To cap or not to cap?

[Adam coffee man]

Newbie question so please excuse me if this a daft one.  I have just started out with a 90mm refractor and until tonight the sessions have been pretty warm.  This evening was the first cold one and I got some condensation on the outside of the tube.  No issues with eps or impact on the session but I am not sure what the best thing is to do to protect 'the precious' when I finish and come back inside.  I have opted for putting the lense caps on the tube before coming in but leaving it in its bag with the bag open to allow it to dry off naturally.  There was no condensation on the eps so I have just capped them and left them unboxed.  All my gear is in a conservatory that has a small radiator that keeps it a few degs above the outside temperature.  

Anyone have any advice?  Would you cap a refractor if the lens itself appeared dry?  Thanks in advance.  Adam

[Guest Tuomo]

I leave everything open for the night. This includes eyepiece caps, ota caps and...well all the caps  Then I pack everything next day.

[Charic]

..........same here, left till morning to put away.

[Uranium235]

For now leave it uncapped until clear.... but I would seriously recommend investing in a dew band - they dont cost much and can keep your objective lens free of dew all night long - even on the dampest, coldest nights.

[Adam coffee man]

Thanks for this....much appreciated.

[ronin]

Usually people leave them uncapped, any moisture then evaportes off. Having said that I suppose many use their scopes away from home so they cap the things to transport them home. To every rule there is an exception.

Whatever you do expect moisture to eventually leave some marks on the objective, nothing you can do about this so occasionally you will need to clean it. Don't worry and do it when you deem necessary do it carefully.

[michaelmorris]

33 minutes ago, ronin said:

Whatever you do expect moisture to eventually leave some marks on the objective, nothing you can do about this so occasionally you will need to clean it. Don't worry and do it when you deem necessary do it carefully.

There is a well respected school of thought that you not clean a refractor lens unless absolutely necessary (i.e. it starts seriously affecting view).  Blow away dust and crud and if necessary very lightly brush this stuff off, but actually cleaning watermarks off the objective should be a last resort.

Astrophysics have produce good cleaning guide for refractors that you may find useful

http://www.astro-physics.com/products/accessories/cleaningproducts/optcs-instructions.pdf

 

 

[Adam coffee man]

Many thanks for your advice folks.  

[N3ptune]

I usually put my eps on sealed ziplocs before I get them inside the house for about 30 minutes, until they absorb some heat. Then I remove them out of the bags and let them dry for the night with a cloth cover. My method for the telescope is a bit more complicated because it's a reflector but it's working to prevent heavy dew on the mirrors. (I  would apply the same technique on a refractor)

- I heat the primary and secondary mirrors outside for 30 minutes at the end of my observation. (With custom made strap heater)

- Then I put the cap on the telescope and put the telescope inside it's +- scealed transport bag.

- I bring the instrument inside my house without opening the bag. And put it in a room where a dehumidifier was running for a few hours at maximum power.

- If the temperature was -15 Celcius outside, I let the telescope rest inside the closed bag for at least 1 hour with the heater on the mirrors. (It's a really low power heater, slow heating, 11 watts for the primary and I think 7 w  for the secondary)

- 1 hours later, I open the bag, put heater off, remove the cap, put a tissue on the opening and let the instrument dry for the night.

My technique prevents water formation on mirrors and lens during the process of warming inside the house.  I did it 1 winter and got absolutely no damages to the commercially coated mirrors so far.