Dew on Newtonian?
Posted 20 November 2012 - 07:58 AM
Posted 20 November 2012 - 08:07 AM
Posted 20 November 2012 - 08:13 AM
Posted 20 November 2012 - 08:28 AM
I have seen steel tube newts experience dew problems with the primary. The steel gets real cold on a very clear night and cools below ambient temperatures. This eventually transfers some of the cold to the primary. As was mentioned, this is only likely to happen under pretty severe dewing conditions. The solution is to insulate the tube interior with cork or some sort of liner.
Posted 20 November 2012 - 09:06 AM
Posted 20 November 2012 - 09:28 AM
Posted 20 November 2012 - 11:00 AM
Posted 20 November 2012 - 11:01 AM
Posted 25 November 2012 - 01:52 AM
In general, with a solid tube newt you will not get dew on the primary (except on the worst of nights). The secondary, however, may dew up more easily.
I had an 8" Skywatcher, solid tube, never dewed up outside, but as soon as I took it inside it had dew on the mirror, due to it being warmer inside then out, in mid winter, always had to leave mirrors uncapped till the dew was gone. Have the same problem with my Skywatcher 10" Flex Tube Dob, it's fine till I bring it inside.
It is exactly the same as if you wear glass, go from cold to warm and they fog up.
If you finished with your scope and a big temp differnce, un cap your mirrors and let the condensation go, else you will end up with mold on your mirrors in time, if left capped going from a cold outside to warm inside.
Posted 25 November 2012 - 02:05 AM
Posted 25 November 2012 - 07:10 AM
Here in the Uk we can have good seeing with bad dew issues.
I'd get a dewshield anyway to remove any stray light. Modern newts tend to have their secondary ver close to the end of the tube so stray light can enter the tube and focuser. A dewshield will kill that problem.
Every single star party I have been to in the UK has seen people who were sure they didnt need a dewshield knocked out on the first night. The following morning there is a run on camping mats at the local camp and hike store as these can be adapted to be a home made dewshield.
Posted 25 November 2012 - 09:47 AM