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Post by Ron Walker on Jun 13, 2022 13:59:06 GMT -7
Posted by: Philostopher1 Aug 26 2017, 06:29 PM
I'll try to keep the rest of my project confined here. Let me know if Admin would like me to post differently.
I just got my Hemispheres from Columbia Metal Spinning. They came out a bit thicker than I wanted. I was hoping for something around .060" and I got .125". No problem these came out beautiful and they are very precise and the cost was under $300- for the pair. In retrospect I should have ordered one.
As I have been noodling over this I started thinking a lot about the aesthetics of the projector. If I am going to commit a couple of years to this project it might as well look nice! Also, I didn't want to commit to drilling away because you can't undrill... Instead, I am going to use it as a form for a Carbon fiber\ Kevlar Starball. I found some high tech looking black and blue weave. This also has the advantage of being very light since I am going to drive this with GT2 timing belts and Nema 17 and 23 motors.
I lost track, but somewhere here I described a fiber glass process if one wishes to make their own spheres. That will be my approach essentially.
My projector is going to be based on the RSA Cosmos design. It's basically a pin hole system with lenses. I have 80-250mm lenses now and am having another 300 made in China. I am lensing everything down to mag 2.5.
The RSA Cosmos SN700
My hemispheres are 180 degrees but I need to go to < 190 degrees to cover any gap from the split starball along the equator. I am going to try to keep that gap within 6". I can easily extend my form and extend the arc a bit before I've "glassed myself" in a corner with the carbon fiber. Milky way and setting circles will be projected from the equator via slides. Eventually planets will be on a rail across the front as seen above.
A lot of work ahead. My biggest concern is of course a perfect star. Unfortunately, physics and finances limit the possibilities. I had hoped that I could cram the light from a high power LED into a 1 mm light pipe integrating rod. You can't. It's like trying to shove a 1" wooden dowel into a 1\4" hole. Either the hole gets bigger or the dowel gets smaller... Damn Physics! So I am going to have to settle for more of a spot than a point. Sigh. I am trying to leave enough wiggle room in the yoke design to accommodate more optics if necessary should an upgrade be possible
The biggest stress and foggy area is getting this machine to work with an integrated software platform of some kind. I think it will be "digilog" for a while. I am approaching this as a three axis CNC with an Arduino interface.
Below is some parts, a few lenses are shown the rest are packaged still.
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Post by Ron Walker on Jun 13, 2022 13:59:35 GMT -7
Posted by: Ron Walker Aug 27 2017, 11:07 AM
Looks like a great project. Don't worry too much about the 180/190 degree thing. Somewhere on these pages is a discussion about this and what Spitz did on their STP projectors and it turns out that you just need to move the light source up a tad in each hemisphere and it all works out just find. One would think that doing that would stretch the stars around the equator but it appears not to be the case and everything works out just fine.
Looking forward to your progress reports.
