What is the power loss going from x-sync to hss

[William W]

I assume the basic principles of HSS for both Nikon and Canon are the same.

The basic principles are the same: I wouldn't extrapolate therefore that the functionalities are the same.

Canon and Nikon vary considerably in some nuances of Flash functionality. I am not au fait enough with Nikon Flash Systems nowadays, to make any definitive statements greater than: there are definitely differences.

***

. . . Normally at sync speed 1st curtain opens, when complete open, than the second curtain starts to close. If the sync speed is 1/250, than the curtain speed is 1/250. The exposure time is 1/250, but the time the curtains are moving is 2/250. And that's the time the flash is using to divide it's power. So 50% will be used for the exposure. . . . When shooting at 1/500, the second curtain starts closing when then first curtain is half way. The total time the curtains will be moving will be 1/250+1/500=3/500. Or in decimals 0.004+0.002=0.006. So a flash duration of 0.006s for an exposure of 0.002s. A loss of 66%.
. . . Unless someone can explain me it's working different.

My simple and only explanation is that I’d caution about extrapolating that the duration of FLASH (i.e total TIME - perhaps milliseconds) of a SERIES of flash pulses is in some way the equivalent in ‘power’ (i.e. light POWER – perhaps Lumens) to the total TIME of a flash which is NOT a series of short pulses.

WW

[george013]

The basic principles are the same: I wouldn't extrapolate therefore that the functionalities are the same.

Canon and Nikon vary considerably in some nuances of Flash functionality. I am not au fait enough with Nikon Flash Systems nowadays, to make any definitive statements greater than: there are definitely differences.

***



My simple and only explanation is that I’d caution about extrapolating that the duration of FLASH (i.e total TIME - perhaps milliseconds) of a SERIES of flash pulses is in some way the equivalent in ‘power’ (i.e. light POWER – perhaps Lumens) to the total TIME of a flash which is NOT a series of short pulses.

WW

Several years ago I did an experiment in a dark place. Camera on tripod, focused on a certain distance. Flash in my hand. Camera on bulb. One shot with the flash on full power. Camera on bulb again and then using the flash manual with 1/8 power for 8 times. Those two exposures where exactly the same.

Look at the link again http://neilvn.com/tangents/high-speed-flash-sync/. We've been both in that discussion that time. There seems to be a different between Nikon and Canon. Nikon is switching to "sync flash" when entering the sync speed time. Canon can have both sync speed or HSS when at sync time. This is an image from Niel van Niekerk. I just copied it to make sure you will see what I want to show you. I know William is not pleased with this. The camera used Canon 5D.

The picture 1/200 f9 has been made twice. Once with normal flash and once with HSS. Completely different exposure. From what I read impossible with Nikon. It's about the loss of 50% of the light. A similar thing happens with Nikon, but between 1/250 and 1/320.

I think my calculations are pretty well for the moment.

George

[dje]

From tests I did some time ago, the length of the HSS "pulse" is varied according to shutter speed, at least in some flash units. The HSS "pulse" must last at least the length of time that the sensor is partly exposed. (If you do the sums, you'll find this time equals the shutter speed plus the curtain speed). For example, in my tests I found that HSS lasted for 7.5 msec for a shutter speed of 1/320 sec and 5.3 msec for a shutter speed of 1/1000 sec. This allows a small amount of power level optimisation for different shutter speeds, ie the faster the shutter speed, the higher the HSS power level.

It's a fairly complex process though and real life exposure tests are probably the best way to go.

Dave

[george013]

From tests I did some time ago, the length of the HSS "pulse" is varied according to shutter speed, at least in some flash units. The HSS "pulse" must last at least the length of time that the sensor is partly exposed. (If you do the sums, you'll find this time equals the shutter speed plus the curtain speed). For example, in my tests I found that HSS lasted for 7.5 msec for a shutter speed of 1/320 sec and 5.3 msec for a shutter speed of 1/1000 sec. This allows a small amount of power level optimisation for different shutter speeds, ie the faster the shutter speed, the higher the HSS power level.

It's a fairly complex process though and real life exposure tests are probably the best way to go.

Dave

That's what I wrote.
But for the exposure time is shorter, the effective use of the flash will be shorter. Read my calculations.

1/1000, sync time is 1/250
Flash time will be 1/250 + 1/1000 = 5/1000. The exposure is 1/1000. So 4/1000 part or 80% of it will not be used.

