Re: Infrared Lightmeter

["Leonard Flanagan" <ldflan@xxxxxxxxxxx>]

Hello Pete.  I am not an electronics whiz, so I can tell you what he did 
only in general terms.  I'll try to get more details for you.  I have 
occassionally thought about putting together a kit form of this thing, if 
there would be enough interest.

Basically what we did was get several data sheets on the little IR sensors 
that are used to pick up the signal from TV remote controls units, and 
compared those sensitivity curves with the curve for Kodak HSI.  Found one 
that matched pretty well.  He mounted it in the end of a project box 
(plastic -- a mistake -- should be metal -- the prototype is now coated with 
foil to prevent IR light leakage from above)and connected it to some type 
simple mysterious electronics that convert the restulting information from 
the senor to current running to a little meter on the top, which is numbered 
from 1-6.  Covered the sensor with a piece of IR filter plexiglass material 
(I am not sure if that was necessary).  On - off switch on the back.

I calibrated the thing by extensively metering various scenes, bracketing 
three stops in both directions, and keeping careful notes.  Took two  rolls 
of 35 mm HSI to calibrate it reasonably well.  I found it best to figure out 
what the range of readings was, and figure an average.   The resulting 
figures are attached to the outside of the meter now with clear tape.  It's 
an ugly machine.

Candidly, it's not perfect, and I haven't been really careful about figuring 
out what is 18% gray or anything.  The main problem is that the meter 
responds in typical daylight scenes only over about 1/3 of its range, and so 
you have to judge carefully to get a reading.  But still, it is definitely 
much better than guessing. Given the cost of the film, I like having it and 
use it every time I shoot HSI.  If I can persuade him to make a second 
generation version, perhaps he can come up with something more sensitive to 
variations in typical daylight scenes, and of course mounted in metal.  I'll 
let you know more soon.

Leonard




_______________________________________________________________
Get Free Email and Do More On The Web. Visit http://www.msn.com
*
****
*******
******************************************************
*  To remove yourself from this list, send:          *
*         UNSUBSCRIBE INFRARED                       *
*       to                                           *
*         MAJORDOMO@xxxxx                            *
*----------------------------------------------------*
*   For the IR-FAQ, IR-Gallery and heaps of links:   *
*  http://www.a1.nl/phomepag/markerink/mainpage.htm  *
******************************************************