Re: Filter/Speed/Meter

["R. C. Lacovara" <lacovara@xxxxxxxxxxx>]

Although I have nothing against using rules of thumb, I mentioned somewhere 
back there that my interest was more in the "photometry" than the photography.

But let me mention one reason that a person might like to use some sort of 
IR meter.

Many of the folks who advise various rules of them also advise bracketing 
from one to two stops on either side of their guess. That's great: as long 
as you are happy to increase your film costs from by a factor of 3 to 5.

And if I were to be cynical, which I am not, ever, I might be tempted to 
observe that if you bracket by two stops on either side of a guess, you 
almost have to get something on the film, unless your guess is almost a 
random choice.

Admittedly, even with a meter in hand one might bracket exposures, and for 
both technical and artistic reasons. But my habit has been more on the 
lines of two exposures (in the visible, with spot or averaging meter). This 
"doubles" the cost of some imaginary ideal exposure system. But it's still 
better than 5 times.

Sensitometry is somewhat dry and of little interest to most photographers. 
Nevertheless, IR film has an effective "ASA" in conjunction with a given 
filter, processing chemistry and regime, and a meter can most certainly be 
made to indicate the exposure needed to get a middle grey on the film. This 
little problem, solved by other folks from time to time, now amuses me. But 
then, I'm a a bit dry myself... ;-)

Regards,

Bob

At 04:08 PM 10/6/00, you wrote:

>Be smart & brave, and forget about light meters altogether.
>Since infrared film, and especially HIE, downright *demands* bright
>sunlight, you only need the Sunny-Sixteen-Rule, with 1/ASA seconds @
>f16.
>With HIE & #87C this translates to 12 ASA, and a typical bracket of
>1/60s @ f5.6 - 8 - 11
>With #25A red you have 50 ASA, and 1/250s @ f5.6 - 8 - 11.
>#89B would be inbetween, 1/125s.
>
>After a while you get a) a much better feel for the film, and more
>importantly b) a much more consistent handling with different
>camera's (switching from all-mechanical manual cameras to electronic
>AF cameras).
>
>All this becomes even more relevant if those SLR-cameras have been
>fitted with a BTFR (between the film rails) filter....that way the
>inboard light meter never sees the IR filter anyway (and it better doesn't
>either with an opaque #87C, as you couldn't see a thing through the
>viewfinder in the first place....;))
>--
>Bye,
>
>Willem-Jan Markerink

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