Dark Star 10" Dob - first proper test

[Stub Mandrel]

I've come into a 'classic' Dark Star 10" dobsonian scope. The mirror looks in poor shape and needs recoating, but in practice it's probably 90% OK.  This is what it looked like before I gently washed the dust off.

This is just a post to record what it's like to look through from someone not very good at looking through telescopes.

Details here:

This was really 'Second Light', but my first attempt was a bit of a failure. Still no finder, but see below.

I used some graphite oil and got the AZ bearing working a lot more smoothly.

I found jupiter by sighting along the corner of the 'box' around the OTA. With a 40mm (x30) or 32mm (x50) plossl three moons and two darker belts were visible, but the planet was very bright. Using a 25mm (x64) I could see more rings and at 10mm (160x) things started to look interesting.

My new x3 ED Revelation barlow appears to be excellent and I went up to 480x but focusing was so critical I struggled to get a decent view. With the 25mm and barlow for x200,  the view was stunning. Focusing was still critical, but by focusing on the moons I could get it right. Seeing caused tiny ripples around the edge of the planet. Not only could I see several smaller rings, but also hints of texture and detail in them. Io's shadow was a perfect little black circle, not a dot, and I could see that the moons were tiny little discs. I waited until Io was supposed to be clear of the disc but only got the faintest hint of it leaving the disc rather late according to stellarium mobile. I switched to the 18s ortho for about x270 and things looked good but Jupiter rapidly went into foiliage.

Over to Saturn. I didn't get long before it went behind a roof. I could see the Cassini division at x200 and Titan was obvious, but too light to see the other moons in such a short viewing window ( a couple of minutes!)

I ventured higher up. Ages around Vega and I couldn't find the Double Double until I used bins to confirm  where it was an which way to slew. At 160x the two pairs were separated so well you could have driven a car between them ?

Sadr looked as if it was in mist but I think to early to see nearby nebulosity, same for the NAN and Pelican, especially as I wasn't 100% sure I was looking in the right place, lots more stars than in my atlas or even Stellarium.

I found a cheap RDF and attached it to the scope, it was very hard to align, using Altair, but it did let me find M57 the ring nebula as by now I could see all of Lyra (and lots of other stars naked eye). Tried for M27, but I just couldn't see enough naked eye to get an accurate alignment as the skies are more light polluted from Sagitta down.

Realised Mars was up but very low down, and by hauling the scope to the back of the garden I could see it for a little while before it hit the roof. I codln't see any poles and just one darker patch near the middle, but no real detail.

On Saturn and Mars it was clear I shoudl have been using the ADC, but with only a few minutes window I didn't have time to set it up.  Even with a GEQ and extension I only get about 30 minutes on these targets, so surprised to get any view using the dob ?

My martian adventures had resulted in the RDF being knocked off its double sided tape and although the sky was finally really looking good, it was nearly Midnight and I ran up the white flag.

 

I've often said that I image because I'm not comfortable looking through eyepieces. With jupiter low down I sat on a chair and spent half an hour or more trying different eyepieces and my barlow, getting the hang of moving the scope around. I found it MUCH more comfortable to view through than any other scope I have used.

In focus the views of stars are incredibly sharp, although (and I recollimated half way through the session) out of focus stars are assymetrical - I suspect focuser tilt).

Having got used to a GEQ it's really hard finding things with an alt-az mount. The GEQ moves up and down or side to side along the lines in my star atlas making it very easy to find things. Clearly having stellarium on the laptop with alt-az lines will help here.

The GEQ is hard to line up near the pole, the Alt-Az is really hard to line up near the zenith. I'm not convinced the 'alt az  is easier' mantra really holds true for objects well above the horizon.

Finally, I thought such a big scope would be a pain to move around. In practice, two journeys to get it out, plus fetching my eyepiece case. Three to put it away, all takes a few minutes, compared to a minimum of three quarters of an hour to get imaging.

I must admit last night has changed my view of visual astronomy, even though I didn't see a lot. By tonight I should have a working finderscope and my aim will be to have imaging and dob happening alongside each other.

Where do I get a 'Dob Mob' application form?

 

[John]

Welcome to the "light side" Neil

[johninderby]

That photo of the mirror reminds me of a moon map.  ?

The ease of use is one of the best things about a dob.

[David Levi]

Nice report. I'm interested to read your comments on using a Dobsonian mount compared with an equatorial mount as I can see that in the future I'll probably be going that way as well.