David Irisarri wrote:
> Hi,
>
> Some days ago I asked if someone could tell me how to know the real
> temperature of a lightbox. I didn´t realize I could use my X-RITE DTP-94
> colorimeter to measure temperature and luminance.
>
That's the colorimeter I have. The Monaco software I have only works to
profile monitors. What software uses it for this other purpose?
> JESSOPS LP45 has two lamps in the corners. Temperature over the lamp is
> 5050 ºK and drops to the center of the lightbox to 4300 ºK. Luminance is
> 1080 cd/m2 but evenness is disgusting all over the surface.
>
I meant to say something about this before. I don't believe it is
possible (at least outside a good lab) to separately calibrate light
source and film/sensor/camera. Certainly in the usual uses of IT8
targets, the calibration is of light and sensor together.
Shooting the reflective target in midday light allows creating a profile
of film or sensor for daylight. In any other light, creating another
profile will give results like daylight, while using the daylight
profile will give images that include the effect of the light
differences; warm early or late light will give a warm image.
Scanning a reflective target in a flatbed or a film target in a film
scanner creates a profile that included the net effect of light source
and scanner system.
Soooo, the light source used to illuminate transparencies need not be of
any particular color temperature, but should be broad spectrum and
stable. The profiling process takes care of the color temp of the
source. It must, however, be rather even in illumination, so that the
different color patches of the IT8 target are evenly illuminated.
A relatively large/close tungsten bulb and thick opal glass sounds
better than what you have just described. Although very warm, which
doesn't matter, tungsten light has the advantage of a broad, smooth,
continuous spectrum, which could matter. Even daylight balanced
fluorescents may have peaks and valleys, I think.
When I used the Oly bellows, 80/4 and slide copy attachment for slides,
my little supposedly 5000K light source and auto WB on the 5D did a nice
job with outdoor slides.
Moose
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