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Re: [OM] metering through filters

Subject: Re: [OM] metering through filters
From: John Pendley <jpendley@xxxxxxxxxxxxx>
Date: Sat, 05 Feb 2000 16:01:22 -0500
Hello, Joseph and Everyone,
This reminds me of two questions I'd appreciate some informed oppinions on.
I grew up being told that keeping a UV or skylight filter on a lens, for
protection of the front element, is a bad idea.  The argument went something
like this.  "Why spend hundreds of dollars on precision glass and then put a
cheap piece of $*&# in front of it?  Beside, it adds another glass-to-air
interface."  What do you all think about the question?
On a related note (this is all "related" to the original topic), if I don't
feel like springing for Schneider or B+W filters, what's good? Tiffen?
Hoya?  Or should I just bite the bullet and go for the German glass?  I
guess it could be worse since I rarely use anything but a polarizer (unless
I keep a UV on all lenses).  That could mount up.
Thanks,
John

Joseph wrote:

> ==========================
> >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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