Re: UV transparency/attempt to explain a spectrophotometer (fwd)

Cor Breukel (cor@ruly46.medfac.leidenuniv.nl)
Fri, 28 Feb 1997 11:08:19 +0100 (MET)

On Fri, 28 Feb 1997, Judy Seigel wrote:

>
>
> On Thu, 27 Feb 1997, Cor Breukel wrote:
>
> > Finally I'am able to contribute some hard data myself..;-).. I did some
> > testing last week with different (clear) film base.
Sniperdesnip

> Cor, do I understand correctly that you have a machine by which you can
> DIAL IN the wavelength, like dialing a radio????.... Would you like to
> have the next "Meeting of the List" at your laboratory?

..Oh oh, got myself in trouble now..but that's wat happens if you want to
play with the big boys and girls..;-)..

Ok, let me first try to explain a spectrofotometer as clear as possible:
(had to dig up the manual again to refresh my memory..feels like all those
experienced contibutors when they say..back in the sixties..12 years ago
when I started..or when I heard my (grand)son say..:-) )

A spectrophotometer is a maschine which uses 2 lamps (a Qaurtz-Halogen for
visible and a Deuterium lamp for the UV spectrum). Via a series of
inginieus mirrors, filterwheels etc. this maschine is capable of producing
a ray of light with a single wavelenght (+ or - 0.5 nm I thought). This
"ray" is send through a little "chamber" called cuvette (about 10*5*40 mm)
made of quartz (doesn't block UV) or glass: blocks UV

(Re. Klaus: I scanned a glass cuvette, it starts blocking Uv at 260 nm, a
bit curious since I thought that Crawford of The Keepers..claims glass
starts blocking at 360 nm, maybe different qualties block differently,
I'll look into that)

So this "single wavelength ray" hits the cuvette and what's in it (usualy
a solution, in this case a piece of clear film), and "behind' the cuvette
a sensor measures the loss so to speak, it gives a read out in either
Transmission (the energy that got through) or Absorbance (the energy that
was left behind, got blocked) which (I think) is equal to Density.
You can use this maschine either to read the Ab. of a single wavelength,
or a continous spectrum, which I did for this filmbase test. I have no
idea if one could test the specific wavelengths of different processes (I
imagine I could make tiny pieces of say cyanotype paper, "read' a
wavelength, thus exposing this tiny bit of cyanotype paper with this
particulair wavelength)

Hope this makes it a bit clear, but bear in mind that I am no specialist
in this field

>
> It isn't clear to me, however, whether that 20-30 min. for cyanotype is
> the reduced printing time, or the 312nm printing time. Our school
> printing time averages around 10 minutes for regular blacklight bulbs,
> mine at home is usually less, so that sounds long -- though maybe there
> are other structural factors.

..I didn't express myself clear enough: The Xray film I use has a blue
base, blocking UV light from 360 nm down. The UV box I use has a Quartz
"tablet", 4 special UV tubes beneath, resulting in a (peak)wavelength of
312nm, well into the "blocked" area of the clear blue base of my film,
thus longer exposurer than needed (I'am in the process of building a
"normal" UV light box)

>
> But that's not why I'm writing -- have you described your procedure in
> enlarging to the Xray film, and I just missed it? If not, would you fill
> in some details about which kind of film (just had a chest X-ray, film
> as big as the New York Times, mammograms only as big as Readers Digest),

My procedure: I enlarge 6*6 negs onto Konica A2 20*40cm Xray film (yes
freeby outdated), develop in D19 (increasing contrast), contactprint this
positive, and develop in D19 again. Have to check the Dmax still though,
but I obtain good VDB and cyanotype prints (at least I think that they are
good, I'll see in Bath..;-) ). Also used dig,. 35 mm negs, but tht's
another story..

Btw this film is quite fast, when I use it in my Pinhole camera, I rate it
at 800-1600 ASA

>
> And here's an afterthought -- is there any way this ingenious device
> can be persuaded to read the sensitivity points of emulsions?

..see above

>
> Thanks again,
>
> Judy
>
>

Cor Breukel
http://ruly70.medfac.leidenuniv.nl/~cor/cor.html
"The Infrared Gallery"
http://ruly70.medfac.leidenuniv.nl/~cor/ir-gallery.html