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Post by Ron Walker on Apr 18, 2022 18:40:17 GMT -7
Posted by: albert Mar 28 2021, 04:29 AM This topic will offer some insight into the inner workings of a Zeiss ZKP 2 projector. Our machine arrived in Bad Toelz on December 14., 2020 . It came to us from a museum in Fulda, they changed to a fulldome video system and had no use for this machine anymore. All the better for us- I am a firm believer in the opto-mechanical tradition. The moment of arrival! The console has three drawers with the power supply and electronics in it. Everything is modular- one of the main transformers has been changed to a toroidal model. All the "German Democratic" electronics have also been replaced, as well as the main motors. The central part of the machine came mounted on a solid steel frame to keep it from warping during the transport phase. Weight about 130 kilograms.
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Post by Ron Walker on Apr 18, 2022 18:45:14 GMT -7
Posted by: albert Mar 28 2021, 06:37 AM The major snag we hit was that the control cables were about 3ft too short. When the planetarium was built in 2012-2014, I had planned for a ZKP 2 machine and a cable conduct was inserted into the floor. So the position of the console was fixed. It cost us an entire afternoon to make additional cables. We had foreseen this and the technician had brought the necessary plugs...each with about 20 soldering points. Since the machine is on a long time loan, we did not want to destroy the original cables. We were a little worried about voltage drops since all the power to the machine is low voltage-high wattage. The console looks like something out of a Russian nuclear power plant...the main lights- dome light, Stars, have two buttons, one is ON one is OFF. They all have a very slow soft start and stop, which does a lot to preserve the lamps. The motors are also equipped with a slow start/stop ramp to avoid overloading the gears. Since the motors are electronically controlled they will turn off if something is binding or blocking the gearing system.
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Post by Ron Walker on Apr 18, 2022 18:47:53 GMT -7
The backside of the console panel shows old fashioned wire potentiometers. Impossible to find these days. Luckily, we have a few spares. The front plates of the console come off with all the pots- it is all a plug in system. No hanging wires everywhere. The motors have a system of switches on the axes of the pots- first the power to the motor is turned on- and only then the axis will move when you turn the pot. Everything is engineered to avoid any abrupt "jerks" in order to protect the machine.
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Post by Ron Walker on Apr 18, 2022 18:52:41 GMT -7
Posted by: albert Mar 28 2021, 06:46 AM The base ring on which the machine is mounted contains the motor for the polar axis, power is transferred thru a shaft going up to the machine. the blue and white dome light is built into the ring- the many light sources produce a pleasant effect of "cloudy sky" due to the multiple shadows of the machine they project into the dome. the lamps are 12volt car lights still available everywhere. Glass filters on top of the reflectors color and diffuse the light. All electrical connections go up into the machine from this ring. The machine itself gets all its power thru series of slip rings. These look fragile but are quite solid. The slip rings on the polar axis- there is one group on the West post and another on the East post. The lower part of the center piece contains a lot of slip rings, too. I hope none of this will ever need replacement. The lead weights in the foregrond are for balancing the machine on the polar axis.
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Post by Ron Walker on Apr 18, 2022 18:54:08 GMT -7
Here is a look inside the South Star ball thru the hole for the lamp holder. The condenser lenses and behind them the copper star field foils can be seen here. And this is a star ball from the outside. The lens is only the size of a fingernail, the entire star ball is not bigger than a soccer ball - 22 centimeters in diameter. the "eyelid" mechanisms are screwed into a thread and can be taken down for cleaning or dusting. The North and South Eyelids have different markings on them and in fact open in a slightly different way.
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Post by Ron Walker on Apr 18, 2022 19:01:00 GMT -7
Posted by: albert Mar 28 2021, 07:00 AM The machine has been installed on the center column, all the electrical connections were made, and we are ready for the mounting of the star balls.. The back of the console shows the massive control cables with their plugs. The cable channel in the floor had to be wide enough to pass thru the plugs! The star balls were cleaned and inspected before mounting them on the machine. Here one can see how small they are. Inside each star ball sits a halogen lamp with 12 Volts/75 Watts. In theory a 100 watt lamp would be possible, but then the star balls will get very hot. There is no cooling fan- all the cooling happens thru convection. The techician here is the only one worldwide who still does the maintenance for the older machines .Zeiss has stopped support long ago...one of the reasons for the unfortunate demise of these machines. In our small planetarium, we will take the risk and continue to use the machine, hoping that nothing will break down that cannot be fixed. And here is the machine finally installed and ready to go! Now all we need is an audience...let's hope the virus will be contained soon.
