Well, like anything there are pro's and cons to using certain telescopes.
The SDM is now a proven performer in my eyes. During Wartook Rise camp in June I used it and thoroughly assessed its performance.
The cooling system works really well and will cool the mirror within 2 hours. You will want to start cooling about an 1 hour before sunset though, just so that you can catch any early planets. I found that the thermal mass of the mirror does take a long time to remove; it is a big chunk of glass and will take much longer to cool.
However, once cooled it performs much better than any telescope I have owned. The views are simply amazing and the detail obtained is wonderful. On the night of the 2nd of June 2007 we were treated to lovely seeing. I imaged for several hours and then decided to pack up. It is my habit to do some visual observing after an imaging run and determine what the seeing was like at the end of a session. I have to say with a 6mm Radian in place the views I got were better than any telescope I have ever looked through (even a Takahashi 130). I could clearly see ovals all the way down to the poles on Jupiter and the detail in the equatorial belts was simply over whelming.
I have attached an image here, which shows some of the views we saw that night.
In terms of tracking this scope is still a little difficult at the extreme magnifications used. It will wander, but I think this can be eliminated a little with more precise balancing of the counter weight. It is managable, but could be made better. It is a testiment to the quality of the scope build and the servocat system that it just needs adjusting a little through each run to keep a planet on the chip. It is afterall a massive dobsonian mount, not really designed for this type of thing; but more than capable all the same.
The upshot is that large telescopes can be used by amateurs to image the planets. The long held myth that these scopes are not suitable for planetary image is now busted. If you follow my experiences and refine my processes a little you will be able to obtain wonderful images with large aperture telescopes.
The SDM is now a proven performer in my eyes. During Wartook Rise camp in June I used it and thoroughly assessed its performance.
The cooling system works really well and will cool the mirror within 2 hours. You will want to start cooling about an 1 hour before sunset though, just so that you can catch any early planets. I found that the thermal mass of the mirror does take a long time to remove; it is a big chunk of glass and will take much longer to cool.
However, once cooled it performs much better than any telescope I have owned. The views are simply amazing and the detail obtained is wonderful. On the night of the 2nd of June 2007 we were treated to lovely seeing. I imaged for several hours and then decided to pack up. It is my habit to do some visual observing after an imaging run and determine what the seeing was like at the end of a session. I have to say with a 6mm Radian in place the views I got were better than any telescope I have ever looked through (even a Takahashi 130). I could clearly see ovals all the way down to the poles on Jupiter and the detail in the equatorial belts was simply over whelming.
I have attached an image here, which shows some of the views we saw that night.
In terms of tracking this scope is still a little difficult at the extreme magnifications used. It will wander, but I think this can be eliminated a little with more precise balancing of the counter weight. It is managable, but could be made better. It is a testiment to the quality of the scope build and the servocat system that it just needs adjusting a little through each run to keep a planet on the chip. It is afterall a massive dobsonian mount, not really designed for this type of thing; but more than capable all the same.
The upshot is that large telescopes can be used by amateurs to image the planets. The long held myth that these scopes are not suitable for planetary image is now busted. If you follow my experiences and refine my processes a little you will be able to obtain wonderful images with large aperture telescopes.
29/04: Getting Collimation Correct
Hi all,
well I spent some time talking to Anthony Wesley a week or so ago and decided that just using my Laser collimator is not really good enough for imaging. He pointed me in the right direction and encouraged me to purchase products from Catseye. They make collimation systems which give you superb collimation for your newtonian. There are three parts to the kit. One tool squares up the secondary to the focusor, and another ensures that the secondary shows all of the primary in the focusor. The final part of the kit (the piece with the red triangle) brings the primary into alignment with the secondary and ultimately to focusor. At this date I am waiting for it to arrive from the US. The manufacturers are a small operation and seem very busy. They were very good in their responses via email and kept me informed about my order. This says more about what their business is about than anything else. The service has been good so far.
