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[OM] metering through filters

Subject: [OM] metering through filters
From: Joseph <joseph@xxxxxxxxxxx>
Date: Thu, 3 Feb 2000 13:26:42 -0800 (PST)
==========================
>moreover, spotmetering through a filter is rife with potential
>for errors anyway, which is why i don't try to spotmeter through 
filters.

uh, how's this different than metering with filters on your camera? 
==========================

It isn't, other than bellows factor being taken into account.
but spotmetering through filters is rife with potential for
metering errors.

Quite simply.  Meters are sensitive to infrared light, and normal color
film is not.  when you use an averaging meter that meters are large
area, the IR light is a small part of the total and does not contribute
to metering error.  when you spotmeter, you are metering a tiny area
that will have a uniform color.  this uniform color absorbs all the
colored light but its color, and IR becomes a larger percentage
of the total.  this contributes to spotmetering errors even without
a filter, but attach a filter and the problem is exacerbated because
the most filters pass IR light.

I standardize my 35mm lenses on 62mm filters, and have a X->62mm stepper
ringt on every lens I own and use 62mm lens caps.  yes, I could carry
a 46->62mm stepper ring on my spotmeter, but it isn't worth the trouble
given the hazards of spotmetering through filters.  Incidentally,
zone VI sells a modified pentax digital spotmeter designed to meter
through filters.  The only filter I'd want to meter through is a
polarizer, but it is just as easy to use a filter factor for that.

Joseph


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