A Better Star Projector

[dkumpula]

So this weekend I was procrastinating from stuff that really needed to get done, so I decided to replace my old star projector that fills my great room ceiling with green 'stars'. The 532nm diode that is the heart of that thing was dying after running ~6 hours a day for 13 years. I dissected the optics from the thing to find two overlapping glass gratings that made a nice 'starfield' breakup which was then furthered by another plastic scan-through grating that rotated to make a waaaay to busy 'sky'.



The replacement I had in mind was centered on a couple things that I had handy. A couple 488nm single mode diodes and a cool little sample grating thingy that my friend Ed (ekeefe) gave me a couple years back. The idea was us use parts that I had sitting around that I'd never use in a regular projector build including old diode mounts, large bounce mirrors and a 3x diode driver that didn't even have Bias pots (!).



This little sample grating has a really nice rotating Earth, a rotating moon, a constellation that draws the line between the key stars in one area and without it in another and finally a static detailed image of another section of the night sky. The last two were what I wanted to incorporate into the replacement star projector, but unfortunately even with 22 feet of throw from floor to ceiling, the throw ratios on those gratings only cover about 1/6 of the ceiling each. Rather than deal with telescoping them, I decided that they should be 488nm 'feature areas' and I'd just fill in the rest of the sky with 450nm using the gratings I salvaged from the old star projector.



Since the constellations were feature areas, I bounced them on separate mirrors, one paired with the grating 450nm stars. In the end, I've got a much improved two color sky that looks much better than any of these silly laser based toys we see for sale. It's definitely not a proper star projector like SpitzSTP collects, but for $0 and a footprint of 6"x4"x2", I'm pretty happy with the results. Oh, and before anyone asks, yes the zero order beam is 5mw even with the brightness pot turned up all the way. Here's a few more pics. The brightly lit room and short throw doesn't do the star fields justice so I'll try to take some pictures of it in the great room tonight after the sun goes down.



-David

[kecked]

Let me know if you want a real sky. I know someone who makes gratings of the real sky. Think it’s 20 million stars. Similar to the saga projector but with more stars. https://microstru.com/DS1_Discs.html

it would be interesting to magnify just a section of the disk and project. I’ve seen this in person and it’s amazing BUT it really needs a much brighter light source than the usual lamps they use. A 9w blue would be spectacular.

last, since your other device is fixed why not mask the first order star.

last2. You could also make your own constellation masks and project those over the random stars to add just a touch of reality. Like say Orion and the Big Dipper and maybe Cassiopeia and pleades. If you do Orion make sure to project Betelgeuse as red and add a lumia for the nebula.

[buffo]

Hey Marc;

Those discs that your friend makes... If you wanted to use that with a laser you would need to first expand the beam to roughly the same diameter as the disc itself, right?

Adam

[kecked]

Hey Marc;

Those discs that your friend makes... If you wanted to use that with a laser you would need to first expand the beam to roughly the same diameter as the disc itself, right?

Adam

id go led with lens system like the projector is made for
i don’t see an advantage using laser light for this. Might not even work as it would scramble the laser like a diffraction grAting. Maybe🙄 Was just pointing out a way to do a reality star setup. These are so good you can use binoculars to pick out stars like the real night sky. I’d love to see this with 100w led on a dome! Ps not my friend. Don’t know they guy. My friend and you may know him dale harder knows him.

[kecked]

Wonder if the guy looking for a one inch beam was looking to do this

[buffo]

Got it - thanks for the clarification!

Yeah, was wondering about the other thread too. We'll see I guess.

Dale does not ring a bell, but honestly I'm pretty far out of the loop when it comes to this sort of thing. DZ or Spitz might know him though.

Being able to use actual binoculars to view the starfield from one of those discs is an amazing thought! Agree that seeing one on a dome would be really cool.

Adam

[kecked]

Got it - thanks for the clarification!

Yeah, was wondering about the other thread too. We'll see I guess.

Dale does not ring a bell, but honestly I'm pretty far out of the loop when it comes to this sort of thing. DZ or Spitz might know him though.

Being able to use actual binoculars to view the starfield from one of those discs is an amazing thought! Agree that seeing one on a dome would be really cool.

Adam

Only limiting factor on brightness is heat the disk is glass and chrome.

[dkumpula]

I'm sure the disks and a good LED source make for a better sky, but . . Lasers!

Here are a couple pics of the star field on the ceiling. It has the two constellation areas and then the 'meh' stars from the difraction gratings. Ideally, I'd have lots of constellations with a white beam source. Someday!




-David

[kecked]

Not bad at all. Maybe a splash of lumia and mask the zero order hot star. Good enough. I just wanted you to know those disks exist. Merry christmas

actual just put a piece of lumia glass as the mask in front of the hot spot!

[dkumpula]

actual just put a piece of lumia glass as the mask in front of the hot spot!

That’s a good idea! It will have to be a tiny piece of lumia glass as they are very close to each other at the aperture window. I’ll play with that tomorrow.

-David