Theres been a few threads lately relating to temperature control and mirror cooling in newtonian scopes.
Here is one solution that is reported to work well for some people.
It consists of a fan sealed at the back of the scope, with a baffle of inner diameter equal or slightly larger than the mirror diameter.
Such an arrangement will much more efficiently cool the mirror by providing air flow around the mirror, but the real benefit is from scrubbing the boundary layer of warm air from the front surface of the mirror and hopefully flushing it out of the tube.
That looks good, Geoff. Installing the baffle would be the trickiest part. And when it's done you'll have people lining up to get a look through the fan.
Good point Tony. Dobbers tend to forget that there is other ways to mount a Newtonian. There I was at Star Camp, and to the horror of EQ-mounted Goto-Newtonian owners, I kept trying to tug at their OTA to centre an object in the field of view.
A practical consideration is insulating the ota from mechanical vibrations from the fan.
I have made a plywood disk to sit on the back of the scope holding the fan. This will be held to the back of the ota with velcro straps and rubber weather strip will seal the disc and provide mechanical insulation.
Even without the baffle it has to be a much better way to cool the mirror than the silly arrangement some GS scopes ship with.
A fan mounted directly to the back of the mirror cell will just bounce air off one small part of the mirror.
I'll be in the process of building another telescope soon and I was thinking of putting two small fans on ether side of the OTA just above the mirror surface, including a larger fan on the back of the mirror. All fans will be sucking not blowing.
I'll be in the process of building another telescope soon and I was thinking of putting two small fans on ether side of the OTA just above the mirror surface, including a larger fan on the back of the mirror. All fans will be sucking not blowing.
Even without the baffle it has to be a much better way to cool the mirror than the silly arrangement some GS scopes ship with.
A fan mounted directly to the back of the mirror cell will just bounce air off one small part of the mirror.
Very true, that's why I changed mine to the sealed configuration after reading that thread from CN you linked to
The op of the CN thread advises that the suggested setup in that article isnt the best way to do it.
A fan blowing across the primary with exit holes on the opposite side cannot channel the warmer air out of the tube without it rebounding and bouncing around in the light path.
It would probably make more sense for the side mounted fan to be sucking rather than blowing.
if you were sucking through the side, I spose it makes sense to draw air from underneath (hole there already), from above (10" hole already) and from holes drilled on the other side to the fan over the mirror???
My new cooling fan arrangement, courtesy of Starklers dodgy workshop productions is having its first light (blow) tonight minus the baffle.
Im hoping the seeing settles down a bit later and Ill try some fan on/off tests.
Putting my ear to the open end of the OTA it sounds like a vacuum cleaner
Even without the baffle it has to be a much better way to cool the mirror than the silly arrangement some GS scopes ship with.
A fan mounted directly to the back of the mirror cell will just bounce air off one small part of the mirror.
I don't know what GS scopes have the fan mounted this way. My gs Factory fitted fan is set way back from the mirror and blows cold air over the entire surface. And it must curl around and blow across the mirror removing the boundary layer at the mirror surface coz it blows dew of the front!
Even without the baffle it has to be a much better way to cool the mirror than the silly arrangement some GS scopes ship with.
A fan mounted directly to the back of the mirror cell will just bounce air off one small part of the mirror.
I disagree Geoff, I have the 12" GSO and the volume of air passing out the top of the tube when the fan is running is very high, it clearly passes over the entire mirror and up the tube, if you have any doubt, try putting the cap on and removing the smaller aperture cap, the wind blows quite strong. Viva la GSO.
my fan that is in the side of my tube is from the top of a cpu in a computer. It could not blow out a candle and from about 30cm or more away, hard to feel the passing of the air. I may get a more powerful one!
