Flash Duration - more important than color temperature and guide numbers?

[Adventurer]

Dear forum members,

 

in another thread here we gently touched the question of having fast light. While everybody is currently still talking about guide numbers and color temp, I would like to raise awareness about flash duration and flash peak values and energy. This is a very old video about a Canon 580 EX II where you see the setup and measurement curves that can be done. As all of you want to know what the most powerful and best underwater strobe in the market is, this is an interesting approach.

 

Years ago I have been involved in such a test.

Maybe a member has the equipment to go for such a setup and can publish the results.

 

Here is the video on youtube: How to measure Flash Duration

[Architeuthis]

I believe that short flash duration is, at present, mostly important for owners of compact cameras and of cameras that have global shutter (Sony A9III).

The flash sync. speeds of most present system cameras (1/160s to 1/400s) are long enough to utilize (most) of the flash duration. It will become, however, a more and more important feature in the future...

 

I think there is also not a single feature that is most important for a good strobe and the others don't count. Color temperature, even light distribution, recycle time, maximum strobe power, compactness and flash duration are separate features and each of them has to be good to make up a good strobe...

 

 

Wolfgang

 

[Chris Ross]

In general round tube flashes are slower.  The old YS-250 had a duration of 1/50 second or so at full power, quickly got faster of course as it was turned down.  There was a post on Wetpixel some time back where someone quoted flash duration times.  Mostly not a problem till you get into 1/400 plus flash sync speed.  I think some flashes might be an issue with for example a manual flash trigger and an Olympus camera which can do 1/400 to 1/500 sync if I recall correctly.  One post is here but there are more I'm sure:  https://wetpixel.com/forums/index.php?/topic/60459-flash-duration/

[Adventurer]

3 hours ago, Architeuthis said:

I believe that short flash duration is, at present, mostly important for owners of compact cameras and of cameras that have global shutter (Sony A9III).

I do not agree Wolfgang. Keep in mind the following. When you try to photo water droplets you will find that your shutter must be set to bulb to archive this.

 

The flash will freeze your foreground. The sharpness of your underwater imaging subject is largely also accounted to bringing fast light to the table. You will observe a pleasing “crispness” if successfully mastered with the right gear.

 

More than 10 years ago I had a lot of issues with Subtronic and Ikelite strobes which had round flash tubes. These were very slow as @Chris Ross pointed out correctly. Occasionally this resulted in an unpleasant movement halo in front of fast moving subjects (a lot of pelagic animals and fast movers such as dolphins and sharks). When I switched to system strobes or other uw strobes that used xenon flash modules (in German: Stabblitzröhren) the problems disappeared. Also my macro shots got crisper.

 

 

[Architeuthis]

9 minutes ago, Adventurer said:

I do not agree Wolfgang. Keep in mind the following. When you try to photo water droplets you will find that your shutter must be set to bulb to archive this.

 

The flash will freeze your foreground. The sharpness of your underwater imaging subject is largely also accounted to bringing fast light to the table. You will observe a pleasing “crispness” if successfully mastered with the right gear.

 

More than 10 years ago I had a lot of issues with Subtronic and Ikelite strobes which had round flash tubes. These were very slow as @Chris Ross pointed out correctly. Occasionally this resulted in an unpleasant movement halo in front of fast moving subjects (a lot of pelagic animals and fast movers such as dolphins and sharks). When I switched to system strobes or other uw strobes that used xenon flash modules (in German: Stabblitzröhren) the problems disappeared. Also my macro shots got crisper.

 

 

 

I cannot follow you, Adventurer: when flash duration (linear tubes) is 1ms to 4ms, you need shutter speeds between 1/1000s and 1/250s and have, more or less (decay of intensity is exponential), the entire light emitted in your photo. Only Sony AIII and compacts are able to do substantially faster sync. With few cameras that are able to sync. at 1/400s (e.g. Sony A1, Oly EM1II or OM-1), you already clip some light from a flash that lasts is longer than 2.5 ms...

 

Even with circular flashtubes that have longer lasting pulses, the action can be frozen to the fastest sync. speed the camera is able to do, at the cost of some light loss. I never heard that such light loss plays a role in macro, as full strobe power is practically never used...

 

I would be interested if you can give the special settings under which you observed these movement artifacts (focal length (I guess this was at WA with quite long exposure times?), shutter speed, aperture, was there ambient light in the play? etc...) - this is very surprising to me...

