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

[Big Stan]

I am trying to get an understanding regarding the loss in power for a Canon 600EX-RT going from x-sync to HSS.

I contacted Canon customer service and received several replies, all filled with double talk, but no answer. It was as if I was trying to get the combination to the safe containing their company secrets.

After several hours of internet search, I found four sources who cited power loss associated with HSS, but there was no consistency. Results ranged from 1 stop to 2.3 stops:

1. The first limitation to be aware of is that you lose about one stop of flash power when you switch to high speed sync.

2. You lose two stops flash power going into HSS. Two stops was also cited on a Nikon blog. Nikon seems to be more forthcoming than Canon.

3. To be continuous, HSS only allows about 20% power (-2.3 EV) resulting in about 40% distance range.

[rpcrowe]

I have never worried about power loss when going from standard sync to HSS... Sure you lose power but, when using HSS and increasing your shutter speed, you will open up your aperture, which compensates in a great degree for the HSS power loss. There is likely no more than a one or at most two stop bottom-line (after calculating the increased aperture used) loss

When shooting with ETTL or when using a flash meter in manual flash, your exposure will be determined and you don't need to do any extra calculations.

Canon has the BEST OF TWO WORLDS AVAILABLE.... Simply have your and camera and hotshoe flash on HSS ALL THE TIME. When you are shooting faster than the maximum sync speed (1/250 second for my 7D and 7D Mk2 and 1/200 for my 5D Mk2) the camera/flash will automatically select HSS and if you slow to the maximum shutter speed or slower, the camera/flash will automatically revert to standard sync. It will pop back and forth between HSS and standard sync as your shutter speed goes up and down. This probably not work when using a third party strobe like Yongnuo...

I was attending a Canon Flash Photography presentation at Calumet Photo in Escondido, CA a couple of years ago. The Canon "EXPERT" giving the presentation did not know that the Canon gear will automatically switch back and forth to and from HSS as the shutter speed changes...

In the Old Navy, we used to say, "An expert is a guy from out of town who has a slide projector"

My primary use for HSS is outdoors for fill light. I will normally be using a -1 or -2 stop flash compensation and will most often have the flash rather close to my subject so the light loss doesn't bother me.

This portrait was done using 1/400 second and HSS. It was shot under a pier in the late afternoon with the breakwater rocks as a background...
I had a Canon 7D2 with 70-200mm f/4L IS lens. I used a Canon 600EX flash on an off camera Stroboflash, Camera-Flip Bracket with a sync cable. I modified the light with a small softbox...

Rather than fill light (this was in the shade) I used the flash to pump in some extra light on the model to separate her from the background rocks.

If you are shooting when the flash is the total light illuminating the subject; as in shooting at night outside with no ambient lighting or shooting in a totally dark studio using flash as the only light - the speed of the flash exposure will normally stop any action and you don't need to worry about the camera shutter speed being high enough to freeze action. The speed of the flash can be controlled by the power settings. At full power, the flash has he longest duration and at minimum power the duration is the shortest...

There MAY be a way to use a higher shutter speed without having to rely on HSS. This might be good when you are shooting with strobes that do not have HSS capability - this is especially true with studio strobes.

I have to watch this video a time or two again to wrap my mind around it and then do some tests...
https://www.youtube.com/watch?v=JflxDO_AvME
If it works, it would be nice...

[george013]

I am trying to get an understanding regarding the loss in power for a Canon 600EX-RT going from x-sync to HSS.

I contacted Canon customer service and received several replies, all filled with double talk, but no answer. It was as if I was trying to get the combination to the safe containing their company secrets.

After several hours of internet search, I found four sources who cited power loss associated with HSS, but there was no consistency. Results ranged from 1 stop to 2.3 stops:

1. The first limitation to be aware of is that you lose about one stop of flash power when you switch to high speed sync.

2. You lose two stops flash power going into HSS. Two stops was also cited on a Nikon blog. Nikon seems to be more forthcoming than Canon.

3. To be continuous, HSS only allows about 20% power (-2.3 EV) resulting in about 40% distance range.

I think it depends on the shutterspeed. Shooting at the sync speed in HSS-mode will not make any difference. The faster the shutterspeed, the smaller the split between the curtains, the more flashpower is used for nothing, just lightening a closed sensor.

George

[Black Pearl]

Would it not be a simple case of testing it?

[Big Stan]

Thank you for your response, thought the dog shots on your web site are great. My kids were raised having a Basset Hound as an older brother.

In your reply you stated, "My primary use for HSS is outdoors for fill light. I will normally be using a -1 or -2 stop flash compensation and will most often have the flash rather close to my subject so the light loss doesn't bother me." I too will be using HSS for outdoors fill flash, only in my case, my subject will not be close to me (bird photography).

