Tuesday, January 29, 2019

Blast From the Past

The last few weeks have brought some on and off work on something I haven't been doing in years.

Telescope making.

I got interested in astronomy as a kid and had my first good telescope by junior high school (a 4" f10 reflector - good is a relative term).  In those days, we'd see stories about people who made their own telescopes complete from grinding a mirror through making a mount for it.  There was a Mars opposition at some time during my high school years, and I bought a kit to make a mirror.  I was going to do it!

Except without someone to guide you through the rough points, it's not necessarily easy.  In my case, I banged the mirror on my work stand (a 55 gallon drum, which my parents graciously allowed in my bedroom) and took a big chip out of it.  Instead of finishing the mirror and painting the chip flat black, the accepted wisdom of how to fix such things,  I tried to grind the chip out and, well, never did get that 8" mirror made.

Fast forward 20 years to about 1990, now an adult working for Major SE Defense Contractor, when I got the bug again.  This time, it was the information age and the internet offered this precursor to the web called Newsgroups.  Buoyed on by the folks on sci.astro.amateur, and with the help of a really great book, I made my first successful mirror and first good telescope.  For those who will understand this, it's a 6" f8 mirror; that is, 48" focal length, and a Newtonian Reflector.  It makes a good size, but like a lot of addictions, it leaves you wanting more.  (I rush to add that those newsgroups are still there today!)

I started a bigger mirror, 10" f6.  I missed the focal length; it came out f5.6 which is still perfectly usable.  This was a more difficult mirror, but a 10" mirror gives a serious advantage over the smaller mirror.  Area goes up as radius squared, so it has a little under 3 times the area as the 6" mirror.  I completed the 10", again with some help from people I met on the newsgroups.  I built the telescope as a Dobsonian, altitude-azimuth style mount.  This is actually the second iteration of the telescope, when I replaced the typical cardboard tube with a metal tube.

By extreme luck, I completed this telescope in early 1994, the year that Comet Shoemaker-Levy 9 crashed into Jupiter.  Nobody in all of human history had ever seen such a thing, and we saw the impact marks on Jupiter from our backyard through this telescope.  Armed with star charts and the old fashioned method of "star hopping" (going from landmark star to star in your finder scope until you find the object you're looking for), I spent several years exploring the sky with it. 

The story goes a bit sideways here.  These telescopes have a lot going for them but they have a serious drawback: they don't track an object so that you constantly have to reposition the scope while looking at a planet or other object to compensate for the apparent motion in the eyepiece.  On higher powers, say 300x or more, the earth's rotation can cause a planet to drift cross the field of view in perhaps ten seconds.  (As a side note, this is half the speed of a clock's hour hand.  A star on the celestial equator goes from east to west in 12 hours.  That's the same as going from 3 to 9 on a clock - only the clock does it twice as fast)

It's now in the early 2000s, and my career had gotten to the point where I had "more money than time" and with that the funds to buy a commercial telescope with a computerized tracking mount and a new feature called "GoTo".  With a GoTo system, you typically tell a handheld controller what object you want to view and it moves the telescope until it puts that object in your field of view.  I literally saw more deep sky objects in my first night with that scope than I used to see in a season without the GoTo feature. 

One night, we set up a test in the backyard.  We put the commercial telescope, an 11" compound reflector side by side with my 10" reflector.  We pushed the same magnification on both scopes.  Both Mrs. Graybeard and I thought the image in my telescope was better. 

This led to a plan to go back to using mine and getting a mount for it that allowed tracking and GoTo.   Much to my surprise, I don't have any pictures of the telescope at that time.  I repainted it blue because the original paint job chipped maddeningly (I bought the tube pre-painted inside and out) . 

This Christmas, I moved the telescope on the tripod out to the shop, as I've done every year, and one of the casters disintegrated - sort of a flat tire.  I had to put wheels on it.  I thought bigger casters would be better than the ones it had, so they got upgraded from 1-3/4" diameter to 4".  A little shop time was required to build mounting hardware for them.  Those are 4" casters simply because I had them.  They were for some project idea or other that got replaced. 

I had some generalized fixing that had to be done.  The mount was loose and I didn't recall how to tighten it.  I figured that out this week.  Finally, the telescope and mount could be reunited.  This isn't "done done" but is pretty close to it. 

The big telescope tube is 12" diameter and 60" long, for scale.  Oh, for closure, look to the right of the black mount and you'll see and odd-shaped blue structure with a white disk on its side.  That's my 6" f8 reflector that I started the story with.  (The black box with the orange strap on a cart is my smoker.)  It's in a square, plywood tube, but it's a Dobsonian style mount, too. 

