Re: Konica 120 infrared

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

On  8 Sep 96 at 18:23, George L Smyth wrote:

> Willem-Jan Markerink wrote:
> > 
> > FWIW, in this Agfa-Gevaert IR book they state that sunlight of
> > 6000Kelvin can be split in 40% visible, 59% heat/IR, and 1% UV.
> 
> Of course, this IR will not be recorded on film.

I know, I know, not *all* of it, but surely something!
If it ain't visible nor UV....what else?....;-))

Also interesting to note the Kelvin temperature....when that
changes, the percentages visible/IR/UV will also change. It is a
Bell(?) curve, centering around a wavelength at which maximum light
emission occurs. This particular wavelength (lamda 'max') is easy to
calculate for a given (color) temperature T, with Planck's formula:

lamda(max) x T = 2.898 x 10^-3

or better: lamda(max) = 0.0029/T

For 6000K this would mean a maximum around 483nm.

All this is also a good explanation why the relative amount of IR
early in the morning and late in the midday increases....if you take
4000K as color temperature, you end up with 725nm....and 3000K 
will give you a maximum of 966nm. 
Away from this maximum, the curve drops rather sharp, 4000K doesn't 
exceed 200nm, 2000K ends at 500nm. The effective range is only a few 
100nm's wide. There must be a formula for this too, but I won't 
bother you (or me....:-)) with it; I have a few charts that tell more 
than numbers....should I scan them?

Anyway, the above is both related to the IR-visible balance with a
red filter, and metering errors if one relies on the amount of
visible light. 

Guenter Spitzing also lists exposure indexes for high noon and later
in the midday; the latter results in a one stop *faster* index using
no filter (160 vs 80ASA), and 1/3rd stop faster for all other
filters (all no-filter visible light readings). 


PS Joe: I found that remark again about spring/summer/autumn
differences, in Guenter Spitzings book: he mentioned that he could
record foliage white on panchromatic film and a green
filter....identical to an unfiltered HIE image....but only in early
spring....summer foliage on panchromatic resulted in light grey,
autumn in dark grey foliage. So it was indeed not a conclusion on IR
reflectance, although Guenter does mention that autumn foliage gives
less IR reflectance. But that is hardly suprising, although the 
visible red/brown vs IR effect is interesting; intense green in 
spring on pan film resembles IR, intense red equals a decreasing IR 
effect.

Other interesting notes in the same chapter: olive trees do rather 
well on IR, unlike most other dry climate trees (any one ever tried a 
cactus?). Alpine plants on the other hand reflect *twice* as much IR 
as plants on sea level....interesting note!

--
Bye,

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The difference 
between men and boys
is the price of their toys

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

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Topic No. 12