Dew

[Solanum]

I took the scope out for the first time at my new place here in the Adelaide Hills and had some trouble with dew. When I was in Mildura dew only occurred in winter late on at night and I would just pack up then.

So, 1) is it worth buying/making some sort of dew shield for my GSO 10" dob to reduce the occurrence of dew on the secondary?

2) anyone know where I can get a battery powered hair-drier or similar to remove the dew from my telrad, finder (and secondary when it occurs)? It's a bit far to run a power cord from the wall to where I set up the scope.

[rmcpb]

Always worth having a light/dew shield with your scope. I have one made from a thin sleeping mat and held to the scope with velcro. It works very well, the only mod I had to do to the scope was to add a small drawer handle to the tube so I could move it easily now I cannot just grab the end of the tube.

As for the hairdryer, try a camping store.

Cheers

[Paddy]

I found with my 12" GSO dob that setting up the fan modification described by Scott Tannehill at

http://www.iceinspace.com.au/63-400-0-0-1-0.html

stopped any dew problems with either primary or secondary and improved seeing. I didn't go the whole hog with Scott's modification - I left the old fan in situ, put a strip of thick (about 15mm I think) self adhesive foam around the tube just a tad above the front of the primary and put the neoprene gasket on the back with a cut out for the fan. The gasket ensures that any air sucked in by the fan travels up the scope and doesn't bounce off the mirror. The foam strip baffle directs ariflow over the face of the primary. I found that the vibrations from the stock fan did not impair the views. In operation, I could feel quite a flow of air out of the front of the tube. Neihter primary or secondary ever dewed up after this mod and I found I could start viewing very quickly because the boundary layer at the front of the primary was removed even before the mirror cooled.

This is a very easy and worthwhile modification, IMO.

[erick]

Yes, you can get 12V hairdryers. When I went looking, it was only at some camping outlets. They normally had a ciggie lighter plug on them. BUT, don't expect them to perform like a mains hairdryer. 240V AC has no trouble pumping out heat from 1200-1800W consumption. You will be lucky to get 100W consumption in your 12V dryer and even that will suck 8A out of your 12V battery. So the output is luke warm but it will do the job and does for mine. But use many times and that 12V battery will be sucked dry.

[sheeny]

The other places to look for 12V hairdryers is caravanning and boating shops.

Al.