when using a gree screen...

[SpiderMonkey]

where exactly should i put lights? and how bright?

Obviously you must getrid of the shadows.. but I everytime when i use the green screen the green lends too much with the other colors and the threshold doesnt work well enough..

In one of my films i did a scene where we wrapped each others heads up in green to make it appear that we have no heads.. some shots worked, the simple ones obviously.. but others you should still see the folds of the scree and when you would blend in the green you can still see a faint outline consisting of different brightness and shadows that didnt get picked up

 

[hunteq]

Key light, 45' to side of subject, 45' vertically.
Fill light, 45' to opposite side of subject, eye level.
Back light, on ground behind subject pointed at subject to bring out separation.
Background lights. One on each side of green screen to illuminate it evenly, and one in the center pointed up if it's large.

 

[gpforet]

The screen must be lit separately from the talent, typically either from overhead with flags, or from each side of the screen, or preferably, both.

Place the talent far enough forward of the screen to reduce or prevent talent lighting from throwing shadows on the screen.

I use the rgb histogram on my 60D to light the screen, moving lights until I have the spike in the histogram as narrow as possible.

Even then, I have difficulties with the green casting reflections on anything reflective in the wardrobe of the talent.

 

[brianluce]

Budget solution is 4' Home Depot flows on each side. You want it even as possible. Try and get at least 6' separation from the subject and screen and also backlight the subject (orange gel works good) to reduce spill.. Make sure you have a real keying software. Not some iMovie Junk Freebie.