Re-vamp of the dob

[TheThing]

A while ago, a very nice chap called Brian Gaze gave me his old 8" dob. As I understand it from him, the dob was made for him by a local astronomy club back in the 1980's some time.

I've always wanted a dob and the plan was to upgrade it slowly, over time, with my little boy helping. Eventually, I hope it will become his scope.

Brian had made it quite clear that, although the main mirror has a removable cover, the dob has been stored in a garage for somewhile with the tube open. The thought was that the mirror, being some 30 years old, would definately need a re-coat.

The dob has sat in my office for a couple of months while work and chores got in the way. Today, I decided it was time to get some work started.

Here are a few pictures: -

The tube is of cardboard, I suspect an old carpet tube.

The focuser was a bit Heath Robinson - a couple of bits of plastic tubing that accept a 1.25" EP and slide in and out to achieve focus.

Down the OTA. The black paint looks worse than it really is. A good hoovering has made it come up much better. You can also see where the focuser is fixed internally. The secondary vanes are held on (barely) by electrical tape. This is just going to be re-newed for now, with a plan to screw/bolt thru later.

External view of the mirror end. The 3 big bolts are for collimation.

The wooden mirror cover.

Gives an idea of how dirty the mirror was after 30 odd years (and also how badly I'm thinning on top!)

The back of the mirror. I'm assuming that 1288mm is the focal length. I'm not sure what the other figures are for. After carefully following Steve Richard's (Steppenwolf's) video tutorial on Face Tube, I washed the primary and it has come up like (almost) new! No need to re-coat after all. There is a blemish, but it doesn't seem to effect the view, so I won't worry too much about it for now.

Down the OTA with the mirror removed, showing the cell.

My little chap helping me to remove the focuser. I then used a cutting tool (thanks Phil - it'll be coming back to you at last this week!) to enlarge the hole. I then fitted a SW single speed Crayford type focuser.

The new focuser in position.

I've collimated it with a laser and am hopeful for a star test tonight, if it stays clear and if I have the energy.

Next job is to screw/glue a metal strip near the focuser so that I can attach a Wixey by its built in magnet. I may freshen up the paint at some point and flock internally, but will just see how it performs first.

Thanks for looking.

[twotter]

What a cool piece of kit and a great project

[Daniel-K]

how did the star test go?

[TheThing]

Not possible at the moment due to a focus issue - see the equipment help section.

[iamjulian]

Nice project, and a great way to cement your son's interest in the stars.

[franco]

love this thread, is the sort of thing i can imagine my grandad doing, making a telescope out of a carpet tube in his shed! all the best with the project

[Astrokev]

The back of the mirror. I'm assuming that 1288mm is the focal length. I'm not sure what the other figures are for.

Thanks for looking.

Hi TT,

Great project - good luck.

The squiggle before the number 1288 is "fl" - focal length, as you assumed.

50.7 will be the FL in inches. I suspect the "3778" is just an ID number to identify the mirror to the manufacturer/tester.

[great_bear]

I'm assuming that 1288mm is the focal length. I'm not sure what the other figures are for.

The "50.7" is the focal length measured in inches.

rgds,

Jeremy.

[TheThing]

Ah, got it, thank you.

[beady eyes]

Hi All:

Fairly new here, so just tripped over this the other day.

The first scope I made (in 2001) was an 8" dob (f/5.8) with a cardboard tube. Your scope brings back memories .

I would suggest putting in a round spider/secondary holder. The lack of diffraction spikes when you are looking at a bright star is nice and it will make the scope relatively unique. I really like the round secondary holder I put in my scope!

ttfn