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Everything posted by Gina

  1. Not the postman but Amazon Prime. Now I have a perfectly good post box and several good sheds to put packages in if I'm out but where did Amazon delivery put it???!!! Somewhere in my quite large garden. How I have to find it!! I've already looked twice so now I'll have to don wellies and search the more overgrown areas. Fortunately they took a photo but ATM I can't place it!
  2. Been thinking about whether I can combine the dehumidifier with the camera cooling to improve power efficiency. Looking at temperatures :- Camera may be -20°C Cold dehumidifier plate/heatsink - a degree or two above freezing Hot side of dehumidifier maybe 20-30°C (or more) Both temperature differences are easily obtained with Peltier TECs. TECs could be stacked with an aluminium plate between with the dehumidifier air cooler mounted on the aluminium plate.
  3. One possibility to reduce condensation in the lens would be to provide thermal insulation of the lens from the cold camera body by using a 3D printed plastic for the CS to T2 adapter instead of the supplied aluminium one. That would then just leave the optical window in the camera itself. Any dampness in the camera would probably condense on the cooled camera body in preference to the electronics or window but I'm rather concerned where it might end up. I'm concerned about cold, damp nights with lots of moisture in the air so I'm still thinking that keeping moisture out of the ASC would be best. I'm unlikely to want to image when it's actually raining.
  4. Ooooh another obsy build on the way - yippee Bring it on...
  5. The lens is directly on top of the cooled camera body and is likely to be several degrees below freezing. I have had moisture inside the lens when I've used it outdoors without the dome and outer ASC casing. OTOH warm air circulating around the lens might warm it up enough to prevent condensation. I'll try it. Then there's the question of how to heat the air. I might try combining cooling the camera with heating the air. Although far less efficient than water cooling, it might be sufficient, particularly if I used two stage Peltier TEC cooling. Using water cooling is not necessarily carved in stone.
  6. Ordered a pair of TEC1-12706 Peltier TECs plus a pair of 40mm square heatsinks from Amazon (Prime) arriving tomorrow or Saturday. OK cheaper on ebay but wouldn't get them until Wednesday or Thursday next week. I have a variety of fans I can choose from. The heatsinks would go on either side of the Peltier TEC.
  7. Both the cooler and heater heat exchangers can be simple CPU heat sinks. 3D printed ducting could carry the air round the system. The air coming out will be warmer than the air going in due to the inefficiency of the Peltier TEC but warmed air is what we want for feeding up into the dome to stop dew both outside and in (though the dehumidified air should not contain much moisture). Seems to me this doesn't need a particularly efficient Peltier TEC and the ultra cheap Chinese ones should do. It only needs to cool the air below dew-point. I wonder if I can make this small enough to put inside the ASC casing. A small tube would be all that is required to take the condensate away.
  8. The simplest dehumidifier would be to blow the air through packets of silica gel which would need replacing every so often with fresh or dried packets. However, experience has shown that the silica gel gets "full" pretty quickly even with the air indoors. The other way is to cool the air below dew-point so that the water condenses out. I could do this with a Peltier TEC. Of course the dried air would then need heating otherwise the dome will be cold and dew will condense on the outside. I guess the cooled and dried air could be passed through a heat exchanger on the hot side of the Peltier TEC and warmed up for feeding up into the dome. This would become a combined dehumidifier and dew heater. Hmmm... I wonder...
  9. Yes, that is just what I was thinking as an alternative. I shall have to think how I can manage it. Ideally, dry(ish) air from inside the observatory. OTOH is the air in the observatory dry? Alternatively, I'm wondering if I could make a tiny dehumidifier.
  10. 4 hours into the print and it's gone wrong!
  11. S@N from Sunday is repeated at 7:30pm BBC4 tonight - that's 20 minutes...
  12. Have ASC and mast indoors, taken the ASC off the mast and opened it up and, yes, it's wet inside. Only a couple of drops of free water but moisture all over the inside parts. I guess I now need to think carefully as to whether trying to keep the inside totally dry is a practical proposition.
  13. The silica gel has turned green so the inside of the main casing is no longer dry though there is no sign of misting of the lens - maybe some on the dome. I shall power down and bring the ASC indoors to investigate.
  14. Now 3D printing the casing, having serviced my Mini printer (and been out a lot).
  15. I had a chance today to talk to another member of the group I'm giving a talk to and she pointed out that most of the group are far from technical and all most will know about photography is to point their mobile phone or camera at what they see and press the trigger. Cameras these days tend to be totally automatic so exposure or aperture mean nothing. I think I may have talked myself into a "black hole"! Also, it seems 40 minutes would be a better length of talk - well, that's good anyway! So... cut out the technical stuff and just fill the talk with lots of pictures. Any technical issues can always be discussed in the Q&A session after the talk. Even things like field of view in degree was considered too technical. This is pretty restricting - seems I need to rethink my whole talk. At least I have a few months in which to do it. Fortunately, I do have plenty of photos of my imaging rigs and observatory which was considered well worth having a substantial section for since I built it myself.
  16. Is it my imagination or do clear skies nearly always coincide with a nearly or full moon?
  17. IMO there aren't enough results to give any significant statistical information. The variation in results far exceeds anything useful.
  18. Yes, the water soaking method is a tad slow!
  19. RSJ = Rolled Steel Joist.
  20. The raindrops dried of naturally during the daytime - we even had some sunshine this afternoon before the clouds came back. Now the clouds have moved away again but been replaced by the nearly full moon. Just the very brightest stars showing. With the dew heater on the dew is gradually going. This is 60s exposure with gain 0.
  21. Here is a design for the casing. The side extension and pillars are for the focus motor (28BYJ-48). The casing is taken up level with the edge of the lens to direct warm air for dew heating.
  22. No night sky images to post due to the weather but I can report that the outer casing is still sealed and dry inside. It does need a more powerful dew heater as I mentioned earlier. Also, I want to be able to dry off water droplets from earlier rain.
  23. I've also come across cases where the seemingly American based word censor objects to English words that have another meaning in the USA. Admittedly that was some time ago and it may have changed.
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