Quoting EI

["Elton N. Kaufmann - Cycloid Fathom Group" <cycloid@xxxxxxxxxxxxxxxxxx>]

I have found some of the posts that quote EI difficult to understand
because I don't know what device is measuring the exposure (camera's
internal meter or separate meter) and through what filter, if any, the
exposure is measured.  Perhaps a convention for quoting EI was established
before  I joined the list?   I understand we use visible light readings and
then have to guess how the IR light  scales with the visible light under
different conditions.  
	I take my reading with a separate meter or thru the lens WITH NO FILTER.
Then I assign an EI to the film (for HIE, an EI of 50 as a starting point)
and set my exposure as if no filter were involved (when using a #25 or
#29).  I de-rate one stop (use EI of 25 as a starting point) for a #87
filter.  This approach usually gives me strong IR effects (sometimes bullet
proof highlights).
Clearly, to get the same shutter speed/aperture setting by metering thru a
Red filter, I'd have to tell my camera that the EI is between 200 and 400.
Here's my confusion.  When list member post EI's, do I understand them as
the value used to trick the camera thru the filter, or the EI sans filter?
For the opaque filters, I gotta believe tis the latter.  

									EltonK
	
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