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Post by Ron Walker on Apr 18, 2022 19:01:43 GMT -7
Posted by: Ron Walker Mar 28 2021, 02:20 PM I too thank the video evolution as I would probably not have the projector I have without it.
Are the drive motors DC? I'm wondering why they are using pots to control the DC output voltage. They would need to dissipate a lot of heat especially at the slow motor operational end. I found it much more efficient to use an AC autotransformer to vary a voltage and then convert to DC to run the various motors.
I see what looks like six tubular light bulbs mounted with the pots. Are these indeed light bulbs that are used to limit inrush current as the resistance of the filament changes when activated?
The slides on the slip rings do look somewhat fragile as the thin "wire" appears easily bendable.
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Post by Ron Walker on Apr 18, 2022 19:02:05 GMT -7
Posted by: Scott T Mar 28 2021, 11:11 PM These are really beautiful pictures - thank you for letting us see the detail.
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Post by Ron Walker on Apr 18, 2022 19:02:26 GMT -7
Posted by: mrgare5050 Mar 29 2021, 03:37 AM That last one is truly one of the most beautiful pictures I can remember!
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Post by Ron Walker on Apr 18, 2022 19:03:08 GMT -7
Posted by: albert Mar 29 2021, 04:24 AM QUOTE(Ron Walker @ Mar 28 2021, 11:20 PM) * I too thank the video evolution as I would probably not have the projector I have without it.
Are the drive motors DC? I'm wondering why they are using pots to control the DC output voltage. They would need to dissipate a lot of heat especially at the slow motor operational end. I found it much more efficient to use an AC autotransformer to vary a voltage and then convert to DC to run the various motors.
I see what looks like six tubular light bulbs mounted with the pots. Are these indeed light bulbs that are used to limit inrush current as the resistance of the filament changes when activated?
The slides on the slip rings do look somewhat fragile as the thin "wire" appears easily bendable.
The drive Motors are servo controlled DC motors. they have a small encoder on the back so the speed is always controlled. So the pots feed into a control circuit and then the control card can be programmed with a speed ramp to avoid "jerking" anything. There is almost no heat generated, and nothing on the pots. The entire machine is completely silent even at higher speeds. How is that on your Minolta?
Most switches are also going into relays - the switches themselves last much longer that way. The tubular light bulbs illuminate the inscriptions on the panel-there is a white board behind the front panel and the light is reflected onto the inscriptions. That way they will not turn brown from the heat of the little lamps.
There is a huge self on the main power supply board to limit the current in the transformers at system startup. Otherwise the fuses would blow. And the wires on the sliding contacts may be spring steel. I have not touched them...rather prefer to be careful here.
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Post by Ron Walker on Apr 18, 2022 19:08:19 GMT -7
Posted by: albert Mar 29 2021, 09:45 AM One of my favorite photos was shot with a 17 mm wide angle lens Fellas, what are your favorite "beauty" shots of your own planetarium? I have spent hours shooting inside the dome, just for the fun of it. this is a weird shot- long exposure for the stars and a short "blip" with a flashlight for the machine, all shot at f/22 or so Highlighting features with a flashlight makes for interesting shots: I admit this is an extreme example- But the machines have a lot of detail and just what you want to show can be lost... Sometimes extreme angles look good- here is one of the shadows of the machine on the dome- they look like clouds- a pleasant side effect. Long time exposures can be augmented a lot if you use a light only for a frction of a second- no flash but a lamp of some kind. This way the stars don't get completely washed out. Another trick I found was to use existing lights on a long time exposure but to dim them down so they are just barely visible to the naked eye.
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Post by Ron Walker on Apr 18, 2022 19:10:15 GMT -7
Finally there is the whole area of shooting things in movement- here is a retrograde of Mars- annual drive only. Exposed one minute. With today's digital cameras experiments become possible that would have taken quite a few rolls of film in the old days....unfortunately the data compression for the upload here kills a lot of details - the original pictures are 20 megapixels... Let me see what you have shot in your domes!
