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Post by Ron Walker on Sept 8, 2022 19:19:54 GMT -7
Posted by: Owen Phairis Aug 27 2008, 02:30 PM Ron, I was comparing the picture of your star balls with a picture of the Novins. There seems to be some large differences as you will notice. The large black plate on yours, seems to be missing on the Novins although there is a similar, but smaller, mounting plate that is part of the planet cage. Even in the pictures of the complete projector there is a remarkable difference. The missing lenses on the Novins are in a separate box to be installed soon. Rons Novins
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Post by Ron Walker on Sept 8, 2022 19:22:42 GMT -7
Posted by: Owen Phairis Aug 27 2008, 03:54 PM Here are pictures of the complete projectors showing Rons and the Novins. There seems to me to be a noticeable difference on the size of star ball plate and how the star ball attaches to the planet cage. I find it interesting..... Rons Novins
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Post by Ron Walker on Sept 8, 2022 19:28:18 GMT -7
Posted by: Ron Walker Oct 9 2008, 09:40 PM The Minolta uses total lens-ed optical projection rather then pin hole projection used by some smaller projectors. The benefit to this is extremely sharp stars. The celestial sphere is divided into 32 sections. Sixteen are projected from the north star ball and sixteen from the south. Each of the 32 separate projectors have a complete optical system with condenser lens, star plate, and projection lens. Looking at one of these projectors from the outside one can see a very unique and simple mechanical solution to the problem of keeping the star projections off of the floor and out of the audience eyes. In front of the lens is a device very much like a doll's eyes. In order to keep the "lid" even with the horizon, the entire mechanism is suspended in a ball bearing surround that is waited by the thin tube at the bottom filled with mercury. No mater what direction the projector is set to, all of the "eye lids" are held level with the spring line. Also, because these "eye lids" are well out of the focal point of the projectors, the star images tend to fade as they reach the horizon very much like they do in nature. This system was first designed for the Zeiss II. Looking inside the star globe you can see several of the 16 projectors condenser lenses placed around the 500 watt lamp seen slightly out of focus just left of center. One of the things that I really liked about this projector was that the brightest stars looked both bright small and with the proper color. Only the two brightest stars have separate projectors so all stars from first magnitude to sixth are projected by the same lens systems. Looking closely at the back of one of the projectors, one can see what looks like a small colored lens. Adding color could have been easily added with just a small filter. It appears that these are actually small extra lenses with color filters that not only color the stars but also add additional intensity to the brightest stars so their size on the dome can be held to a reasonable size. If you look carefully you can see several in the above picture in several of the projectors. I really don't want to take one of these apart as the alignment is somewhat critical. However if the above is true, this is even more then I would expect from the engineering. I will say that whatever they did, the projected sky looks extremely realistic.
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Post by Ron Walker on Sept 8, 2022 19:31:41 GMT -7
Posted by: Owen Phairis Oct 10 2008, 12:05 PM Thanks to Adam, we have a diagram of what the optical and mechanical breakdown is: This one is for a Venus projector, however, I believe they are all very similar. Owen
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Post by Ron Walker on Sept 8, 2022 19:36:42 GMT -7
Posted by: Ron Walker May 18 2009, 10:24 AM I have gone forward and desided to clean all of the optics as a certain amount of dust and oily film build up is inevitable. Also, it was suggested to me that what I thought were small lenses on the star plates might indeed be blobs of melted material and this could be blocking some star holes. Upon removing the condenser lenses for cleaning, the thin metal star plates become visable and there is now no doubt that these are indeed small intensifying lenses. I have found that all of the first magnitude and brighter stars each have their own extra intensifying lenses so that these brightest stars do not grow in size on the projection dome, but just are projected brighter. This also allows for the subtle coloring of these stars as well. All about the lens-ed stars you can easily see the small holes for the 2nd through 6th magnitude stars. Also confirmation that this projector was indeed made for a 30 foot dome and not just adjusted for compromise settings. This supports my theory that if one wants all of the projected stars to appear star like, one is very probably limited to 4 or 5 magnitude max unless other optical means are employed for the brighter stars. Also after some thought and viewing, I can understand why the Academy projector limited their star-field to about 3500 stars. Once you pass through the 5th magnitude it becomes very difficult to see fainter stars. They become objects that appear more out of the corner of ones eye rather then just objects one can just look directly at. Don't get me wrong, I personally like having the extra layer of stars down to the 6th magnitude as it makes the star field more "real" as one sees in nature, but I doubt the casual observer would ever notice the difference.
