RE: UV light box construction
I built a light box last year for 12x20 which has been working fine. I couldn't find any explanation of why the distance between the tubes should be X and why the distance to the neg should Y so I set up a spreadsheet to calculate the light level at various points across the film plane in order to find X and Y such that the variation in light level was insignificant. I ended up with x=6cm and y=18cm which gives a theoretical 13% difference in light intensity centre to edge. Of course the calculations are based on assumptions which are not correct - such as infinitely long tubes and zero reflectance from the sides. I think the results of the calculations err on the conservative side and you could probably increase X and reduce Y by some considerable amount before any variation became 'material'. I'd be happy to send the spreadsheet (Excel) should you wish to see it - and anyone else on the list. Practical advice - paint the inside white. Also I built my box upside down I think - the box sits face up with the tubes near the floor and the printing frame goes on neg facing down. I don't think that has any material impact on results. Geoff Chaplin ジェフ チャップリン geoff@geoffgallery.net www.geoffgallery.net Skype: geoffchaplin1611 UK mobile (英国の携帯電話): +44(0) 7770 787069 Japan mobile (日本の携帯電話): +81(0) 90 6440 7037 Japan land line / fax (日本の電話とファクス): +81(0) 166 92 5855 -----Original Message----- From: Ken Sinclair [mailto:photo1@telusplanet.net] Sent: 22 February 2009 03:15 To: alt-photo-process-l@usask.ca Subject: UV light box construction Hi all... I am now in possession of a sheet of baltic birch, 12 BL tubes, ballasts and the correct number of 'tombstones' and am almost at what one might call the 'final, too-late-to-change design' stage. I plan on having the lamps on one 'surface' of the birch 'plate' and the ballasts on the upper. I have planned to have this "rack" sitting on a 1 inch support around the interior of the box to facilitate easy access when (and if) any of the parts need changing. Before I commit the sheet of plywood to the table saw, I have to believe that some users may have found there to be an optimum distance between the lamps, along with the distance from the lamps to the top of the print frame. Practical advice would be very much appreciated. Ken Quando omni flunkus moritati (Red Green's Possum Lodge)
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