How does 580EX II light output compare to Alien Bees or others?

[Shenanigans]

I'm just trying to visualize the difference in light output of a 580EX II and an Alien Bees 1600-series light or the new AB Max 640.

The speedlights are "rated" with guide numbers, and the studio lights with watt-seconds and effective watt-seconds, but I can't seem to find a conversion formula that would allow me to figure out the relative power of these two very different types of lights.

Any ideas?

[Curtis N]

When I fired the 580EX II and the B1600 into the same umbrella, I got 4 stops less light from the 580EX II. So that would put it at about 40 wattseconds for practical purposes.

In other words, it would take about sixteen 580EX II's to equal the output of one B1600.

[Wilt]

Some time ago on POTN, this flash test was published
http://photography-on-the.net/forum/showpost.php?p=5109312&postcount=1


In taking measurements for these tests, I participated and measured for several of the flash units tested. The conditions of the test were for ISO 200, 6' away from light, measured with incident flash meters. (Consistent groundrules for the tests in all cases)...

Metz 45CT4 (fixed 35mm coverage angle):
Full = f/22.0
1/2 = f/16.3
1/4 =f/11.3

Metz 54MZ at 50mm lens coverage angle
(Canon 580EX should have just a bit more power than a Metz 54, judging by the GN58 vs. GN54 (meters))

Full = f/16.6
1/2 = f/11 +0.7
1/4 = f/8 +0.7
1/8 = f/5.6 +0.8

According to the tests, if we had measured an AB1600, it would have measured f/32 +0.4 at ISO 200 and 6' distance to meter

Two f/stops more light would mean 4x the unit count of the Metz 54 (or Canon 580) to equal the AB1600 (f/32 + 0.4). I can't explain the difference in outcome vs what Curtis measured. Factor of 4 outcome difference (ours 4:1, Curtis 16:1. Some of the difference might be factored by Curtis' test were indirect (fired into an umbrella), Roberts and my tests were direct.

[apersson850]

At the 35 mm coverage angle, the Canon 580 EX II has a guide number of 36, not 58. At 50 mm coverage it's 42.

The high guide number of 58 for the 580 EX II is valid only when zoomed to 105 mm coverage angle. When firing into an umbrella that's of no interest, since the concentration of light doesn't make any difference.

[Wilt]

From Anders GN42 rating, this brings up an interesting point -- which echoes that guide numbers are optimistically stated...

Metz 45CT has GN45 in meters or GN149 in feet. That is for ISO 100. According to that, the 6' distance reading should be about 1/3 of the way between f/22 and f/32. Converted to ISO 200, it should be 1/3EV or so between f/32 and f/45. Instead, we measure f/22, or less power than the stated GN by -1.3 EV.

And Metz is not alone in the optimism!

[Curtis N]

I can't explain the difference in outcome vs what Curtis measured. Factor of 4 outcome difference (ours 4:1, Curtis 16:1. Some of the difference might be factored by Curtis' test were indirect (fired into an umbrella), Roberts and my tests were direct.I don't think any comparison is worth much unless the same modifier is used. When people ask about the power of a hotshoe flash vs. a studio strobe, they usually aren't contemplating using either one directly. Even if the specification for coverage angle is the same, you can't compare the circular coverage of a strobe + reflector vs. the rectangular coverage of a flash unit.

That doesn't mean my test is universally definitive, either. You could get somewhat different results with a softbox or diffusion screen, perhaps. My test did not account for the light lost past the edges of the umbrella.

[Wilt]

I don't think any comparison is worth much unless the same modifier is used. When people ask about the power of a hotshoe flash vs. a studio strobe, they usually aren't contemplating using either one directly. Even if the specification for coverage angle is the same, you can't compare the circular coverage of a strobe + reflector vs. the rectangular coverage of a flash unit.

That doesn't mean my test is universally definitive, either. You could get somewhat different results with a softbox or diffusion screen, perhaps. My test did not account for the light lost past the edges of the umbrella.

Agree. That is the dilemma of any comparison of lighting units...equalizing all the variables. It is hard to find a softbox that all flash units have a means of being fitted to, for example. While a speed ring adapts most studio lights, not all have speed rings; same could be said of speedlights, too. I guess the umbrella might be an equalizer, but we don't all own the same brand and model of umbrella either, to be able to conduct decentralized testing.

[apersson850]

I think I read somewhere that the guide numbers for electronic flash guns are calculated with the assumption that you are shooting in an environment where you have a white ceiling and white walls not too high/far away. They does of course help the flash, as some of the light that hits these walls/ceiling bounces back onto the main subject again.

So if you go outdoors, the effective guide number is lower than the rating says.

[Wilt]

I think I read somewhere that the guide numbers for electronic flash guns are calculated with the assumption that you are shooting in an environment where you have a white ceiling and white walls not too high/far away. They does of course help the flash, as some of the light that hits these walls/ceiling bounces back onto the main subject again.

So if you go outdoors, the effective guide number is lower than the rating says.

I've read the same thing about assumption of ceiling and walls.

[bobbyz]

Did some quick tests with my AB400 and 550ex (don't have 580exII).

Both shot into a bounce umbrella. Measurements taken at 10 feet away with L358. Both 550ex and AB400 at full power. Gave enough time in between shots. ISO100.

550ex at 24/28mm zoom setting, got f4.0 at 10 feet.
AB400, got f4.5.

With 550ex pointed stright on me, no umbrella, at 10 feet got f8.0 at 24/28mm zoom.
With AB400 pointed at me, 10 feet, got f8.0.

With 550ex zoom increased to 50mm, I got f11 at 10 feet.

Seems to me 550ex is almost same power as my AB400.

[Curtis N]

Bobby,

The B400 is most definitely more powerful than a 550EX, though if you measure direct light, the reflector and fresnel lens of the flash unit will concentrate the light into a narrower beam (even at a wide zoom setting).

Your results with the umbrella are puzzling. Were you using the standard reflector on the B400?

[Mike Fulton]

When I fired the 580EX II and the B1600 into the same umbrella, I got 4 stops less light from the 580EX II. So that would put it at about 40 wattseconds for practical purposes.

In other words, it would take about sixteen 580EX II's to equal the output of one B1600.
I love your tech-ie talk Curtis! Seriously I do - your passion for light inspires me!

Thanks for all you do on this forum, it is truly inspiring to me!

[bobbyz]

Bobby,

The B400 is most definitely more powerful than a 550EX, though if you measure direct light, the reflector and fresnel lens of the flash unit will concentrate the light into a narrower beam (even at a wide zoom setting).

Your results with the umbrella are puzzling. Were you using the standard reflector on the B400?

Curtis, I need to double check. I do have one new refelctor which has that sanded look compared to shiny ones.

I am going to try these tests in a medium SB as well as a shoot through umbrellla. That should cover most of typical shooting conditions.

[rudy_216]

Roughly based on the wattsecond power of the two the AB400 should be twice as powerful as the 580EX. That is based on electrical power only and it is aproximate. Then you have to take into acount the output of each flash bulb.