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  #11  
Old 21st November 2019, 04:18 PM
Mike O'Pray Mike O'Pray is online now
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Wow, John, it sounds as if Slim Pickens had less trouble releasing the H bomb from the B52 in Dr Strangelove than what was involved here .

Let us know how it goes. Specifically I'd be interested to know if the safe baffle level that worked with the old lamp does so with this new one or whether it means closing the baffles just a bit more so the light level is much the same

Thanks

Mike
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  #12  
Old 21st November 2019, 06:03 PM
John King John King is offline
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Default Light baffles

This is actually quite a simple arrangement. One tube (fixed to the lamp base socket) which does not rotate, into which you insert the bulb to fit the 9 pins into the socket. You are working blind fitting the bulb which can be difficult, get it wrong, bend one of the pins and the bulb is scrap! The fixed tube is a very close fit with only a little wriggle room to get the pins inserted easily. This tube has triangular shaped slots in 3 rows up the tube and at 90 degree intervals around the circumference. which the outer tube which has a clearance of only about .5mm has similarly placed triangles but angled in the opposite direction to those on the inner tube, is fitted over the inner tube. It also has a fixed arm at right angles to the tube which links into a push/pull slider fixed to the outer casing.

Push the slider one way and you allow the max light to escape, pull the other way and you can exclude all light from escaping. Quite a simple arrangement in fact but one that works. It is graduated 1 to 10 on the outside of the case and I find about 2-3 is enough to work comfortably in my darkroom without risk of fogging the colour paper.

For B&W you can open up fully to 10 and I have yet to fog any B&W paper. (I don't bother using the red filter supplied.)

Last edited by John King; 21st November 2019 at 06:11 PM.
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  #13  
Old 21st November 2019, 07:06 PM
John King John King is offline
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Default Light levels

I will be working with B&W this evening so will let you know about the levels with colour later. I imagine that I may have to reduce the apertures just a tad. Although if the effectiveness of the sodium had diminished and the old bulb was less effective I may actually get away with it being just that bit lighter.
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  #14  
Old 7th December 2019, 09:07 PM
M Stewart M Stewart is offline
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Interesting - one of my other hobbies is very basic metrology. Gauge blocks, optical flats and similar.

The professionals use a small sodium lamp for checking how flat the gauge blocks are, using optical flats and fringes. I wasn't in to paying out £400+ for one of the lamps, and at the time I was looking for one, surplus low pressure sodium street lamp lanterns appeared on eBay. Problem solved for around £20 for two! I knocked up a frame to hold the lamp vertical, added some diffusing plastic sheet, and bypassed the day-night light sensor. Job done.

My Youtube video of the warm-up sequence has proved amazingly popular for something close to watching paint drying.

Warm-up
https://youtu.be/PI__yN01VoU

Green fringes
https://youtu.be/hqsVXA5S2xM
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  #15  
Old 8th December 2019, 10:06 AM
John King John King is offline
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The new bulb is definitely better. With colour I seem to be getting almost no cyan fogging with extended exposure and I didn't have to increase the adjustment slider to get more light - the new bulb is brighter.

When I did the 1st session using B&W I had the adjustment wide open at 10 and it is so light I can read small print by the light given out. (even with my cranky eyes). The main differences I have noticed are the transformer does not buzz like it used to, it now merely 'hums' and the max brightness takes quite a bit longer to get there. Not that this bothers me because I can be sorting out paper, negatives rinsing water etc whilst it warms up

I will be keeping the old bulb as a spare should this one fail. Although old and not as good as the new one it is a fall back option. However it was well over 20 years old, so the new one it may well see me out. Or colour materials be no longer available.

Last edited by John King; 8th December 2019 at 10:10 AM.
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