Archived posting to the Leica Users Group, 2001/09/18

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Subject: Re: [Leica] Filter Factors
From: "thomas schofield" <tdschofield@msn.com>
Date: Tue, 18 Sep 2001 13:51:44 -0700

The filter factor also changes throughout the day, depending on the 
temperature of the light.  Some guides to filter factors list them as 
noontime and sunrise/set factors.  Same is true for tungsten, etc.  A yellow 
or orange filter has a lower factor near sunset.  They also vary with type 
of film - panchromatic v. orthochromatic film.  The Zone VI meter is 
calibrated to respond to light similarly to panchromatic film, so they claim 
that it responds properly when reading through filters.  Although I have not 
tried it, they claim that you can use it to measure how much effect you are 
having through the filter, for example, on reducing the value of the sky 
with your yellow filter.

But as Jim said, if you meter TTL, you do not have to worry about this 
stuff.

Tom Schofield


>Shel Belinkoff wrote:
> >
> > Everything I've read, including the information sheet packed
> > with my new filters, indicates that the filter factor for a Medium
> > Yellow filter (Y2) is 2X, or 1 stop.  So, while checking my gear
> > this morning I decided to check the needed exposure compensation using
> > two Pentax spotmeters, the digital Zone VI modified meter and the
> > standard, but calibrated, Spotmeter V.  Both showed that the needed
> > exposure compensation would be about 1/3 stop more with the filter
> > than without.  I metered off a white truck, the overcast sky, and a
> > building. Always about 1/3 stop. Off some other colors there was a
> > slight
> > difference in the readings between the Zone VI meter and the standard
> > meter, which is to be expected, but in no circumstance did either of
> > the meters indicate the need for an additional full stop with the Y2
> > filter.
> >
> > I suspect this discrepancy may be due to the sky being overcast and
> > there being less blue light for the filter to absorb.
> >
> > Since I'll be doing some work with hand-held meters and manual
> > cameras, can we discuss this situation a bit.  One thought that
> > crossed my mind was to make the exposure readings off a grey card,
> > which I'll try later when I'm outside and away from the computer.  Any
> > thoughts on that idea.
> > --
> > Shel Belinkoff
> > mailto:belinkoff@earthlink.net
> > --
> > To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html
>
>Instead of pointing it at the sky, Shel, try pointing at a grey wall so the
>color of the object you are metering is not an effect.
>An extreme example is if you meter green foliage or green anything though a 
>red filter.
>Well the red aborbs all the green so you'd be over exposing like a sun of a 
>gun.
>You've got to meter off a neutral non color Get the filter factor I'd 
>think.
>
>
>Mark Rabiner
>
>Portland, Oregon
>USA
>
>http://www.rabiner.cncoffice.com/
>--
>To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html


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