> Now to the subject. I acquired a light meter, (well it looks like a light
> meter) Minolta Air-shields fluoro-lite meter model 451. At the time I bought
> it, I didn't know exactly what it was, neither did anyone else. (flee market
> $5.00 so I purchased it anyway). It turned out to be a device for measuring
> exposure of newborns to Billy Reubin lights (sp?). UV light source hospitals
> use to treat jaundice conditions in newborns.
That's bilirubin - I noticed my UV tubes were also used for
hyperbilirubinemia - which is basically a vitamin D deficiency.
> The unit is a digital unit, is calibrated in micro-watts per square
> centimeter and seems to work real well for measuring UV output of anything.
> It also has a real neat feature, especially for me as I use the sun as my
> exposure source, it measures accumulated exposure, in both time and mw/c2. I
> guess the nurse just sets the unit by the baby, and then checks it from time
> to time to see when the little beggars done. However, when the fluffy whites
> are scudding across the sky you can just check the accumulated UV memory on
> the unit to see when your total exposure is up.
>
> Now the bad news, the unit is made by Minolta Camera Co. and distributed by
> Narco Scientific, Air-Shields Division, Hatboro, PA 19040 and retails for
> $1200. Probably a person can find these units available used at some of the
> larger medical/hospital supply outfits.
>
> Has anyone else played with such a unit? I will report on the results I get
> over the next couple of months of testing, If I ever get another decent print.
Hey Rand, where's this flea market? (:-) How often do you pick up $1200
items for $5? You sure it ain't hot? (;-)
Seriously, it should be a great help in judging exposures, although I
suspect you'll find that the accumulated exposure on a clear day isn't
really the same as what you think is an identical reading on a cloudy day.
Contrast varies alot with alternative processes according to the intensity
of the light source. Thus photographers a hundred years ago used to print
some negatives in direct sunlight and others in open shade. The only
explanation I've seen of this is in Mike Ware's recent book "Mechanisms of
image deterioration in early photographs" - he explains it as a kind of
reciprocity failure. Generally you have to compensate for long exposures
by giving a little extra so the sensitized material will behave as
predicted. The same thing can also happen at the other end of the scale -
a really intense short exposure isn't the same as a much longer exposure
to a less intense light source.
Philip Jackson
pjackson@nla.gov.au