Relative Flash Power (Canon 430EX and 580 EXII)

[cfusionpm]

So I've had a 430 EX for a while and recently got a 580EXII. Is there a quick reference to relative power between the two? I know the 580 is more powerful, but by how much? Like 1/4 power on the 430 equates to what power on the 580? I've flipped through the manuals and didn't see any ratings regarding power; only distance. It would be nice to have a little reference chart or something I could memorize to avoid a lot of trial and error when using them for key/fill.

Thanks!

 

[Lodd]

For fill light i'd suggest TTL mode -0,7 stops.
Why using it manually when you have an advanced meteringsystem in both your camera and flash?

I don't know if Canon has anything like the Nikon CLS but if they do. Trial and error shouldn't take more then a few seconds

 

[Derrel]

I have absolutely NO IDEA why Bob Atkins wrote this article with the GNs listed in meters...

from Guide to Canon EOS Speedlite System - Page 2 - photo.net

• 430 EX-II Guide Numbers, ISO 100, in Meters
• 24mm GN=23
• 28mm GN=26
• 35mm GN=32
• 50mm GN=35;
• 70mm GN=38
• 105mm GN=43


580 EX-II Guide Numbers
• 14mm GN=15
• 24mm GN=28
• 28mm GN=30
• 50mm GN=42
• 70mm GN=50
• 80mm GN=53
• 105mm GN=58

 

[Big Mike]

More to the point of what Derrell has laid out. The max Guide Number of the 580EX is 58 meters. The max Guide Number of the 430EX is 43 Meters. Go figure

I've flipped through the manuals and didn't see any ratings regarding power; only distance. It would be nice to have a little reference chart or something I could memorize to avoid a lot of trial and error when using them for key/fill.

Guide Numbers (GN) is given as a distance, but it's a rating on the light output of a flash unit.

The way to use GN, is to divide the GN by the distance, to get the aperture you would need to use.
So as an example, if your subject is 5 meters away, the 580EX (at 105mm zoom and ISO 100 and full power) you would divide 58 by 5, which is 11.6. So you would use an aperture around F11 to F13.
Same scenario for the 430EX, and you get 8.6, so an aperture close to F8.

That's roughly about one stop difference, so twice as powerful.