twitch Sorry to be pedantic, but shutter affects ambient up to sync speed, after which it affects both ambient and flash. That's why if you want max effect from fill flash you should shot at sync speed. Whether "max" is actually enough for the effect you are after is a different matter. I'd consider this to be one of the semantic little idiosyncrasies of the HSS implementation, rather than the generality covered be the dot points We might be better conceiving our exposures knowing that for speeds above sync, the output of the flash unit itself is throttled. If we want to break it right down, we could argue that shutter speeds shorter than the flash blitz also affect the exposure, or that the flash could then be considered ambient.

12-03-2010, 03:11 AM	#23
amoringello Veteran Member Join Date: May 2008 Location: Virginia, USA Photos: Gallery Posts: 1,562	Quote: I just re-read our posts and I think we misunderstood each other, sorry, that's a first on an internet forum ha! so true! :-)

12-03-2010, 12:24 PM	#24
Rondec Loyal Site Supporter Join Date: Mar 2009 Location: Gladys, Virginia Photos: Gallery Posts: 27,662	Doesn't having iso 80 effectively increase sync speed by half a stop over cameras that only have iso 100 available?

12-03-2010, 12:50 PM	#25
twitch Veteran Member Join Date: Nov 2009 Posts: 4,571	Originally posted by Rondec Doesn't having iso 80 effectively increase sync speed by half a stop over cameras that only have iso 100 available? You have a good point, having ISO 80 on the K-5 certainly makes 1/180 more achievable.

12-03-2010, 01:33 PM	#26
amoringello Veteran Member Join Date: May 2008 Location: Virginia, USA Photos: Gallery Posts: 1,562	Except when talking about flash vs ambient light. ISO affects sensor sensitivity, so both flash and ambient light are affected. It will bring down the brightness of the sun, but will also affect flash. So lets say your flash was just not quite powerful enough to overpower the sun... adjusting ISO half a stop would not help to bring you half a stop closer to overpowering ambient light. A faster shutter speed would.

12-04-2010, 03:26 AM	#27
flyer Veteran Member Join Date: Jan 2008 Location: Ste-Anne des Plaines, Qc., Canada Posts: 2,013	Originally posted by eddie1960 but one of the reasons a lot of people shooting went medium format as the ability to sync at any speed Not all medium format can sync at any speed. Only the medium format with a leaf shutter in the lens can sync at any speed. If your medium format has only a focal plane shutter, the sync speed is actually often slower than APS-C DSLR.

12-05-2010, 09:05 AM	#28
tibbitts Pentaxian Join Date: Apr 2007 Location: Oklahoma USA Posts: 2,196	I had never thought about this, but given that higher-end 35mm cameras had 1/250th sec flash sync, what's with the 1/180th? My 35mm cameras (spotmatic, a-1) had horizontal cloth/rubber shutters, but certainly higher-end cameras seemed to offer 1/250th with metal vertical shutters. Shouldn't we be at 1/350th or something with aps? Paul

12-08-2010, 04:36 PM	#29
omega leader Veteran Member Join Date: Jan 2008 Location: Niagara Region, Ontario Canada Photos: Gallery Posts: 417	Sync speed isn't really important at all. Go look at strobist. Though I've discovered that the best investment I've ever made is a used studio strobe and good quality ND filters.

12-08-2010, 05:31 PM	#30
amoringello Veteran Member Join Date: May 2008 Location: Virginia, USA Photos: Gallery Posts: 1,562	Originally posted by omega leader Sync speed isn't really important at all. Go look at strobist. Though I've discovered that the best investment I've ever made is a used studio strobe and good quality ND filters. Can you point to the specific posting? Note sure where that ever came up... I know he has a segment on how useful sync speed is, and how to over-clock your sync speed (or something similar). Sadly that requires that your camera can fire a flash above its sync speed. Something which PENTAX crippled and you cannot make use of. Without fast sync speed, ND filters does nothing but make matters worse -- unless you have strobes capable of overpowering the sun to begin with. But then you're just pulling everything down within proper exposure for an otherwise unattainable aperture. TOTALLY different arena from what faster shutter speed allows.