So yet another small mod and working towards they SDM being a great planetary scope.
well I spent some time talking to Anthony Wesley a week or so ago and decided that just using my Laser collimator is not really good enough for imaging. He pointed me in the right direction and encouraged me to purchase products from Catseye. They make collimation systems which give you superb collimation for your newtonian. There are three parts to the kit. One tool squares up the secondary to the focusor, and another ensures that the secondary shows all of the primary in the focusor. The final part of the kit (the piece with the red triangle) brings the primary into alignment with the secondary and ultimately to focusor. At this date I am waiting for it to arrive from the US. The manufacturers are a small operation and seem very busy. They were very good in their responses via email and kept me informed about my order. This says more about what their business is about than anything else. The service has been good so far.
So yet another small mod and working towards they SDM being a great planetary scope.
12/04: Another Much Needed Mod
With the success of the Nappy, I thought about a couple of issues over the last couple of weeks that related to this mod.
The first of which was that during viewing, the counter weight that I installed really over balances the whole system. Also the nappy tends to stop the scope from cooling naturally just for viewing. This can lead to stars being not quite crisp at the start of a session. Something that I really am not prepared to tolerate. After all, it is a nice mirror.
So with this in mind I set about making the Nappy a removable mod depending on what I am doing at the time. Pete kindly donated some water proof shade cloth, meaning that it stops water from penetrating it and ergo it will stop cold air from escaping. Pete also donated a couple of feet of velco too. Thanks mate, all donations gladly accepted. I went and got a further 2.5m of velcro to complete the task.
As you can see in the image below, I used contact adhesive to fix the velcro into position along the edges of the mirror box.
I also bought some butterfly nuts to put on the long bolts which hold the counter weight. That way I can undo the counter weight quickly and remove it if I am only interesting in viewing the heavens. It also means I can put it on really quickly too, should the seeing be such that I want to image immediately.
So the end result is now I can now remove the counter weight at will and the nappy also. It fits quickly and firmly all the way around and prevents cold air from escaping.
Until next time.
The first of which was that during viewing, the counter weight that I installed really over balances the whole system. Also the nappy tends to stop the scope from cooling naturally just for viewing. This can lead to stars being not quite crisp at the start of a session. Something that I really am not prepared to tolerate. After all, it is a nice mirror.
So with this in mind I set about making the Nappy a removable mod depending on what I am doing at the time. Pete kindly donated some water proof shade cloth, meaning that it stops water from penetrating it and ergo it will stop cold air from escaping. Pete also donated a couple of feet of velco too. Thanks mate, all donations gladly accepted. I went and got a further 2.5m of velcro to complete the task.
As you can see in the image below, I used contact adhesive to fix the velcro into position along the edges of the mirror box.
I also bought some butterfly nuts to put on the long bolts which hold the counter weight. That way I can undo the counter weight quickly and remove it if I am only interesting in viewing the heavens. It also means I can put it on really quickly too, should the seeing be such that I want to image immediately.
So the end result is now I can now remove the counter weight at will and the nappy also. It fits quickly and firmly all the way around and prevents cold air from escaping.
Until next time.
12/04: Second Shake Down
With the new mods completed I ran a shakedown on the weekend of the 31st of March. The mirror cooled extremely rapidly with the new 'Nappy' on the base of the mirror. The mirror was down below ambient after 2 hours. It was about 15.4 degrees at ambient and the mirror was 13.2 degrees. I then left it until following morning. However, once again I managed to get condensation drops onto the mirror surface (I have now decided what I will do when I am cooling the mirror, I will lay it nearly horizontal to eliminate this issue). I tried to clean this off which was a mistake. It resulted in me having to take the mirror out mirror box and give it a descent clean on the Monday morning.
Getting back to the mirror temperature; when I awoke the following morning, the mirror was so near ambient that I felt that I did not need to do any further cooling. It had kept pace with the falling temperature during the night and was only 0.4 of a degree above ambient. The seeing of course was as to be expected and not very good. There was no images gained during this test. Well none I would publish here.
In terms of the balance, I found that this was almost sorted. The image of Jupiter was consistently pulling to the right of the screen, but very slowly. I could easily get a colour and a half of data done before I needed to move the scope. I found that the extension cable that Darren got for me at Snake Valley works really well and allows me to make adjustments without causing any vibrations during imaging. I do still need to work on some final turning of the balance but I am much encouraged. I am thinking that there is a slight imbalance to the focusor side of the scope now and will need to conduct some tests to get this balance as close to perfect as possible.
