22 Inch Compact Scope Finished - Page 3

tnott · #41 16-09-2009, 09:17 AM

In viewing, I have noticed a tiny bit of springiness in the scope when pointed lower down near the horizon. This is mentioned as a potential problem in The Dobsonian Telescope book.

It is not much and since the scope has a drive system it doesn't affect viewing, but I notice that Obsession's 22" version adds a length of steel to the tips of each of the foldable side bearings.
http://www.obsessiontelescopes.com/t..._UC/index.html

Might see if I can add this reinforcement to my scope too if it doesn't increase setup time and fits easily.

StarGazing (Alex) · #42 04-10-2009, 07:11 PM

Wow what a great job you did, looks fantastic. Good luck with it and I wish you the clearest of skyes. By the way I saw on Starmaster site they were looking at making faster dobs...... Might be the future ????

Alex.

tnott · #43 15-10-2009, 10:01 PM

Faster mirrors have a range of potential problems - they take an enormous amount of time and skill to make compared to slower ones (ie. are much more expensive), need a coma corrector (a new design is needed for beyond about F3.5), have much smaller collimation tolerances and the diffraction limited field of view is much smaller.

I don't know if they could ever be produced on a large scale.

But, this mirror has allowed me to get fantastic views in a convenient package without a tall ladder - so I am happy!

StarGazing (Alex) · #44 15-10-2009, 11:34 PM

Glad to hear all is going well with new scope. I admire your courage in building a technical scope, wish I could........maybe one day. How is the argo & stella cat combo working for you ?. I am looking to upgrade mine in the near future with a motorised goto set up. How did you install the encoders for the argo ?
Alex.

tnott · #45 24-10-2009, 07:37 PM

Due to the weather we have had over winter down south this year I have only had it out about 6 times, so I am still working the bugs out of the GOTO.

The last time I took it out (Saturday) I was having problems with the accuracy of the pointing. When I got home I discovered that the central azimuth bolt was wildly loose so hopefully the problem is now fixed.

On previous occasions though the combo worked really well. I like the "tour" function of the Argo and the tracking of the servocat is really smooth.
Everything depends of the accuracy of the scope and the positioning of the encoders though.

The Azimuth encoder is attached to the central pivot bolt, like a standard installation.

Because of its U-shape the Altitude encoder is attached to a double encoder arm (look at the photos on the first page of this thread and you'll see my setup). One arm is 3mm steel and is fixed to the alt. bearing via thumbscrews and threaded inserts. The other, supplied by Stellarcat, is aluminium with a slot in it and slides over a spacer on the rocker.

You can tell if the encoder is positioned properly when you move the scope up and down. If the arm with the slot in it doesn't move up and down with respect to the spacer when you do this, then the encoder is at the central point of rotation. If you have some play in the setup then you can mark the spot with a line in order to save time next time you set it up, though I didn't need to.

This is how it has been done on the Obsession UC scopes too. If you look at the pics you can see a line so that the arm and encoder can be positioned properly each time.

tnott · #46 18-11-2009, 08:30 AM

Update:

After a long, wet winter I took the 22"out for a good workout at the Vicsouth Star Party on the weekend. Was really happy with how the scope performed optically and mechanically. For a full report see:
http://www.iceinspace.com.au/forum/s...676#post523676

Encoder setup seems to be working well as pointing accuracy was generally within 1/2 a degree both nights, the same as an 18" SDM next to me.

I have added 6mm thick steel struts across the tips of the altitude bearings but am not convinced they make much difference to the stability of the scope as it was pretty good before.

If you squint, you can see the struts in the photo with my scope in the background. In the foreground is an interesting all aluminium 16" dob not quite finished.

naveedmerchant · #47 09-05-2010, 02:14 PM

Tim, I am planning to start my project and wanted to make something lightwieght with short focal length like yours and needed some advice. I have group of friend and we have access to all tools and evn lathe.

Would appreciate if you can share any design details or any basic details.

Many thanks in advance

tnott · #48 10-05-2010, 10:14 PM

I've got lots of info I can send you if you PM me your email address.

Iceaxe (Joe) · #49 30-05-2010, 12:51 PM

Well done may all your nights be clear ones.

Joe

Paul Hatchman · #50 03-06-2010, 07:22 PM

Quote:

Originally Posted by tnott

Encoder setup seems to be working well as pointing accuracy was generally within 1/2 a degree both nights, the same as an 18" SDM next to me.

That's a really great looking scope. You must be really happy with it!

You should look into the "mount errors" function on the argo. On my 20", I do a mount errors alignment on 5 stars and just use the Index Error and Non-Perpendicular Axes error terms. It gets me pointing to within 15' or better, often less than 10'.

Cheers.

astroron (Ron) · #51 03-06-2010, 08:50 PM

Hi Tim, great scope

I have an Obsession clone 16" f 4.5 mirror, which as I grow a little longer in the teeth is getting heavier

Is that design compatible with said mirror

I have not long ago did a trip to Perth and back with the 16" in the car, it took up a lot of room and was heavy to move about.
I hope to do a trip to Northern Australia next year and a lighter scope would be a God Send

Cheers

tnott · #52 12-06-2010, 08:37 PM

This or any lightweight design would be compatible with a 16'' mirror as it is not too big.

Other designs may be simpler to construct though, like the 3-pole Highe one sold commercially by dobstuff.com

The UC design has lots of steel components that need to be cut, bent and welded.

astroron (Ron) · #53 13-06-2010, 08:35 PM

Other designs may be simpler to construct though, like the 3-pole Highe one sold commercially by dobstuff.com

Dennis Steele, Dobstuff is not in business at the moment.
No explanation given.

tnott · #54 19-06-2010, 07:34 PM

Mmmm...

Looks like you'll have to design and build your own!

astroron (Ron) · #55 19-06-2010, 08:03 PM

Quote:

Originally Posted by tnott

Mmmm...

Looks like you'll have to design and build your own!

I was after the design,so as I can build my own, just wanted to get to see what it looked like