RE: good source for UV tubes?

On Tue, 13 Jan 2004, Sandy King wrote:

> How do you determine speed point? This makes a lot of difference in
> evaluating the effective printing speed of different light sources,
> especially if there is a difference in contrast between the lights.
> With most processes I set the speed point at 90% of Dmax, though with
> processes like carbon and/or perhaps gum it makes sense to use Dmax
> itself. But with some processes it makes more sense to set the speed
> point in the mid-tones.

Sandy, Just between us, don't tell anybody, I don't do speedpoint, in fact
if you asked me to define it to save my life I'm dead.

I came up with this figure by counting steps on the 21 step, from the
first differentiated shadow to highest highlight. And as I recall I did it
two ways, how long it took each set of bulbs to get to the same number of
steps, and the difference between strips with same time of exposure
exposed by each set of bulbs.

These were, it seemed to me, the *practical* measures for everyday
printing (and as noted I didn't know any other). I did it when neighbor
was beginning cyanotype and troubled by very long exposures. He had bought
BLB. I lent him my BLs, which cut his time dramatically (possibly more
than 20%, that was to be conservative and from memory). I used his tests
and then some of my own -- this was probably 5 years ago, and I can't
SWEAR no other anomalies were involved, but frankly the difference had as
far as I know been widely stated and accepted, which was the reason I
bought the BL to begin with. I can't remember what the sources of that
info were, but yours is the first I've ever heard to the contrary.

Which of course proves nothing... tho it occurs to me that *speedpoint*
may not be the ultimate criterion for actual printing. I'll also add
that neighbor then bought BL bulbs and, using them with same light table,
same paper, same coating procedure, same emulsion and same contact frame,
continued with the better speeds.

> I have done quite a number of comparison tests for printing speed of
> BL and BLB tubes but never observed a difference of over 10%. Bear in
> mind that there are many factors other than the the type of tube
> itself that can impact printing speed.

What medium did you make these tests in? All may not be the same.

> Although the BLB tubes print slightly slower than BLs, however we
> might describe or experience "slightly," I actually prefer them
> because the weird light highlights particles such as dust and lint
> that settle on the printing frame and this makes it much easier to
> avoid dust spots on the print.

You are looking at your negatives under UV light? That's another thing I
was taught -- a no-no.

Judy
Received on Tue Jan 13 14:27:01 2004