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I'm looking at flashes, specifically the Canon 430EX II and 580EX II. Unfortunately, it's kinda tough to wade through all of the specs and make any sense out of them. I'm not sure what specs matter, and what don't. The only specific question I have is, what determines the maximum/minimum shutter speed that you can use with a flash, and what spec tells you that?

Really, I need a primer on flash specifications, and Google has been no help. What is 'guide number' and how do you calculate it? What is 'auto f/stops'? What are your experiences with Speedlights? Hmm...

Guide number is a measure of how powerful the flash is. It's nominally the distance (in feet) that the flash can illuminate a narrow field of view to an acceptable exposure at certain conditions. The 580EX II has a guide number of 191, while the 430EX II has a guide number of 141. Both of these flashes have excellent features when used with a Canon EOS camera. Either one would be an excellent addition to your kit. They fully support ETTL2, so metering is automatic. These flashes' settings can be set from the EOS camera's menus rather than using the buttons and displays on the back of the flashes. They automatically zoom to match the focal length of the lens as you zoom in and out. They have tilting heads so the light can be bounced off of the ceiling or a wall for diffuse lighting rather than a harsh direct flash.

Maximum sync speed for standard flashing with the EOS Digital Rebel line is 1/200th of a second. The EOS xxD line goes up to 1/250th. However, either the 580EX II or the 430EX II will support high speed sync mode, which will let you get correct flash exposure at up to the maximum shutter speed of the camera. You'll have to turn on high-speed sync mode from the flashes' controls, and you'll lose some effective flash power, but with high-speed sync mode turned on, you can use as fast a shutter speed as you like with either of these flashes.
http://www.rpphoto.com/howto/view.asp?articleID=1026

I have the 580EX II and use rechargeable AA batteries. Other than being quite heavy, it works extremely well and is very easy to use.

Cool. I've been thinking of a wireless flash setup for my GF1 (since I hate direct flash). Yeah, it's annoying how X-sync speeds are so limited (my GF1 is limited to 1/160), I guess photographers had to live with that (or less, say, 1/100) for 40 years or more. A good FP-flash would make 1/2000 photography a cinch. Although the strobing can be annoying for some.

Bit the bullet and bought an external flash for my GF1 today.

The DMW-FL360. It's the smallest flash Panny has that supports FP-Sync, Rotatable and bouncable head, and wideangle flip cover. The maximum guide number is only 36, but I'm looking mainly to use this as a bounce and fill flash, so I'll generally be working relatively close up.

PS I should point out that flash model numbers usually correspond to their guide numbers (in metres). So the Canon 580EX's guide number is 58m (191 ft). My FL360 has a guide number of 36m, as does the Oly F36R. Easy!

Interesting. So since I just picked up a 380ex as part of an old Rebel 2000 film camera kit, that corresponds to 38m (125ft)?

ludi wrote:

Interesting. So since I just picked up a 380ex as part of an old Rebel 2000 film camera kit, that corresponds to 38m (125ft)?

Yes, the 380EX has a guide number of 38 (m) with a 105mm lens on a film (135) body.

http://photonotes.org/cgi-bin/flash-specs.pl?flashType=canon380ex

Excellent. I see by the specs listed on that page, my flash is actually spreading too much light for a half-frame body. No big deal considering what I paid for the bundle, and I got some pretty good results using ceiling diffusion at a baby b-day party Saturday.

You could always manually pick the closest equivalent focal length, but it is usually better to err with a wider flash angle than one that's too narrow.

Should also point out to anyone reading this that Nikon bucks the nomenclature trend - the SB600 for example, does not have a 60m guide number .