Re: IR exposure on overcast days

[Ben Kreunen <ben@xxxxxxxxxxxxxxxxxxxxxxx>]

At 01:09 PM 12/1/99 -0500, you wrote:

>I recently read Laurie White's book on IR photography and was puzzled by one
>of her exposure recommendations.  She said that on overcast days, one should
>under-expose from the meter reading.  Apparently she uses an SLR and meters
>through a #25 filter on the camera's lens.... this indicates
>that on overcast days there is a higher proportion of IR in the ambient light
>than there is on sunny days.

Your camera's light meter measures mostly visible light... the light on 
overcast days is very blue.... you have a red filter blocking out the blue 
light so your camera thinks it is darker than it really is and increases 
the exposure. Metering technique may also play a part in this.

>In a similar vein, do IR practitioners adjust their EI for the season?

My Hasselblad doesn't have a light meter so I use a 35mm camera as a light 
meter, metering without any filters and I don't adjust my EI at all, but 
then other people do, so you'll still have to find out what works for you.

Cheers

Ben

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