At 08:47 02/02/99 -0600, you wrote:
>>>>That red barn will be out by 2 stops if you read it, the blue sky will be
>>out by at least a stop, and the wheat field will also be inaccurately
>>exposed. >>
>
>what color are the CDS cells accurate with? Huh? Blue is out 1-stop...
>red is out 2 stops (which way?) yellow? green? Aha! Cartruse!
It's likely that a spotmeter would use silicon blue cells, which have a
similar response to the human eye. CdS cells tend to be more sensitive at
the red end, which is why TTL meters based on CdS cells tend to underexpose
b/w film through red and orange filters - exacerbated by the film's
*decreased* sensitivity at the red end. They're also too slow to work
usefully in a spotmeter.
I guess Zone VI's mods to the Pentax spotmeter are intended to match b/w
film's curve better than an unfiltered Si cell would. Having said that, my
Si-celled OMs *also* underexpose through a red filter, though not by two
stops. I always meter without the filter, and add the filter factor.
Richard
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