Posted 26 September 2007 - 03:48 PM
Is there a formula to tell you how many fc you will get from a fixture at a certain distance? Ive read up on the Inverse square law, and i know that if you chose your stop for a certain asa, you have the fc info on the can.
But suppose i was short of people to move lights around and i wanted to get the lights in the right position ... is there a formula to tell me that if i put a 10k 20 ft from a subject...i will get x fc???
Posted 27 September 2007 - 03:53 PM
Other than that, experience teaches you how much exposure you can expect with certain units at different distances. This will get you in the ballpark, and then you use your light meter to find more accurate exposure.
Posted 27 September 2007 - 05:38 PM
Like michael said, most companies can supply you with photometric information. Here's an example from Kino Flo for their blanket light.
There are also generic photometric tables in the back of the American Cinematographer Manual that will get you in the ballpark.
Edited by Chris Keth, 27 September 2007 - 05:42 PM.
Posted 27 September 2007 - 07:16 PM
Posted 27 September 2007 - 08:13 PM
The photometrics also need to be used as a very rough guide; bulbs gradually become less efficient and dimmer (and often color shift) the more they are used.
Yup. I remember from cleaning fixtures in school that a dusty fresnel could sometimes cut a whole stop!
Posted 28 September 2007 - 08:01 AM
I just worked with a DP who lit a night scene during the day by subtracting the ambient sky from his meter readings as he set up and focused each light during the day. he only spent 3-4 minutes tweaking once the sun went down. GOD it was great. his kungfu was strong.
Posted 01 October 2007 - 08:31 AM
his kungfu was strong.
wow, that´s really a strong kung fu. where exactly did he take the readings?