So here is my dilemma, I want my flash output to be reduced by 2 stops FEC to keep from over flashing my subject and if going to HSS automatically reduces flash output power by 2 stops do I still dial in -2 stops or let switching to HSS automatically provide the -2 stops?

[Big Stan]

Thank you. While very few sites provide any quantifiable information regarding HSS loss in power, they all agree that there is a definite loss in output power switching to HSS and there is an addition loss going to shorter exposure. Here is the way one guy explained it,
"f11 @ 1/200 (sync) 1:1 flash and ISO 100 would equate to f2.8 @ 1/800 1:1 flash in HSS and ISO 100
You lose four stops of flash power, two for going into HSS and another two for going up two stops of SS.
Even though your flash is firing at full power you are getting an effective 1/16 of actual light.

[george013]

Thank you for your response, thought the dog shots on your web site are great. My kids were raised having a Basset Hound as an older brother.

In your reply you stated, "My primary use for HSS is outdoors for fill light. I will normally be using a -1 or -2 stop flash compensation and will most often have the flash rather close to my subject so the light loss doesn't bother me." I too will be using HSS for outdoors fill flash, only in my case, my subject will not be close to me (bird photography).

So here is my dilemma, I want my flash output to be reduced by 2 stops FEC to keep from over flashing my subject and if going to HSS automatically reduces flash output power by 2 stops do I still dial in -2 stops or let switching to HSS automatically provide the -2 stops?

Let me put it different. Sync is 1/250. Both curtains are open, flash lightens the whole sensor. Now we use HSS and 1/500. Flash starts at the moment the first curtain opens and ends when the second curtain is closed. But the second curtain starts closing when the first curtain is half way. You're loosing 50% of the power.
I'm not sure, but the flash/camera still calculates the needed power but the distance at which it can be used will be less. Not sure about that.

George

PS.

I remember a discussion a few years ago. http://neilvn.com/tangents/high-speed-flash-sync/

[Dave Humphries]

Hi Stan,

I will normally be using a -1 or -2 stop flash compensation and will most often have the flash rather close to my subject so the light loss doesn't bother me." I too will be using HSS for outdoors fill flash, only in my case, my subject will not be close to me (bird photography).

You haven't said whether the flash will be on your camera or not.

Some may assume it will be, but you asked about the 600EX-RT, which has the ability to be triggered reliably and wirelessly at a significant distance. So - you might be doing what I did last year; setting up the flash on a light stand near where the birds perch or fly and just shooting from a distance, but still requiring a fast shutter speed, hence HSS, because of the telephoto lens, ambient light level, etc.

Even if you had intended to shoot with flash on camera, perhaps* you can apply the idea I have mentioned, it'll save the flash power which gives quicker recycle times.

* While other times it'll be a complete non-starter because the bird in question is the far side of a river in the wild.

Were you going to try this with the flash power set manually, or via eTTL and FEC?

Clearly if you're shooting the flash power set manually, losing approx. 2 stops isn't really an issue.

That said, you'll probably chimp and determine whether the flash was bright enough (or too bright) in the first few shots anyway, so whichever way, you'll just adjust the power, or FEC until you achieve what you want, or discover that you cannot - due to lack of power and excessive flash to subject distance as much as anything.

Don't forget to zoom the flash head to 200mm if shooting with it on camera, assuming it's not set to Auto-zoom with lens focal length changes. Whereas if it is off-camera and closer to the birds, you may not want to do that.

Good luck and do show us the results please.

Cheers, Dave

[rpcrowe]

For flash on or near the camera (using some sort of bracket)... Here's what I would do: I would add a flash extender such as the Better Beamer or a DIY extender. This would increase my flash power towards to the center of the frame (or the entire frame with 300+ mm focal lengths)... I would use the camera in manual mode and the flash in ETTL mode with a -2 stop starting point... BTW: I would manually set the flash to the longest focal length possible...

Here is a decent video about flash compensation...
https://www.youtube.com/watch?v=WwEykf_mg6E

This seems like a good eBook regarding flash and birds or other nature subjects...
http://www.glennbartley.com/FlashEbook.html

However, I strongly suspect that you can get the equivalent information free on various Google directed sites, rather than spending twenty dollars on the eBook.

There are lots of sites that tell you how to use the Better Beamer and how to build a DIY Flash Extender.

BTW: My Better Beamer was designed to fit the Canon 550EX. I now use a 600EX RC flash but, I secure the Better Beamer to the 600EX with a length of "Gaffer's Tape". NOTE: Gaffer's tape leaves no residue. Duct tape is a cheaper alternative but, will leave adhesive residue on your flash.

[george013]

With all respect, but the question was how to get an understanding of, not dealing with.