Here is an image below that shows the scope setup in my front yard on the morning of the 1st April
Until next time.
Getting back to the mirror temperature; when I awoke the following morning, the mirror was so near ambient that I felt that I did not need to do any further cooling. It had kept pace with the falling temperature during the night and was only 0.4 of a degree above ambient. The seeing of course was as to be expected and not very good. There was no images gained during this test. Well none I would publish here.
In terms of the balance, I found that this was almost sorted. The image of Jupiter was consistently pulling to the right of the screen, but very slowly. I could easily get a colour and a half of data done before I needed to move the scope. I found that the extension cable that Darren got for me at Snake Valley works really well and allows me to make adjustments without causing any vibrations during imaging. I do still need to work on some final turning of the balance but I am much encouraged. I am thinking that there is a slight imbalance to the focusor side of the scope now and will need to conduct some tests to get this balance as close to perfect as possible.
Here is an image below that shows the scope setup in my front yard on the morning of the 1st April
Until next time.
29/03: The Mods Begin
Hi all,
well today after I got my paperwork completed I rang Anthony Wesley (Bird) and talked to him about some of the issues relating to the SDM. We also talked about his latest collection of Data, which I am very envious about. Anyway he suggested that my mirror could not cool properly if there were any holes in the system. We talked about a lot of other things like field rotation and his impending purchase of a Titan mount.
Next I rang Dave P and we talked about some of the ideas Bird and I had discussed. Next I rang Pete and he came over just as I was setting up the scope in the lounge room.
First thing we tackled was the imbalance issue. I set up the camera on the scope (including all the connection wires and power cables) and put the camera and filter wheel in place. Then I released the clutch and watched the secondary end head for the ground. Both Pete and I said you know what. Clearly the mirror is out of balance when the camera is in position and this would account for why I had trouble keeping the image of Jupiter and Saturn in the viewing panel while imaging at Snake Valley. I then grabbed a couple of old magnets from around the place and put them on the mirror cell. They are reasonably heavy. We noted that the scope immediately came to a halt, but we both thought it needed more weight. Pete then suggested that I could get a piece of iron bar or lead and bolt it onto the mirror box for a more permanent solution, Peter Read had made provision for this in his design with the bolts already in place and longer replacement bolts for the Job (Thanks Pete for the bolts). We headed down to Metal Fabricators and picked up a lump of iron just for the job. On the way back we picked up some black plastic and 100 mile an hour tape to fill the back of the mirror cell (see below)
When we got back, I immediately started to get the holes drilled in the iron bar. The trusty Hilti once again did the hard work. Once the holes were drilled I bolted the bar into place and checked the balance of the scope with the camera and filter wheel in place. The mod was successful and now the scope is nicely balanced with the camera in place. It is slightly out of balance when just using the eyepice, but I can live with that.
Next we set about sealing up the bottom of the mirror box to improve mirror cooling.
As most would know the bottom of the mirror box on these scopes is open to the air. The idea being that it aids in cooling of the mirror when observing during the night. The trouble is that when using active cooling the cold air is escaping from the any place with the slightest crack. The black plastic I bought would be the solution to that problem. Pete and I carefully fitted into place the plastic and sealed up all the holes. It is a temporary solution to the problem, but it is working (mirror being cooled right now and retaining all the cold air. After 1.5 hours the mirror is 1 degree below ambient and the difference is getting greater). It also helps solve another problem I was having. When cooling I was getting a lot of dew on cold plate in high humidity and when I pulled the cooling system out of the truss; water would drop onto the mirror (this only happened once). This was because the mirror box was in the vertical position and open to the humid environment. Now I can cool the scope in an angled position and the dew can simply run off the plate down the side of the box, thereby avoiding the mirror altogether. Also the dew formation should be severly reduced due to the air being dried out and no longer in contact with the entire atmosphere.
Next mod we made was to the cooler itself. We set about putting foam tape over the entire edges of the unit. Before I had it on the bottom of the cold plate, which was to act as a seal and protect the top of the mirror box. Unfortunately at Snake Vally I had trouble getting it out one night and accidently put a deep scatch into the timber. So we now have more foam on it and the chances of a serious scratch occurring now is extremely remote. All the sharp edges are now covered in foam. Also the seal is much better now too. (see below)
So now for some more field test, I hope to try this on the weekend and I will give you an update then.
