Chester

Chester is a 24” f/3.75 Kriege-style Dobsonian telescope of my own making. The road was long in making this telescope because I tried so many different approaches to optimization only to return to the Kriege style, which is where I should have gone in the first place.

Since these photographs were taken, I’ve dumped the Kriege style cell, which warps thin, fast, large mirrors, and built one in the style of JPAstroCraft. It made a world of difference. I’ve also installed a sidereal Tech drive system using the ServeCat motor/encoder units. It now drives in RA, but is not push n track. My next scope will be Sidereal Tech with Push n Tack. I’ve shrouded it, installed my 80mm finder, and a few other things.

He was a copy of the Obsession Ultra Compact and his name was Black, the 7^th in a series, but it was so wiggly-jiggly that I destroyed the telescope and put the optics into this scope instead. Below is this original version [summer 2013]. This photo shows it before the ServoCat and shrouds were installed.

I am much happier with the traditional Kriege design [Chester]. David Kriege is a champion to have written the book [The Dobsonian Telescope: A Practical Manual for Building Large Aperture Telescopes] on this design and offered it to the world. Thank you David.

The summer of 2014 saw the completion of the primary mirror and the construction of the telescope. The mirror warpage was difficult to take control over, so I reworked the mirror. It took ten days from grind to final figure. The final figure was established using he SIT test invented by Bill Thomas. Dan Bakken gave me his old ServoCat [Gen 1] from Hercules, his 41” monster, thank you Dan. I will not use Argo Navis nor DSCs on this scope, I like the hunt. My next personal scope, a 31.5” f/3.6 will incorporate the Argo Navis and a later generation ServoCat.

The mirror on this scope was a lousy piece of glass. Years ago Dan Bakken and I bought two 24” blanks from Jan Benz for next to nothing, the glass was of unknown type, but looked like Pyrex. Dan took one and I sold the other to Jeff Draper. When I wanted to build another 24” scope for myself I asked Jeff if I could buy it back, and he said no. So Bakken sold me his. It turned out to be stressed and I could not figure it, so I had Greg Wilhite anneal it. It took three times in the annealing process before it began to cooperate. It still has goofy stuff inside the glass, but seems to be holding structure. 8^th time is a charm, right? Trying to beat this glass was a test of my fortitude, but I should have just thrown it away. I am way past the point of diminishing returns. Time will tell. Mystery glass is a pain in the butt. I had a 24” f/3.7, Black #6, and enjoyed his as much as any telescope I’ve ever had. Selling him around 2002 was a mistake. He wasn’t optically nor mechanically perfect, but what a fun scope to use. This scope will hopefully surpass Black, it’s built better, and the optics will be superior.

The secondary mirror is 1/11 wave, has a minor axis of 5.5”. That’s really, really large. For some reason I thought that I ought to go big with the SIPS feature, but my brain must have been deselected that day. I’ll trade it over to the 31.5” telescope and put a 4.5” secondary on this one later.

I used English Chestnut stain on him, so I named him Chester. I was going to continue the “Black” series, using Ebony stain and Polyurethane, which my altitude bearings are. It’s pretty, but I’m glad I went with English Chestnut.

Baltic Birch 18mm wood throughout the scope makes for a strong but heavy machine. This dog weighs in at just under 300#. With stuff on it the weight is right at 300#. He loads up onto my ’95 Chevy Suburban [Spike] easily with 8’ ramps and 8’ steel 1.5” square wheel barrow handles.

A top hat makes the inside even darker, this idea from Ben Brown, an observing buddy. I know lots of gurus like to say “no shroud, just proper baffling”, but I like shrouds, and I like a barrier between little kids and my mirror. I do most of my observing not alone, and this is one more level of safety.

Speaking of safely, I like fast scopes that don’t require an elevator. Being atop a tall ladder in the dark no longer works for me, so my scopes tend to be between f/3 and f/4.

Here is the final figure data sheet from the SIT test. The data sheets are similar to the Foucault data sheets but the information is arrived at in a totally different way. For fast mirrors Foucault testing is subjective and ambiguous. With SIT testing, it is extremely subjective, repeatable and accurate. The data sheet shows an incredibly small P-V wave-front error, but I make no claims that his mirror is this accurate. But it is nice to have high-precision data sheets.

My goals with Chester are:

1] Finish my Herschel II list. I already hold Herschel Certificate #28 from 1986. I did this.

2] See 20 + solar system moons. I still haven’t nailed Phobos or Dimos. When it was at opposition in 2020, California had severe smoke.

3] Observe the Barnard Dark Nebulae. That bored me, I moved on.

4] Share the universe with my friends, family, and anybody interested. All the time.

5] Whack quasars. I’ve only seen 3, and I want to get more. Haven’t gotten around to this yet.

6] Finish my Andromeda Galaxy Globular Cluster hunt. I’ve seen many and want to log more. Haven’t gotten to this yet.

7] Look at all the regular stuff I’ve always looked at. Still at it.

8] Enjoy it while making a 31.5” f/3.6. I started it and am making it f/3, plan on selling it and making a 42” f/3 meniscus mirror for a large portable Dob. I hope to start the 42” around 2024 and finalize it around 2026.

If you’d ever like to look through Chester, I live in Lathrop California, I’m an active member of the Stockton Astronomical Society, I hold Herschel Certificate #28 [and now the HII certificate] and I do most of my observing in the Sierra Mountains east of Stockton. Find me, we’ll go gawk.

Jeff Baldwin