22 Inch Compact Scope Finished - Page 2

Kevnool (Kev) · #21 26-02-2009, 07:38 PM

Congrats Tim its a real credit to you.
Areal Gem....cheers Kev.

tnott · #22 26-02-2009, 08:59 PM

BTW - eyepiece height at zenith is 73" or 185 cm- my height. I use a small 2-step ladder with a padded handle to grip to, especially for the vertically challenged viewers. A small step stool also is enough for most people.

Most components were obtained from the local Bunnings or Coventry Fasteners. Wood was 12mm Gaboon Ply (usually laminated to make 24mm) from Duck Flat Wooden Boats. Ebony Star was from Parbury (make sure you use the Touchstone finish).

Steel Parts were sourced and cut from a Laser cutting place. Bending, drilling and welding can be done at any metal shop. Close supervision is required usually!

Plastic bits, including Teflon can be obtained from most plastics supply places or Parbury.

The design was reverse-engineered from many photos of the Obsession UC and its antecedents, as well as using The Dobsonian Telescope for the engineering specs.

astropolak (Joe) · #23 26-02-2009, 09:12 PM

Tim
Great looking scope, please tell us more about your creation when you have the time...

Joe

Rodstar (Rod) · #24 28-02-2009, 07:30 AM

Looks fantastic, Tim. I know what you mean about the difference in brightness with the larger aperture.

What is your favourite EP combination with this scope?

I was intrigued by your description of IC418. I see orange, not blue and red. I will have another look mext time the conditions are nice and steady.

tnott · #25 28-02-2009, 09:01 PM

I guess everyone's colour perception is slightly different- esp. at these subtle levels. The eyepieces I like best depend on the object I am viewing. M42 looks fantastic through the 28mm UWAN(0.8 of a degree and 80X), larger galaxies like M83 are fabulous through the 13mm Nagler (180X) and the planetary nebulae are best at higher power in the 9mm Nagler (260X).

I do really like the immersive nature of the UWAN though.

I also think I need a planetary eyepiece or two around the 300-400X range since I have tracking and the parracor is not compatible with most barlows. Clayton bay is a place were really good seeing is common, being surrounded by water and having no hills around.

GrahamL · #26 01-03-2009, 07:39 AM

great job Tim

,, So whats the next one going to be ?

tnott · #27 01-03-2009, 06:01 PM

Well, I now have a 5''ETX, a 10"compact dob for home and a 22" scope for dark sky viewing nights. Don't think I'll be building another one any time soon.

To get a similar doubling of light like I did from the 16" I would have to go to 30" and that size would not be very easy to move around.

Unless I had a special trailer. Mmm.....................

skies2clear · #28 04-03-2009, 09:39 AM

Tim, your work is inspirational indeed. Congratulations.

I see Kennedy puts the finishing touches on his primary mirrors by using the star test. Very dedicated.

Anytime you need a lift, let me know!

Clear skies
Nick

tnott · #29 09-03-2009, 10:32 AM

A few more photos.
One shows how the scope folds up into only 2 components for transport.

Another couple of the whole thing set up.

tnott · #30 09-03-2009, 10:35 AM

Few more.

gary · #31 10-03-2009, 02:08 PM

Quote:

Originally Posted by tnott

Forgot to mention - mirror is a beautiful piece of work by Steve Kennedy. He specializes in thin, fast mirrors 22 inches and up.

http://www.kennedy-optics.com/

Hi Tim,

I had the pleasure of spending a couple of evenings looking through
Steve's personal 32" f/3.66 telescope manufactured for him by Mike Zammit of Starstructure
and fitted with his own mirror.

Steve certainly makes some of the best commercial mirrors on the market
and the views were bright and crisp. Steve spent some time as an optician
for Celestron in California.

Gary Myers was on hand to tweak the ServoCAT, Howie Glatter was there
helping collimate it, I fielded Argo Navis questions and Al Nagler was
keen to try out the 13mm Ethos prototype in it. As Al confirmed, mirrors
of these focal lengths definitely benefit from the Paracorr, which I note you are using.

Picture of Steve in front of his scope and the RV he moves it in the background.
The back of the RV folded down so you could roll the scope in and I think Steve
mentioned it was originally designed for transporting race cars.