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Post by Ron Walker on Sept 8, 2022 19:37:39 GMT -7
Posted by: charles jones May 20 2009, 12:08 PM Perhaps, research in their promotional material, would have uncovered the "bright star" lenses in the Minolta, but this is certainly an interesting find. I find it amazing that Minolta did this and wonder if Zeiss, with their "pre-fiber optic" projectors, did it as well.
I know the second generation of Zeiss projector had separate optical projectors with separate lamps for a number of the bright stars, but mounting lenses on the star plate is a different story.
Thanks, Ron for bringing this to light, so to speak.
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Post by Ron Walker on Sept 8, 2022 19:38:40 GMT -7
Posted by: Ron Walker May 21 2009, 10:38 AM
I wish I could find more info on the Minolta. Other then an ad from the period I can find nothing.
I don't think Zeiss did it, at least not in their full size projectors. When the II came out the first magnitude stars were projected over 20mm in diameter. I'm sure this is why the "ruff" was added under each star globe to carry the individual projectors for the first and second magnitude stars. When the Mark VI came out, faster optics complimented a new arc source allowing smaller holes for all of the stars and allowing the brighter stars to be placed back on the star plates.
Like most projectors, the Minolta uses separate projectors for Sirius and Canopus as they are negative magnitude stars. The lenses on the star plates is the first I've ever heard of and I don't know if anyone else has ever done it. There are no f numbers on the lenses but I should be able to get a rough estimate by measuring the focal length and the open aperture of the lens. Whatever it is, they did their homework as the projected sky is very realistic.
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Post by Ron Walker on Sept 8, 2022 19:39:17 GMT -7
Posted by: moonmagic May 22 2009, 02:27 PM I "think" the early Zeiss (through the model VI), then Goto and perhaps eventually (to some extent) even Minolta projected a number of the bright stars with individually aligned and focused optical projectors that plugged into the sides of each of the star balls or were hard wired. This was done in some cases because the star was bright and in other cases because of the stars color. I recall from seeing production literature on the Goto Mars (GX10-12) and also that big boy at Vanderbilt and the one formally at St. Louis, they had about 2 dozen seperate star, galaxy and nebula projectors mounted along the plate beneath each of the star balls. Some of them also projected variable stars.
On the Goto Mars (GX10-12) stars like Vega, Capella, Arcturus, Altair, Pollux, Antares, Canopus, Achernar, Centaurus, Crux, Sirius, Procyon, Rigel, Betelgeuse, Aldebaran, & Spica MAY have been projected by individual projectors. In addition nebula and cluster projectors were provided for the Large and Small Magellanic Cloud(s) M-31/NGC 224 Andromeda Galaxy; M42/NGC 1976 Orion Nebula; NGC 869-884 Perseus Double Open cluster; M44/NGC 2632 Praesepe; NGC 5139 Centaurus; and M-13/NGC 6205 Cluster in Hercules. Finally, two variable stars Mira and Algol
That's 27 individual projectors.
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Post by Ron Walker on Sept 8, 2022 19:40:02 GMT -7
Posted by: charles jones May 22 2009, 05:25 PM It is interesting to me the various schemes that have been used by the opto-mechanical projectors to create a more natural sky.
For a simple sky of 800-900 stars, it is possible to only vary the diameter of the star image to represent their brightness. If you want to project stars to the 5th or 6th magnitude (difference between the first mag. and sixth magnitude is, from what I remember, something like a 100:1), the method must be enhanced in some way.
Korkosz came up with a projector that essentially had three different star balls with three different sized lamps, projecting only certain magnitude stars from each one. Some stars projected were from two hemisphere projectors, then another group from four quartered projectors, and a third group from four more quartered sphere projectors--an idea ahead of it’s time. Cumbersome, but probably vary effective.
