Moisture woes

[D4N]

Last night I noticed my objective had started to frost up so gave it a blast of the hairdryer but then realised that it had also frosted up on the inside, between the lens elements.

I had frost on the outside of the objective, between the first lens pair, behind the first lens pair and in front of the second lens pair.

I've got it sat inside with a big bag of silicate stuffed into the focuser tube and plan on building a dew heater.

Does anyone have any other tips that might help?

I want to avoid having to bring the scope inside from the obsy or remove that camera between sessions if I can.

/Dan

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[StuartJPP]

I think you were too aggressive with the hair drier.

Are you using any sort of dew guard/heater?

[opticalpath]

I would say it boils down to two things:

- steps to prevent moisture condensing on the objective in the first place, whilst the obsy. is open. 

- steps to ensure that moisture-laden air is not trapped in the obsy. when it's closed.

A dew shield and heater should tackle the first issue.  I'd suggest using only gentle heat, but use it ALL the time .... every session from start to finish, whether you expect dew or not. (That advice is based on experience with closed-tube SCTs and Mak-Newts - I'm assuming it's also applicable to refractors .... but happy to be corrected if not.)

For the second point, invest in a cheap digital max/min thermometer/ humidity meter to monitor the humidity in your obsy. when it's closed.  If you are seeing high humidity levels, take steps to reduce it, such as active ventilation or a desiccant dehumidifier.

My obsy. is often at 100% humidity when I close it down.  I invested in a desiccant dehumidifier and use it on a 2 or 4 hour timer to thoroughly dry out the obsy. after every session - peace of mind!  I don't run it 24 hr. but I do leave a low wattage light bulb burning under the scope all the time during the damp seasons.  You might even consider leaving your dew heater switched on at low power 24 hr/ day.

To remove the moisture already in your scope, I would give it time - leave the silica gel in there for several days.  And I would keep the dew heater on or provide some other source of gentle warmth during this time to help to evaporate and drive out trapped moisture. 

Adrian

[D4N]

Stuart, just a dew shield at the moment but planning on a dew heater now.

The moisture must have been there before I used the hairdryer, it is the first time I've used it this year.

Thanks Adrian, I'll look into what I can do to keep it dryer in the obsy and hopefully I can get the moisture out of the scope.

I have just installed a thermometer in there as part of my focuser upgrade

/Dan

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