I connected the controller computer to the mount and turned it on.  It acted like I'd turned it off the minute before.  Never missed a beat.  There's still a little bit of maintenance to do on things but it's usable.  The thing is, I haven't used it since the year was in single digits, like '08 or '09.  Our neighborhood trees (including my own) have grown up so much that it's difficult to see the sky, and what we can see is light polluted.  To use it now, the 4" casters won't cut it.  Those are fine for the porch, but to get it out to where it can see even a sliver of sky, I need 20 or 26" mountain bike tires on the mount.  Or garden cart wheels.  And that's another redesign and building project.


  1. Way cool!

    I built an 8" in high-school with stuff I bought from Edmond Scientific. Spent one winter in the basement walking around, and around, and around a little table my Dad built for me to hold the blank.

    I always wanted to put a "Clock Drive" on it so I could use it for photography, but never happened.

    Wound up giving it to a 2nd cousin who had a ball with it.

  2. It turns out that building telescopes is a lot like building ARs.

  3. Replies
    1. I have a few, but did more with the store-bought (Celestron) scope and mostly planets. It turns out when you take pictures of things dimmer than planets that it's very hard and involved. Other than collecting the light with the telescope, it's all done at your computer. It's all about processing the images.

      A reality is that it's the only way to "see" some things. Some things you see great pictures of are just dim fuzzy spots. With a GoTo system, I'd be pretty sure I was looking at the nebula (or whatever), but I'd have to do tricks to convince myself it was really there.

  4. But look at what you can get today for $5:


    1. He was too kind about that $5 Vivitar. I'm so old I remember when Vivitar used to produce good stuff. Kinda like Bell & Howell.

      All in all, what he said was pretty good and it was a good review. Covered the important points well.

  5. Oddly enough I have a book called Amateur Telescope Making published by Scientific American - 4th edition of 1962. The first edition was published in 1935 and the book takes you through ALL stages of making reflectors and refractors including a lot of mathematics.

    They don't write books like that any more, eh?

    Phil B

    1. They do, but that set of three books from the 1930s is really a classic. It was republished about 10 years ago. The big publisher in the business is Willmann-Bell. Those three volumes are on that page. I have three of the original, 1930s editions.

      The were originally aimed at guys who were working with machine tools during the day and were captivated by the idea that when you make a mirror, the surface has to be right to within millionths of an inch. One of the first places in America that became a center for telescope making was Springfield, Vermont. There was lots of manufacturing in the area.

      Their annual convention, called Stellafane, is still going now, a hundred years later. I went to it in the early 90s.

  6. Another blogger who does telescopes:


  7. My wife’s grandfather gifted me his NexStar 8 GPS when he realized he couldn’t get it out of the garage to set it up anymore, and that I was the only one in the family with an inclination for astro-work. While I’d like to try and build something eventually, getting the ‘big scope’ out to take moonshots with my daughter is pretty awesome for now. I’m constantly amazed at the level of precision required for getting good astro shots (other than the moon, which is much, much easier), because like you said, you’re just “collecting the light” with the scope. I’ve had reasonable luck, and it’s very different than terrestrial photography, so there’s always something new to learn.

    My best stuff lives here:

    1. You've got some very nice work at that site.

      I have a friend who retired about 5 years before me who was very much into photography - and moved out to New Mexico for the superior skies. It was a lesson for me when he used his C8 only as a mount for a small refractor. He used the C8 with a guide camera to autoguide the Celestron. That's why there's a small (66mm) refractor on top of my Newt in that photo. I just never got it working well enough.

      Planets are much easier than deep sky objects. I had my most success using a webcam on the Nexstar 11 GPS and stacking minutes of video. Most were using the mount as an alt-az. The peak of that was in 2003 when we had that particularly good Mars opposition and I was able to get a few good pictures of Mars. I have photographed all of the planets, although several are rather "star like" (Neptune, Uranus, Mercury).

  8. I haven't been involved in backyard astronomy since high school, but I thought with the proper application of computer control you could make the Dobsonian mounts do an OK job of tracking. Is that not true? Or just easier to use a traditional mount. (Nice looking scope by the way.)

    1. It is possible to track with an altaziumth mount like a Dobsonian. The most common way it's done is with motors on both axes and some slick algorithms that keep track of everything. A lot of commercial mounts are made this way, but the tech hadn't made it into homemade scopes back then. Not sure about now, but I imagine it's there.

      The drawback to this is that everyone jumps at doing photography and this system gets image rotation over the course of a long exposure. You've probably noticed how the view of the moon appears to rotate from moonrise to set on any day - it's that effect. "How long is too long?" depends mostly on magnification

      I had read somewhere that a high-end observatory being built was going to use an alt-az mount and add image rotation drive for the instruments. The typical alt-az just supports a telescope so much better than an equatorial, like the one holding my big blue beast.