[Phil Rudin]

While this is all very interesting the question is how will this apply to real world photography.

 

With the Sony A7R V the top flash sync speed is 1/250th. If you add the UWT or Turtle flash triggers you can shoot at much higher sync speeds with a strobe equipped for high speed. I have posted photos taken with the Sony 90mm macro to show sync speeds of 1/4000th and 1/8000th second using the Marelux Apollo III strobe set to HSS.

 

Set to MTL you can shoot as high as 10 FPS with mechanical shutter. Also attaches is a serious shot at six FPS with consistent exposures over all six frames. You can see real world use on the front page of a 5 FPS burst of the model moving. Also with the Marelux Apollo III set in MTL which keeps the exposures consistent over the burst. To do this you need a strobe with very fast recycle times. Flash duration is irrelevant if the strobe does not recycle fast enough to keep up with the frame rate.

 

I have also used the HSS mode in real world photos where ambient light overpowers the scene.

 

With a camera like the A9 III with frame rates up to 120 FPS I don't think flash duration will be very reverent as I think you would burn out the tubes very quickly if you were trying to sync at those speeds.

 

Photo1 1/4000th #2 1/8000th Series at 1/250th. all at ISO 100.

 

 null

[DreiFish]

1. Cameras with faster flash sync speeds are the ones that primarily benefit. Today, the only full-frame systems that fall within that scope are the Sony A9 III (1/16000s?) and Sony A1 (1/400s full frame, 1/500s in APS-C crop).

 

2. Higher sync speed is primarily useful for sunball shots where you want to knock down the ambient light exposure as much as possible using shutter speed rather than ISO & Aperture, so that the flash illumination in proportionally brighter. (If you stop down your aperture for this shots, this also reduces the effective flash illumination.)

 

3. Higher sync speed is not all that important for confined environments with limited ambient light such as caves or inside wrecks. There, even a strobe with 1/100s full output would be fine since you can shoot at lower shutter speeds and 'freeze' action.

 

4. Backscatter (in their video reviews) has published the flash duration for some recent strobes. I have added these numbers to the Strobe Comparison table pinned at the top of this forum:

• Ikelite DS230/232 (round tube flash): 1/107s at GN29; 1/200s at ~GN24; 1/320s at ~GN19 
• Backscatter HF-1 (2x Straight Tube Flash): 1/440s at GN40; 1/900s at GN34
• Sea & Sea YS-D3 (2X Straight Tube Flash): 1/600s at GN32
• Retra Pro Max (round tube flash): 1/600s at GN22

5. You can easily test flash duration at home without any specialized equipment. Simply take shots of a white wall at increasing shutter speeds while keeping ISO and Aperture the same  (you can even do it above the flash sync speed of your camera) and compare exposure to determine at what point the exposure drops (i.e. the shutter is open too little time to capture all the light output). Once your shutter speed exceeds the flash sync speed of your camera, part of the image will be black (exposure blocked by the shutter), but you can compare the exposure in the part of the image that remains lit. 

 

6. High Speed Sync DOES NOT get around flash duration limitations. It only gets you around the flash sync speed limitations of the camera. In HSS mode, the flash fires continuous short durations bursts, to try to illuminate the scene during the shorter period when the shutter is open. In HSS mode, you can think of the strobe acting very similar to a continuous light source like a torch. The shorter the shutter is open, the less strobe light you'll register. So a strobe with a 1/600s flash duration like the Retra, if shot in HSS mode at 1/1200s for example, will basically put out only 1/2 the amount of light that you would get at 1/600s. There's no free lunch here. This also means that HSS doesn't give you any advantage for sunball shots if trying to shoot them at shutterspeeds faster than the strobe's flash duration. 

 

7. I have a Marelux Apollo 3, Inon S-220 and Supe D-Max I plan to test the flash duration for shortly. 

 

8. Flash duration is roughly proportional to power output (in the same strobe). So if flash duration is 1/600s at full power, it should be around 1/1200s at 1/2 power, and so on. 

 

 

 

 

[Adventurer]

27 minutes ago, DreiFish said:

You can easily test flash duration at home without any specialized equipment.

no you cannot.

 

what you described is a test for x-sync speed, not flash duration.

 

you are all mistaking the effect of shutter speed for flash duration.

