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Modding an Old Scope (imgur.com)

submitted 1 year ago* (last edited 1 year ago) by atx_aquarian to c/telescopes

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Hi, Lemmians,

I wanted to share my experience messing with an old Dobsonian-style scope. My parents had a Coulter Odyssey 10.1" covered by a trash bag since somewhere around the early 90s. We used to have pretty dark nights back then, but the light pollution crept up over the years, and it probably went a couple of decades without any use, so they sent it with me after a visit.

It didn't take long before I was shopping for eyepieces and realizing the original focuser was a sore spot, as it was only a locking sliding tube--no knobs or gears for smooth, precise adjustment. I started thinking about what else I would change and, with their blessing, I decided to have a little fun changing it up.

Not all my changes were improvements, but it was rewarding to tear into it and put it back together with some of my own taste applied.

Full album: https://imgur.com/a/I9Mj1kT

before after

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[–] chrislon_geo 2 points 1 year ago* (last edited 1 year ago) (1 children)

Great work! I started with the 8" version of the same scope, and yes, the focuser sucked. Are you having any issue reaching focus with the new focuser? I think the focal plane is fairly close to the secondary and some eyepieces may not reach focus even when racked all the way in. I ended up getting a low profile focuser, but have yet to test it.

[–] atx_aquarian 2 points 1 year ago

Thanks!

Yep, the new focuser didn't get me the same range as the old one, and some eyepieces (but not all) couldn't focus, at first. I ended up chopping an inch off the bottom of the tube to move the primary mirror "up" an inch towards the secondary. That pushed the scope's focal point/plane one inch towards the focuser, which, so far, seems to have parked it right where I needed it. That modification would have widened the cross section of light hitting the secondary, too, but I think it was subtle enough that I'm still catching the full primary aperture. This weekend, I'll point a laser down the edges and confirm whether it's all still hitting the secondary and not spilling around the edges.

In the imgur album link in my post, there are some pictures of that surgery, in case you're curious to see how involving that was. (It looks like imgur initially only shows the first ~10 shots of the album, but there are more hidden if you click the "show more" button.)