Best Regards

Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Phone +61-2-9457-9593
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au

tnott · #32 10-03-2009, 07:11 PM

Great! Thanks Gary

I will definitely need a trailer if I ever go up in aperture again!

GrahamL · #33 15-03-2009, 06:42 PM

Sure is compact alright Tim

.. Whats the hole in the light baffle for ?

even at 3.66 gary thats one monster of a scope

gary · #34 17-03-2009, 12:32 PM

Quote:

Originally Posted by nightstalker

even at 3.66 gary thats one monster of a scope

Hi Graham,

It certainly is!

One thing that you see a lot of North American big Dob owners have which
I don't come across on observing fields here in Australia are ladders with 'half steps'.
That is, step ladders with twice as many steps as 'normal'.

The reason I thought of this is that I recollect Steve Kennedy had
a particularly good ladder with his own scope. Larry Mitchell also
had a very reassuringly sturdy ladder with half steps for his 36" in Texas.

Undoubtedly there are observers here in Australia that have them, but I have
never climbed up one on an observing field at a star party here.

The 'half steps' of course take away a lot of the sting from when on a normal
ladder standing on one step makes you too high above the eyepiece and
the step below it makes it too low.

The half step ladders are then often further embellished with additional
handrails at the very top, so once you get up there you can lean into
them in a really relaxed and comfortable way. As we all know, when you
are relaxed up there it is much easier to concentrate on the observing.

In Australia, they can undoubtedly be purchased from specialty ladder suppliers
or might even be standard in the fruit picking areas. If you walk into most
generic hardware stores in Sydney, I have yet to see one.

Anyway, with Tim's short focal length the ladder is probably the least of
his worries, but I would be curious to hear from any observers here in
Australia who own a step ladder with 'half steps'.

Best Regards

Gary

tnott · #35 17-03-2009, 07:47 PM

Quote:

Originally Posted by nightstalker

Sure is compact alright Tim

.. Whats the hole in the light baffle for ?

The hole in the baffle is situated directly behind the secondary to let air through and further reduce the wind profile. Don't want it to act like a sail or vibrate excessively in a breeze.
Easy to do, but as for how much difference it makes.

I think one of the first additions to the parachute was a hole in the top to cut down on turbulence and make it more controllable. Not sure of the exact aerodynamics though.

tnott · #36 03-09-2009, 10:14 PM

Well the scope continues to perform excellently, though the weather in the southern states has been a bit cloudy the last few months.

Spoke to Steve Kennedy the other day and he was really pleased that I had got the mirror into a working telescope so quickly. Apparently a lot of his mirrors go to big dob builders that have looong lead times for completion.

Also mentioned that he might be going to even faster focal ratios with the development of a new special Parracorr for F3-ish mirrors.

The current parracorr works fine in this scope. Images are much flatter and sharper than a F5 without.

erick (Eric) · #37 03-09-2009, 10:37 PM

f3!!!! My goodness - will it look like a fruit bowl?

Satchmo · #38 04-09-2009, 08:04 AM

Quote:

Originally Posted by tnott

Also mentioned that he might be going to even faster focal ratios with the development of a new special Parracorr for F3-ish mirrors.

There will be limits to what an F3 Paracor can do in that eyepieces themselves ( even Naglers ) aren't designed to handle such fast light cones. I don't see much practical point in going faster than F3.5 on a 20" or F3.3 on a 24", as the scopes are allready quite eyepiece friendly in a dob.

Ian Robinson · #39 05-09-2009, 11:42 PM

Quote:

Originally Posted by tnott

Thanks,

Yes a two person lift or up two planks with wheelbarrow handles and trolley wheels. I can lift it myself - just- but wheeling it around is much easier and safer. The handles take less than a minute to bolt on and off.

Just curious .... how heavy do you reckon the OTA (with optics in it of cause) would be ?

Very long term project in mind .... but as a equatorial not a dob.

tnott · #40 07-09-2009, 08:48 PM

Yeah I thinks the same. F 3 would only be useful on really big scopes.

I can't remember the exact weight or find where I wrote down the calculations. I think it is almost exactly the same as an 18" Obsession due to the 1.7" thin mirror.

It is interesting that Obsession itself is now building a 22" version of this scope.