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> Spitz A-1 planet projectors., Or wierd things for any optical planetarium.
Ron Walker
post Mar 8 2012, 07:55 PM
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There has been a lot of talk lately of making some extra projectors to supplement larger machines. Anything from a Spitz Jr. to a Zeiss VI will benefit from an extra image or two. For me and my Minolta there are some little things that I would like to expand upon. Little things like adding some nebulosity to the Pleiades to the never ending need for an extra constellation outline projector or two. These basic projectors can be used for almost anything and the talk about a new planet, Sun, Moon projector for Charlie Miller's outreach planetarium kind of pushed me over the edge to come up with a simple inexpensive design to make these units.

If there is a good idea out there one can save a lot of time by just borrowing the design idea. The planet projectors for the Spitz A-1,2 is one of these ideas. A simple plate angled at 23.5 degrees relative to the latitude shaft makes a simple but effective platform for all the ecliptic objects one would normally like to represent. Banana plugs and jacks make it easy to move any projector to the proper place relative to the time and position of the object. I will talk a bit more detail about this plate later but for right now the construction of the projector shall take precedent.

The unit is basically a small slide projector with a light source, an image to be projected, a lens, all within a body to hold things together, and finally a way to mount it. A small locking universal joint makes a good mount as the projector can be quickly and easily manipulated to project anywhere on the dome. It is very important that we find parts and materials that are inexpensive (what I mean is cheap) so where can we find universal joints that are cheap.

Harbor Freight Tools is always a good place to look for such things and the third hand jig appears promising. They come on sale from time to time and are available for just a few dollars each.

Attached File  3rd_hand_from_HF.JPG ( 43.11k ) Number of downloads: 2
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Ron Walker
post Mar 9 2012, 10:48 AM
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Opening the blister pack reveals four small universal joints and a few other odds and ends for the "good junk" box. These are not the "cat's meow" of universal joints but are certainly good enough for our purpose which is to aim a small projector in a proper direction and hold it there. Basically when these are on sale, each UJ prices out to less then a buck. It is certainly not worth the time or expense to try and make these from scratch.

Attached File  complets_third_hand_jig.JPG ( 44.45k ) Number of downloads: 2
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Ron Walker
post Mar 9 2012, 10:57 AM
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Removing one of the UJ from the third hand jig and we have.

Attached File  one_universal_joint_removed.JPG ( 41.5k ) Number of downloads: 2


Since this unit was not designed for its new intended purpose which is to mount on either a Spitz A-1 like planet plate, mounting will be required via banana plugs. They come in two flavors, pin and spring flange. I would recommend the spring type as they can be inserted and removed many times and still hold the projector tightly as well as make electrical contact. I would recommend the dual type, (designed for power and ground) as they make for simple mounting of the projector.

Right now I only have some pin type around and will use one so you can see my mounting idea.

Attached File  bananna_plug.JPG ( 42.46k ) Number of downloads: 2


When making the mounting plate one must place the female jacks 3/4 of an inch apart so they will mate with the duel plug shown above. I would also mount the sets of jacks one inch apart so there will be no problem running a set of contacts to a particular switch on the control panel.
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Ron Walker
post Mar 9 2012, 11:05 AM
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We now need to take our first UJ set...

Attached File  one_universal_joint_removed.JPG ( 41.5k ) Number of downloads: 0


and take it apart.

Attached File  uv_joint_taken_appart.JPG ( 27.67k ) Number of downloads: 1


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Ron Walker
post Mar 9 2012, 11:29 AM
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Since these parts were not designed for their new purpose, a little machining must be done to modify them. The first part will be the base end.

Attached File  first_part_to_machine.JPG ( 45.25k ) Number of downloads: 1


This ball end was originally designed to slide along the central support rod and hold the magnifying glass in place. A small thumb set screw is tightened to hold it in place. You could simply mount the ball end with a screw in place of the thumbscrew.

