I have a Canon 70D, what is a better flash ... is it Speedlite 320EX or 430EX II?

[Pobox7a]

70D

[Pobox7a]

70D

[Skirball]

The 430exII is a more powerful flash with additional features, so it could be called the “better” flash.  Either flash will work with any of Canon’s digital SLRs including the 70D.

But no, to answer your second question, you can’t use them for movies.  All Canon flashes are strobes, they provide a temporary burst of light for still photography.  For movies you need continuous lighting.

[MikeSowsun]

The Canon 320EX does have an additional continuous LED light for video, but the reviews I have read said it is not very bright and of limited use. 

[ScottyP]

I had a 320 and the continuous LED light was horrible. Any movies you'd shoot would feature friends and family cursing and shielding their eyes in a horrible harsh spotlight. Kind of like the creatures in that Vin Diesel movie Pitch Black.

[Skirball]

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@ScottyP wrote:
I had a 320 and the continuous LED light was horrible. Any movies you'd shoot would feature friends and family cursing and shielding their eyes in a horrible harsh spotlight. Kind of like the creatures in that Vin Diesel movie Pitch Black.

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Lol!

[TCampbell]

Omit the trailing 0 in any Canon speedlite flash model and that's the flash "guide number" when measured in meters. e.g. the 320EX has a guide number of 32. The 430EX II has a guide number of 43.

The "guide number" is the distance that the flash can adequately illuminate a subject assuming (a) ISO 100 and (b) f/1.0 aperture. The ISO is no problem, but the f-stop can be a bit confusion. The industry standard is to use f/1.0 BECAUSE it makes the actual math easy. Just divide the guide number by the f-stop you actually plan to use.

43 meters works out to about 141 feet. Suppose you're shooting at f/5.6, then: 141 ÷ 5.6 = 25 feet. So the flash can illuminate a subject adequate at 25 feet if you use ISO 100 and f/5.6. Of course you can increase this distance by bumping up the ISO... increase the distance by a factor of 1.4x for each stop of ISO you add.

It's nice to have a bit more power because the flash looks better when you bounce it or use lighting modifiers (which tend to eat a bit of the light.)

Incidentally... the Speedlite 430EX II does have a built-in focus-assist beam which allows your camera to focus in extremely dark situations (it's a red LED which projects a pattern that the camera can use to accurately lock focus.)