Good points, thanks.
kt
On Mar 24, 2006, at 10:38 AM, Dave Soemarko wrote:
> << 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 12:50:25 2006
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