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Post by Ron Walker on Jun 13, 2022 14:05:33 GMT -7
Posted by: Philostopher1 Aug 27 2017, 01:47 PM QUOTE(Ron Walker @ Aug 27 2017, 11:07 AM) * Looks like a great project. Don't worry too much about the 180/190 degree thing. Somewhere on these pages is a discussion about this and what Spitz did on their STP projectors and it turns out that you just need to move the light source up a tad in each hemisphere and it all works out just find. One would think that doing that would stretch the stars around the equator but it appears no to be the case and everything works out just fine. Looking forward to your progress reports. Hi Ron! There is a problem with moving the light source up in my design centered around the LED emitter. I have to use a fisheye lens because the direct viewing angle of the led for the Nichia 319 is only 120 degrees. Also the emitter is too big and the lens cuts the apparent image of the emitter down about 1/2. The Led emitter is approximately 3 mm whereas a small short arc similar to Spitz is <0.8mm. I know John Hare at Ash enterprises developed a drop in LED lamp for the Spitz A3P, 512, and 1024. I don't know about the STP. I'd like to see it. I digress. The main problem is that leds don't have an even Lambertian distribution pattern. (see graph)  There is a hot spot in the center. The fisheye greatly helps to homogenize this out but there is a little less light off center tapering off as the angle increases. Then there is another problem. The led image the pinhole produces becomes more elipsoidal as the viewing angle increases. So the best compromise is to drop the lamp below the horizon. It's frustrating. I only need to extend the angle of 3 degrees so I am going to introduce a slight offset into the sky to compensate. I don't think it will be noticable except to me, you or someone that lives and breathes planetariums.... I tried to solve part of the spatial\lambertian distribution problem with a light pipe integrating rod. (IOS Optics was kind enough to loan me some to try) It certainly homogenizes the spatial distribution but there is a numeric aperature problem from the led to the rod. Again an apparent image of a large emitter, thus bigger star. Of course, it doesn't solve the problem of the off axis "elipsoidalization" on the larger angles... The LEP (light emitting plasma) sources are promising, but still the plasma envelope is about the same size as the led emitter where the plasma forms. And they are a nightmarish setup do to routing the RF source to them through slip rings etc. A lot of trade offs. Really the xenon arc lamp is ideal. And as you know, lens projection overcomes all of these problems (with their own). I originally planned this. I had hoped to accomplish it with 12 used camera lenses. The star plate size is highly limited to the sensor or film size. A large format lens would work great but now the cost goes up to $500- each. I am too poor for that game. So I'll live with larger stars until I can replace the light source. This is where my perfectionism becomes agonizing. |
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Post by Ron Walker on Jun 13, 2022 14:06:12 GMT -7
Posted by: Ron Walker Aug 28 2017, 11:20 AM
Perfectionism is a pain that I totally understand.
The STP uses a small arc that is projected down into a small hemispherical front surface mirror that provides a "fake" light source that is visible from anywhere inside the pin hole projection sphere. That same technique was also used in the model "B", "C", as well as the larger single ball projectors.
I thought that I've had before is to divide the star ball into several sections, probably five minimum, four around the horizon up to 45 degrees and one directed toward the zenith. One would need to block off each section so that that the LED for each section would not provide light to other star holes.
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Post by Ron Walker on Jun 13, 2022 14:06:41 GMT -7
Posted by: Philostopher1 Aug 28 2017, 12:17 PM
QUOTE(Ron Walker @ Aug 28 2017, 11:20 AM) *
Perfectionism is a pain that I totally understand.
The STP uses a small arc that is projected down into a small hemispherical front surface mirror that provides a "fake" light source that is visible from anywhere inside the pin hole projection sphere. That same technique was also used in the model "B", "C", as well as the larger single ball projectors.
I thought that I've had before is to divide the star ball into several sections, probably five minimum, four around the horizon up to 45 degrees and one directed toward the zenith. One would need to block off each section so that that the LED for each section would not provide light to other star holes.
Interesting. I am trying to visualize this. So essentially, is there a half-dome front surface mirror at the equator of the starball with the arc lamp above with a lens system to focus it on the mirror? Wouldn't this create a shadow from the lamp? The segmented idea is good. You and another friend proposed this as I was getting started on my project. It does solve the homogeneity issue with the led but raises the parts count.
Cree makes a smaller LED with a 2mm emitter in their XPE series but it is square... The Nichia 319AT, though bigger around 3 mm is hexaganol (and significantly brighter). The difference is , eh hem, night and day lol. To get a smaller point the fisheye or a hemispherical mirror is still required.
Do you have a picture of the Spitz mirror arrangement?
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Post by Ron Walker on Jun 13, 2022 14:07:34 GMT -7
Posted by: charles jones Sep 6 2017, 09:13 PM
Maybe I can shade some light on this.
This is a voice from the past. Yes, Ron I still check out Planetarium Forum now and then.
I think I can help with how the Model B and the mirror projected. These are pictures from the Spitz patent for that projector. A very powerful zirconium arc lamp was mounted at the zenith of the star globe. The lamp projected a narrow beam of light. It was also made brighter by adding a lens system. It The lamp projected straight to the mirror ball and reflected out. Fact is the image of the arc actually can be seen from far more than 90 degrees from the source. Check it with a Christmas tree ornament. This gave it the ability to move the mirror upwards to compensate for the space between the hemispheres. The ball had to ability to make the light visible over 220 degrees or more.