Even the early Peerless pinhole projection planetarium (mentioned elsewhere in the forum), appears to have two star ball projectors, perhaps with different lamps. Maybe one globe was for the Milky Way, but I suspect the projector divided the stars into groups of brightness. Anyone know?
Spitz, keeping things simple, came up with the separate lenses mounted on the star globe for the brighter stars—easy to do for the pinpoint projection system.
Zeiss had separate optical projectors with separate lamps for the brightest stars (I think 20 – 40 projectors?) Can you imagine having to change out all those lamps?
Goto copied Spitz on their pinpoint projector planetariums and Zeiss with their optical planetariums.
Now, Ron has shown us that Minolta was able to use separate “lenses” for the brightest stars on the same star plate as the other stars and project the combination optically. That is quite a feat for it’s time!
And the newest Zeiss projectors use fiber optics which enables them to intensify the brightness without always making larger images.
I cannot imagine video projection planetarium ever achieving this unless the projection system is doubled or tripled, in some way, with each projector at a different level of brightness for different groups of stars. Is this possible?
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Post by Ron Walker on Sept 8, 2022 19:44:46 GMT -7
Posted by: Ron Walker May 23 2009, 12:42 PM QUOTE(moonmagic @ May 22 2009, 02:27 PM) * I "think" the early Zeiss (through the model VI), then Goto and perhaps eventually (to some extent) even Minolta projected a number of the bright stars with individually aligned and focused optical projectors that plugged into the sides of each of the star balls or were hard wired. This was done in some cases because the star was bright and in other cases because of the stars color. I recall from seeing production literature on the Goto Mars (GX10-12) and also that big boy at Vanderbilt and the one formally at St. Louis, they had about 2 dozen seperate star, galaxy and nebula projectors mounted along the plate beneath each of the star balls. Some of them also projected variable stars.
On the Goto Mars (GX10-12) stars like Vega, Capella, Arcturus, Altair, Pollux, Antares, Canopus, Achernar, Centaurus, Crux, Sirius, Procyon, Rigel, Betelgeuse, Aldebaran, & Spica MAY have been projected by individual projectors. In addition nebula and cluster projectors were provided for the Large and Small Magellanic Cloud(s) M-31/NGC 224 Andromeda Galaxy; M42/NGC 1976 Orion Nebula; NGC 869-884 Perseus Double Open cluster; M44/NGC 2632 Praesepe; NGC 5139 Centaurus; and M-13/NGC 6205 Cluster in Hercules. Finally, two variable stars Mira and Algol
That's 27 individual projectors.
The original Mark II used f4.5 Tessar lenses and projected 1st magnitude stars as large as 40mm in diameter on a 20 meter dome. Zeiss made upgrades for the Mark II which became the Mark III and IV. An addition of two "ruffs" at the base of each starball carried individual projectors for the 42 brightest stars up to the 2nd magnitude. This allowed the decrease of projected star diameter to 27mm on a 20 meter dome.
When the Mark VI was built, the projection lenses were changed to f2.5 Planar lenses and the 1KW projection bulbs were replaced with brighter arc lamps. Because of the added brightness, all of the star holes were reduced in size and many of the brighter stars were placed back on the star plates. Only the brightest 15 remained as separate projectors.
We all know how adept the Japanese manufacturers were at "borrowing" from Zeiss and others for their own deigns, so it is not surprising that the developments of the 1968 Zeiss Mark VI would find there way into mid 70's projectors.
One of the positive things about putting the extra lenses on the star plates themselves is that besides the brighter and easily colored stars, they don't require separate light sources and will stay in proper alignment.
As best as I can measure, the lenses used on the Minolta star projectors is between f3.5 and f2.5. Since they are an optical company I can not imagine them scrimping on these lenses. From casual observation I would guess the brightest stars are not more then 5mm in diameter on a 30 foot dome.