Update, 2.1 hours and mirror temp was at 2.4 degrees below ambient. When I turned off the cooler the mirror only rose by 0.3 of a degree in 1/5 hour. It seems that the cooling was successful.
well today after I got my paperwork completed I rang Anthony Wesley (Bird) and talked to him about some of the issues relating to the SDM. We also talked about his latest collection of Data, which I am very envious about. Anyway he suggested that my mirror could not cool properly if there were any holes in the system. We talked about a lot of other things like field rotation and his impending purchase of a Titan mount.
Next I rang Dave P and we talked about some of the ideas Bird and I had discussed. Next I rang Pete and he came over just as I was setting up the scope in the lounge room.
First thing we tackled was the imbalance issue. I set up the camera on the scope (including all the connection wires and power cables) and put the camera and filter wheel in place. Then I released the clutch and watched the secondary end head for the ground. Both Pete and I said you know what. Clearly the mirror is out of balance when the camera is in position and this would account for why I had trouble keeping the image of Jupiter and Saturn in the viewing panel while imaging at Snake Valley. I then grabbed a couple of old magnets from around the place and put them on the mirror cell. They are reasonably heavy. We noted that the scope immediately came to a halt, but we both thought it needed more weight. Pete then suggested that I could get a piece of iron bar or lead and bolt it onto the mirror box for a more permanent solution, Peter Read had made provision for this in his design with the bolts already in place and longer replacement bolts for the Job (Thanks Pete for the bolts). We headed down to Metal Fabricators and picked up a lump of iron just for the job. On the way back we picked up some black plastic and 100 mile an hour tape to fill the back of the mirror cell (see below)
When we got back, I immediately started to get the holes drilled in the iron bar. The trusty Hilti once again did the hard work. Once the holes were drilled I bolted the bar into place and checked the balance of the scope with the camera and filter wheel in place. The mod was successful and now the scope is nicely balanced with the camera in place. It is slightly out of balance when just using the eyepice, but I can live with that.
Next we set about sealing up the bottom of the mirror box to improve mirror cooling.
As most would know the bottom of the mirror box on these scopes is open to the air. The idea being that it aids in cooling of the mirror when observing during the night. The trouble is that when using active cooling the cold air is escaping from the any place with the slightest crack. The black plastic I bought would be the solution to that problem. Pete and I carefully fitted into place the plastic and sealed up all the holes. It is a temporary solution to the problem, but it is working (mirror being cooled right now and retaining all the cold air. After 1.5 hours the mirror is 1 degree below ambient and the difference is getting greater). It also helps solve another problem I was having. When cooling I was getting a lot of dew on cold plate in high humidity and when I pulled the cooling system out of the truss; water would drop onto the mirror (this only happened once). This was because the mirror box was in the vertical position and open to the humid environment. Now I can cool the scope in an angled position and the dew can simply run off the plate down the side of the box, thereby avoiding the mirror altogether. Also the dew formation should be severly reduced due to the air being dried out and no longer in contact with the entire atmosphere.
Next mod we made was to the cooler itself. We set about putting foam tape over the entire edges of the unit. Before I had it on the bottom of the cold plate, which was to act as a seal and protect the top of the mirror box. Unfortunately at Snake Vally I had trouble getting it out one night and accidently put a deep scatch into the timber. So we now have more foam on it and the chances of a serious scratch occurring now is extremely remote. All the sharp edges are now covered in foam. Also the seal is much better now too. (see below)
So now for some more field test, I hope to try this on the weekend and I will give you an update then.
Update, 2.1 hours and mirror temp was at 2.4 degrees below ambient. When I turned off the cooler the mirror only rose by 0.3 of a degree in 1/5 hour. It seems that the cooling was successful.
23/03: First Shake Down
Well I took the scope to the Snake Valley camp to test it out.
Several things arose from the shake down.
First, this optical system rocks. The images presented by the mirrors were spectacular and tack sharp. Every person who viewed through it made comments about how sharp the stars looked. Targets like NGC 4945, M104 and the Tarantula resolve really well, in fact I found that I could see a cluster of stars at the centre of the Tarantula. I had never seen this before.