This patent is really all about the unusual artificial horizon. When the star globe approaches an upside down position, the normal cup artificial horizon prevents the light from hitting the mirror. So this is what was devised: The cup had slits on opposite sides for the light to hit the mirror. To hide the image of the light source through the slits, the mirror ball was blackened on opposite sides. In order to work together, the mirror ball was geared to the cup. This causes the ball to rotate as the cup changed position.
There are some drawbacks with this system of projection. The loss of light through the use of a mirror ball is greater than light projected through a fisheye lens. Hence, Spitz this special, very bright arc lamp, which you wouldn't want to use in a small projector. Then there is the matter of the very complex artificial horizon. And the matter of blocking stars at the zenith of each hemisphere with the lamp. Not sure what Spitz did about this Polaris would be is the position of the lamp.
I have a full pdf of the patent and description if you like.
Charles
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Post by Ron Walker on Jun 13, 2022 14:07:51 GMT -7
Posted by: Strgzr Sep 6 2017, 09:46 PM
Awesome stuff! You guys blow my mind!
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Post by Ron Walker on Jun 13, 2022 14:08:44 GMT -7
Posted by: Philostopher1 Sep 6 2017, 10:07 PM
QUOTE(charles jones @ Sep 6 2017, 09:13 PM) *
Maybe I can shade some light on this.
This is a voice from the past. Yes, Ron I still check out Planetarium Forum now and then.
I think I can help with how the Model B and the mirror projected. These are pictures from the Spitz patent for that projector. A very powerful zirconium arc lamp was mounted at the zenith of the star globe. The lamp projected a narrow beam of light. It was also made brighter by adding a lens system. It The lamp projected straight to the mirror ball and reflected out. Fact is the image of the arc actually can be seen from far more than 90 degrees from the source. Check it with a Christmas tree ornament. This gave it the ability to move the mirror upwards to compensate for the space between the hemispheres. The ball had to ability to make the light visible over 220 degrees or more.
This patent is really all about the unusual artificial horizon. When the star globe approaches an upside down position, the normal cup artificial horizon prevents the light from hitting the mirror. So this is what was devised: The cup had slits on opposite sides for the light to hit the mirror. To hide the image of the light source through the slits, the mirror ball was blackened on opposite sides. In order to work together, the mirror ball was geared to the cup. This causes the ball to rotate as the cup changed position.
There are some drawbacks with this system of projection. The loss of light through the use of a mirror ball is greater than light projected through a fisheye lens. Hence, Spitz this special, very bright arc lamp, which you wouldn't want to use in a small projector. Then there is the matter of the very complex artificial horizon. And the matter of blocking stars at the zenith of each hemisphere with the lamp. Not sure what Spitz did about this Polaris would be is the position of the lamp.
I have a full pdf of the patent and description if you like.
Charles
Thank you Charles!
I remember you from around 2008 on here! I had a GOTO M1 and was working on a dome for it. That's a depressing story so I won't go there.
Very interesting indeed. This is along the lines I was thinking. I hadn't considered the horizon cut-off. Very clever. I never knew about Zirconium Arc Lamps! I just read up on them. Sounds like they have a very short life do to the zirconia heating and melting down. Not to mention a high voltage power supply.
A lot has changed since then (2008) with LED technology and the dramatic lowering of costs. I just bought a 36, and two 12 channel slip rings from Amazon!
I am still a bit stuck on my LED lamp arrangement. As I mentioned, I am using a hex emitter led from Nichia and a 6-element fisheye lens for a smartphone ($15- Amazon!)
