RE: colors for colorizing digital negatives

Another example is the application of UV-protection coating on prints
(either through laminating or spraying). To our eyes , the coating is quite
transparent, but to the UV light, it is opaque as it blocks the UV
radiation.

Dave S

-----Original Message-----
From: Dave Soemarko [mailto:fotodave@dsoemarko.us]
Sent: Friday, March 24, 2006 1:39 PM
To: alt-photo-process-l@usask.ca
Subject: RE: colors for colorizing digital negatives

<< I don't have a transmission densitometer, but just looking at the
negative against the light and laying it over newspaper text, I can't see
any noticeable difference in transparency between the different colors (my
hypothesis would have been that the blue ink is more transparent than the
others). >>

Hi Katharine,

This is because what is transparent to the eye might not be transparent to
the UV, and vice versa. If you use a transmission densitometer, it might not
help either because a densitometer is using a light source that is mainly
designed to measure something visible to the eye, that is, it is using
visible light as the source and measure how much light is passed through (or
reflected in the case of reflection densitometer).

In the visible spectrum, we are actually quite used to this
concept/phenomena. One example is the use of darkroom safelight. Let's say
we start with a white light. If you put a red filter over it, the light
becomes safe for b/w paper. If you put a blue or green filter over it, it
will expose/fog the paper. If you look at the filters themselves, you might
feel that one color is not strongly more transparent to the other. For our
eyes, both are transparent because we can see both colors. For the paper,
however, the red filter is "opaque" because it blocks all the light that can
expose the paper.

It is the same concept except that it extends to the UV range.
 

Dave S
Received on Fri Mar 24 12:44:43 2006