Re: Konica IR 750 with tungsten lights

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

On 27 Jan 97 at 8:31, hannu.jarventaus@xxxxxxxx wrote:

> Hello!
> 
> Last week I tried to get some info for using Konica IR indoors
> with 'hot' lights. I got one answer from Ed Scott (thanks Ed), and it
> confirmed my thoughts about the films sensitivity with tungsten lights.
> 
> I shot one test roll at EI 400 and bracketing the exposure with 1 stop.
> The film was developed with Ilfotec LC29 (1+19) 8 min at 20C, which
> gave a little bit thin negative with EI 400 (EI 200 was quite good).
> So I decided to develop 10 min, and the negatives look good.
> 
> I usually shoot Konica IR 750 with EI 100 outdoors. 
> This was of course push processing of some degree, but I think
> Konica IR 750 can be 2-4 times more sensitive indoors with
> tungsten ligths.
> 
> Any other opinions?

I wouldn't exactly say 'more sensitive indoors', it's just that the tungsten 
lights emit relatively much more IR than is present in daylight. It 
is your light meters inability to translate 'warmer light' into 
'relatively more IR' which causes the need for a higher ASA setting.
If you look at the typical spectral emmission curve of tungsten vs 
daylight, it is obvious why: the lower color temperature of tungsten 
(colder temperature = warmer color!) vs daylight means that the 
wavelength of peak output is shifted towards the red, and with it the 
entire part of wavelenghts in the IR-spectrum.
The same thing happens if you shoot at noon vs sunset/sunrise: 
sunset/sunrise results in a warmer color (lower color temperature), 
which means relatively more IR, which might require an additional 
step under exposure compared to your meter reading. [combine this 
with better shadow effects, and you have a reasonable explanation why 
IR works better early in the morning and late in the afternoon]

All this compensating stuff does not apply if you meter *through* an
IR-filter (our famous TTF reading....;-)), since then you only record
the *actual* amount of IR, and do not rely on a certain % of IR
present in the visible reading.

--
Bye,

       _/      _/       _/_/_/_/_/       _/_/_/_/_/
     _/  _/  _/               _/       _/  _/  _/
     _/  _/ illem    _/     _/ an    _/  _/  _/ arkerink
                     _/_/_/  



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


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

------------------------------