On Wed, 11 Dec 2002 13:02:42 +0100, "Xm@n" wrote:

>> Exposure is an art using a science. Try both and see which works for
>> you. Of course if you are using TTL metering you don't really care.
>
>Not so sure about that. For a B&W filters I have found that usually need
>+0.3 or some +0.9 EV.
>The best way is to sacrifice 1 roll of film and do some testing without
>filters, with filters and different situations.
>Two important things for testing is: keep notes and tell the lab to develop
>the prints WITHOUT correction.

Even easier, without the need to use film:
- meter a large, neutral-colored smooth-toned
area (a sidewalk or street works well...)
at a particular angle without the filter on,
noting the EXACT exposure needed.
- put the filter on, and meter again, in the same
light, noting the EXACT exposure needed.
- compare the second reading with the reading
predicted by applying the marked filter factor
(2=1stop, 4=2stops, 8=3stops - guess the
"inbetweeners"...) - the difference is the
correction value that must be applied to the
metering when using that fiilter (it can be set
on the meter by adjusting the compensation, or
by adjusting the film-speed rating - but remember
to remove the compensation when removing the
filter...!).
BTW, on Nikons, I find that exposure must be
increased by 1/2 the filter factor for all colored
filters, i.e., 1/2 stop for weak colors, 1 stop
for orange, 1.5 stops for red...