Attached File  side_mount.JPG ( 45.44k ) Number of downloads: 2


This saves the use of any machine tool but only allows the use of one UJ per third hand jig as the other three will definitely require some machining.

So off to do some simple machining.
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Ron Walker
post Mar 9 2012, 03:20 PM
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The first job is to drill a #24 (is that right, I just did it and have forgotten allready...OLD... (IMG:http://www.observatorycentral.com/style_emoticons/default/huh.gif) ) ....

Attached File  drill_hole_for_tap.JPG ( 24.61k ) Number of downloads: 2


This allows me to tap a 10/32 thread for mounting.

Attached File  tap_10_32.JPG ( 30.92k ) Number of downloads: 2


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Ron Walker
post Mar 9 2012, 03:28 PM
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Now I have a universal mount for either a banana plug....

Attached File  stud_monun_on_banana_plug.JPG ( 22.34k ) Number of downloads: 1


or for mounting on any other projector such as the "ruff" below the star ball on my Minolta planetarium.

Attached File  Minolta_mount.JPG ( 39.03k ) Number of downloads: 0


As I mentioned before this could be a projector for a little nebulosity to surround the Pleiades. Mounted on the projector, once aligned, it should stay properly aimed until I want to change it.

Sorry about the dust. I haven't worked with this for a while. I must come up with a big bag to protect the finished projector when this thing gets back together.
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Ron Walker
post Mar 9 2012, 03:39 PM
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Once this banana mount is plugged into the main board, you can see how easy it will be to mount a projector.

Attached File  stud_on_banana_pluged_in.JPG ( 21.02k ) Number of downloads: 0


It takes only seconds to reassemble the entire universal joint.

Attached File  complete_banana_mount.JPG ( 25.58k ) Number of downloads: 0


I could mount one of my TPT projectors to this mount but I think we can come up with something a bit more sophisticated. The far left projector mounting end originally had a side thumb screw to hold a small alligator clip. One could still use this system to mount the projector but I noticed that the end hole was just about right for a 1/4-20 tap and so added one for a more permanent bolt to hold the projector.
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Ron Walker
post Mar 9 2012, 03:49 PM
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Someone, and I can't remember who (and I do apologize for that) had sent me some small prisms and a couple of small lenses. The went into my "good junk" lens box so I pulled one out for this experiment.

Attached File  100mm_fl.JPG ( 41.84k ) Number of downloads: 0


They have a focal length of about 100mm (4 inches) and are about 1/2 inch in diameter.

Thank you for whoever sent them to me.
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Ron Walker
post Mar 9 2012, 04:03 PM
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Since virtually all of my small projectors (planet, direction, constellation outline) use small miniature lamps with a bayonet base, and since many of these bulbs are either extravagantly expensive or no longer manufactured, I have decided to switch many of them over to LED's. Now wanting to have to replace all of the existing sockets, I looked around and finally found some that are replacements for car lights. They are miniature bayonet and have the current limiting resister built in. Also 12 to 16 volt DC is rather easy to generate and control, I decided this type of light would save a lot of work and made it one of my basic standard lamps. At $1.99 they are cheap and will probably outlive me if I don't abuse them much.

Attached File  LED_bulb.JPG ( 78.2k ) Number of downloads: 1
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Ron Walker
post Mar 9 2012, 04:06 PM
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For new projector construction, Owen very kindly sent me a bunch of miniature bayonet sockets for experimentation.

Attached File  Owen_socket.JPG ( 68k ) Number of downloads: 2


Thank You Owen.
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Ron Walker
post Mar 9 2012, 04:12 PM
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This makes it very simple to standardize on this small LED bulb and I am ready to start building a small projector.

Attached File  LED_in_socket.JPG ( 46.37k ) Number of downloads: 1


I think the body of the projector can be made of standard schedule 40 plastic plumbing or electrical pipe. It can be painted any color later to blend with the machine it is used on. The question is, will 1/2 inch pipe be big enough or should I go with 3/4 inch? This might require a trip to Home Depot.

