Balancing light help
Posted 05 May 2007 - 05:10 PM
Consider this balance situation. Let's say you are shooting in one room of an apartment in San Francisco. The apartment has a room with a spectacular view of the city out of a window. It has been decided that in this particular room, there will be a shot including both the interior of the room with it's tungsten light and a partial view out of the closed window with daylight coming through. Lets say your getting a reading of 2 from the light inside the room and a reading of 22 from the window daylight. It's ok for the exterior to be overexposed by a stop/stop and a 1/2.
What type of film would you use and why? What tools (roscoe scrims, ND gels, 85 filters etc.) and methods would you use to balance the light in this situation to obain a proper exposure?
I know everything is generally speaking, I just wanted some feedback on how you guys would go about shooting this situation. Any information would be extremely helpful as I am just beginning to learn about cinematography.
Posted 05 May 2007 - 06:35 PM
Posted 05 May 2007 - 07:08 PM
I guess one question is why would the tungsten practicals be on inside the room, unless it was dusk or very overcast outside?
This is a situation that was given in a class of mine, which I didn't fully understand the solution too. My professor is not the easiest guy to get some time with, so I decided to post the situation here instead to get some help. I guess the whole point he was trying to make was to be able to balance two extreme readings of tungsten and daylight, even if the situation doesn't make much sense. Or perhaps I completely misunderstood the situation.
In my notes I have a Daylight ext./tungsten int. situation, an HMI int./daylight ext. situation and a night situation with a city view through the window and tungsten lit int.
If none of this makes sense to you, perhaps you could just help me to understand the general principles of balance?
Posted 07 May 2007 - 11:54 AM
Bascially you have two light sources which will show up differently. Daylight has a bluer tone relative to tungsten, tungsten is orange relative to daylight. Tungsten lights made for photography should be about 3200 degrees kelvin, daylight approximately 5500 (though this is not a constant as cloud cover, shade, or sunrise and sunset may change this). Many house hold tungsten lights have an even lower color temperature, meaning they look even more orange relative to daylight, even more orange than 3200K photo lights. This is where a color temperature meter can come in very handy, as you can read different light sources and see what color temperature they really are, especially when you have to use house lights in a location. Guessing can sometimes lead to undesired results.
You could balance your tungsten lights to the daylight source. You would need to use CTB gels to make the tungsten lights match the daylight. At this point you would need to decide if you wanted to pump up the tunsgten lights to the f-22 or f11 1/2 (if you wanted the outsdie to be 1 1/2 stops brighter). CTB takes away about 2 1/3 stops of light, so you would need very strong tungsten sources to match the level of light as well as the color. Or you could still CTB the tungsten lights, but use neutral density filter on the window, which would change the intensity of the light but not the color characteristic, to keep from having to use a lot of tunsgten light to match the level of the daylight. ND gel takes down 1/3 of a stop for every .1 increment (so ND.3 would take down 1 full stop, .9 would take down three stops, etc.). Now your light would be consistent with with daylight color temperature all around. You could use a daylight balanced film, so your daylight balanced light will look "white". If you had to use a tungsten blanced film at this point, where tungsten light is "white", then your daylight balanced light sources would look blue. You would need to then add an 85 (orange) filter to make the light appear "white" on the film.
You could also leave your tungsten sources alone, and decide to put CTO (orange) gel on the window to make your daylight match your tungsten light, which will also take the light level down about 2/3 a stop. Again you could also use ND gel to bring the light level from the window down, or use more powerful tungsten light. In this case since the tungsten lights are left alone, and the daylight has been corrected to tungsten color temperature, you could use tungsten balanced stock and have the light look "white" as is.
I hope that helped some. If you do have access to a color temperature meter, you maybe want to just walk around with it and take some readings from various light sources and see what you get. Also, it can be helpful to take a video camera, set to manual with the white balance set either on daylight or tungsten preset and do some different lighting set ups and see what they look like.
Posted 07 May 2007 - 05:25 PM
Thank you very much for that clear and concise explanation and for taking the time to write back. That helped a great deal.
Thanks so much again,