lumens & f-stops

[Christian Janss]

I'm trying to find an equation that links lumens output and the corresponding t-stop. I'll be using 200 ISO film and I'm trying to determine what type of projector I'll need to use to get a certain t-stop on a screen at about 10' - 12'.

If anyone knows where I can find this info on the net I'd be much obliged, I don't have access to a cinematographer's manual.

 

thanks.

[Laurent Andrieux]

First don't mistake beetween lumens and lumination (fc, lux)...

 

the flux i(n lumen), caracterizes the whole luminous energy provided by a luminar, it wil depend a lot on the enlighted surface.

 

See, let's take a fresnel lens or an open face projector for instance. You know the f-top, as well as the lumination, will vary according to the enlargment,and depend on whether you provide a flood or spot beam.

 

The flux doesn't depend on this, since the whole energy remains the same. It just doesn't enlight the same surface...

 

But there are diagrams that show what lumination you get at a given distance, in different positions (flood, medium flood, spot) for a given projector.You will find them from its manufacturer. Try Ianiro, Arri, Desisti or any other one you know. May be browsing their web sites would be successfull...