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moonmagic
post Mar 9 2012, 11:56 PM
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This is really an excellent idea Ron. While I've never had your flair for making things or building things it still takes me back to the days of attempting to add new things to a small A-1. Very clever! mm
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Ron Walker
post Mar 14 2012, 11:33 AM
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QUOTE(moonmagic @ Mar 9 2012, 10:56 PM) *
This is really an excellent idea Ron. While I've never had your flair for making things or building things it still takes me back to the days of attempting to add new things to a small A-1. Very clever! mm


Thanks mm
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Ron Walker
post Mar 14 2012, 12:57 PM
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Some thoughts about brightness, lenses, and light.

As I looked out last night a view Venus and Jupiter in conjunction I became very aware of there massive brightness compared to the stars that surrounded them. This is perhaps one of the biggest failings of most planetarium projectors. These two planets, especially Venus, are never imaged at their proper perceived brightness. Nor, might I add, at there proper diameter. While only nature is exactly accurate (ant she has here cloudy days as well) we who strive to duplicator her must deal with the realities of limitations. Most often $$$ and size restraints. Even the largest and most expensive planetarium projectors compromise and tend to make the planets larger in size then the stars so they can be easily identified by the viewer. So how close can we get to perfection without breaking the bank, let's see.

The ideal would be a point spot of light that is very bright. This can only be accomplished with a bright light source and a fast (low f stop) lens. A projector is basically a camera in reverse so we can understand that to project a very small dot of light we need either an extremely small hole or a very long focal length lens. To project the same size image for a given distance, one can increase the size of the projected dot if one increases the focal length of the lens. Taken to the extreme, if the focal length of the lens is half the distance to the screen, the image projected will be the same size as that projected. Thus, if we wanted a 1/2 inch diameter projection of a planet we could have a 1/2 inch diameter hole at the focal plain of the projector but the lens would need to be half way to the dome which is impractical to say the least.

While we would like to make the image dot like, the costs of optics will limit us and we will have to make do with larger then life planet. So, since we certainly want to keep the size of the projected image small we must solve the problem with image size and lens focal length. We also have the problem of image brightness to contend with. The smaller the hole projected, the dimmer the image appears. This is how all star balls work. The brightest stars very often require additional optics even in pin hole projectors to keep their size within reason and yet brighter on the projection dome. This is why virtually every projector for a planet is an optical projector. This gives us our second limitation, we need a large enough hole to get enough light through for a bright planet.

Why not just use a colimating lens like the bright star lenses on many projectors you might ask. The projector would be much to long to be practical. Think of how far away the light source is from the star ball. No, we must also work within the physical constraints of the device we are building. A lens with a six inch FL would require a projector about eight inches long and would be straining the size limitations for most small projectors. Also, the longer the FL of a lens, the greater the diameter required for a given transmission of light to project an equally bright spot on the dome. This is why wide angle lenses tend to have a smaller diameter glass for a given f stop. That is why telephoto lenses are often "slow" and wide angle lenses "fast".

What is this idiot talking about (I can sense the vibrations this far away (IMG:http://www.observatorycentral.com/style_emoticons/default/blink.gif) ). Let us say you have a wide angle lens with a 1/2 inch FL and it is a very fast f1. The clear aperture of the lend would need to equal its FL thus it would need a clear aperture of 1/2". Not that hard to make a piece of glass that size. Now let's say we want a six inch FL telephoto lens of the same speed. We would need a clear aperture of six inches which makes for a rather large piece of glass. If we were OK with one stop less of light gathering power with a f2 lens, out wide angle lens would only require a 1/4 inch clear aperture but our telephoto would still require a three inch one.

