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Dobsonian dew control and practical upgrades

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Hi all,

So I'm now the proud (and sore - it's heavy!) owner of an OOUK VX16 400mm Dobsonian, and am now learning how to use it and figuring out all the things I need to add on to make it really usable in my environment - but would appreciate some advice from other Dob owners!

I managed to get a first light tonight - lots of cloud about so it was a bit hit and miss but I managed to collimate fairly well and look at some bright stars. Defocused, tube currents were very, very obvious - I'd kept it outside in a shed for half the day but it was still clearly a bit warm (the back of the mirror measured 5c compared to 0c ground temp on infrared). After about an hour it was down to temperature, but I was struggling with eyepieces dewing up. About half an hour later to warm up the eyepieces, the finderscope was completely dewed over, and both the primary and secondary had a degree of dew on them. The ambient temperature was about 1-2c with humidity around 70-80% by the met office and 50% by my local sensors.

I also had some issues pointing the scope. I figure a RACI finder and/or Telrad would be worthwhile upgrades - the Explore Scientific RACI finder looks ideal - so will aim to upgrade those. The azimuth bearing seems very tight - it takes a lot of effort to get moving, so fine pointing adjustments are really hard. Thinking I may need to renew some bearing surfaces; I am using a few paving slabs as a base so it's got a fairly flat surface to rest on. Altitude I didn't quite get balanced right so need to shift that around a bit more and then can slacken the brake off.

I called it a night and put the scope back in the shed - while I can move it around fairly well on the sack truck I bought for it, I'm definitely going to get it a Telegizmos 365 cover so I can leave it set up in situ for longer periods. We're in a fairly damp area - low lying, 25m from a small stream - so suffer quite a bit from dew.


The mirror cell has a position for a 12V fan which I've now bought from OOUK, which I suspect will help quite a bit with both dewing of the primary and tube currents/cooldown - will fit this once it arrives and see if it helps.


I'm also thinking that as a beginner in observational astronomy (imaging for a few years now) a digital setting circle is going to help a lot with finding my way around and building up confidence - is the Nexus DSC still the way to go?


Do I need to consider dew heaters for either the eyepiece/tube, or secondary or primary? What else should I consider for dew control?

Any tips on things to consider with finderscopes?

Any other hints and tips for practical accessories for larger Dobs?


Lots of questions - grateful for any advice!

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