Dew Event Horizon

[Nightspore]

 

This time last year I set up my modified ST102 with Astrozap dew tapes around the objective, the RACI and a Kendrick press on RDF heater. I had it mounted on the Porta II/Hal-130 combo.

 

 

As a consequence I needed a four channel controller which can be seen above. As far as I can recall it all worked relatively well combined with a Sky-Watcher 7ah powertank. Unfortunately, due to my disability, the Porta II/Hal-130 combo didn't get out that much. So consequently neither did the ST102 and I don't think I used it more than once with the dew gear. This year when I realised I could use the ST102 on the AZ5 everything changed and the ST102 got out much more regularly.

 

 

I've replaced the TS Optics (GSO) rotating focuser with its Sky-Watcher equivalent. It only has one finder shoe so I use a reflex sight.

 

 

A couple of nights ago I took the ST102/AZ5 out and around 01:00 put the Astrozap tape around the objective and fitted the RDF heater. I reverted to my old Hitecastro 'mini' two channel dew controller. I used to use this with my ST80 as I only needed two channels. The powertank is new as my old tank's battery went a bit brown bread after I neglected to charge it properly (a lesson I've learned!). The RDF soon cleared of condensation but I thought the objective was taking its time. When I took the Astrozap tape off the scope to inspect it I thought it wasn't particularly warm to the touch. I decided to turn the controller up from half way to full power. The Astrozap was still a bit cool I thought in my opinion. I went inside and dug up a Rother Valley Optics custom dew tape I'd bought for the ST102 (shown in picture) but never used. This was much more successful and felt warmer. However, the humidity was 95% by now and everything was dripping anyway. I've ordered a new Astrozap tape in case there's something wrong with the old one. I never had any trouble with ST80's and don't with the ED72. I was wondering if I just needed more power with the ST102's dew shield as it is approaching five inches in diameter and quite heavily built?

Any thoughts?

[+Graham]

I always run 2 dew bands side by side on my GT 81 for imaging.

Never had a single problem with dew even in the most extreme conditions.

[Nightspore]

56 minutes ago, Graham said:

I always run 2 dew bands side by side on my GT 81 for imaging.

Never had a single problem with dew even in the most extreme conditions.

That's interesting, I might try that. 

[BAZ]

You might have to upgrade the size of the battery too to cope with that for longer periods. If I remember right the Sky Watcher packs are 7 A/hrs, which are quite small.

[Nightspore]

3 hours ago, BAZ said:

You might have to upgrade the size of the battery too to cope with that for longer periods. If I remember right the Sky Watcher packs are 7 A/hrs, which are quite small.

I was thinking the same thing.

[Nightspore]

I was also wondering if the wide spaced Fraunhofer doublet objective of the ST102 contributed to this (convected heat) situation?

 

http://www.scopeviews.co.uk/SW102.htm

[+Bino-viewer]

Well thats a new one on me : i always though that 'Doublet' lenses on refractors were always mated together,

and i assumed this aided their fast cooldown and kept them perfectly collimated.

 

I hadn't realised that some designs had a spacing in between ??

 

 

[Nightspore]

3 hours ago, Bino-viewer said:

Well thats a new one on me : i always though that 'Doublet' lenses on refractors were always mated together,

and i assumed this aided their fast cooldown and kept them perfectly collimated.

 

I hadn't realised that some designs had a spacing in between ??

 

 

I think they all were until Fraunhofer. It's bloody complicated lol. 

 

https://www.telescope-optics.net/achromats.htm