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Post by Ron Walker on Sept 8, 2022 19:45:12 GMT -7
Posted by: moonmagic May 24 2009, 10:00 PM I've seen a number of Minolta and Goto machines over the years. They all produced great star fields, in my opinion. The old MS-10s and 15s were incredible. I think the MS-10s and the IIB were about the same? Anything above the Goto Mars for 40' domes and higher were wonderful star fields as well. While of course, considered the top of the line, Zeiss star fields were always spectacular, perhaps partly because they were usually in the largest domes and because most produced more stars than could be seen with the unaided eye. [5,500 stars vs. 7,500-8,000 is an incredible visual display difference] Yet, a small Goto Venus in a 20-30 foot dome is stunning.
Of course, I thought what I saw under a 12' dome with a Spitz A-1 when I was 8 years old was incredible! The great thing about Spitz is the number of people that have been exposed to planetariums and astronomy over the years because of the basic concept of creating a less expensive projection device that did almost everything done by the majorly more expensive suppliers.
(Years later when I saw Zeiss's in Rochester, NY., Atlanta, GA and at Chapell Hill I was awe-struck each time.) In the 70's the shows in Atlanta (Fernbank) were disappointingly poor, Chapell Hill had some of the best special effects there, while Rochester (Strasenburgh) had the most creative and original shows I've ever seen. They were the difference between seeing an elementary school play vs. a Broadway production. Strasenburgh was theatre at its best beginning to end. Script writing, naration, special effects, production ALL A+++. Truly theatre of the stars. They also used the planetarium and its capabilities throughout their show and not just as a backdrop. It's been years, I wonder what they do today? Yet with this all said, I am still convinced that it usually comes down to either one person who gives a live show or one person who makes the decisions and sets the tone for the production of a pre-recorded show that makes the real differences. There is truly something magical about a planetarium married to a person who can hold the rapt-attention of his auidence in the palm of his hand. It IS real theatre.
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Post by Ron Walker on Sept 8, 2022 19:47:17 GMT -7
Posted by: charles jones May 28 2009, 11:06 AM On the subject we started about bright star projectors:
I have a correction to make regarding the Zeiss bright star projectors in the Mark IV projectors. I had indicated that there were separate projectors and lamps for approximately 50 of the brighter stars. Yes, there are separate projectors but apparently not separate lamps for each.
I had time to visit Griffith yesterday. The old Mark IV is on display, hidden in a corner of the basement gallery. You can get up close to it.
It appears that there are two lamps contained in the thin, circular drum at the base of each star globe. Attached to this are the individual bright star projectors, each fitted with a prism system so that each projector can be rotated and tilted. It seems obvious that light for each projector comes from one of the two lamps inside the drum and must be redirected through prism or mirror systems.
This, of course, is a much better solution than having 50 or so lamps to change out every few months.
The drum appears to be 2" - 3" thick, large enough to contain a lamp. The bright star projectors seem to be mounted within an approx. 120 degree arc on either side of the drum. But, of course, the projectors can be aimed to cover areas of the sky between the two 120 deg. arcs.
On another note: The new Zeiss projector at Griffith is absolutely amazing and projects the most REALISTIC planetarium sky I've ever seen. All the stars are pinpoints. The bright stars are brighter, not bigger. Too bad the projector is not used more in the show. The current show only incorporates the Zeiss projector for about 10 minutes--the rest being pre-recorded video projection.
