[rollei_list] Re: Rolleiflash and Guide Number
- From: Marc James Small <marcsmall@xxxxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Sun, 29 Nov 2009 20:56:45 -0500
At 07:50 PM 11/29/2009, you wrote:
>Thank you very much Charlie, I used the wrong number to multiply the
>first time, now: 36 (ISO 50) x 1.4 (to ISO 100)= 50.4, in other words
>51 (167 for feet) like the flash manual indicates for ISO 100.
>
>BTW, Charlie does not participate in the list topics very much, but I
>can assure he owns an impressive knowledge and practical experience
>about photographic technical issues, analog and digital, I suspect he
>could only be a great pro photographer.
Contemplate the square root of two, Carlos. All will be made blindingly clear.
We have these discussions all the time on the
Rollei List. I had my hair singed when Ed set me
right around 1995 about the proper relationship
between the European and International f-stop scales.
Carlos, please give us a quick formula for
converting, say, a Guide Number calculated in
feet at an ASA of 25 in 1955 to a current
scale. Bear in mind that the ASA scale shifted
in 1959. This is not a trick question: I am
curious. I do almost no flash work but, when I
do so, I tend to use Guide Numbers even when I
have some sort of more sophisticated system to
suggest an exposure -- and GN's are vital in
doing contre-jour exposures, unless you have a one-degree spotmeter at hand.
But, shucks, I still regard the move from the
154-game season to he 162 games and the addition
of that horrid "designated hitter rule" to have
been the death of US Baseball. It will collapse. Just give it time.
Marc
msmall@xxxxxxxxxxxx
Cha robh bàs fir gun ghràs fir!
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