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Hi, I've been working on a DIY fan for my 10" Skywatcher newt. My plan is to measure the ambient temperature and the mirror temperature with two separate thermistors and control the fan speed depending on the temperature difference. My question is, does it make sense to use the fan if for some reason the ambient temperature is higher than the mirror? The fan is sucking the air out the tube at the moment.
Hi all. I'm hoping for some advice on a subject which I know has had a lot of air time, but which I'm still wrestling with. Firsty, I know I get dew on my secondary mirror and it has wrecked many a DSO photgraphy session. I've fitted a home made heater, and this seems to fix it. It's insulated with neoprene, and runs at a very low wattage (about 0.4W) , so hopefully not too much turbulence. Next step is to do the same to the guide scope, which also mists up after about an hour, and then maybe the primary with a very low wattage. The main puzzle for me is this: Some folk say the mirrors are huge heat reserves, and take ages to cool down, during which time they cause turbulence. But other folk say the mirrors drop in temperature rapidly and go below the dew point, and then suffer condensation. I suspect theres some truth in both statements, but this doesnt simplify how to deal with it. Probably the main consideration is that the primary is much less ikely to suffer dew than the secondary, and so they have different problems and solutions. It would be easy to say that turbulence is in the eye of the beholder, but for sure when I'm focussing - using the camera and Live View with high screen mag - there appears to be turbulence aplenty even after an hour of cooling and before putting the secondary heater on. Of course this could be atmospheric, rather than tube currents. Rather than go through all my (muddy) thinking, can I just ask some direct questions please which relate to all this. 1. Is the small amount of heat on my secondary likely to cause any significant turbulence? 2. Is the turbulence that I see on the screen likely to be caused by the OTA? 3. I havent actually seen dew on the primary - but I've read that low grade condensation can affect the reflection. Is heating of the primary maybe just unneccesary? 4. If I heat the guidescope with a belt at about 2.5W, might this adversely affect the guiding property? 5. If I use an exhaust fan to cool the primary, is there any prospect that the air current will: a. increase dew on the primary and/or secondary by drawing in more damp air? b. reduce dew on the primary and/or secondary by evaporation? I'd be really grateful for any help with this. My next step is to wire up some kind of controller, and it would be useful to know what I'm likely to need to run before doing this. Many thanks
Decided to put cooling fans on my newtonians a 200pds and a 130pds ,used a 120mm on the 200 and a 80mm on the 130pds ,i used, Be Quite silent Wings2 fans they use rifle bearings and are so quite German made, i did the 200 first and was impressed with this make so ordered the same make for the 130 pds it comes with a lead with four wires but only needed neg ang pos so snipped other two out , made a disc from plastic and cut out around collimation screws on primary then used velcro to attach to OTA fitted a 2.1mm dc socket on to the disc then bought a usb lead to 2.1mm barrel though i may fit another 2.1mm socket on my power box and use 12v either way it works ,i used a dimmer on the 200pds but it doesnt need it and wouldn't use it again but its fitted now so will leave in place.