> Date: Mon, 22 Oct 2001 09:20:49 -0700
> From: "Icoz, Evrim" <[EMAIL PROTECTED]>
> Subject: EOS 550ex vs strobes
> 
> I put my 550ex and 420ex on auction to go to a full manual 
> set up 

As long as you retain one shoe mounted system or a torch like
a Metz 45 just in case, this is a wise decision. You get extra 
versatility, much more power, lightformers at your choice....

> When I read specifications about strobes, like in 
> www.alienbees.com , they quote power is w/s. 

Yes. This is the most practicable way of comparing.

> I am trying to figure out how that compares to guide numbers 

Not at all. The guide number depends on the lightformer very much.
Using a softbox you will have a smaller guide number than with
a parabolic metal reflector. 

Studio flash manufacturers usually state a guide f-stop,
which is metered with a standard reflector in 2 meters
distance, making studio flash somewhat comparable to each 
other. Compact units with say 1000 W/s will typically
render one f-stop more than separate generator/lamphead
setups, because the cable between generator and flash head
loses some power.

> and specifically to 550ex power. 

The 550 EX has a guide number of approx 40 for 35 mm lenses
at 100 ASA. Flash compact units of 250 W/s typically return
calculated guide numbers around 45 with standard reflectors.

You can check for more info on lighting at my DIY lights guide:
http://www.photoquack.de/tutorials/diylights.htm

hth,

-- 
Michael Quack <[EMAIL PROTECTED]>

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