 

please try to get your head around this another time. I know it’s counter intuitive and may be difficult to sort out.

 

If you have a fast moving subject you can freeze it in your frame with a very fast and strong strobe, even if you expose for 3sec or bulb. There is no need to discuss x-sync speed or new fancy global shutter or HSS for this, it is not the application and irrelevant.

 

 

Edited June 13 by Adventurer

[Adventurer]

31 minutes ago, DreiFish said:

but you can compare the exposure in the part of the image that remains lit. 

Sorry - I must apologize for reading to quick. That part is valid and DreiFish is right. He correctly explains the difference.

 

However the readout speed of your camera sensor must be able to keep up with the strobe, if it’s really fast. 

[DreiFish]

2 hours ago, Adventurer said:

Sorry - I must apologize for reading to quick. That part is valid and DreiFish is right. He correctly explains the difference.

 

However the readout speed of your camera sensor must be able to keep up with the strobe, if it’s really fast. 

I gotta hand it to you Adventurer -- I was about to come back with a somewhat snarky reply that you should try it for yourself before concluding it can't be done 🙂 Very graceful, and definitely no hard feelings. We all read things too quickly sometimes. 

 

But of course I was going to bring proof that the test can be done, so here it is. A series of images taken with the Canon R5C (nominal x-sync speed of 1/250s) in full frame mode at ISO 100, F22 (w/ 15mm fisheye). Ambient light is minimized and flash exposure is from 1 Marelux Apollo 3 shot at full power in Manual (not MTL) mode. Marelux rates this as GN44 (but keep in mind I have the diffuser on and a 1/4 CTO gel, which should drop that to GN32 or even lower) Distance from flash to wall is about a 1.4 meters or 5 feet. 

 

1/50s

 

1/60s

1/80s

1/100s

1/125s

1/160s

1/200s

1/250s

Up until this point, the shutter doesn't block any of the light, and the exposure remains the same.

 

1/320s

 

Here we're starting to see that the shutter is faster than the flash sink speed. But the illumination remains constant in the lit portions of the image. 

 

1/400

 

Here we already see not only a larger portion of the frame blocked by the shutter, but also the illumination of the brightest portion has dropped. Here are the raw histograms for 1/320 and 1/400 side by side. So already we're faster than the flash duration. Based on this, I'd estimate the flash duration for the Marelux Apollo 3s to be somewhere around 1/350s at full power.

 

 

The rest of the series shows what you'd expect -- increased portions of the frame blacked out by the shutter, and decreasing illumination in the portions of the frame still lit.

 

1/500

 

1/640 

 

1/800

 

1/1000

 

1/1250

 

1/1600

 

1/2000

 

And here are the histograms to illustrate the drop-off in flash illumination at higher shutter speeds where exposure is shorter than the flash duration.

 

 

You should be able to use this method to measure flash duration at least up to 1/2000s. I'll shortly test to see the flash duration also at lower powers for the Apollo 3s.

 

Edited June 13 by DreiFish

[DreiFish]

And now for Marelux Apollo 3 flash durations at lower power, Photos taken at 1.4-1.5 meters from the wall.

 

Full Power - Level 12 (Advertised GN 44 -- Estimated GN from measurement, 32) = ~1/350s

 

Half Power - Level 11 (Advertised GN 32 -- Estimated GN from measurement, 22) = ~1/600s

 

 

Level 10 (Advertised GN 27 -- Estimated GN from measurement, 19) = ~1/700s

 

 

Level 12 in MTL mode  (Advertised GN 22 -- Estimated GN from measurement, 19) = ~1/700s

 

 

 

 

[DreiFish]

Same measurement done on the YS-D3 led to the following estimates:

 

GN 32 - 1/500s

GN 22 - 1/600s

GN 16 - 1/800s

GN 11  - 1/1500s 

[Adventurer]

9 hours ago, DreiFish said:

There's no free lunch here. This also means that HSS doesn't give you any advantage for sunball shots if trying to shoot them at shutterspeeds faster than the strobe's flash duration. 

Here is one of your practical applications @Phil Rudin as asked above.

 

Also as previously mentioned faster light gives you crisper (sharper) subjects in photography.

 

I must thank @DreiFish for putting so much work in his answer. He illustrated it very well with his example pictures and I could not have it explained better. 
 

