Dew formation on 8" Newtonian primary mirror

Hi Moorefam,

You are not alone.  

I have only just purchased a Newtonian, but I will comment that this winter/spring in New Zealand dew formed on my GSO RC8 carbon primary mirror from just after the middle of the night onwards.   I did not have significant dew problems the previous year.  

A dew band  around the bottom end of the telescope solved the problem. [I also had to use a dew heater on the 2ary and dew shield to address all the dew problems].  

I did not notice an increase in FWHM, although my site has poor seeing (3-4arcsec).    I am not sure where you are based [other than being in the Northern Hemisphere - the winter reference is a giveaway], but I would note that the site at remote telescope  I subscribe to in Spain has also suffered from terrible dew problems this northern hemisphere winter.

While one should not draw inferences from such a  small sample, I do wonder whether there is a useful study to be done into whether there has been an increase in dew levels around the planet due to climate change.  A warmer atmosphere holds holds more moisture.... 

With climate change, increased urbanisation and Elon Musk's satellites, it could be a bleak outlook for our hobby.

Brian 

*Last comment made somewhat tongue-in-cheek - but it is all very unsettling.

When I used newts and sitting long sessions it did happen (of fogging up the primary). As I mentioned in another thread a (long) blast of hairdryer power will settle this for the remainder of the night. After the first 5-10 minutes the turbulence inside the tube settled to what was previously. I was planetary imaging when the instances of primary fogging occurred and I could not see any permanent detrimental effect.

i use the kendrick  newton dew heaters  for primary mirrors. it works really  great,the mirror keeps dry.

https://www.teleskop-express.de/shop/product_info.php/info/p7542_Kendrick-Primary-Heater-for-8-inch-Newtonian-Primary-Mirrors.html

Ryan Jones:
...

Yes there is more moisture in the air in southern climates this year due to a weather system called El Niño. Yes it’s climate change because it is a change from last years climate. Will it change back ? Yes, next year, when the climate changes again. - tongue in cheek

... and El Nino Events are expected to increase in probability and in extent due to global warming.
While we should not attribute anything to global warming - there's also a normal fluctuation around the average climate - the trend is very clear. I assume however that dew on our mirrors will be one of the smaller issues to deal with ...

CS Wolfgang

Great discussion here!
Question to the team: my understanding is that the proper way to warm up the primary mirror is through a Kendrick plate glued to the back of the mirror itself. The disadvantage of this solution is that you have to be careful when washing the primary, as the Kendrick should not be submerged in water. At least this is the indication of the producer.

I have read here a different approach (maybe I misunderstood), that is to place instead a stripe around the bottom of the tube, close to the primary mirror. The stripe is clearly more convenient than the Kendrick, but I have some doubt i about its functionality, because in this case there is no direct heat transmission to the primary and the heat might generate turbulence inside the tube. Has anybody here experienced this configuration?

Let me add that heating the secondary is, in my experience, a must. Instead, I experienced fogging of the primary only once in the last two years, but this is clearly dependent on the observatory site weather. When it happens so rarely, the hairdryer solution proposed by @andrea tasselli comes very handy.

Many thanks and clear skies.
Mau