Second, this mirror gathers light. All the targets were bright even at 228x. When it came to the planets, Saturn was really bright, I could see bands, Cassini easily, 5 moons, and the crepe ring. Jupiter was insanely bright. Several people commented jokingly that they had little Jupiters before their eyes for several minutes afterwards. Contrast was great and detail in the bands and on the GRS was clearly visible. OMI torus produced a lovely mirror despite the wait.
Third, imaging at hi resolution proved to be impossible over that weekend. The target would drift erratically over the live panel, when I tried to correct this problem, I had little control over the outcome. Initially I thought that this was purely a counterweight related issue. However, I think that this is only part of the problem. Having now read the manual on the servo cat system. I think I have discovered reasons why imaging was impossible and very frustrating. On the hand pad, there is a switch to control the slewing rates of the scope. I had it set on the jog setting which will tend to over correct when guiding. It should have been set on guiding. Additionally, if I read the manual correctly, there is a sync function which will hold the pointing and prevent drift. I need to set this once I get my target on the screen. Furthermore, I can change a speed setting on the servocat from speed 1 to speed 2. This apparently tightens up guiding for high magnification targets. I will try to test this on this coming weekend if I get the chance.
Fourth, the current cooling system as constructed is able to cool the mirror, but not sufficiently to release the core heat. I could get the mirror down 0.5 degrees below ambient but as soon as I turned off the system, the mirror temp would begin to rise and remain stable at 2 degrees above ambient. This is partly brought about by the inefficient design I have devised. I really need to cool the mirror to 4 degrees below ambient to be effective and cool the core of the mirror. I have some ideas to counteract this. One of which is to place the current peltiers into the sides of the mirror box either just above or just below the mirror surface. I tend to think that the position would be better just below the mirror surface. All four would be placed at different positions around the mirror box, and this would stop a further problem that occurred over the camp. That being:
When using the cooler in humid conditions, condensation builds up on the cold plate. So much so that when I go to remove the cooler, which is a lid design, water drops onto the mirror. This cannot be allowed to continue for several obvious reasons. The first being that while the water is pure, it could be interacting with pollens and dust on the mirror. This could deggrade the coatings and cause some etching. Also I have noted there is some slight staining now on small parts of the mirror surface, which I am sure will come off with the first cleaning. I think it would be better if I could also view with the scope while it is being cooled and avoid water being spilled on to the mirror surface.
So with all that in mind, I have a few tasks to undertake in the next month or so.
Until next edition.
Several things arose from the shake down.
First, this optical system rocks. The images presented by the mirrors were spectacular and tack sharp. Every person who viewed through it made comments about how sharp the stars looked. Targets like NGC 4945, M104 and the Tarantula resolve really well, in fact I found that I could see a cluster of stars at the centre of the Tarantula. I had never seen this before.
Second, this mirror gathers light. All the targets were bright even at 228x. When it came to the planets, Saturn was really bright, I could see bands, Cassini easily, 5 moons, and the crepe ring. Jupiter was insanely bright. Several people commented jokingly that they had little Jupiters before their eyes for several minutes afterwards. Contrast was great and detail in the bands and on the GRS was clearly visible. OMI torus produced a lovely mirror despite the wait.
Third, imaging at hi resolution proved to be impossible over that weekend. The target would drift erratically over the live panel, when I tried to correct this problem, I had little control over the outcome. Initially I thought that this was purely a counterweight related issue. However, I think that this is only part of the problem. Having now read the manual on the servo cat system. I think I have discovered reasons why imaging was impossible and very frustrating. On the hand pad, there is a switch to control the slewing rates of the scope. I had it set on the jog setting which will tend to over correct when guiding. It should have been set on guiding. Additionally, if I read the manual correctly, there is a sync function which will hold the pointing and prevent drift. I need to set this once I get my target on the screen. Furthermore, I can change a speed setting on the servocat from speed 1 to speed 2. This apparently tightens up guiding for high magnification targets. I will try to test this on this coming weekend if I get the chance.
