Astro Miser

Hi Gina, I want to congratulate you on a fascinating thread and read (its taken me several hours :-). In fact I have signed up to this forum just to leave comment for you. I am just beginning in astrophotography and I'm doing a lot of research. Reading your thread I see that making a good ASC is actually much more difficult than it first seems. I see the main problems are weather proofing and cooling (I will ignore focusing, covering, electronics and software ect for the moment). I was thinking how I would go about this myself with little money and no 3d printer. I will try to describe my ideas for comment. I know a lot of details need working out and are all important but I'm interested if this kind of setup could work in principal. For my simplest setup with no cooling. The dome would be mounted on top of a piece of 4 inch plastic drain pipe, say 3 feet long and open at the bottom. The camera would be placed inside a food container/drinks bottle with a neoprene/rubber "diaphragm" that the lens could be pushed through (like someone putting on a dry suit). Silicone grease could be used around the lens barrel to help sealing and allow the lens to rotate. The cables are sealed into holes in the container and simply fall out the bottom of the pipe. The camera container could be mounted by a bracket to the inside of the pipe. The advantage of this setup is that if any water gets into the top will simple run down the inside of the pipe and out the bottom. Dew control and day time cooling: If you can imagine dividing the pipe in two, lengthwise, by say a piece of flat aluminium so that you have two half pipes. Air could be blown up one side into the dome and down the other side. A resistive heating element could be added to warm the air and in turn heat the dome and lens. During the day this would keep everything at ambient. I think only a small airflow would be needed. A mesh (think flour sieve) could be fitted in the bottom to keep the wildlife out. Now a cooled version: I was reading about cooling DSLRs and came across this: https://sites.google.com/site/beppelastrofilo/home/canon-1100d-mod-filter-removal-direct-cooling-electrical-dew-control A quote from the above link: "The sensor develops about 4 watts, while the Peltier cell, if supplied to the maximum rated voltage of 15.4 volts, delivers a power more than ten times greater (45 Watt). This energy surplus is not an advantage, but quite the opposite. The mistake that many fall into is precisely that of using very powerful TECs, thus thinking of reaching higher cooling temperatures, but the opposite is true. In fact, the temperature reached by the heatsink (T diss) is proportional to the power produced by the device and the sensor cools down to a temperature (Tsens) equal to: T diss - (ΔΤ is in any case always lower than the theoretical maximum the cell is capable of. , but I won't dwell on this point). This means that, with the same ΔΤ, the greater the power delivered by the TEC, the hotter the heatsink will be and, consequently, the less cold the sensor will become. On the other hand, the real ΔΤ also varies as a direct function of the ratio between current power and maximum rated power of the cell. The curves representing these two functions cross at a point that determines the correct parameters to be set to obtain maximum cooling efficiency." It is clear to me that for efficient cooling 3 things are imperative 1, The removal of a LOT of heat, 2) The insulation from heat conduction, convection and radiation of the object being cooled, thus reducing the problem to removing the heat generated internally, and 3) A well chosen peltier device run at the 'sweet spot'. Back to the design. Expose the bottom of the camera (the flat bit) by cutting a hole in the bottom of the food container and sealing it with silicone. Attach the peltier cold side to the camera so that the hot side protrudes through, a L shape copper block could extend the hot side down and to the side. The container could be filled with polystyrene balls (or similar), desiccant bags and wrapped in ally foil. I was thinking that a heat-sink could be made by folding copper sheet many times (with gaps for air flow) and fitting it into the 'hot' side of the pipe. The advantage here is that it can be made quite long (as the pipe is long) increasing the surface area. Alternativly, standard heat sinks could be bolted together side by side and then turned on end to fit the pipe. A fan blows air up the hot side of the pipe, over the heat-sink, into the dome and down the other side. This should give more than enough heat to keep the dew off the dome and lens. Because the camera is sealed in a container any frost should form on the outside of the container and when it melts it should drip out of the bottom of the pipe (the danger is that the peltier could get wet). Other electronics and stuff could fit into the 'cold' side of the pipe. Thanks for reading and what do you think? John