Date: Wed, 28 May 1997 21:38:16 -0400 (EDT) From: Perry Malouf <pmalouf@access.digex.net> To: cp@opus.hpl.hp.com Message-Id: <aabcdefg2105$foo@default> Subject: Re: LUX FORMULA?
Steve wrote:
> does anyone have the formula for converting camera light readings to lux
> levels for terrariums?
I saved the messages that were posted to the listserver,
regarding this topic.
Here is what Chris Teichreb wrote:
> ...following is the guide they give for converting your
> camera's reading to approximate foot candles (f.c.) of
> light. As Clarke pointed out, you can only do this
> with manual camera's, not the automatics.
>
> Method 1
>
> Set ASA to 100
> Aim at white sheet in area where you plan on putting plants
> Set f-stop to f4
> Adjust shutter speed until you get the correct exposure. The
> inverse of the shutter speed=f.c. of light eg: an speed of
> 1/250th second is equal to approximately 250 f.c. of light.
>
> Method 2
>
> Set ASA to 20 and shutter speed to 1/125th second.
> Focus on white paper as above.
> Adjust f-stop until you get the correct exposure.
> Use table below for conversion to f.c.
>
> f2.8 32 f.c.
> f4 64 f.c.
> f5.6 125 f.c.
> f8 250 f.c.
> f11 500 f.c.
> f16 1000 f.c.
> f22 2000 f.c.
>
> As they mention, using the camera is not as accurate, but
> is good for the hobbyist. At least now I don't have to worry about
> building a light meter (even though I should!).
A contributer named Walt wrote:
> Here is the method of getting footcandles in a greenhouse using a
> camera.
>
> You need a camera that can be set manually.
>
> Set the asa at 200.
>
> Set the shutter speed at 1/125
>
> Aim the camera at the light source. (The greenhouse glazing)
>
> Read the f-stop for a correct exposure.
>
> If the f-stop is: Your Greenhouse light level is:
>
> 2.8 32 footcandles
> 4 64 footcandles
> 5.6 125 footcandles
> 8 250 footcandles
> 15 1000 footcandles
> 22 2000 footcandles
>
> This comes from the "Greenhouse Gardener's Companion" by Shane Smith.
Good luck,
Perry Malouf
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