Fourth, the current cooling system as constructed is able to cool the mirror, but not sufficiently to release the core heat. I could get the mirror down 0.5 degrees below ambient but as soon as I turned off the system, the mirror temp would begin to rise and remain stable at 2 degrees above ambient. This is partly brought about by the inefficient design I have devised. I really need to cool the mirror to 4 degrees below ambient to be effective and cool the core of the mirror. I have some ideas to counteract this. One of which is to place the current peltiers into the sides of the mirror box either just above or just below the mirror surface. I tend to think that the position would be better just below the mirror surface. All four would be placed at different positions around the mirror box, and this would stop a further problem that occurred over the camp. That being:
When using the cooler in humid conditions, condensation builds up on the cold plate. So much so that when I go to remove the cooler, which is a lid design, water drops onto the mirror. This cannot be allowed to continue for several obvious reasons. The first being that while the water is pure, it could be interacting with pollens and dust on the mirror. This could deggrade the coatings and cause some etching. Also I have noted there is some slight staining now on small parts of the mirror surface, which I am sure will come off with the first cleaning. I think it would be better if I could also view with the scope while it is being cooled and avoid water being spilled on to the mirror surface.
So with all that in mind, I have a few tasks to undertake in the next month or so.
Until next edition.
13/03: Arrival of the General
Well my scope has arrived and I have to say it looks lovely and it is huge, much bigger than I thought it would be. Peter delivered the scope on the morning of the 8th of March 2007. Every part of the scope is superbly finished and installed. (see below)
First night I took it down to my parents place to give them a bit of a look. My mother is interested in astronomy, so she got a bit of a buzz out of it. I saw nice tight stars and Saturn was a nice image although the mirror was no where near ambient nor was the seeing anything above average.
On Friday 9th MarchI had second light with some buddies. We looked at globs, nebs and galaxies. Most of the galaxies I had never seen before. The nebula's were very bright. I could resolve the core of Omega Centauri easily, one of the best views in light polluted Adelaide.
Today I set it up in the living room to undertake some more cooling tests. I noted on Friday night that the mirror actually got warmer during the night rather than cooled, especially after I had the cooling system on for nearly 3 hours before I set it up. After discussion on the forum with people who have large mirrors and Anthony Wesley who is the resident peltier cooling sytem expert, I have come to the conclusion that the mirror is just releasing core heat and so the sensor says that it is getting hotter. So on nights when I want to image, I will need to start the cooling early in the afternoon. Today I tested this by cooling the mirror for 5 hours. You can see in the image below the ambient temperature was 18.0 degress and the mirror temp was 17.4.
In that image you can also see how the peltier system sits on top of the mirror box. I am considering installing some more peltiers in the sides of the box, so that active cooling and topping up can be conducted over the course of a night.
In addition, today I set up the camera system for a dummy run to determine whether I needed to lengthen cables. To my good fortune everything looks good and seems to work well. (see below)
And; for all those wanting to see this mirror, here it is and nicely centre spotted too. Finally here and ready for use.
Until next installment.
First night I took it down to my parents place to give them a bit of a look. My mother is interested in astronomy, so she got a bit of a buzz out of it. I saw nice tight stars and Saturn was a nice image although the mirror was no where near ambient nor was the seeing anything above average.
On Friday 9th MarchI had second light with some buddies. We looked at globs, nebs and galaxies. Most of the galaxies I had never seen before. The nebula's were very bright. I could resolve the core of Omega Centauri easily, one of the best views in light polluted Adelaide.
Today I set it up in the living room to undertake some more cooling tests. I noted on Friday night that the mirror actually got warmer during the night rather than cooled, especially after I had the cooling system on for nearly 3 hours before I set it up. After discussion on the forum with people who have large mirrors and Anthony Wesley who is the resident peltier cooling sytem expert, I have come to the conclusion that the mirror is just releasing core heat and so the sensor says that it is getting hotter. So on nights when I want to image, I will need to start the cooling early in the afternoon. Today I tested this by cooling the mirror for 5 hours. You can see in the image below the ambient temperature was 18.0 degress and the mirror temp was 17.4.
In that image you can also see how the peltier system sits on top of the mirror box. I am considering installing some more peltiers in the sides of the box, so that active cooling and topping up can be conducted over the course of a night.