1/500, sync time 1/250. Just easy numbers.
Flash time will be 1/500 + 1/250 = 3/500. The exposure time is 1/500. So 2/500 part or 66% of it will not be used.

George

[William W]

. . . At the moment I think that comparing and contrasting the similarities and differences of how Canon and Nikon Flash systems work is generally interesting, but probably not directly useful to Stan, who, in his OP states that he is using a Canon 600 Series Speedlite.

I am not sure what other commentators have used as their test vehicles, because such has not disclosed.

That comment is NOT meant to demean the value of general commentary about ‘High Speed Sync’, but rather to re-iterate the commentary in Posts # 14; 15; 16; 18 and 21 are definitively in respect to the testing of and the use of CANON 430 and 580 Series Speedlites, with various CANON DSLRs.

WW

[george013]

. . . At the moment I think that comparing and contrasting the similarities and differences of how Canon and Nikon Flash systems work is generally interesting, but probably not directly useful to Stan, who, in his OP states that he is using a Canon 600 Series Speedlite.

I am not sure what other commentators have used as their test vehicles, because such has not disclosed.

That comment is NOT meant to demean the value of general commentary about ‘High Speed Sync’, but rather to re-iterate the commentary in Posts # 14; 15; 16; 18 and 21 are definitively in respect to the testing of and the use of CANON 430 and 580 Series Speedlites, with various CANON DSLRs.

WW

Stans question was also a general question about HSS. And I think I answered that question. The image I showed form Van Niekerks site shows what happens with sync speed and HSS flash. Two images with the same f-number and shutter speed. It can't be more clear. By the way, I think it's a bug in the Canon software.

Stan wanted to use the flash in HSS, 1/1000. The flash he's askingabout,Canon 600EX-RT, has a guide number of 60. Under the circumstance he mentioned it will be 10. I'm sure there are minor correction possible. But this is the basic idea.

George

[William W]

It’s late down here and it has been a long day . . . but here goes my wrap of the situation … [E&OE]

. . . Stan wanted to use the flash in HSS, 1/1000. The flash he's askingabout,Canon 600EX-RT, has a guide number of 60. Under the circumstance he mentioned it will be 10. I'm sure there are minor correction possible. . . .

Yes I read that.

Yes Stan's Flash (the 600Series) has a GN = 60m (at ISO100).

As per my previous and depending upon what camera Stan is using, I expect that the 'corrected' GN when HSS is activated and the Shutter Speed is 1/1000s will be about or LESS THAN GN = 30m (at ISO100).

Stan mentioned that he is using a “Flash Extender” – this will surely be a lens which focuses the flash into a narrow beam. Practically that might add a little bit of MFWD. Let’s say for example it adds another 5mtrs of ‘corrected’ GN, so that brings him up to GN = 35m (at ISO 100).

Now let’s assume that Stan is shooting BIF in reasonable daylight and he wants to fill under the bird’s wing at FEC minus 2 stops (which he stated in post #5). So we can assume that the exposure for the AMBIENT light will be at about: F/5.6 @ 1/1000s @ ISO 125. (let’s assume ISO 125 = ISO 100, for the convenience of our rough calculations)

Therefore, to have the Flash able to be used as FILL and to be able to dial in FEC = -2stops , then the SPEEDLITE needs to be situated at a MFWD of about 6.25mtrs from the Subject . . .
and if the Flash Extender adds 10mtrs of GN, then the Flash can be at about 7mtrs from the Subject . . .
and so on.

If we do rough calculations in “F-stops” so we can guesstimate how far away the flash can be and allow for the 2 stops of FEC that WILL NOT BE dialed in – then (at an assumed corrected GN = 35mtrs (at ISO100)) a rough guess is that the Flash should be situated at about 12.5 mtrs to make the ‘correct’ Flash Fill exposure.

Obviously, we could bump the ISO. . .
As we bump the ISO there will be increase in the GN . . .
But we will just go around circles, because we have to stop down the aperture on the lens, to keep a consistent AMBIENT EXPOSURE.

Much depends on how ‘effective’ is this Flash Extender that Stan is using.

BUT, even if the Flash extender is very effective and it brings the Flash when ‘corrected’ to its original GN (i.e. GN = 60mtrs at ISO100), then for an effective Flash as Fill, the Speedlite Unit will need to be at a distance of no less than about 10mtrs from the Subject to pull a shot at F/5.6 @ 1/1000s @ ISO100 from the Speedlite to be able to to have FEC = -2stops dialed in and used at daytime if reasonable sunlight is the AMBIENT light.

