Message-ID: <3A89008A.ACC26695@bellsouth.net>
From: John De Armond
Newsgroups: rec.crafts.glass
Subject: Re: Light Q below
Date: Tue, 13 Feb 2001 04:38:18 -0500

Mike Firth wrote:

>  It is possible to buy color balanced fluorescent bulbs, just as it is is
> possible to buy color balanced incandescent bulbs.

The problem is, even the best color balanced fluorescent lamp still
emits the strong lines of mercury.  We can't see them (or at least
not notice them) but film does.  It is practically impossible (short
of some sort of narrow band optical interference filter) to
eliminate these lines.  These lines make the results show a
characteristic blue-green cast.  Best to just avoid the problem by
using other light sources.  This tends to NOT be a problem with
(some?) digital cameras.  My kodak digital camera has a white level
setting for fluorescent lamps that eliminates the problem.

Note this
> It is also possible to
> change to color temperature of incandescent bulbs by increasing or
> decreasing the voltage to the bulbs.  If you look at my site and look at the
> pictures I took at the Corning Museum photo lab, you will see what I
> consider a very good picture of a glass, the quality of which is entirely
> due to their lighting.  The bulbs are over driven (higher voltage) to
> increase their color temp.  This is just an addition to the other good
> answers.

Those are nice pictures.  I do the same thing in my studio.  I use
the common 500 watt shop quartz-halogen shop light (modified with
cooling holes) driven with 240 volts as my main illumination
source.  The 2kw of light and heat is very bright and very hot.  I
have dielectric mirrors (available from Edmund Scientific for about
$50 ea.) that pass visible light but reflect infrared to deflect the
heat when necessary.  I made some clamps that hold them in front of
each light.  Note that one cannot just slam 240 volts on these lamps
or the bulb will burn out.  I use a Variac to run the voltage up
gradually.  Bulb life is relatively short at a few tens of hours but
since one can now buy these bulbs by the dozen at Home Depot or what
not, no big issue.

I've put a few pictures on my web page here:

http://personal.bellsouth.net/~johngd/files/glass/

File studio.jpg shows my little setup.  Since most of the
photography I do these days is for Ebay, I've converted my dedicated
studio to a temporary one.  This one can be quickly folded up and
out of the way so the space can be used for other things.  The
backdrop is hung from a couple of shelf hangars with the ends turned
up and a hunk of conduit.  The gray sheet is a photography backdrop
that comes on a roll.  Rolls of cloth can also be hung.  Note the
rounded curve as the backdrop approaches the table.  Properly done,
this technique, known in TV as a "round room", removes the junction
between the wall and floor and makes the photographed object appear
against an infinite background.  This photo was taken with my
digital camera under color balanced fluorescent lamps.  One can see
the limitation of the camera's correction in the shadow behind the
backdrop which took on a blue tinge.  The variac that drives the
lamps can be viewed in the extreme right just to the right of the
"Grainger" box.  This is a 240 volt variac purchases off Ebay and is
plugged into a 240 volt heater outlet.  It is wired with a couple of
120 volt convenience outlets for the shop lights.  Suitably labeled
and painted "warning red" of course!

The small light on the arm is a spot light.  This light is used to
provide shadow suppression and for highlighting.  It is often the
only light used for small objects and when the "halo of light"
effect is desired.  A detail of the light is at mini_cool.jpg.  This
is a pro compact video light.  It uses the integral reflector bulbs
pictured at quartz_light.jpg.  This lamp's reflector is coated with
a dielectric thin film reflector that allows infrared light (heat)
to pass out the back while reflecting practically all the visible
light.  Thus the light is practically cold with very little heat.
The REALLY  neat thing about these lights is that they are available
in this exact form factor in ratings from 20 watts at 12 volts to
360 watts at 120 volts.  The 360 watt lamp is intended for overhead
projector use and is available at Office Depot, etc.  With the 12
volt lamp, one can simply clip wires to the pins and hang the lamp
from a suitable support.  It can be operated from a battery charger
which will supply an over-voltage that will bring the color
temperature up to what film needs.

Another really neat thing about these integral reflector lamps is
that if you want to achieve the effect Mike shows here:
http://users.ticnet.com/mikefirth/c-99glry.htm with the goblet
photos near the bottom of the page, one can simply place some
aluminum foil over the lamp, poke a small hole in the foil and
voila! An instant spot light.

If using film, especially slide film, one still must use tungsten
balanced film or else filter daylight film.  I don't like filtering
because it costs an F stop or two.  As bright as these lights are,
they are relatively dim compared to daylight or to photoflashes.
The type of film matters too, but then that's the topic of a whole
'nuther post :-)

John