The point source is still too big for my OCD nature and this arrangement you shared could help. But I am leaning towards creating a point under the fisheye lens by focusing a high intensity LED into\onto a medium of some kind. Maybe a 1\2 ball lens with a diffuse surface, or a round cut gem quality Sapphire and scatter the light. They both have inherent issues... I may go this route, (the mirror ball) if my other schemes fail. With modern LEDs high lumen density is easily achievable. I would NOT try to reproduce that gear system though. I was planning on using the projector mount for the cut off as RSA Cosmos does. Not as elegant as Spitz but simple. This gets me thinking about a horizon cup though. I could fit one around the fisheye lens body should I satisfy my point source problem.
Well, I am a planetarium nut so if you can share a pdf that would be awesome!
philostopher1@gmail.com
Thanks again!
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Post by Ron Walker on Jun 13, 2022 14:09:11 GMT -7
Posted by: Ron Walker Sep 7 2017, 01:10 PM
QUOTE(charles jones @ Sep 6 2017, 09:13 PM) *
Maybe I can shade some light on this.
This is a voice from the past. Yes, Ron I still check out Planetarium Forum now and then.
I think I can help with how the Model B and the mirror projected. These are pictures from the Spitz patent for that projector. A very powerful zirconium arc lamp was mounted at the zenith of the star globe. The lamp projected a narrow beam of light. It was also made brighter by adding a lens system. It The lamp projected straight to the mirror ball and reflected out. Fact is the image of the arc actually can be seen from far more than 90 degrees from the source. Check it with a Christmas tree ornament. This gave it the ability to move the mirror upwards to compensate for the space between the hemispheres. The ball had to ability to make the light visible over 220 degrees or more.
This patent is really all about the unusual artificial horizon. When the star globe approaches an upside down position, the normal cup artificial horizon prevents the light from hitting the mirror. So this is what was devised: The cup had slits on opposite sides for the light to hit the mirror. To hide the image of the light source through the slits, the mirror ball was blackened on opposite sides. In order to work together, the mirror ball was geared to the cup. This causes the ball to rotate as the cup changed position.
There are some drawbacks with this system of projection. The loss of light through the use of a mirror ball is greater than light projected through a fisheye lens. Hence, Spitz this special, very bright arc lamp, which you wouldn't want to use in a small projector. Then there is the matter of the very complex artificial horizon. And the matter of blocking stars at the zenith of each hemisphere with the lamp. Not sure what Spitz did about this Polaris would be is the position of the lamp.
I have a full pdf of the patent and description if you like.
Charles
I'm thinking that Polaris would be 23.5 degrees off from the dead end of the star hemisphere, the offset for processional motion. They probably did some prisms for the bright stars blocked by the lamp itself. Like they projected the south stars with the A3P etc..
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Post by Ron Walker on Jun 13, 2022 14:09:35 GMT -7
Posted by: Ron Walker Sep 7 2017, 01:16 PM
QUOTE(Strgzr @ Sep 6 2017, 09:46 PM) *
Awesome stuff! You guys blow my mind!
Trouble is we blow our own minds as well. blink.gif
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Post by Ron Walker on Jun 13, 2022 14:10:01 GMT -7
Posted by: charles jones Sep 7 2017, 06:47 PM
Actually because the star globes and planet projectors are tilted 23 1/2 deg., Polaris would be just about where the arc lamp is. But I think you are right in that Spitz probably had small prisms to project an "offset" Polaris or other stars.
But can you imagine stringing the power cable to the lamp around various stars till it reached the base?
Charles
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Post by Ron Walker on Jun 13, 2022 14:10:35 GMT -7
Posted by: charles jones Sep 7 2017, 06:53 PM
Did any of you know that the earliest Spitz Model A, had a plastic dodecahedron supported at both the north and south poles, much like your typical earth globe. Hence, stars were eclipsed momentarily as the star projector turned.
I had read the early instruction manual for this early Spitz. It actually mentions that Polaris will disappear occasionally. Can you imagine?
Charles
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Post by Ron Walker on Jun 13, 2022 14:11:05 GMT -7
Posted by: mrgare5050 Sep 8 2017, 01:33 AM
QUOTE(charles jones @ Sep 8 2017, 01:53 AM) *
Did any of you know that the earliest Spitz Model A, had a plastic dodecahedron supported at both the north and south poles, much like your typical earth globe. Hence, stars were eclipsed momentarily as the star projector turned.