George

[Big Stan]

Thank you , George, very succinctly said.

Shooting birds in flight (BIF) with a goal to fill the under wing area is a split second operation, I am not good enough to tweak the settings on the fly. As it is, I can barely keep the bird in the center of the frame. And, if I miss the shot, the bird will be out of sight before I am able to recover.

That said, I will be shooting with a 400mm lens at 1/1000-sec from a gimbal mount (or hand held) with a flash bracket and a flash extender.

The only question remaining is when using HSS, should I dial-in an FEC value or not dial-in FEC?

[george013]

Thank you , George, very succinctly said.

Shooting birds in flight (BIF) with a goal to fill the under wing area is a split second operation, I am not good enough to tweak the settings on the fly. As it is, I can barely keep the bird in the center of the frame. And, if I miss the shot, the bird will be out of sight before I am able to recover.

That said, I will be shooting with a 400mm lens at 1/1000-sec from a gimbal mount (or hand held) with a flash bracket and a flash extender.

The only question remaining is when using HSS, should I dial-in an FEC value or not dial-in FEC?

I don't think you've the answers on your first questions yet.

George

[Big Stan]

I agree. I can only hope I get a reply before the sun goes nova.

[William W]

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

Confusion in the use of technical terms appears to is adding to your dilemma.

Probably that is the wrong question or at the least the wrong way to ask it especially to a technical person at Canon.

I find it easier that I do NOT think about the Flash's "Power Loss" when it is switched to HSS.

As you are probably aware, the Canon Speedlite when it is active in HSS, serves series of rapid pulsed flashes. It is my opinion that is serves very little theoretical and mostly zero practical purpose comparing the (technically correct) 'flash power' in HSS to what is the 'Flash Power' when it is acting as a Speedlite and used with a camera's Tv at or slower than Max xSync.

I find it much easier to compute/compare in terms of MFWD . (Maximum Flash Working Distance) as extrapolated from the Guide Number.

In this manner I can recommend/report that typically (my experience is with 430s and 580s series - but I expect that 600 Series will be very similar) when HSS is activated you can count on loosing about 20~30% of MFWD as calculated by the GN. Note this is even if the Camera is set to Tv = X Flash Sync . . so we are talking about just switching on HSS.

As George correctly implied the loss then increases as the Tv gets faster. So for example if your X-Flash Sync is 1/200s - at 1/400s you can expect to loose about 30% MFWD. At 1/800s expect about 40% loss and at 1/1600 maybe about 50% loss.

By using the MFWD you then can compute where the FLASH HEAD needs to be placed so that it has its 'full power potential' to be used for Flash as Fill when the unit is in HSS mode.

Note the relevance of Dave Humpries' question asking where will the Flash be located.

***

I too will be using HSS for outdoors fill flash, only in my case, my subject will not be close to me (bird photography).

So here is my dilemma, I want my flash output to be reduced by 2 stops FEC to keep from over flashing my subject and if going to HSS automatically reduces flash output power by 2 stops do I still dial in -2 stops or let switching to HSS automatically provide the -2 stops?

If I have explained the above usefully, then you will understand that the direct answer to the question is complicated.

More specifically and not as an answer to the question but an explanation of it, there are three possible outcomes:

1. The Flash might be located beyond the MFWD at an exact distance where the 'loss of power' might just be equal to the FEC that you would wanted to dial in - in which case if you don't dial in FEC in then you will probably will get something useful.

2. The Flash might be located at any other distance beyond but not exactly equitable to the FEC you wanted to dial in: in which case if you dial in FEC then you will get something not so useful.

3. (what I would do) If the Flash is in a position such that, taking into consideration the Rules of Thumb I provided above concerning the loss of MFWD, the Flash is located closer than the subsequently approximated MFWD from the Subject, then you can be reasonably assured that you have enough 'power' in the flash to act as the Key Light - in which case you can then apply FEC and be reasonably assured that your results will be consistent.

Note however that the FEC 'numbers' in HSS might not necessarily relate exactly to the FEC 'numbers' when you have used Flash as Fill when HSS was NOT activated.

So, to firstly get your own Rule of Thumb for the 600 series Flash and secondly to confirm exactly what FEC you require, after you have approximated the maximum working distance for the flash a few test shots in HSS would be in order. And those test shots should be taken at every (full stop) of shutter speed that you might use. For example if you normally use 1/640 and 1/800s then just use 1/800 for your test of FEC: but if you use a range 1/400 to 1/1600, then make FEC tests at 1/400; 1/800 and 1/1600.

WW

[William W]

. . . Shooting at the sync speed in HSS-mode will not make any difference.

Incorrect apropos Canon. Please see my previous.

