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Post by scotttucker on Apr 15, 2024 22:38:33 GMT -7
This thread is just to log an experiment in making some constellation art projectors. Step 1 - ask my wife to make a simple sketch of cygnus.  |
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Post by scotttucker on Apr 15, 2024 22:51:50 GMT -7
Step 2 Photograph the sketch and import it into Inkscape (a free software package). 3. Use the 'trace bitmap' function to produce a Scalable Vector Graphic version of the picture (at the same time tick the 'invert image' option so that you get white lines on a black background). You can play with the 'brightness cutoff' settings to remove the imperfections on the sketch (pencil marks, sellotape etc) you can also rotate the image so it is the right way up!  |
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Post by scotttucker on Apr 16, 2024 13:05:03 GMT -7
I am relying on the fact that constellation art does not have to exactly match up to the projected stars (unlike constellation stick outlines). My back up for this claim is that even the classic Zeiss at the London Planetarium did not quite follow the lines / positioning exactly - there is a bot of artistic license. Here is a really bad picture of the classic Zeiss orion (taken through the eyepiece of my old viewmaster)  |
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Post by scotttucker on Apr 16, 2024 21:47:18 GMT -7
Step 4 -Get the digital image printed on to a good old fashioned 35mm slide.
I have sent mine off to Digitalslides.co.uk. It costs £3 per slide. Their communication was extremely quick - I asked them if they could make sure the image would be 14mm long on the actual slide which they said was no problem.
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Post by scotttucker on Apr 16, 2024 21:53:59 GMT -7
I forgot to mention - you could use the projection formula to calculate the size that the image had to be on the slide. I used a far more rough and ready method for this experiment- I spent a little time in the dome with a tape measure. I think that the long axis of Cygnus takes up nearly half of a star plate diameter (which works out at roughly 14mm or thereabouts.)
As long as the focal length of the projection lens matches that of the projector, things should line up reasonably well.
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Post by Ron Walker on Apr 17, 2024 12:04:01 GMT -7
I meant to answer this sooner but I need to find some material that I have somewhere but forgot. Anyway, I have had some luck with using inkjet printable material used for overhead projectors. It is available for laser printers as well. Blacks are not totally opaque or perhaps I'm a bit picky after using Kodalith film. www.amazon.com/Printable-Transparency-Overhead-Projectors-Printers/dp/B08MKXTN3H |
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Post by scotttucker on Apr 17, 2024 22:40:05 GMT -7
Ahaaa! I feel another branch of this experiment coming on. Thanks Ron. 10 sheets of laser transparency ordered from e-bay. It will be interesting to compare home made vs commercial printed slide - although I suspect my dodgy old printer will not produce brilliant results.
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Post by Ron Walker on Apr 18, 2024 11:59:16 GMT -7
I found out that if your printing black letters on a clear background these things work fine as intender. However, when doing a constellation outline with a lot of black and thin clear lines, the black areas do not print as opaque as one would want. I doubt that any visitor would care if there was a bit of "fog" projected around the outline. It drives me nuts but that's what happens when your a vertically challenged perfectionist.
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