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I don't think HSS is the right approach for this. (I'm rephrasing some notes from earlier commentsearlier comments I made that maybe deserve to be a proper answer.)

HSS works with fast shutter speeds by pulsing very rapidly over a longer period of time, effectively emulating a continuous light. (And, importantly, this reduces the available power. More on that a few paragraphs below.) With fast-moving subjects, though, the fact that the HSS light isn't really continuous may, as Joanne C points outas Joanne C points out, be causing a multiple-exposure strobe effect.

I don't think HSS is the right approach for this. (I'm rephrasing some notes from earlier comments I made that maybe deserve to be a proper answer.)

HSS works with fast shutter speeds by pulsing very rapidly over a longer period of time, effectively emulating a continuous light. (And, importantly, this reduces the available power. More on that a few paragraphs below.) With fast-moving subjects, though, the fact that the HSS light isn't really continuous may, as Joanne C points out, be causing a multiple-exposure strobe effect.

I don't think HSS is the right approach for this. (I'm rephrasing some notes from earlier comments I made that maybe deserve to be a proper answer.)

HSS works with fast shutter speeds by pulsing very rapidly over a longer period of time, effectively emulating a continuous light. (And, importantly, this reduces the available power. More on that a few paragraphs below.) With fast-moving subjects, though, the fact that the HSS light isn't really continuous may, as Joanne C points out, be causing a multiple-exposure strobe effect.

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mattdm
mattdm
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Basically, the flash sync speed is the fastest duration for which the whole sensor is exposed with a focal plane shutter (as found in modern dSLRs). At higher shutter speeds, a slit made between the first and trailing shutter curtains moves across the sensor, exposing only part of it at a time. This is usually quick enough to not cause weirdness, but a flash pulse is even shorter. That means that without HSS, only the part of the frame exposed when the flash fires will be properly lit. Outside of that band, you'll get underexposure.

Leaving aside flash for a second, If your subject is moving very rapidly, the moving object may in fact become distorted, because the entire frame isn't moving at once. The Wikipedia article on shutter speed has an example of this effect on helicopter blades.

So, while high shutter speeds can freeze motion, with a focal plane shutter, they may do it oddly. It's better to use a fast flash pulse to expose the whole frame at once.

HSS combats thisworks with fast shutter speeds by pulsing very rapidly over a longer period of time, effectively emulating a continuous light. (And, importantly, this reduces the available power. More on that a few paragraphs below.) With fast-moving subjects, though, the fact that the HSS light isn't really continuous may, as Joanne C points out, be causing a multiple-exposure strobe effect.

But even not taking that into consideration, unless ambient light is overpowering, HSS does not allow you to shorten the effective duration of an exposure.

So: that's a really long way of saying using HSS is not working in your favor.

If the ambient light is really strong and you need fill light in combination with a fast shutter speed for proper exposure, then HSS can be very useful.

Basically, the flash sync speed is the fastest duration for which the whole sensor is exposed. At higher shutter speeds, a slit made between the first and trailing shutter curtains moves across the sensor, exposing only part of it at a time. This is usually quick enough to not cause weirdness, but a flash pulse is even shorter. That means that without HSS, only the part of the frame exposed when the flash fires will be properly lit. Outside of that band, you'll get underexposure.

HSS combats this by pulsing very rapidly over a longer period of time, effectively emulating a continuous light. (And, importantly, this reduces the available power. More on that a few paragraphs below.)

So: that's a really long way of saying using HSS is not working in your favor.

Basically, the flash sync speed is the fastest duration for which the whole sensor is exposed with a focal plane shutter (as found in modern dSLRs). At higher shutter speeds, a slit made between the first and trailing shutter curtains moves across the sensor, exposing only part of it at a time. This is usually quick enough to not cause weirdness, but a flash pulse is even shorter. That means that without HSS, only the part of the frame exposed when the flash fires will be properly lit. Outside of that band, you'll get underexposure.

