Comparing the Power Output of an AB400 to a 580 EX II

Can't put my mind around how to do this, with a meter. My question -- just how much more light, if any, does an AB400 produce?

AB400 has f/11 + 0.2EV measured at 10' ISO100, using standard 7" reflector which covers 80 degree...about Guide Number 120.
For apples-to-apples comparison, the speedlight has to have its zoom head set to about 26mm (FF) coverage --which isn't available, you likely only have 24mm (84 deg) or 35mm (63 deg) coverage angle to choose from. Set the zoom head to 24mm (84 degree FF) coverage angle, set the f/stop to f/2 and see what distance is displayed, multiply 2*distance to get Guide Number for the speedlight.

Guide Number AB400/Guide Number speedlight = n

If n = 1.414, AB400 puts out 2x as much light (one f/stop)

At 50mm coverage angle, the 580EX has GN130...roughly the same output intensity. Since I don't own a 580EX, I can't tell you the claimed GN for 24mm...and the speedlight claims are always optimistic compared to what you would actually meter!

Wilt wrote in post #10354080
AB400 has f/11 + 0.2EV measured at 10' ISO100, using standard 7" reflector which covers 80 degree...about Guide Number 120.
For apples-to-apples comparison, the speedlight has to have its zoom head set to about 26mm (FF) coverage --which isn't available, you likely only have 24mm (84 deg) or 35mm (63 deg) coverage angle to choose from. Set the zoom head to 24mm (84 degree FF) coverage angle, set the f/stop to f/2 and see what distance is displayed, multiply 2*distance to get Guide Number for the speedlight.

Guide Number AB400/Guide Number speedlight = n

If n = 1.414, AB400 puts out 2x as much light (one f/stop)

At 50mm coverage angle, the 580EX has GN130...roughly the same output intensity. Since I don't own a 580EX, I can't tell you the claimed GN for 24mm...and the speedlight claims are always optimistic compared to what you would actually meter!

Thank you. So the a b800 would roughly put out a stop and a half more?

Here is the 580EX Gn chart from the manual.
There is a 28mm setting which should closely correspond to Wilt's numbers for an AB400.

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28mm only fills 74 degree AOV, which is why I used 24mm for my suggestion...84 degrees AOV is closer to 80 than 74 is.

Using GN92 vs. GN120, the 580EX would be about -0.9EV less powerful than AB400; and about -1.9EV less powerful than an AB800.

But, again, I have to warn that a typical speedlight flash GN is overstated, compared to what a flash meter would measure!

I actually just did a quick, unscientific, comparison test on this... Here's a blog post with pics / results: http://camaraphotograp​hy.wordpress.com …bees-400-comparison-test/

No light meters... In this day and age, with an LCD, I just can't justify the $ for one...

CamPhotog wrote in post #11894311
No light meters... In this day and age, with an LCD, I just can't justify the $ for one...

The reason for using a light meter...

• More accurate relative light output setting (light A: light B)
  
• Faster exposure determination

CamPhotog wrote in post #11894311
I actually just did a quick, unscientific, comparison test on this... Here's a blog post with pics / results: http://camaraphotograp​hy.wordpress.com …bees-400-comparison-test/

No light meters... In this day and age, with an LCD, I just can't justify the $ for one...

So your 580ex is more powerful than AB400.

Wilt wrote in post #11894392
The reason for using a light meter...

• More accurate relative light output setting (light A: light B)
  
• Faster exposure determination

Less trial and error adjustment, using a meter vs. shooting and chimping.

+1. I never used anything other than a manual camera until digital came along. Heck most cameras I've owned didn't even use a battery! But a light meter is gold and much more accurate than the LCD (when calibrated of course).

mattograph wrote in post #10353721
Can't put my mind around how to do this, with a meter. My question -- just how much more light, if any, does an AB400 produce?

Is the AB400 a 400 ws light? I use Norman ML400 (400ws) monolights and they measure about 2 1/2 stops brighter than my 580 flash (f3.5 vs f8 at same distance and spread - measured with flash meter).

An Alien Bees B400 is 160 Watt seconds.

TMR Design wrote in post #11898230
An Alien Bees B400 is 160 Watt seconds.

OK. That would be about 1 1/2 stops less than my numbers then. (Confusing name - AB B160 would seem better).

CamPhotog wrote in post #11894311
I actually just did a quick, unscientific, comparison test on this... Here's a blog post with pics / results: http://camaraphotograp​hy.wordpress.com …bees-400-comparison-test/

No light meters... In this day and age, with an LCD, I just can't justify the $ for one...

With histograms now on cameras a flash meter isn't really required. When I set up my lighting I always go by the histogram. Usually in 2 or 3 shots I've nailed the settings.

You might nail the lighting to remove the blinkiezzz but, matching the ambient, or up or down from ambient will be hard pressed.

Setting the amount ( shadow level ) of light and where it will fall off on a face will not show on an LCD

Matching the light from one side to the other, will not show up on an LCD

We can all ( well most of us ) do it by guess and sight but, when you star to wonder how they did that or that lighting is crisp and dead on, it will not have been done by an LCD histogram.
-----

With a light meter, checking light output compared to another would have been but a few clicks away.

TopHatMoments wrote in post #11898369
You might nail the lighting to remove the blinkiezzz but, matching the ambient, or up or down from ambient will be hard pressed.

Setting the amount ( shadow level ) of light and where it will fall off on a face will not show on an LCD

Matching the light from one side to the other, will not show up on an LCD

We can all ( well most of us ) do it by guess and sight but, when you star to wonder how they did that or that lighting is crisp and dead on, it will not have been done by an LCD histogram.
-----

With a light meter, checking light output compared to another would have been but a few clicks away.

Not to mention the fact that balancing flash with ambient or between strobes can't be done without a light meter. Sure, you (referring to cristphoto) can guess and use the histogram and chimp on the back of the camera but what do you do if you're working on a series of shots and they're done at different locations at different times of day but the look must be consistent?

How would you possibly achieve the same balance between flash and ambient? Are you really going to chimp on each shot and then look and compare on the computer? If not it's not going to happen. That's the perfect example of a shot that needs to be calculated and done by the numbers.