WW

[William W]

Would it not be a simple case of testing it?

Indeed. I concur Robin.

But it is very important to know exactly what to test (for). I read internet sites that expand on HSS - some you tube videos have the flash positioned at a place obviously exceeding what would be the MFWD - that only shows to me a complete lack of understanding: other (written) sites do not refer to the MFWD even by alluding to the flash's placement relative to the Subject.

In simple terms when you switch to Canon HSS, to have all the capabilities and functionalities available to use, the first premise is that the Speedite must be within a distance of the 'calculated[' MFWD using the GN and then the REDUCTION of that MFWD by (roughly): 20%; 30%; 40% or 50% for Shutter Speeds of: x-flash sync; 1stop faster; 2 stops faster; 3 stops faster.

WW

[Manfred M]

Stan - I don't have a definitive answer for you on HSS, but part of the reason is that there does not seem to be one and I have not found any documentation on line as to the "real world" impact. Unfortunately, the camera manufacturers have not published any data, so any answers are going to be at best "educated" guesses, unless someone has gone out and done some experimental work.

George is correct as to the reason that there is a power loss is that when one is shooting at shutter speeds at or below the synch speed of the camera, the second shutter blade does not start to move until the first one is completely out of the way and the whole sensor is completely exposed to the light.

The moment we utilize HSS, we are shooting as shutter speeds where the second shutter blade starts moving down before the first one has cleared the entire travel, This means the sensor is partially blocked at all times and rather than striking the sensor, part of the light strikes the shutter blades and does not contribute to the exposure. The faster the shutter speed, the smaller the slit between the blades and the less light can hit the sensor. This suggests that in HSS, there isn't a constant drop in the amount of light associated with shooting in that mode.

The other thing that happens when shooting in HSS, the flash is pulsed very rapidly in order to act as a continuous light source when shooting in that mode. This means that the circuitry has to discharge a lot more power for each time that the flash fires. I have not found any information in the literature that explains how this happens. There is a finite amount of power in the flashes capacitor available for discharge, so the flash manufacturer has to make some decisions on how this power is controlled. A slower shutter speed will require more pulses of power than a high shutter speed. At some point insufficient power will impact the colour temperature of the light. A subject that is closer is going to require less power output than a subject that is farther away, and I have not seen any information as to how this is determined for HSS.

The bottom line is that HSS is a bit of a technology kludge and that might be the reason for a lack of information that you are looking for.

[William W]

. . . The moment we utilize HSS, we are shooting as shutter speeds where the second shutter blade starts moving down before the first one has cleared the entire travel, This means the sensor is partially blocked at all times and rather than striking the sensor, part of the light strikes the shutter blades and does not contribute to the exposure.

Hi Manfred,

A pedantic, but in Stan’s case a relevant point: for Canon gear you do not necessarily need to be at a Shutter Speed faster than X-Flash Sync to incur a “loss”.

Canon Speedlites and DSLR combinations allow HSS to be engaged at the shutter speed equal to X-Flash Sync. (at least the combination that I have tested).

I have seen this confuse quite a few photographers who have left HSS engaged, but returned the Shutter Speed to Max x-Flash Sync.

WW

[george013]

Incorrect apropos Canon. Please see my previous.

WW

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

You're right, about my comparing normal and HSS flash at sync speed. It starts with a loss of 50%.
I don't know if HSS would be possible in sync speed. I don't think so. Theoretical no problem.

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.
Before some smart guy stands up, this is for curtain shutters.

George

PS.

The first assumption of Stan is correct if the loss of 1 stop is the same as a loss of 50%

[george013]

Thank you , George, very succinctly said.

Shooting birds in flight (BIF) with a goal to fill the under wing area is a split second operation, I am not good enough to tweak the settings on the fly. As it is, I can barely keep the bird in the center of the frame. And, if I miss the shot, the bird will be out of sight before I am able to recover.

That said, I will be shooting with a 400mm lens at 1/1000-sec from a gimbal mount (or hand held) with a flash bracket and a flash extender.

The only question remaining is when using HSS, should I dial-in an FEC value or not dial-in FEC?

I reread your posts. I was thinking you where joking shooting birds with a 400mm lens and flash.

Your flash, the Canon 600EX-RT, has a guide number of 60. The guide number is distance*f-number at 100 ISO.
If your camera has a sync speed of 1/200 and you shoot at 1/1000 the curtain movement will take 1/200+1/1000=6/1000s. That's also the HSS flash time. It means 83% of the flash power is lost. When recalculating the guide number, that will become 10. So in principle you're shooting in these circumstances with a flash with a guide number of 10. And when shooting with 400mm it might even be less.
Calculations and theory just out of my thumb. Maybe somebody might correct it.

George