Heater Tape & Controller For My C9.25 OTA

[M4lcs67]

Hi all,

Only had one opportunity to use my new scope once since I got it. However on it's first outing the front element dewed up big time even with the dewsheild on. I am therefore fooking at a dew prevention system and am currently looking at an Astrozap heater tape and controller.

I am told that if I put a suitable heater tape on I wont need the dewsheild. Hope that someone can confirm that this is the case as it is going to be a real pain faffing around putting a dewsheild on as well. I know I am going to get something before I use the scope again as it is pretty much unusable at the moment.

Thanks

[Northern Soul man]

Hi Ya Malc, these larger SCTs really suffer with dew, due ( I know same word different spelling) to the large surface area of the corrector - I got a controller off e bay - the 4 channel version (Hitecastro) and works really well, remember these summer nights are prone to a moist atmosphere - so winter will be a little better (wished I could observe from Mars - nice and dry) I have the flexible dew and heater tape combined - blumming expensive £75.00 nicka but really works well, but a good blast from a hair dryer will work just as well - but electrics and a moist environment spell danger so be careful - oh and glad the op went well been watchin your posts - take care mate - have a look on e bay can't remember the outlet but keep looking. I know that heat close to the corrector seems the exact opposite to what we need ( a well cooled optical path - leaving the scope out to cool down) the dew heater controller is variable so set it to just above the air temp as to not degrade the optical path ( I know that when star testing the optics - some nights the airy disc is "boiling") - its a fine line between a clear corrector and heated tube currents - remember that the atmosphere will always degrade the image more than the defects in the lowered contrast that an SCT will give you ( the secondary mirror obstruction).

Take care mate - hope that helps a little - go for the dew shield and heater - you'll have to mess around with the settings on the heater a little as every nights observing is different - some nights are "wetter" than others - but with that set up your gonna have some real pleasure under the stars. Regards Paul

[brantuk]

I've used SCT's for some time now and they do really need dew control on some evenings. I use a Kendrick Digifire 7 controller with 4 outputs and it's never let me down. A 10" band round the corrector is the minimum you'd need and I would suggest a dewshield as well. The dewshield helps to keep dew off but also serves to shield off stray light entering the ota when observing from a light polluted area.

I sometimes have a band round the primary too, as well as the eyepiece (or bv's) and finder scope. A low heat output hairdryer is fine for periodic use so long as you don't blow directly onto he corrector plate. Sudden changes in temperature can cause it to crack. I just swish warm air round the inside of the dew shield - but if the dew's getting heavy it's probably time to pack up anyway.

[faulksy]

or you can make your own i did i have a heater on my correctot e.p. and both ends of my finder all indapendantly controlled. as brantuk says good idea to use a dew shield as well that way you can keep heat down to a minimum on your corrector and also stops stray light entering your o.t.a.