12 February 2009

Wireless flash tip with ST-E2

Wireless flash can be quite a confusing thing. Most people seemingly don't understand how to use one flash properly, let alone two, three or more. But, once mastered, flash opens up creative possibilities the like of which you've never seen before. For proof, just hop over to Strobist and see for yourself. 

Now, there are several ways of controlling wireless flashguns in the Canon system. My personal favourite and the most versatile is to have a Speedlite 580EX II on camera and use it as a non-firing Master controller. But that is an expensive option. Cheaper, and almost as versatile is the ST-E2 Speedlite transmitter. It doesn't have the same range as a Speedlite, but it is discrete and offers most functions you're likely to need in general shooting. It even acts as an AF Assist beam in low light - great if you're a gig photographer working in low light.

One issue with the ST-E2 though is that it doesn't control three groups of flashguns (
A, B and C) only two (A and B).... or does it? Well yes and no. There are two ways of looking at it:

Guide Number / Aperture = Range
Manual flash powers is one. The box to the right shows the basic calculation for flash powers. Simply take the guide number of your flashgun (580EX = 58, 430EX = 43, 220EX 
= 22 etc) and divide it by the aperture setting you want to use. This gives you the range your flash needs to be from the subject. You can then change the flash power manually to alter the guide number. This works because once you set a flash power manually in slave mode, it drops out of being in any group and then just waits for a trigger signal. So if this is method one, what's method 2?

Well, method two has some level of automation. If you use ratio control on the ST-E2, there is no triggering of a Group C flashgun. Try as you might, it won't happen. So what do you do? Take the ratio control off groups A and B and then you can use flash exposure compensation to brighten or darken a group C flashgun that will now fire. So there is now automatic flash exposure control from group A and B (with no ratio control) and also for Group C with Flash exposure lock. Cunning hey?!

Hit the comments with your thoughts....



Chris Shepherd said...

"This gives you the range your flash needs to be from the subject."

in what? meters? feet? cubits? Yorkshire teacakes?

blabpictures said...

No, it's Eccles cakes actually :-)

In meters. Guide Numbers are calculated in Meters so the unit carry through. If you look on the back of the Speedlite 580EX II (or 580EX, 550EX) you'll see a range scale that measures in Meters. The 430EX and 430EX II show a figure in Meters.

Flash CFn 0 allows this to be switched to feet when set to option 1.

Unknown said...

I am just realizing that I may actually be able to control 3 430EX II flashes with this method.

My interest is for portraits in a home DIY studio ..

1 x celling bounce flash
1 x umbrella flash
1 x white background 'blow out' flash?

Perhaps I dont need a third flash? (I am a newbie) Or even a third flash in a C group?

I may be better off with two flashes in group A and one flash in group B... ?

I dunno.. it will be fun experimenting.

Any opinions? Tips been there> Done that?

One thing I lack confirmation on is - will the ST-E2 on my Powershot G11 really assist the focus in low light with no flash involved...? Or does it just operate in conjunction with flash gun use.. (I had some conflicting info from a Canon employee on this.. first yes, then no)