Lighting the scene? Temp?!
Lighting the scene? Temp?!- special effects and filmmaking
What do you guys mean by colour temperature? (3500K etc?) How does this effect a scene, what temps should I be using? How do I check out the temp? etc?
Daylight and Tungsten are the 2 Color temperatures. Daylight is 5600 Kelvin and Tungsten is 3200 Kelvin. These temperatures can be achieved by how you gel your lamps. Most of the lamps you use in your home are tungsten. HMI's are daylight. Tungsten can be converted to daylight by adding CTB which is blue gel. Daylight can be converted to tungsten by adding CTO which is orange gel.
Well actually every light has a temperture... film is balanced for either daylight, or tungsten.
unless your using real film, most $1000-range DV camcorders have white balance, which in effect compensates for the varying light temperatures.
Suppose you had a light bulb whose filament would never melt, no matter how hot it got, and that would take as much electric current as you cared to put through it. With no current flowing through it the filament is at room temperature and emits no visible light. Now if you start to apply electric current to it, slowly raising the temperature the filament will start to glow. Experience tells us that it will first glow red, but as we raise the temperature the light will slowly turn from red to white.
As we perform this experiment let's pass some of the light through a prism, splitting the light into its various colors, and projecting those colors on a screen. At first the screen is blank. Then as we apply current to the filament we will see red at one end of the spectrum. As increase the current we will see green, then blue and finally violet appear, but they will not be as strong as the red. However, as we continue to apply more and more voltage the other colors grow stronger until the green is as strong as the red, then the blue and finally all the colors are of the same intensity and the filament glows white hot.
Sunlight exhibits the characteristic that all the colors in the visible spectrum are equally intense, provided that the light has not been tainted by passage through the atmosphere. Light from most man made sources is not equally distributed across the visible spectrum but is more intense toward the red end.
So what is color temperature? Well it is not the temperature of your light bulb. When scientists do the above experiment they do not use a filament. They use a hollow block of metal with a hole drilled in it and they measure only the light that comes from inside the block. This is called a "cavity" experiment and color temperature refers to the temperature of the cavity.
Daylight film has its dyes adjusted for a light source of 5500°K. With this light the intensity of all the colors is pretty much equal. Household tungsten filament bulbs have a color temperature of about 2800°K and the red is stronger. Photos taken with daylight film under tungsten light will produce Caucasian skin tone with a decidedly reddish or orange tint. To correct this either use tungsten balanced film (which is less sensitive to red) or use a blue filter to attenuate the red. Or use electronic flash. The color temp of electronic flash is 6000°K, close enough to 5500°K for most people's tastes.
Video cameras have some provision for adjusting the color temperature. Most consumer video cameras (the only kind I have ever owned) do this automatically. More expensive pro cameras may give you more control.
If you are rich enough to afford a color temperature meter and a complete set of filters you can shoot whatever film you want and adjust the color temp to your liking. If you are poor like me just buy an 80A filter and use it when shooting under tungsten. When shooting under fluorescent light use an FL filter. These cost less that $20 each.
Finally, I want to say to those of you out there with Ph.D.s in physics that I realize that I have oversimplified things a bit.
Actor, sunlight has a blueish cast to it though. And I'd suggest using tungston film and buying a sunlight filter, because the sun is a much brighter light source and less of a hassle when loosing stops due to the filter.
Gamecat--you are right, but I refer you to my last paragraph. I oversimplified things. If I had not then the post would have been about 10 times longer, and it's long enough as it is.
True sunlight, observed above the Earth's atmosphere, is actually flat across the visible spectrum. Skylight, light reflected from and diffused by the atmosphere, does indeed have a bluish cast, evidenced by the fact that the sky is blue. The color temperature of skylight is 11,000°K.
Your strategy of using tungsten film and a "sunlight" filter (85B amber) works. I personally prefer to use daylight film. If I don't have enough light for the filter the lab can color correct when making the print, a third stratey I forgot to mention. The trouble with having the lab color correct is that technicians don't like to do it. It's more trouble for them and for some reason they don't charge extra. At least my local still lab doesn't. I'm pretty sure the movie labs all do.
Many labs do charge for "color correcting" It's called a TIMED print. Film printers have three lights (and God help me I cannot remember what they are, I should know, I'll probably remember in a hour or something- red,blue and yellow I think)Anyway, the lab can change the color tone of your film by tweeking these three lights. Timed prints can be expensive and you usually only get them when you do your final print, unless you have money.
Color temp. can be a tricky issue, but I love trying to deal with different color temps. on set, as long as it's not too big of a headache.
Astronomer's use degrees Kelvin to judge one type of star from another and kelvin temp. is also used in many other fields other than photography, chemistry for example.
Didn't you guys take science in High School?
It's green dude... Red Blue and Green
The problem with correcting for daylight in post is that you´ll overexpose the blue color. The print will look a little different than if you corrected it in camera.
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