Footcandle Question

[Jay Kelley]

I have a shoot tomorrow and my Gaffer is asking the following.. An answer would be great!

 

I need to know the nessesary footcandles for my camera (Running at 24p standard shutter 1/48) to read about 90% on a 20% (or so) gray card.

 

Please let me know if you have the answer to this.

 

Thanks

 

Jay Kelley

PS It's good be back

 

www.jay.kelley.com

[David Mullen ASC]

I'm not sure what "90% of a 20% gray card" means.

 

The general rule is that you need 100 fc to shoot at f/2.8 on 100 ASA film (at 24 fps / 180 degree shutter). So you can calculate from there. For example, on 400 ASA film, you'd need 25 footcandles to shoot at f/2.8.

[Jay Kelley]

Sorry David

 

I meant 90% on a waveform monitor.. Is there an ASA equivilant for the 900 based on certain settings?

 

I seem to remember 800asa but I am not sure.. What do you use?

 

Jay

[Phil Rhodes]

Hi,

 

Gah, again this obsession with rating video cameras at a given ASA and metering.

 

A light meter is only useful in the most general sense when shooting video. Video requires finer control over exposure than you can generally achieve with a meter to get good results. The picture monitor is effectively a grid of 2,073,600 spot colour and light meters which tell you what's going on far better than some arbitrarily determined and probably wrong ASA rating.

 

Phil

[aitch]

Sorry but...what an answer! I love it.

[David Mullen ASC]

The Sony F900 is about 320 ASA to 400 ASA at 0db with a 1/48th shutter speed in tungsten light with no filter (the "B" filter setting), so my calculation of needing 25 fc to achieve f/2.8 for 400 ASA should hold true -- but Phil's right, this seems a strange way of going about things...

 

Often you find yourself exposing something differently in daylight than in a night interior; often the F900 behaves more like a 500 ASA stock in those settings (i.e. I'm probably slightly underexposing the signal on purpose because highlights should feel less exposed in night scenes.)

 

I still don't get what you want to be "90%" on a waveform monitor. Something at 90 IRE would be nearly white in tonal value, or more like a really light gray.