245mm photographic Newtonian

[darditti]

I have been accumulating the parts for this project for some time, and it has now reached fruition.

This is the second rebuild of this telescope. Originally the optics were in an Orion Europa OTA that I bought off Peter Grego (it was featured in his book on the Moon). I disliked the original tube and tube rings (thin and wobbly) and focuser (1.25 inch plastic) and the spider assembly (clunky and wouldn't collimate properly). The original tube was used to cast a concrete pier on which the telescope now stands (I also use my C11 on this pier).

The first rebuild used a plastic tube and a 2" metal R&P focuser and a re-designed spider/secondary assembly, made from a bent aluminium ruler and other bits. This was an improvement, but the plastic tube was still too flexible and collimation too variable (this is the telescope shown in my book).

Having found that what I wanted could not be bought in the UK, I bought a 12" diameter, 48" long, 0.1" thick aluminium tube with aluminium rotating tube rings machined precisely for it from Parallax Instruments in the States. These were very expensive to import (far more than I paid for the original scope), but well worth it. Joe Nastasi at Parallax is a great guy. He painted the outside of the tube metallic grey, and the inside the blackest matt black I have ever seen.

I also bought a JMI Next Generation motorised low-profile Crayford focuser from Optcorp.

I adopted a spider design I saw on the Royce optical website, consisting of three unsymmetrical curved vanes, and I made this out of a strip of thin springy steel I found in a car park. I screwed this to a simplified version of the first rebuild secondary collimation system, and installed three M8 thumbscrews with nylon tips to allow adjustment without tools.

I basically incorporated every kind of adjustment I could think of in this rebuild, to try to create my ideal, completely adjustable Newtonian. The tube is rotatable (easily and smoothly), the focuser is rotatable and collimatable, the secondary can be rotated, angled and translated in all planes.

The original primary cell worked OK but was too small for the new tube, so I had to devise an arrangement of mounting bolts to take up the space. I also cut holes in the solid back of the cell and installed a fan (this was in the earlier rebuild).

I incorporated an exceptionally large amount of back-focus. This was accidental and due to a miscalculation. However, it allows the possibility of using a radial guider, which is normally impossible (or difficult) with Newtonians. It also places the secondary far enough down the tube that it is unlikely to dew (which used to be a problem). However, the secondary now doesn't fully image the primary and really needs replacing with a bigger one. The telescope can be used visually, but it required two stacked 2" extensions plus eyepiece to achieve focus.

On first assembly and bench-testing with a laser, the scope proved to be in almost perfect collimation already, which shows that I built it quite accurately.

In my opinion, the major triumph of this project has been the Royce spider. I have experimented with lots of spider designs before, but this one combines strength with non-obstructiveness better than any other I have tried.

The completed telescope is heavy, but the Astro-physics 900 will cope with it easily. It will live in my run-off shed, where I intend to alternate it with the C-11.

David

Some pictures:

Looking down the tube with primary cell and focuser fitted

JMI focuser

Back of the scope, showing fan and switch

Spider on the drawing board

Full secondary assembly

Spider centred

Rotating tube rings fitted

[Psychobilly]

Nice Project

Billy...

[ChrisEdu]

Now, that looks like a 'man's' shed!

[hellibird]

Now, that looks like a 'man's' shed!

The woman's MS is too bad for her to enter...

... but her study is no tidier.

[Doc]

I'm more jealous of your shed.

I would love one of them.

[hellibird]

Our sheds seem to be multiplying; now David has built two, I fear they may reproduce if left unsupervised.

[ChrisEdu]

Better buy some shed contraceptives!

[ollypenrice]

Poor David! All that work on a most interesting instrument and all he gets is reaction to his shed. It IS a good shed, though... There was a Python sketch along these lines. I trust you don't have Two Sheds, David??

I'll be interested to see if the curved spider proves to ba a boon for imaging.

Olly.

[ChrisEdu]

Poor David! All that work on a most interesting instrument and all he gets is reaction to his shed. It IS a good shed, though... There was a Python sketch along these lines. I trust you don't have Two Sheds, David??

I'll be interested to see if the curved spider proves to ba a boon for imaging.

Olly.

Oh yeah! Nice project, too! Now, back to the shed....

[darditti]

I've actually got four sheds: this one (workshop and astrojunk/bike store), a Summer House [removed word]-telescope-control warm room, the run-off shed for this telescope, and the run-off roof shed for the C14 (recently extended). And I am also a composer, like Mr Jackson in the sketch. And, unlike him, I do sometimes compose in the shed: the Summer House also contains an electric piano. Most people seem to have lots of sheds round here. Two sheds would be well below average for Middlesex Man, I suggest.

David

[barkis]

A very rewarding project David. No better way to spend free time, than to renovate, or refurbish a decent instrument. I did a job on a 6" f8 Newtonian a few months ago. Hardly a Herculean task, but very enjoyable. The owner was a local radio announcer [removed word] disc jockey. He was delighted with the result.

Please post pics. of the finished article.

Ron.

[ChrisEdu]

I've actually got four sheds: this one (workshop and astrojunk/bike store), a Summer House [removed word]-telescope-control warm room, the run-off shed for this telescope, and the run-off roof shed for the C14 (recently extended). And I am also a composer, like Mr Jackson in the sketch. And, unlike him, I do sometimes compose in the shed: the Summer House also contains an electric piano. Most people seem to have lots of sheds round here. Two sheds would be well below average for Middlesex Man, I suggest.

David

Well, it wouldn't do for you to be under-endowed in the shed department! I currently have no sheds, having demolished my 10' x 12' at Easter to make way for a pool.

[darditti]

What use is a pool for astronomy? Are you going to spin it to create a giant parabolic mirror?

David

[ChrisEdu]

What use is a pool for astronomy? Are you going to spin it to create a giant parabolic mirror?

David

That thought has occurred to me before now when it's been cold enough to freeze the water. Last winter, the pool cover got submerged and ended-up resembling a parabola.

[darditti]

Here are the photos of the finished telescope set up for imaging. Two configurations: one with an ED80 mounted on a rail (this actually was the supplied dovetail for a C-11, hence orange) as a guider, with DMK camera, the other (which I intend to be the usual one), with just a 50mm elbow finder mounted on the rail, and DMK camera fitted to an OAG. Imaging camera in both cases is the QHY8. The ED80 has to be removed before closing the shed, as it doesn't fit in, but this is easy. The second configuration can be left exactly as-is.

The JMI focuser is connected to the AP GTO control box, thus the scope can be focused remotely over serial link, as well as steered, for which I use either PulseGuide or TheSky, operating on PCs in the warm shed about 5m away. I image from there, not the house, because it is fairly close, while the house is 30m away, and I do have to go back and forth a lot to adjust the guiding setup, camera orientation etc.

David

[ChrisEdu]

Cool! Nice shed!

[hellibird]

Cool! Nice shed!

They are nice.

You see parts of two sheds in those pictures; the run-off roof from one shed is above the run-off shed which houses the rebuilt telecope.

[ChrisEdu]

Thread should be renamed - shed [removed word]!