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Post by Ron Walker on Apr 18, 2022 19:11:01 GMT -7
Posted by: Ron Walker Mar 29 2021, 10:10 AM QUOTE(mrgare5050 @ Mar 29 2021, 03:37 AM) * That last one is truly one of the most beautiful pictures I can remember!
I must agree. I really like the bright blue sky. I think I must add a bright blue sky as well as some white clouds floating through. Since my doors actually extend beyond the horizon I will need to project from the center of the room.
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Post by Ron Walker on Apr 18, 2022 19:11:31 GMT -7
Posted by: Ron Walker Mar 29 2021, 10:42 AM QUOTE(albert @ Mar 29 2021, 04:24 AM) * The drive Motors are servo controlled DC motors. they have a small encoder on the back so the speed is always controlled. So the pots feed into a control circuit and then the control card can be programmed with a speed ramp to avoid "jerking" anything. There is almost no heat generated, and nothing on the pots. The entire machine is completely silent even at higher speeds. How is that on your Minolta?
Most switches are also going into relays - the switches themselves last much longer that way. The tubular light bulbs illuminate the inscriptions on the panel-there is a white board behind the front panel and the light is reflected onto the inscriptions. That way they will not turn brown from the heat of the little lamps.
There is a huge self on the main power supply board to limit the current in the transformers at system startup. Otherwise the fuses would blow. And the wires on the sliding contacts may be spring steel. I have not touched them...rather prefer to be careful here.
It is interesting that the pots are only in the control circuits as they appear to be rather heavy duty like they are designed for control of heavy current or motors directly.
When I rewired and went to a more "brute force" type of control, all of my variable power sources are switched before the 120 volt AC Variacs where the current is at its minimum. This then drives various transformers to provide the lower voltages required to run the various motors and lamps. Full wave rectification is provided after the step down transformer for those circuits that require DC current. All in all it has worked very well for me.
The projector itself is quite silent. The only sound if you really concentrate is from two whisper box fans on each star ball. They are run in series and then powered by the star ball lamp circuit so they are sure to come on with the 500 watt lamps. Since each box fan at full power is actually at half voltage they are extremely quiet. The drive motors make no noise at all as they are all enclosed within the projector proper.
There is a tad of hum/vibration that I can hear at the control desk from the Selsun readout motors but is not heard in the visitor area. I am somewhat of a nitpicker here but it has never been enough for me to do anything about it probably because it comes and goes as the load on the readout gears changes with load. It is easy to just let the system move a bit more and things go silent.
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Post by Ron Walker on Apr 18, 2022 19:17:14 GMT -7
Posted by: Ron Walker Mar 29 2021, 10:52 AM QUOTE(albert @ Mar 29 2021, 09:45 AM) * One of my favorite photos was shot with a 17 mm wide angle lens Fellas, what are your favorite "beauty" shots of your own planetarium? I have spent hours shooting inside the dome, just for the fun of it. this is a weird shot- long exposure for the stars and a short "blip" with a flashlight for the machine, all shot at f/22 or so Highlighting features with a flashlight makes for interesting shots: I admit this is an extreme example- But the machines have a lot of detail and just what you want to show can be lost... Sometimes extreme angles look good- here is one of the shadows of the machine on the dome- they look like clouds- a pleasant side effect. Long time exposures can be augmented a lot if you use a light only for a frction of a second- no flash but a lamp of some kind. This way the stars don't get completely washed out. Another trick I found was to use existing lights on a long time exposure but to dim them down so they are just barely visible to the naked eye. Finally there is the whole area of shooting things in movement- here is a retrograde of Mars- annual drive only. Exposed one minute. With today's digital cameras experiments become possible that would have taken quite a few rolls of film in the old days....unfortunately the data compression for the upload here kills a lot of details - the original pictures are 20 megapixels... Let me see what you have shot in your domes! I must say the interior of your planetarium looks like some secret government board room, just beautiful. I have not spent the time I should with taking pictures inside the dome. I have a few attempts here and there but no real effort. It is something I need to do but I have so many other things that should take priority. I have to agree that wide angle lenses do take some of the best pictures and here is a quick one from the control console. It kind of makes the dome look twice as big with a Zeiss III in the center. After I add a nice deap blue sky like you have I will redo this image. I will also clear off some of my accumulated junk to make things more presentable.
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