# Thread: Foot candle to aperture and ISO.

1. ## Re: Foot candle to aperture and ISO.

Those 10,000 lumen LEDs that are offered for pre-order are only \$25. You won't be charged until the lights are shipped. B&H does business the same way.

2. ## Re: Foot candle to aperture and ISO.

Originally Posted by Bill Burk

Use the square root of the film speed for the f/stop and use the footcandles for the shutter speed.
Not so, Bill. His Exposure Formula requires readings in candles/sq.ft. (not foot candles) and then the shutter speed is the reciprocal of candles/sq.ft. Other than that you're correct.

3. ## Re: Foot candle to aperture and ISO.

Originally Posted by Jerry Bodine
Not so, Bill. His Exposure Formula requires readings in candles/sq.ft. (not foot candles) and then the shutter speed is the reciprocal of candles/sq.ft. Other than that you're correct.
Right. Since a Weston Master indicates that:

Take the square root of the film speed and use that for your f/stop.
When you have taken an average reading with a Weston Master light meter...
Set the Shutter speed to the number the needle points at.

4. ## Re: Foot candle to aperture and ISO.

Originally Posted by Bill Burk
...
Set the Shutter speed to the number the needle points at.
Set the shutter speed to the reciprocal of the number the needle points at; e.g., if it points to 25 c/sq.ft. set the shutter to 1/25 sec. Having established the combo of shutter speed and f/stop, it's a simple matter to adjust the shutter speed for any other f/stop.

5. ## Re: Foot candle to aperture and ISO.

If using a Weston master why not just transfer the reading to the exposure calculator?

6. ## Re: Foot candle to aperture and ISO.

It is the reciprocal, and you want the square root of the arithmetic film speed. And right Weston meters indicate candela per square foot. Shutters mostly leave off the 1/ . If there is time the exposure calculator is useful.

But the exposure formula is easy to use in a pinch:

Set the f/stop at the square root of film speed and set the shutter to whatever the meter needle points at.

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