I think Jez may have been teasing the other Ian, Ian, but for the record
(and for those who are using reversal film!), you have to take the square
root of the sum of the squares. Your method would underexpose a little.
GN of T20 + T32 is 38 - the root of 400+1024
Piers
-----Original Message-----
From: olympus-owner@xxxxxxxxxx [mailto:olympus-owner@xxxxxxxxxx] On Behalf
Of Ian Manners
Sent: 27 January 2004 14:01
To: olympus@xxxxxxxxxx
Subject: [OM] Re: GN of 2 T32's
Hi Jez
>OK Ian - what's the effective guide number of a T20 plus a T32? :-)
I'm not that Ian but it would be 42, I normally work it out as aprox's, ie
a T32 + T32 = (32/2)+32 = 48
a T32 +T20 = (20/2)+32 = 42
I always divide the lowest powered light source by 2.
This isnt accurate but normally good enough for field work if you are using
negative film 100ASA and up.
Cheers
Ian Manners
http://www.comkal.net/photo/
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