Re: Melles Griot filter info

[ADavidhazy <ANDPPH@xxxxxxxxxxxxxxxxxx>]

Willem-Jan,

> Aha....mmm....this begs the question why anyone would mount such a
> deep-IR sensitive sensor in a lightmeter that normally is only used
> to read visible light....whatever it misreads for IR film because of
> this, it would misread perhaps even more for visible applications
> (perhaps the relative amount of error increases?....only a tiny
> amount of wanted IR, and still the same amount of unwanted IR).
> (in which case the design should include a IR-block filter right from
> the factory)

Yup ... in some meters there is indeed included such a filter but the function
of this filter is simply to decrease the relative amount of long wave IR to non
problematic levels. In those where the sensoir itself is not sensitive beyond
"light" (however achieved) there is of course no practical way to measure IR
but of course we know that no meter is totally immune from reading wavelengths
beyond 700nm. 

This being the case, then the question is "how much residual IR sensitivity is
there and how far out into the IR does it go?". Well, CCD's are inherently very
sensitive to near IR and from curves I've seen their relative sensitivity keeps
climbing even beyond 1000nm. (But my memory is not as good as it used to be)

On the other hand, if the cell's sensitivity dies off at 900nm then, of course,
(as I stated earlier) the film's reach into IR is the same as that of the film
and no additional thought need be placed on eliminating those wavelengths that
are beyond 900nm.
                     
... I believe we are on the same wavelength!

cheerio,
andy

Andrew  o o  0 0 o . o  Davidhazy, Imaging and Photo Tech
         \/\/\/\/\/\/          http://www.rit.edu/~andpph
__________|        |_____________________________________


 

In any case, 






 

> --
> Bye,

> Willem-Jan Markerink


>       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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