Dew

[lhuchison]

Does anyone know why my Telrad dews up quite quickly but my finder scope stays clear as a bell? The finder is a stock 9x50 SW. but recently its all i can use due to conditions.

I now have a homemade dew shield on the Telrad which keeps it at bay.

[fredster]

I find all my finders dew up equally fast, had to add active dew control to everything if i want a decent session. Not sure why the Telrad would go quicker than the optical finder.

[umadog]

If it dews faster then it's cooling faster. The glass on the Telrad is very exposed whereas finder scopes usually have a dew shield. That is likely the cause of your difference. If you stay out longer then probably the finder will dew over too.

[lhuchison]

Thanks question answered.

[pajr777]

The Telrad probably emits radiation more quickly as well as it's black, which will also cause it to cool more quickly.

[jabberwocky]

My telrad dews up very fast, it's the one thing you can just wipe with a cloth though.

[pajr777]

When I made my dewshield for my OTA I had some left over foam mat so I also made a shield for the Telrad using the template downloaded from this page: http://www.homebuiltastronomy.com/downbino/HomeBuiltAstronomy-TelradDewShield.html

[fredster]

I found the even my home dew shield only delayed the dew by 10-20mins. Had to add some active dew control, which wasn't too bad as i already needed it for the Mak and refractor. I use this from Telescope House:

http://www.telescopehouse.com/acatalog/Dew_heater__BCF__for_Telrad.html

[pajr777]

I found the even my home dew shield only delayed the dew by 10-20mins. Had to add some active dew control, which wasn't too bad as i already needed it for the Mak and refractor. I use this from Telescope House:

http://www.telescope...for_Telrad.html

Is that a standalone solution or do you need extra gubbins to go with it?