One can easily see our new dilemma and compromise as we must not only limit the length of a projector but also its diameter. If the physical size didn't stop us, the price of the glass would. Thus compromise is the name of the game. Also imitation is the sincerest form of flattery so what do the big boys do. I am limited to those projectors that I have, but every one of them uses a FL of between two and four inches in length. An example would be the Minolta Venus projector has a three inch (75mm) FL lens that projects a hole 0.22mm in diameter to the screen. The image at fifteen feet is about one inch (25mm) in diameter. No longer a point as in nature but certainly a useable compromise. The lens aperture appears to be about f2.8 which appears to be the norm for auxiliary lens systems. The standard Spitz projector used for virtually everything on the A3P uses a two inch (50mm) lens. The lens is smaller in diameter but its shorter FL keeps it at a f2.8.

So what can we use to make a decently bright yet small image. Maybe we can't. That is the compromise. Perhaps that is the reason virtually all planetarium projectors project such large size planets. First to see them quickly in relationship to the stars, and to make them brighter then the stars.

I go through all of this so you can see my thinking when I try and design various elements from projectors to slip rings. I don't just pull figures out of my hat so to speak. None will be perfect, but all will work, be as inexpensive as possible, and hopefully easy to build with easily accessible parts.
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moonmagic
post Mar 16 2012, 01:37 PM
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Yes, what Ron said! mm
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Ron Walker
post May 2 2012, 03:30 PM
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OK, worked outside this morning and now need to do something this afternoon so I thought I'd actually finish one of the many things I've started even if there is no interest.

Anyway, a good cheap projector needs to be placed on the SCM (super cheap mount) so I'll call it the SCP (super cheap projector). Now this unit can be used to project, the Sun, the Moon, any planet, a satellite, nebulosity, a very bright star, whatever. While I got my start making SCP's with toilet paper tubes,

http://www.observatorycentral.com/index.ph...post&p=7648

I thought that a step up in quality would not upset any of the build it cheap crowd. The only requirement is to use readily available and inexpensive materials. Since I tend to build things with what I have on hand, I decided to use 3/4 inch plastic water pipe schedule 40.

This will require mounting of the lens (any lens will do) I showed above, and a mount for the light source.

A simple 3/4 inch pipe cap should do the trick.

Attached File  3_4_cap.JPG ( 69.47k ) Number of downloads: 2
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Ron Walker
post May 2 2012, 03:33 PM
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Out to the mini lathe and soon the 3/4 cap becomes a lens mount.

Attached File  lens_mounted_in_cap.JPG ( 69.65k ) Number of downloads: 1


This size cap will allow the mounting of a lens up to 26mm in diameter. Very versatile.
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Ron Walker
post May 2 2012, 03:37 PM
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Another visit to the lathe and we have a lamp mount.

Attached File  bak_soket_side.JPG ( 53.2k ) Number of downloads: 0


A view from the inside shows the mounted LED bulb.

Attached File  interior_with_led.JPG ( 37.36k ) Number of downloads: 0


You could put almost any miniature bulb socket up to and including a car size bayonet bulb. I am using an LED because I don't want heat and really don't need excessive brightness. My plan for this projector is to add a slight nebulosity around the Pleiades star group.
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Ron Walker
post May 2 2012, 04:20 PM
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With a simple projector like this, we will be projecting a simple small hole, either as a sharp point (planet, etc.) or as an out of focus patch. I probably will not use a perfect circle as my image but it all depends on what things look like 15 feet away on the dome. With this in mind and already stretching our budget with the lens and light source, we will not require any kind of condenser lens system. We will mount the image close to the light source so as to make total use of its brightness.

So we now gather the parts we need to complete the projector.

Attached File  needed_parts.JPG ( 24.77k ) Number of downloads: 2


We have a section of 3/4 inch pipe, a pipe coupler, and the lens and lamp mount end caps.

One last thing we need is something to make out image out of. I would suggest a heaver gauge aluminum tin such as a pie plate or in my case a lasagna pan. Might as well enjoy life as we build things.

Attached File  aluminum_pan.JPG ( 36.63k ) Number of downloads: 1
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