On what we have discussed, my general opinion is that the birds are going to have to be flying reasonably close by to get the Flash close enough to have any effective Flash as Fill using HSS at Tv = 1/1000s. . .

But, where will the flash be located?

Let’s assume the birds will be at about 10 mtrs from the flash and it is reasonable to assume that the flash will be mounted on the camera.

Lets’ say it is a 135 Format camera (aka “full frame”) . . .
the FoV at 10mtrs SD is about 860mm x 570mm which I guess is doable, but it will be a very quick sweep/pan to pull a shot of a Bird in Flight.

If the camera is APS-C Format, then the FoV at 10mtrs SD is about 550mm x 360mm, making sweep and pan that much tighter again.

If the camera is APS-H Format then the FoV is about 680mm x 460mm at an SD = 10mtrs

WW

[george013]

It’s late down here and it has been a long day . . . but here goes my wrap of the situation … [E&OE]



Yes I read that.

Yes Stan's Flash (the 600Series) has a GN = 60m (at ISO100).

As per my previous and depending upon what camera Stan is using, I expect that the 'corrected' GN when HSS is activated and the Shutter Speed is 1/1000s will be about or LESS THAN GN = 30m (at ISO100).

Stan mentioned that he is using a “Flash Extender” – this will surely be a lens which focuses the flash into a narrow beam. Practically that might add a little bit of MFWD. Let’s say for example it adds another 5mtrs of ‘corrected’ GN, so that brings him up to GN = 35m (at ISO 100).

Now let’s assume that Stan is shooting BIF in reasonable daylight and he wants to fill under the bird’s wing at FEC minus 2 stops (which he stated in post #5). So we can assume that the exposure for the AMBIENT light will be at about: F/5.6 @ 1/1000s @ ISO 125. (let’s assume ISO 125 = ISO 100, for the convenience of our rough calculations)

Therefore, to have the Flash able to be used as FILL and to be able to dial in FEC = -2stops , then the SPEEDLITE needs to be situated at a MFWD of about 6.25mtrs from the Subject . . .
and if the Flash Extender adds 10mtrs of GN, then the Flash can be at about 7mtrs from the Subject . . .
and so on.

If we do rough calculations in “F-stops” so we can guesstimate how far away the flash can be and allow for the 2 stops of FEC that WILL NOT BE dialed in – then (at an assumed corrected GN = 35mtrs (at ISO100)) a rough guess is that the Flash should be situated at about 12.5 mtrs to make the ‘correct’ Flash Fill exposure.

Obviously, we could bump the ISO. . .
As we bump the ISO there will be increase in the GN . . .
But we will just go around circles, because we have to stop down the aperture on the lens, to keep a consistent AMBIENT EXPOSURE.

Much depends on how ‘effective’ is this Flash Extender that Stan is using.

BUT, even if the Flash extender is very effective and it brings the Flash when ‘corrected’ to its original GN (i.e. GN = 60mtrs at ISO100), then for an effective Flash as Fill, the Speedlite Unit will need to be at a distance of no less than about 10mtrs from the Subject to pull a shot at F/5.6 @ 1/1000s @ ISO100 from the Speedlite to be able to to have FEC = -2stops dialed in and used at daytime if reasonable sunlight is the AMBIENT light.

On what we have discussed, my general opinion is that the birds are going to have to be flying reasonably close by to get the Flash close enough to have any effective Flash as Fill using HSS at Tv = 1/1000s. . .

But, where will the flash be located?

Let’s assume the birds will be at about 10 mtrs from the flash and it is reasonable to assume that the flash will be mounted on the camera.

Lets’ say it is a 135 Format camera (aka “full frame”) . . .
the FoV at 10mtrs SD is about 860mm x 570mm which I guess is doable, but it will be a very quick sweep/pan to pull a shot of a Bird in Flight.

If the camera is APS-C Format, then the FoV at 10mtrs SD is about 550mm x 360mm, making sweep and pan that much tighter again.

If the camera is APS-H Format then the FoV is about 680mm x 460mm at an SD = 10mtrs

WW

All based on a corrected guide number of 30. I showed some calculations and assumptions in post 20 how I come to a corrected guide number of 10. Where does that 30 come from?
I think Stan and others, among whom my person, got some idea what's going on basic.

