Does 2400ws strobe produce the same light as one 4800 strobe?

[10990877]

Do two 2400ws strobes (using one head for each generator at full aiming at the same subject) produce the same amount of light created by one 4800ws strobe (say Speedotron) or the equivalent of the light produced by 3600ws strobe? 

I need a lot of light for the wet plate photo shoot.

Sorry if this question has been asked before.

Thanks in advance.

[AJG]

Other things being equal (reflector efficiency, length of cable from the power supply to the flash head, etc.) the 4800 should be the same as two 2400 power supplies.  But if you're comparing a power supply with a 45 degree reflector to the same power supply with a soft box or umbrella on the same light head, the light output will be lower with the softer source. 

[10990877]

@AJG

Thank you very much for your answer. Yes. now it is clear.

I've been thinking the answer is obvious but I started to think whether there might be a hidden issue when my light meter started working properly.  

[rodeo_joe1]

It's going to be close, but not necessarily give the identical amount of light. 

Flash energy (Watt-seconds or Joules) tells you the amount of potential energy contained in the capacitors that supply the flash tube. Not all of that energy gets transferred to the tube(s). There's always a cutoff voltage that can't sustain the flash discharge any longer - maybe 50 volts or thereabouts. Meaning that a fraction of the stated energy stays in the capacitors. This retained energy may be greater with a higher-rated and larger flash tube.

Then there's the efficiency of the reflectors and the tubes, and the flash duration(s) relative to the shutter speed used. Lower energy flashes will generally have a shorter flash duration to, say, t0.1 light output. Therefore the effective exposure might be greater for two lower energy flashes than for one flash with twice the rating; depending on the shutter-speed chosen. 

In short: It's not an exact linear relationship, with quite a few unknown variables that can make a noticeable difference. The only real test is to try it and see. 

[laurencecochrane]

On 11/5/2022 at 2:53 PM, rodeo_joe1 said:

It's going to be close, but not necessarily give the identical amount of light. 

Flash energy (Watt-seconds or Joules) tells you the amount of potential energy contained in the capacitors that supply the flash tube. Not all of that energy gets transferred to the tube(s). There's always a cutoff voltage that can't sustain the flash discharge any longer - maybe 50 volts or thereabouts. Meaning that a fraction of the stated energy stays in the capacitors. This retained energy may be greater with a higher-rated and larger flash tube.

Then there's the efficiency of the reflectors and the tubes, and the flash duration(s) relative to the shutter speed used. Lower energy flashes will generally have a shorter flash duration to, say, t0.1 light output. Therefore the effective exposure might be greater for two lower energy flashes than for one flash with twice the rating; depending on the shutter-speed chosen. 

In short: It's not an exact linear relationship, with quite a few unknown variables that can make a noticeable difference. The only real test is to try it and see. 

Since when has shutter speed HAD ANY EFFECT ON FLASH EXPOSURE ? Bar limited focal plane shutter sync speed limits. Only aperture has an effect on flash. But every photographer knows this ?

Edited November 7, 2022 by laurencecochrane

[laurencecochrane]

On 11/3/2022 at 12:40 PM, AJG said:

Other things being equal (reflector efficiency, length of cable from the power supply to the flash head, etc.) the 4800 should be the same as two 2400 power supplies.  But if you're comparing a power supply with a 45 degree reflector to the same power supply with a soft box or umbrella on the same light head, the light output will be lower with the softer source. 

Cable length  UNLIKELY but can ONLY effect recharge times not flash output as this is of FIXED CONSISTANT VALUE by the capicitors discharge to the flash head

Edited November 7, 2022 by laurencecochrane

[ellis_vener_photography]

On 11/3/2022 at 6:17 AM, 10990877 said:

Do two 2400ws strobes (using one head for each generator at full aiming at the same subject) produce the same amount of light created by one 4800ws strobe (say Speedotron) or the equivalent of the light produced by 3600ws strobe? 

I need a lot of light for the wet plate photo shoot.

Sorry if this question has been asked before.

Thanks in advance.

The best way to do this whether you have a single 4800 watt-second pack or two 2400 watt-second packs, is to use a bi-tube, or if using Speedotron Blackline , a quad-tube head. 

[rodeo_joe1]

On 11/7/2022 at 11:36 AM, laurencecochrane said:

Since when has shutter speed HAD ANY EFFECT ON FLASH EXPOSURE ? Bar limited focal plane shutter sync speed limits. Only aperture has an effect on flash. But every photographer knows this ?

Since forever. The t0.1 duration of a flash can vary anywhere from about 4milliseconds to 10ms or longer. With higher energy (=bigger storage capacitor) flashes having a longer discharge time. 

If you only ever use a 125th s (8 millisecond) focal-plane shutter and pissy little speedlights, then it's largely irrelevant, but using a leaf-shutter at 1/500th s and with several hundred Watt-seconds of studio strobe is different. 

That leaf shutter is only open for a nominal 2 milliseconds, and even a small hotshoe speedlight has a t0.1 duration longer than that. With a powerful studio strobe, that 2ms shutter might leave nearly half of the flash energy unharvested. 

Here's the time-intensity trace of a moderately powerful flash:

A 2 millisecond shutter time gets you precisely half of the available exposure. 

"Every photographer knows this?" 

Yeah. Like 'every photographer' knows that an electronic flash only lasts for 1/1000th of a second, and that you can increase film speed 2 or more stops by just giving a longer development time? 

A popularly-held fallacy is still untrue, no matter how many people buy into it.

Oh, and BTW, all cables have electrical resistance, which is proportional to their length. More resistance = more power loss. I'm talking about the cables from the power-pack to the flash head. Not mains cables, because I don't think you can get a 2400 Joule monolight.

Edited December 23, 2022 by rodeo_joe1

[rodeo_joe1]

Just to show it's not all theory, and can even affect modern focal-plane shutters; I did a series of shots from the highest X sync speed of my D700 (1/320th sec) down to 1/60th.

The Metz 60CT-4 flash was at full power for all shots, and the ambient room light was low enough not to register an image on its own. I chose the aperture to give an acceptable exposure at 1/60th second shutter speed, and all that was altered between shots was the shutter speed. 

As you can see, there's a slight drop in exposure even at 1/125th, while the shots at 1/250th and 1/320th are well under-exposed.  

This completely aligns with the flash duration trace above. Where a 3ms exposure only captures about 65% of the total light that the flash puts out.

I suspect that the flash duration of a high-power studio strobe would be even longer than that of the Metz 60CT-4.

[mark_schafer1]

Also consider that different flash manufactures use the nominal power differently. Check the published f-stop readings on the respective spec sheet, it’s not all linear, or logical. I find the Profoto pro heads extremely efficient… Then do some testing yourself…