In addition, today I set up the camera system for a dummy run to determine whether I needed to lengthen cables. To my good fortune everything looks good and seems to work well. (see below)
And; for all those wanting to see this mirror, here it is and nicely centre spotted too. Finally here and ready for use.
Until next installment.
While I waited for the delivery of my SDM I decided to confront the cooling issue, with the construction and design of the top plate peltier cooling system. The idea being that peltiers are employed to actively cool the mirror of the SDM from above rather than a system that cools from below such as that employed by Anthony Wesley. The system is broken into to several parts. There are peltier coolers with heat sinks installed onto an aluminum plate, a perspex plate to isolate the heat, and fans that blow air onto the cold plate.
So I rang Peter Read and got him to measure the top of the mirror box and with those measurements I went and got a 6mm perspex and a 4mm aluminum plate (cold plate). I also picked up 4 Dick Smith coolers to canabalise.
My first step was to measure up the perspex so that the peltiers from the Dick Smith coolers could fit through to the aluminum plate. (see insert)
The reason for the perspex is to isolate any ambient or peltier heat that might influence the cold plate and in turn prevent the colling system from working at its peak.
Once I had the perspex marked out I enlisted the help of my friend Peter to hold the perspex steady while I cut the holes out. Upon completion of this task I commenced installing the peltiers onto the cold plate through the perspex. (see below)
To maintain registration I simply used the stainless steel plates from the inside of the Dick Smith coolers and transferred this onto the cold plate. I then screwed the peltiers onto the cold plate with the screws that held the original stainless plate and peltier onto the cooler box.
My next issue was how to make the wiring look neat and tidy and connect it all together. I decided to feed the wiring down through the perspex plate' (see below)
and then feed them across the cold plate and into a central box on the peltier side. (see below)
Then I installed the cold plate fans and to ensure that the fans were far enough off the plate I used some pvc tubing to act as spacers. (see below)
The height above the cold plate has two purposes. The first being to clear the screw heads that hold the peltier coolers in position. The other being that computer fans work best when they have room to push the air away from the cold plate.
The completed system can be seen below.
I bench tested the unit by placing a temperature sensor inside of a box about the approximate size of the mirror box. Bench tests show that the unit will cool this space to 4 degrees below ambient and maintain the temp if ambient does not drop. If ambient is dropping it will continue to keep pace with the falling temperature.
So I rang Peter Read and got him to measure the top of the mirror box and with those measurements I went and got a 6mm perspex and a 4mm aluminum plate (cold plate). I also picked up 4 Dick Smith coolers to canabalise.
My first step was to measure up the perspex so that the peltiers from the Dick Smith coolers could fit through to the aluminum plate. (see insert)
The reason for the perspex is to isolate any ambient or peltier heat that might influence the cold plate and in turn prevent the colling system from working at its peak.
Once I had the perspex marked out I enlisted the help of my friend Peter to hold the perspex steady while I cut the holes out. Upon completion of this task I commenced installing the peltiers onto the cold plate through the perspex. (see below)
To maintain registration I simply used the stainless steel plates from the inside of the Dick Smith coolers and transferred this onto the cold plate. I then screwed the peltiers onto the cold plate with the screws that held the original stainless plate and peltier onto the cooler box.
My next issue was how to make the wiring look neat and tidy and connect it all together. I decided to feed the wiring down through the perspex plate' (see below)
and then feed them across the cold plate and into a central box on the peltier side. (see below)
Then I installed the cold plate fans and to ensure that the fans were far enough off the plate I used some pvc tubing to act as spacers. (see below)
The height above the cold plate has two purposes. The first being to clear the screw heads that hold the peltier coolers in position. The other being that computer fans work best when they have room to push the air away from the cold plate.
The completed system can be seen below.
I bench tested the unit by placing a temperature sensor inside of a box about the approximate size of the mirror box. Bench tests show that the unit will cool this space to 4 degrees below ambient and maintain the temp if ambient does not drop. If ambient is dropping it will continue to keep pace with the falling temperature.