I had read the early instruction manual for this early Spitz. It actually mentions that Polaris will disappear occasionally. Can you imagine?
Charles
-------------------------------
I actually love that Charles - you could say - look, the Polarians are trying to signal us, saying WHO GAVE YOU PERMISSION TO USE US AS YOUR NORTH STAR?
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Post by Ron Walker on Jun 13, 2022 14:11:29 GMT -7
Posted by: Philostopher1 Sep 8 2017, 09:33 PM
QUOTE(mrgare5050 @ Sep 8 2017, 01:33 AM) *
-------------------------------
I actually love that Charles - you could say - look, the Polarians are trying to signal us, saying WHO GAVE YOU PERMISSION TO USE US AS YOUR NORTH STAR?
Ron and Charles, I want to thank you for sharing the polar mounted lamp arrangement. For the last couple of days I have been talking to my mentor Casey Stack and an engineer at Edmund Optical. It's looking like this arrangement may be best. As we know, moving a pinhole farther away from the irradiant source produces a smaller image of the source on the screen or film.
Moving my LED up to the pole and focusing it on a sphere effectively doubles the distance from the source to the pinhole. And as Ron pointed out allows simpler flexibility in shifting any necessary angular offset required because of the yoke. Still, my led of choice will have an emitter of 3mm. The Zirconium arc lamp had a 0.3 mm arc!! There is just no way to achieve that artificially. Still this arrangement may help significantly. Now I need to get a ball lens coated with enhanced aluminum. Anyone know of a company that does this inexpensively for amateur telescope mirrors?
Another thread that I have revisted was eyeglass lenses for star correction. The 3x ones work quite well except the angular divergence increases from the center to the edges. I haven't official measured this. It's quite dramatic though. Pieces could be selected to bend the star direction to our will. I was looking at my sky atlas and it would only be a dozen or so for the northern hemisphere.
I got more parts today!!
Slip rings and copper tape to make my own!
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Post by Ron Walker on Jun 13, 2022 14:12:06 GMT -7
Posted by: Philostopher1 Sep 9 2017, 02:00 AM QUOTE(mrgare5050 @ Sep 8 2017, 01:33 AM) * ------------------------------- I actually love that Charles - you could say - look, the Polarians are trying to signal us, saying WHO GAVE YOU PERMISSION TO USE US AS YOUR NORTH STAR? Ron and Charles, I want to thank you for sharing the polar mounted lamp arrangement. For the last couple of days I have been talking to my mentor Casey Stack and an engineer at Edmund Optical. It's looking like this arrangement may be best. As we know, moving a pinhole farther away from the irradiant source produces a smaller image of the source on the screen or film. Moving my LED up to the pole and focusing it on a sphere effectively doubles the distance from the source to the pinhole. And as Ron pointed out allows simpler flexibility in shifting any necessary angular offset required because of the yoke. Still, my led of choice will have an emitter of 3mm. The Zirconium arc lamp had a 0.3 mm arc!! There is just no way to achieve that artificially. Still this arrangement may help significantly. Now I need to get a ball lens coated with enhanced aluminum. Anyone know of a company that does this inexpensively for amateur telescope mirrors? Another thread that I have revisted was eyeglass lenses for star correction. The 3x ones work quite well except the angular divergence increases from the center to the edges. I haven't official measured this. It's quite dramatic though. Pieces could be selected to bend the star direction to our will. I was looking at my sky atlas and it would only be a dozen or so for the northern hemisphere. I got more parts today!! Slip rings and copper tape to make my own! Also, I just stumbled on this, hope you all enjoy it! A very early movie entertainment piece about planetariums. youtu.be/B0o9IQbbVGQAnd here's some stars. The only edit was cropping and converting to 640 x 470. My camera is 8 megapixels and was about 7 feet away. It photographs on the blue side. This is the Nichia 319 A hex emitter LED with the fisheye as seen on a previous post in this thread. There was a shaded 60 watt bulb on in the room and a big mosquito zapper. Here's the test rig. |
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