I've not done anything with my 200PDS over the years to protect it from dew, however it always ends up dripping wet at the end of a session here in the UK. What, if anything, do people do to address this with their basic Newtonians?
Skywatcher 200 PDS dew protection
Well Written Engaging
Nothing. Let it drip. Beats frosting all the times. Seriously, as long it can dry afterward it's fine. And as long you keep the secondary dew-free. Although I had occasions when even the primary fogged over. That was pretty much game over.
andrea tasselli:
Nothing. Let it drip.
I see lots of people using dew heaters, but I'm not sure they are needed. What is your view for a Newtonian? I also see people adding thermal blankets to the end of their scopes ... needed or not?
Well Written Engaging
Recently I've had both primary and secondary fog over on both my 150PDS and 250PDS. The 150 seemed to dew over far more often than the 250 which has only done it twice in a year, adding a rear fan and an approx 8" dew shield to the 150 seems to have fixed that.
For the dew shield I copied the really nice way this attaches to the scope and printed the whole thing as a solid hood for the scope. I'm exposed to wind so like the sturdiness of a completely solid dew shield.
https://www.thingiverse.com/thing:4946772
Also bought a secondary dew heater for the 250 but have not had chance to use it yet. Slightly concerned it may affect star shapes but that's better than a fogged mirror. https://shop.4tronix.co.uk/products/secondary-mirror-heater
For the dew shield I copied the really nice way this attaches to the scope and printed the whole thing as a solid hood for the scope. I'm exposed to wind so like the sturdiness of a completely solid dew shield.
https://www.thingiverse.com/thing:4946772
Also bought a secondary dew heater for the 250 but have not had chance to use it yet. Slightly concerned it may affect star shapes but that's better than a fogged mirror. https://shop.4tronix.co.uk/products/secondary-mirror-heater
Helpful Engaging
Andy Wray:
I see lots of people using dew heaters, but I'm not sure they are needed. What is your view for a Newtonian? I also see people adding thermal blankets to the end of their scopes ... needed or not?
What is needed is a longish dew shield. I make mine using foam sheet, the one used for camping if you see what I mean, with the reflective bit on the outside. In the long run I'd get a secondary heater as well but the dew shield should keep things at bay for few hours. I mean, I know as I have used them countless nights. Primary fogging is an issue only with the worst weather, which normally means not very suitable for deep sky imaging but very suitable for hi-res planetary imaging. There are guys who added a heating system connected to dew point sensors in oder to keep the mirror temperature just above the dew point. Interesting stuff if you are into tinkering with your kit. Otherwise a rear fan moving the air along (or across) should do it. I had none so I used to blast the primary with hot air from an hair-dryer and that fixed it for few hours. Crude but effective.
Helpful Engaging Supportive
I have the same scope. Can't be eliminated under all conditions but can be ameliorated
1) I use a flexible dewshield - originally for an 8 inch SCT
2) Try to keep it off wet dewy grass - less moist air drawn up through the tube by the fan
3) I inspect it every now and again and blow the secondary (first area to dew up) with a hairdryer if it's a humid night and going down below the dew point
Some conditions are pretty hopeless though —after 5h or so on a humid night the primary fogs up and not much can be done
Tim
1) I use a flexible dewshield - originally for an 8 inch SCT
2) Try to keep it off wet dewy grass - less moist air drawn up through the tube by the fan
3) I inspect it every now and again and blow the secondary (first area to dew up) with a hairdryer if it's a humid night and going down below the dew point
Some conditions are pretty hopeless though —after 5h or so on a humid night the primary fogs up and not much can be done
Tim
Helpful
i use the kendrick mirror dew heaters,for primary and sec.
i just keep it on a low heat,keeps the mirror dry.
for the outside of the scope,just let it dry by itself.
https://www.teleskop-express.de/shop/product_info.php/info/p7542_Kendrick-Primary-Heater-for-8-inch-Newtonian-Primary-Mirrors.html
i just keep it on a low heat,keeps the mirror dry.
for the outside of the scope,just let it dry by itself.
https://www.teleskop-express.de/shop/product_info.php/info/p7542_Kendrick-Primary-Heater-for-8-inch-Newtonian-Primary-Mirrors.html
Tristan Campbell:
Recently I've had both primary and secondary fog over on both my 150PDS and 250PDS. The 150 seemed to dew over far more often than the 250 which has only done it twice in a year, adding a rear fan and an approx 8" dew shield to the 150 seems to have fixed that.
For the dew shield I copied the really nice way this attaches to the scope and printed the whole thing as a solid hood for the scope. I'm exposed to wind so like the sturdiness of a completely solid dew shield.
https://www.thingiverse.com/thing:4946772
Also bought a secondary dew heater for the 250 but have not had chance to use it yet. Slightly concerned it may affect star shapes but that's better than a fogged mirror. https://shop.4tronix.co.uk/products/secondary-mirror-heater
That 3d model was great for my 150PDS