11/03: September 2006
Well as most of you know, I have ordered an 18" truss Obsession style scope from SDM (http://www.sdmtelescopes.com.au/index.html), which comes with Servocat and Argo Navis. They are a local Australian manufacturer of these scopes. Peter, the owner and builder is a real nice guy. He really wants to please. The scope is tailor made to my needs. Things like an extra heavy duty focusor board, shortening the truss poles to allow for imaging needs.
Which brings me to my next point. Yep, I plan to use this new scope to image the planets. I figure that I will get some nice extra resolution over the C9.25. Since resolution is proportional to aperture I am going to be happy with an extra 25% more resolution. Not sure if this is unrealistic, but I think that this is possible.
So I hear you all say what about cooling a scope like that. Yep, all ready thought of that. To image the planets we all know that active cooling is a must. With the C9.25 I keep the scope outside under a tarp during the year. This helps keep it permacooled. When I do image, I usually give the scope a blast with the Lymax cat cooler. Well in the SDM ("The General")cooling presents an entirely different problem. For imaging; the mirror needs to be within 0.6 of a degree of ambient temperature. This ensures that tube currents or wave fronts are not present to distort the image. Typically, mirrors will not keep up with ambient cooling during the night. To get around this problem I plan on replacing the mirror cover plate with an aluminium; 5mm thick. On top of the cover plate I will mount 5 peltier coolers. The plate will act like a cold plate. On the underside I will install 5 fans to blow cold air down onto the mirror. This will in effect create a refrigerator. I anticipate that cool down should be somewhere between 35-60 minutes. I am thinking the mirror should read somewhere 2 degrees below ambient before I attempt to turn off the peltiers. Then all I need do is wait for equalisation.
Now the mirror itself is the real cost in the operation. SDM installs for me an OMI Torus mirror. OMI typically produce mirrors with 1/20 wave or better. Since Celestron produces mirrors around 1/8-1/12 I figure that the SDM mirror should produce incredible results. Besides the diameter of the mirror will allow and encourage me to do more DSO viewing. I have been told it will open up a hole new universe. Many faint galaxies in the C9.25 will be bright with good detail. Many galaxies that I have never seen will also now be available for viewing.
Furthermore, with the new DSI II pro and drizzle software which locks onto two stars for stacking I might even be able to image some of the nice DSO's.
So in effect this really does become the ultimate scope. Well at least that is the plan. We shall see.
Which brings me to my next point. Yep, I plan to use this new scope to image the planets. I figure that I will get some nice extra resolution over the C9.25. Since resolution is proportional to aperture I am going to be happy with an extra 25% more resolution. Not sure if this is unrealistic, but I think that this is possible.
So I hear you all say what about cooling a scope like that. Yep, all ready thought of that. To image the planets we all know that active cooling is a must. With the C9.25 I keep the scope outside under a tarp during the year. This helps keep it permacooled. When I do image, I usually give the scope a blast with the Lymax cat cooler. Well in the SDM ("The General")cooling presents an entirely different problem. For imaging; the mirror needs to be within 0.6 of a degree of ambient temperature. This ensures that tube currents or wave fronts are not present to distort the image. Typically, mirrors will not keep up with ambient cooling during the night. To get around this problem I plan on replacing the mirror cover plate with an aluminium; 5mm thick. On top of the cover plate I will mount 5 peltier coolers. The plate will act like a cold plate. On the underside I will install 5 fans to blow cold air down onto the mirror. This will in effect create a refrigerator. I anticipate that cool down should be somewhere between 35-60 minutes. I am thinking the mirror should read somewhere 2 degrees below ambient before I attempt to turn off the peltiers. Then all I need do is wait for equalisation.
Now the mirror itself is the real cost in the operation. SDM installs for me an OMI Torus mirror. OMI typically produce mirrors with 1/20 wave or better. Since Celestron produces mirrors around 1/8-1/12 I figure that the SDM mirror should produce incredible results. Besides the diameter of the mirror will allow and encourage me to do more DSO viewing. I have been told it will open up a hole new universe. Many faint galaxies in the C9.25 will be bright with good detail. Many galaxies that I have never seen will also now be available for viewing.
Furthermore, with the new DSI II pro and drizzle software which locks onto two stars for stacking I might even be able to image some of the nice DSO's.
So in effect this really does become the ultimate scope. Well at least that is the plan. We shall see.