Leaving aside flash for a second, If your subject is moving very rapidly, the moving object may in fact become distorted, because the entire frame isn't moving at once. The Wikipedia article on shutter speed has an example of this effect on helicopter blades.

So, while high shutter speeds can freeze motion, with a focal plane shutter, they may do it oddly. It's better to use a fast flash pulse to expose the whole frame at once.

HSS works with fast shutter speeds by pulsing very rapidly over a longer period of time, effectively emulating a continuous light. (And, importantly, this reduces the available power. More on that a few paragraphs below.) With fast-moving subjects, though, the fact that the HSS light isn't really continuous may, as Joanne C points out, be causing a multiple-exposure strobe effect.

But even not taking that into consideration, unless ambient light is overpowering, HSS does not allow you to shorten the effective duration of an exposure.

So: that's a really long way of saying using HSS is not working in your favor.

If the ambient light is really strong and you need fill light in combination with a fast shutter speed for proper exposure, then HSS can be very useful.

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mattdm
mattdm
  • 143.6k
  • 52
  • 421
  • 745

I don't think HSS is the right approach for this. (I'm rephrasing some notes from earlier comments I made that maybe deserve to be a proper answer.)

Basically, the flash sync speed is the fastest duration for which the whole sensor is exposed. At higher shutter speeds, a slit made between the first and trailing shutter curtains moves across the sensor, exposing only part of it at a time. This is usually quick enough to not cause weirdness, but a flash pulse is even shorter. That means that without HSS, only the part of the frame exposed when the flash fires will be properly lit. Outside of that band, you'll get underexposure.

HSS combats this by pulsing very rapidly over a longer period of time, effectively emulating a continuous light. (And, importantly, this reduces the available power. More on that a few paragraphs below.)

Normally with flash, shutter speed has only an insignificant effect on exposure, because the flash pulse is so short and so bright relative to the ambient light. If your flash pulse lasts for ¹⁄₁₀,₀₀₀th of a second, it doesn't matter if the shutter is open for ¹⁄₃₀0th or ¹⁄₁₈₀th of a second around that pulse — only the flash duration will have any noticeable effect. (Unless the ambient light is very, very strong.)

HSS changes this, basically back to the way it is without a flash. Since the light is on for the whole duration of the exposure, shutter speed determines both your motion-stopping ability and reduces the power available from the flash.

So, why is this all important?

Primarily: the fastest shutter speed on your Canon 1000D is ¹⁄₄₀₀₀th of second, whereas at the lowest (non-HSS) power, the flash duration for your 430EX is about three times faster. Canon does not publish the specs, unfortunately, but this is typical for T.1 duration of this class of flash. (Since it's a steep curve, it's hard to decide exactly when it's meaningful to start and stop measuring — T.1 is the most useful standard, but T.5 numbers are usually quoted. This tangent is probably a whole separate question!)

Anyway, the point is: if you want to freeze motion beyond ¹⁄₄₀₀₀th of a second, you need to use a flash strobe (at reduced power). If there's too much ambient light to do that, you're pretty much stuck — but HSS won't really help any.

Let me go ahead and show this with some numbers:

At a normal-lens (50mm-e) field of view, your flash has a guide number of 34 meters — a decent amount of power. But just turning on HSS reduces this to 17. Since flash power is relative to GN squared, that means just using HSS has cut the flash's output level by two stops. Assuming aperture and ISO where already where you want them, you have to increase the shutter duration four times. This is clearly counter-productive to the goal of freezing motion.

But, it's worse than that! That guide number of 17 is only for a HSS flash duration matching a shutter speed of ¹⁄₂₅₀th. As you go faster than that, you cut out more and more of the "continuous" HSS light, reducing power further. By the time you get to ¹⁄₄₀₀₀th of a second, you're looking at a guide number of about 4! This is something like a tenth the power you'd get from using the camera's built-in pop-up flash, and _about what you'd get with your 430EX at its lowest manual setting of ¹⁄₆₄ power — which, again, gives a flash pulse about 3× faster than your fastest shutter speed.

So: that's a really long way of saying using HSS is not working in your favor.