Re: B&W IE

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

On 14 Oct 96 at 16:36, JoePaduano@xxxxxxx wrote:

> Robert-- A quick word or two. Camera meters do not read infrared radiation,
> no matter what some people may say . There are meters that can be purchased
> that are calibrated to read only infrared radiation, but they are specialty
> meters.
>                                                                          joe

Joe, for sake of simplicity I did not comment on your previous notes
on this, but onboard cameras *do* read infrared. The fact that they
are rather insensitive to IR doesn't alter that. You only run into
the confusing problem of recalibrating the ASA setting for the
opaque IR filters; in which case modern cameras need a much higher
setting because of an IR block filter in front of AF and AE sensors.

Separate meters are in general much more sensitive to IR, even to
the point that they give quite accurate reading through a #87C. At
least my Gossen Sixtomat Digital is. I (and a another listmember
as well!) would not consider fabricating a sliding IR-filter for
this meter if it wouldn't be the case.

Here's my rule of thumb:
For a bare light reading (no filter in front of either lens or hand 
held meter), start with 400 ASA, add +3 stops for #25 red, +4 for #87 
and +5 for #87C. That means 50 ASA for #25, 25 ASA for #87 and 12 ASA 
for #87C.

Now with #25 most onboard camera meters will do okay with a TTF
reading (Through The Filter), the opaque series however will not be
okay. You can easily check and calibrate your camera by taking the
bare light reading as your guide: with a filter mounted (TTF),
adjust the ASA setting until the autometering shows the same time
and aperture as without filter and the above ASA setting.

The advantage of the TTF metering is that it takes into account the 
time of day, ie the relative amount of IR compared to the overall 
visible amount. Light in the evening and early morning containts 
relatively more IR than at high noon; a bare light reading would 
suggest more IR than there actually is.

Yet in spite of all this: it still doesn't take into account the variations in
development, so no matter how exact you calibrate, you still need to
bracket +/- 2 stops until you have shot at least a dozen films under
various circumstances, and you got the hang of this film, and more 
important: the various results it can create.

Willem (and in the end we all do the same) Jan

--
Bye,

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      The desire to understand 
is sometimes far less intelligent than
     the inability to understand


<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]

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Topic No. 8