Re: Building UV exposure unit (was Re: new to list)

I disagree with Dave about the need for a
ventilation fan. Even with the ballast mounted
outside of the exposure unit the temperature of
the tubes will build up to close to 100 degrees
with long exposures, and at that temperature
their output will decrease by up to 50% or less
than the output at 70 degrees F. I have verified
this with a light integrator which actually
measures light output. One might be able to get
away without the fan if your exposures are ten
minutes or less but for consistent results with
processes that do not allow much control in
development I would definitely recommend a
ventilation fan.

Sandy

>Bulb to paper distance is 2 1/4" in my exposure unit. I don't think this
>dimension is very critical. The bulbs are spaced close together, there's a
>1/2" gap between them. It always produces very even and consistent
>exposures.
>
>I did not install a ventilation fan on my unit, and I've never had heat
>buildup become a problem. The ballasts are mounted on the exterior of the
>unit, so that helps keep it cool inside. I also drilled (4) 1 3/4" holes in
>the sides of the unit, for ventilation.
>
>My exposure unit is mounted on the wall of the darkroom, requiring very
>little space. There's a homemade vacuum easel hinged onto one side of it.
>It's very fast and easy to load and use.
>
>Dave in Wyoming
>
>----- Original Message -----
>From: "Christina" <darvida@gmx.at>
>To: <alt-photo-process-l@sask.usask.ca>
>Sent: Wednesday, November 03, 2004 9:49 AM
>Subject: Re: Building UV exposure unit (was Re: new to list)
>
>
>I will build one this weekend....got the whole stuff here.
>If I´m finished I will show the workingprocess on my homepage if anyone is
>interested.
>
>I will use 8 UV-Bulbs á 8W and a fan to cool it.
>Yours Christina
>
>P.s. can you tell me the distance paper-bulbs that you use?
>
>
>-----Original Message-----
>From: Dave Rose [mailto:cactuscowboy@bresnan.net]
>Sent: Mittwoch, 3. November 2004 17:09
>To: alt-photo-process-l@sask.usask.ca
>Subject: Building UV exposure unit (was Re: new to list)
>
>Welcome to the list.
>
>If you're handy with tools and able to design & fabricate, building an
>exposure unit is an easy weekend project. Construct a wooden box to hold
>your bulbs and bulb sockets. 1"x6" boards with a thin plywood backing works
>well. Position a large piece of sheet metal immediately behind the bulbs -
>otherwise they won't turn on. Go to a electrical supply house to buy the
>bulbs and associated hardware.
>
>My homemade exposure unit has (8) Sylvania F20T12/350BL flourescent tubes in
>it. Exposures range from 1.5 to 8 minutes for gum, and 5 to 15 minutes for
>cyanotype.
>
>Best regards,
>Dave Rose
>Big Wonderful Wyoming
Received on Wed Nov 3 20:42:39 2004