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 |