In article <32F0A5AE.1AF@dl.ac.uk>, h.owen@dl.ac.uk says...

>Can anyone with technical knowledge of meters answer this query?:
>I'm using B/W film in a Nikon F70/N70, and would like to know how
>TTL metering is affected when using strong filtration. What I mean is,
>if I use an orange, red or deep red filter, how many stops will the TTL
>exposure value be out by, compared with that required to give correct
>exposure on B/W film? I assume the difference would be caused by the
>difference in spectral sensitivity between the film and the meter. Is
>this correct? I'm using ordinary panchromatic film (FP4 etc.).
>Also, how would this change when using Infrared film, or with other
>types of TTL meter (i.e. is there a difference between manufacturers)?

I used to find laughable the old advertising about TTL metering that
indicated that it automatically corrected for filter density/color.
It doesn't. I have not checked the N70 meter, but all Nikon meters
I have tried require the following filter compensations: deep yellow,
+ .5 stop; orange, + 1 stop; red, + 1.5 stops. Green and light yellow
filters also require some compensation. To check for the needed meter
color compensation, read a broad, evenly-lit grey surface without the
filter - then put the filter on, reset the aperture to allow for the
filter factor (one stop for deep yellow, two for orange, three for
red - generally), and reset the ASA until the meter centers while
reading the same grey subject in the same light. The difference between
the original ASA set, and the new one required to center the meter, is
the compensation required when using that camera and filter. BTW, this
has an application in color work, also, since pure colors occupying
most of the frame will also cause mis-readings for both the ambient-light
meter AND the TTL flash meter...
IR is a very different story, and needs experimentation to find a
reasonably useable ASA setting for your camera, film, and filter.
Hope This Helps