Quote:
Originally Posted by erick
Suggest that you take the opportunity to "seal up" the end of the dob so the air from the fan doesn't bounce back off, but is forced around the mirror and up the tube. Folks seem to think that this restricts dew formation on the primary. Seemed to achieve that in my 12".
|
I agree with Eric here. I did the Scott tannehil mod on my 12" GSO
www.iceinspace.com.au/63-400-0-0-1-0.html
and found it eliminated dew formation on primary and secondary and significantly reduced time to cool the primary compared to a fan cooling the back of the mirror. Its a very easy mod. You can feel the airflow coming out of the front of the scope. I found that I didn't have to mount the fan on Velcro as vibrations were negligible with the standard GSO fan, so I just put the neoprene membrane around it. But if you have to install a fan, its a very simple way to do it. The whole job, including putting the baffle in front of the primary took only about 20-30 minutes.
The scope that I now have doesn't get dew on the primary. Tim, its maker, reckons that this is due to the large mass of the mirror. I've always thought that the way the mirror box directs airflow from the fan across the front of the primary was a factor. I became convinced of this at Snake Valley on Saturday. Peter Batchelor's 16" LB primary with dew guard and shroud was covered with dew and mine was clear as a bell with no shroud. I don't think Peter's primary had less mass than mine, just a fan that only blows on the back of the mirror.