Taking measurements from my four-UV tube commercial 'diazo' printer:-
The tubes are effectively about 320 mm long, 80 mm away from the print
surface. Examination of the cross-section of my plain paper iron-based
prints (e.g. platinotype) suggests that the image substance extends about
50 microns (0,05 mm) deep into the substrate.
Whence, as Euclid would have said, by similar triangles, the maximum radius
of the circle of confusion in an image ideally contact-printed with this
source is given by:
320 x 0.05 / 80 = 0.2 mm
(Sorry - I can't manage a diagram in ASCII - draw one for yourself)
This assumes perfect contact between neg and paper and an infinitely thin
image layer in the negative; the reality will be worse. Now, I reckon my
ageing eye can resolve 0.15 mm at its near point. So all my prints are
perceptibly fuzzy. Help! I *knew* there was something wrong! Where can I
get a UV 'point' source in sunless 240-volt-land? I've already got the
vacuum frame.
Mike