From: jay@metran.UUCP (Jay Ts)
Newsgroups: rec.photo
Subject: Re: 80A 80B 80C Which filter?
Date: 31 Dec 92 03:14:33 GMT
Organization: Metran Technology, Tampa, Florida

pjs@gvgdsd.GVG.TEK.COM (Peter J. Stonard) writes:
: I have a couple of questions about colour balance.
: 
: Given that I am using common daylight balanced C41 print film,
: and wish to take pictures using available electric light,
: which blue filter should I use?

If you were using slide film, I would say just forget it, unless you
want to spend upwards of $700 on a color meter (which still will not
work well with streetlights) and hundreds, if not thousands, of dollars
on color correction filters.

You can keep reading to get some idea of why.

: I assume the number 80
: filter has A,B,C variations to cater for the various color 
: temperatures of different artifical light sources.

The 80[ABC] filters are for converting specific color temperatures
to daylight (5500K).  The 80A is for 3200K tungsten lights, and the
others are for lights that are even bluer.  Note that 3200K is probably 
already bluer than anything that you you are now using as roomlights.
In other words, if your incandescent bulbs are of the common household
variety, none of these filters are going to get you to daylight.

: The electric lights are a variety of incadescent bulbs and
: discharge lights seem in the street.

Streetlights are entirely different.  They do not emit a continuous spectrum,
and do not produce "black body" radiation, as incandescents do.  To correct
for them, you need color correction filters, and a method of determining
what values to use.  The film manufacturer may have data sheets on that,
or you can use a color meter (which may not work well), and then you will
have to experiment to get the optimal values.

Now, if you want to *mix* incandescents with streetlights, you've got a
real problem!  Because the correction filtration that works with one will
NOT work with the other.  You can correct for one lightsource or the other,
or sort of average, but you will still get funny colors, because different
parts of the scene will be more, or less, lit by each light source.

Give up yet?  No?  Well, it might be possible to filter the incandescent
lights to approximate streetlights, and then filter at the camera for that.

: As I may have daylight pictures on the same roll I would like
: to stick with standard processing and printing, and use the filter(s)
: when needed. I realise that if all exposures were under the same 
: lighting conditions the printer could correct for the 
: yellowish light.
: 
: What if I want to combine a long exposure with artifical light,
: using the blue filter, and add a flash for freezing motion or
: lighting the subject? Is there a yellow gel that compliments the 
: blue filter, that can be placed over the flash?

Try this:  with whatever lighting you have, photograph a grey card (such
as Kodak Gray Card) and then photograph your subject in the same light.
When having the negatives printed, tell the printer to filter for the
grey card in that frame, and use that filter pack for the rest of the
frames.  Since you have the advantage of being able to correct at the
printmaking stage, you might as well use it!

If your local mall 1 hr. lab cannot handle this, then I suggest you take
your work to a professional color lab.  Get a contact sheet made, and then
only have the frames you really like enlarged.  It may be more expensive
than the 1 hr lab, but it's A LOT less than the color meter and correction
filters!
-- 
Jay Ts
uucp mail: uunet!myrddin!tscs!metran!jay
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Newsgroups: rec.photo