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Post by Ron Walker on Sept 8, 2022 19:50:08 GMT -7
Posted by: Owen Phairis May 28 2009, 11:19 AM QUOTE(charles jones @ May 28 2009, 11:06 AM) * On the subject we started about bright star projectors: I have a correction to make regarding the Zeiss bright star projectors in the Mark IV projectors. I had indicated that there were separate projectors and lamps for approximately 50 of the brighter stars. Yes, there are separate projectors but apparently not separate lamps for each. I had time to visit Griffith yesterday. The old Mark IV is on display, hidden in a corner of the basement gallery. You can get up close to it. It appears that there are two lamps contained in the thin, circular drum at the base of each star globe. Attached to this are the individual bright star projectors, each fitted with a prism system so that each projector can be rotated and tilted. It seems obvious that light for each projector comes from one of the two lamps inside the drum and must be redirected through prism or mirror systems. This, of course, is a much better solution than having 50 or so lamps to change out every few months. The drum appears to be 2" - 3" thick, large enough to contain a lamp. The bright star projectors seem to be mounted within an approx. 120 degree arc on either side of the drum. But, of course, the projectors can be aimed to cover areas of the sky between the two 120 deg. arcs. On another note: The new Zeiss projector at Griffith is absolutely amazing and projects the most REALISTIC planetarium sky I've ever seen. All the stars are pinpoints. The bright stars are brighter, not bigger. Too bad the projector is not used more in the show. The current show only incorporates the Zeiss projector for about 10 minutes--the rest being pre-recorded video projection. Interesting! I agree, The Zeiss IX produces the best sky I have ever seen. Wish I had known you were going, as I am in LA on assignment and would have met you there. Here is a close-up of what Charles is talking about.... Owen - Zeiss IV at Griffith Observatory -
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Post by Ron Walker on Sept 8, 2022 19:55:08 GMT -7
Posted by: Ron Walker Jun 22 2009, 05:45 PM As I continue with the cleaning of the Minolta projector I keep finding new and interesting ways the imaginative people working there solved certain projection problems. First I must say that the optic are built very well. Every outer lens surface of the star condensers was covered with a dirty oily film. No doubt this is the first time these optics have been cleaned since the projector was installed. Before cleaning: After cleaning: Haven taken several of these projectors apart, I can tell you that the insides are virtually spotless and none of the various projectors have needed any cleaning of any of the internal optics. The star plates with clean holes and clean bright star lenses needed no cleaning at all. Albert raised the question off line as to how this projector reproduced the naked eye images of the various nebula, galaxies, and star clusters this machine reproduced. It has been mentioned that many of the larger projectors used separate projectors for these objects much the same as they used separate projection optics for the brighter stars. Since Minolta managed to mount extra lenses onto the star plates and since it did indeed project many of the deep sky objects with uncanny realism, I endeavored to research the design once again to see exactly how this was done. As I was cleaning the south pole region projector it occurred to me that the large and small Magellanic clouds would probably be projected by this particular star place. Since its condenser lens was one of the dirtiest (since it spend most of its life at the very bottom of the machine this seemed normal) I desided that it was a good candidate to check out the condition of the other optical surfaces. Needless to say they were clean indicating the excellent design of the optical support mechanics. With the double condenser removed, the star plate was exposed and upon close inspection I could see two areas that appeared "roughened" on the otherwise smooth star plate. Looking through the lens end toward a light source I could see the nebulous looking clouds at these roughened points. How did they manage this. Taking the locking ring off, the thin metal star plate is easily removed and by placing it over a light source much is revealed. I know I should have used a tripod for these close up shots but they give you a good idea of how it is done. Here you see part of star plate #8 (the furthest south star plate) and you can see it was made for the Mark II and a 30 ft. dome. The small notch to the right is for alignment in the projector. One of the "rough areas" is revealed as a substantial number of small holes placed very close to one another in the shape of the large Magellanic cloud. The roughness was caused as the holes were punched from the opposite side of the plate. This is the side of the plate that faces the condenser lens set. You will note that the normal star holes are slightly bent out toward our view reinforcing the theory that the holes were punched from the projection lens side of the plate. I note that there is even some coloring on one edge of the cloud.
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Post by Ron Walker on Sept 8, 2022 19:56:53 GMT -7
Turning over this plate revealing the side facing the projection lens shows the simple magic used in this clever design. We can easily see two small pieces of frosted glass mounted over the heavily punched areas representing the Magellanic clouds. With a light source placed under the star plate (the normal position) you can easily see the defuse image of the large cloud presented to the projection lens. A more vertical view shows the clouds more clearly as well as some of the stars in the vicinity. This side of the projection plate is enclosed in the body of the projector, the projection lens cannot see the small piece of glass, only the defuse image of the clouds which are then projected with surprising realism to the dome above. Since this entire projector is a scale model of the Zeiss, I would imagine that this technique was developed with the German projector. However, since I have never seen first magnitude star lenses mounted directly on a star plate before, I can only wonder. One would need to see an original star plate from a Zeiss projector to know for sure. Either way, the design and construction of this machine is most amazing as is the realism of the star field projected.
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