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Monthly Archives: January 2020

In which some of the advantages of traditional Dobsonian telescopes are demonstrated …

19 Sunday Jan 2020

Posted by gfbrandenburg in Uncategorized

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Darwin B recently built, in nearly record time, an interesting, two-truss, tubeless, collapsible, travel-ready Newtonian scope at our DC-area telescope making workshop, using an 8″ parabolic mirror with a short focal length that he bought.

He mounted it on a commercial alt-az tripod, as you see here. It will definitely collapse and fit either in a suitcase or fit in carry-on spaces on an airplane.

Unfortunately, there are some drawbacks, as he is the first to admit:

  • The lack of any sort of light shielding is a huge problem virtually anywhere within a hundred miles of a city;
  • The ultra-cantilevered mount makes it very wiggly; images essentially never stabilize. It’s also extremely susceptible to breezes.

To quote from a recent email from him:

==========

So let me first plead mea culpa!

1. Anywhere near DC-MD-VA, open structure telescopes are TRULY instruments of the devil! (How do I come to fully agree with you on this point? Well Tuesday morning before dawn, in the cold, I set up near work – well that 70mm mirror does an incredible job collecting light from a wide area! That also explains my difficulty at CC the other night.)
2. I am asking for “un-attainium” with my scope: big aperture, fit as 2nd item carry-on, have a good mount, and be useful locally.
3. Perhaps many people would be better off traveling with binoculars- smaller & less hassle than a scope. And would do a great (limited) job anywhere.
So what to do?
1. Fix what I can on this scope and accept limitations- fix spider, swap sides for saddle, and add a shroud. Limit to low & medium power and enjoy.
2. Since I have an 8” f/6 mirror, build a scope for around here & car travel: and not have the limitations of the other scope. I already have many/most of the parts for a design similar to your 6” f/8. Like you say, it’ll be steady, and I can crank up the power a bit for moon&planets. It just has to have the mount break down flat like an IKEA.
So, I’ll be up at the shop next Tuesday nightto drill holes to flip saddle. I should have other things done or started.
So – now you have a pretty ringing endorsement for your thoughts.
I can compare my current effort to a beach house or a boat; wouldn’t want to live there year-round. BUT they can be fun, within limits.

Mining at the Observatory (sort of…)

03 Friday Jan 2020

Posted by gfbrandenburg in Hopewell Observatorry, Telescope Making, Uncategorized

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Tags

jackhammer, maintenance, masonry, observatory

We have been concerned with the status of some of the columns that are part of the roll-off-roof of the Hopewell Observatory, so we decided to remove a couple of courses of cinderblock to see what was inside. It turned out to be built much more sturdily than they appeared. and removing those two layers of cinderblock ended up being a much harder job than we expected. We had to build a very strong ‘crib’ to hold the upper part of the 9-foot-tall column in place while we removed the lower foot-and-a-third.

In the video, you see me using a small hand-held air-hammer with chisel to clean up the underside of the upper part of the column, so that the new solid cinderblocks can be mortared into place. The buzzing noise you hear is the air compressor.

We didn’t realize there was rebar (reinforcing iron bars) and concrete poured into most of the ‘cells’ of the 16″ by 24″ columns. Now we do.

How I left it: two solid blocks and some plywood in case our cribbing and jacks give way
How I left it: two solid blocks and some plywood in case our cribbing and jacks give way
You are looking up towards the majority of the column
You are looking up towards the majority of the column

(In the summer of 1970, between my junior and senior years, I found a job in Brooklyn working on a rodding truck for the local electric power utility, Con Edison — a hard and dirty job that made me itch constantly because of all the fiberglass dust that was scraped off the poles we used to clean out the supposedly empty, masonry, electric conduits that went from one manhole to the next. I guess I pissed off our truck crew’s supervisor, so the very day that I was about to quit to go back to college, I was told that I was being transferred to a jack-hammer crew, where I probably would have gone deaf. This woulda been me, except I quit)

Image result for jackhammering

 

After that was done, I trimmed some of the trees to the west. Constant struggle with the shrubbery!

 

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