Especially point 6. and 5. in his initial answer are very worthwhile reading. I hope 🙏 less people skip over that too fast 😎😉

 

To me strobe speed ( and I do not mean recycle time with that ) is just as important as strobe power (GN, Ws etc).

[Adventurer]

9 hours ago, DreiFish said:

7. I have a Marelux Apollo 3, Inon S-220 and Supe D-Max I plan to test the flash duration for shortly. 

I can get access to a D-Pro and wonder if that one is also in the fast or slow strobe category. I think you can derive some insights from the D-Max, so I am curious about your readings on that one.

 

Also interested in the Kraken KRS160, if anybody has values for that one.

[Barmaglot]

9 hours ago, DreiFish said:

This also means that HSS doesn't give you any advantage for sunball shots if trying to shoot them at shutterspeeds faster than the strobe's flash duration. 

I don't think you can draw any conclusions about HSS based on the flash duration in normal mode. Because HSS fires a fast series of flickers instead of a single continuous pulse, its actual duration is completely different from regular flash. I haven't done specific testing, but with 1st gen Retra Pro flashes, UWT trigger and a Sony a6300, I got similar results shooting sunballs with HSS, 1/2000s and f/8 as with normal flash, 1/160s and f/22.

[DreiFish]

5 hours ago, Barmaglot said:

I don't think you can draw any conclusions about HSS based on the flash duration in normal mode. Because HSS fires a fast series of flickers instead of a single continuous pulse, its actual duration is completely different from regular flash. I haven't done specific testing, but with 1st gen Retra Pro flashes, UWT trigger and a Sony a6300, I got similar results shooting sunballs with HSS, 1/2000s and f/8 as with normal flash, 1/160s and f/22.

 

You can draw the conclusion that in HSS mode the flash will, at best, put out the same amount of light as it would have in the same time period in non-HSS mode. So, for instance, if you shoot it at 1/250s in normal and HSS mode, the HSS mode will at best produce equivalent elimination, but, most likely, actually less.

 

With a perfect HSS implementation, if you go to a speed that's twice as fast as the flash duration, you'll get 1/2 the full illumination. But that's the best you can get. In practice, you'll probably get less than half because the zenon flash is less efficient firing a series of short bursts than one long burst during the same time period.  (assumption, but it seems logical to me-- happy to be corrected. Do zenon flashes actually put out proportionally more of their light output in the initial portion of a flash than the second half of the flash duration? This is a questions of physics that I don't know the answer to).

 

I'm not sure the example you gave can be used to conclude much of anything, especially since you've added the "similar" qualifier.

 

F8 is 3 stops brighter than F22

1/2000s is  3 and 2/3 stops darker than 1/160s. 

 

So probably you actually got about 2/3 to one stop less flash light on your subject in HSS mode than you did shooting 1/160s F8, but also 2/3 stops less ambient light. It's a wash -- and you would expect the results to look different. But they're not 'better' -- you don't actually create any greater difference in comparative illumination between the foreground subject and the background.

 

If HSS allowed you to perfectly capture the full output of the flash over a shorter duration, then shooting at F8, 1/250s should put the exact same amount of light on the foreground subject as shooting at F22, 1/2000s. And allow te exact same amount of background ambient light to fall on the sensor. It would be a wash from an illumination perspective. (Though, granted, you'd get better resolution because of the wider aperture and more ability to freeze motion because of the faster shutter speed. So perhaps you'd got a sharper image without diffraction effects and motion blur. But the illumination would stay the same.)

[DreiFish]

On 6/14/2024 at 2:06 AM, Adventurer said:

I can get access to a D-Pro and wonder if that one is also in the fast or slow strobe category. I think you can derive some insights from the D-Max, so I am curious about your readings on that one.

 

Also interested in the Kraken KRS160, if anybody has values for that one.

 

I mis-spoke -- I have the D-Pro (newer), not the older D-Max. I started testing it, but only got half-way because of some issues with my flash trigger (waiting on a replacement). Anyway, I can share a few details:

 

1. Flash duration at full power is 1/300s. So.. not fast, but adequate.

2. Color temperature unmodified is 6400k

3. Guide number (in air) is GN20.

4. Beam is nice, wide, without hotspots (as you would expect from a circular flash tube strobe). Here's a photo, and next two are the YS-D3 (dome diffuser, also GN20) and Marelux Apollo 3 (no diffuser, GN29)

 

Edited June 15 by DreiFish