George

[Big Stan]

George, Thank you for providing the reference to http://neilvn.com/tangents/high-speed-flash-sync/. It was very helpful. One difference between the objective of the experiment and my objective; the experiment was focused on over powering the sun and I am looking toward using fill light to increase contrast in my bird photographs.
So, here are my conclusion based on the experiment:
There is a loss of about 2 stops in using HSS and the Nikon D3 and the Canon 5D has similar linearity.
OK, the question remains, if there is a ~two stop loss going to HSS (as cited in the experiment) and I desire to use two stops of negative FEC to avoid over-flashing (using ambient light), does going to HSS satisfy the two stops or do I have to use additional stops of negative FEC?

[William W]

. . . Where does that [guide number of] 30 come from?

From my 13 years of testing and using Canon Speedlites with numerous Canon DSLRs.

Refer to posts #14 and #16 specifically.

WW

[Manfred M]

There seems to be a different between Nikon and Canon. Nikon is switching to "sync flash" when entering the sync speed time. Canon can have both sync speed or HSS when at sync time.

I can set the HSS to start at either 1/325 sec OR 1/250th sec on Nikon; where 1/250 is sync speed. I'm not sure how consistent this is across different camera models.

I have no doubt that there is a difference in flash implementations between Nikon and Canon, as they handle FEC differently too.

[george013]

My knowledge is based on how the assumption how the curtains work and the HSS flash duration. Looking at the practical results of Van Niekerk I'm pretty close.
I don't know where you get the 2 stop loss from. The loss of power is dependent on the shutter speed. It starts with 50% and when using 1/1000 it's 83%, when my calculations are right. When the corrected guide number of your flash is 10, than that means you've enough light to lighten an object at 10m with a f5.6 at 100ASA.
I can't help you further. Read Williams post. Except that you've to recalculate everything based on a guide number of 10.

George

[george013]

I can set the HSS to start at either 1/325 sec OR 1/250th sec on Nikon; where 1/250 is sync speed. I'm not sure how consistent this is across different camera models.

I have no doubt that there is a difference in flash implementations between Nikon and Canon, as they handle FEC differently too.

That was another test of Van Niekerk discussed here. The camera goes over the sync speed but doesn't go in HSS, you can see a band. The strange thing in that discussion was that that band showed different when using a non Nikon flash.
When I found that link back I'll show it.

George

PS.
I think it was this one http://neilvn.com/tangents/auto-fp-f...on-d300s-d700/

[William W]

. . . There is a loss of about 2 stops in using HSS and the Nikon D3 and the Canon 5D has similar linearity.

OK, the question remains, if there is a ~two stop loss going to HSS (as cited in the experiment) and I desire to use two stops of negative FEC to avoid over-flashing (using ambient light), does going to HSS satisfy the two stops or do I have to use additional stops of negative FEC?

Addressed in Post #14 and Post #27, rephrased and condensed here -

1. If you want to talk in “stops” and flash “power” then there is an initial loss of about 2 stops when you activate HSS, with most canon gear, it is actually a little less than two stops.

2. There will be more than 2 stops “loss” of Flash “power” as you shorten the Shutter Speed – (Neil’s website that George linked to shows that).

3. You want to use 1/1000s, which will be about 2 stops faster than the X-Flash Sync of a Canon DSLR, so you will (in rough terms) “lose” around 3~3½ stops of flash “power”.

4. For the Flash to act as Fill and be filling at about 2 stops under the Ambient, (which I understand is what you want), then the Flash will have to be located at about 5.3 meters from the Subject if you are shooting on a reasonable sunny day and you are not using the “Flash Extender”.

5. If the Flash is located closer than about 5.3 Meters to the Subject or you are using a "Flash Extender", then you will have to use some FEC to attain the desired -2stops under the ambient .

6. If the Flash is located farther than about 5.3 to the Subject, then the Flash will fill at LESS than -2stops under the ambient.

WW

But, as I mentioned I find it much easier (and IMO more correct) to refer to and think of any loss when switching to HSS as the loss of the MFWD, (Maximum Flash Working Distance) and not of a loss in "stops" of flash "power".

The salient point being that to use all the functions of any flash in any mode: the Flash must be located at or closer than the MFWD.

[William W]

Stan, from your experiences in 2014 you should have some idea of how far (i.e. distance) that you can "reach" with your 600 series flash in HSS mode and a good idea of the worth of the "Better Beamer"?


The fact is, if you are now wanting to shoot BiF on a reasonably sunny day, or even an overcast day, and not birds shaded by trees as you did before in 2014, you will need a lot more flash, even if you only want to fill at -2stops under the ambient.

WW