Maksutovs Galore

IMG_4489 (Large)I only heard about this odd telescope type by accident really.

It had its own little history section in a collection of ATM Journal articles some years back.

Being only “invented” by at least three people independently during WW 2, most elected to keep them secret, Bowers being in German-Occupied Netherlands and Maksutov in Russia. However, Maksutov got his published in a journal, and first come is first recognized. The premise is simple: a curved optical component with no real magnification called a “meniscus” is placed in front of a regular spherical mirror, cancelling out spherical aberrations.

Little happened to the design after the war. In 1956, John Gregory published a design in Sky and Telescope and Allen Macintosh created the Maksutov Circulars meant to make designs and help available to amateur telescope makers.

Later, this pair organized a group of people to get some glass blanks “slumped” to the correct shape is order to make it faster and cheaper to make these telescopes.

Before I get into the guts of the matter, one has to understand CLEARLY the effort required for this type of scope:

You need to be able to control the curves you generate, both on the mirror and the corrector to a fairly fine degree, and the final thickness of the corrector affects the performance of the finished telescope. Generally people do the mirror and corrector in parallel

A number of these blanks were made in the late 1950’s, in the sizes 4 1/2″,5 1/2″, 8″ 10 3/4″ and the huge 11 1/4″. The reason for the odd sizes was they require a mirror blank SLIGHTLY larger than the optical. Many of these were made and purchased (about $30 for the 4 1/2″ size and $130 for the huge 11 1/4″ version. Even now, more than 50 years on, many of these raw blanks are still extant , never having been made into telescopes. I think they ran into the same problem I did with my first, an 11 1/4″ bought in 2008: they are simple in theory but execution is another matter.

A lot of these have been passed on in estates and are being sold off by people who don’t know what they are or think they are more trouble than just getting a commercial scope. Same with me. I built a number of smaller mirrors to get a handle on grinding, I found some small correctors to start on that won’t break me if I fail the first one or two times. The cheap Schmidt Cassegrains along sunk them. A flat corrector is cheaper to make in larger sizes, so the Maksutov is now an niche design relegated to only a handful of makers. One maker still remain: Questar with their 3 1/2″ and 7″ models. A 12″ model was limited to only 16 examples (one in Greater Vancouver). Intes-Micro and Aires of Russia still make them to order but not a regular production of them and AstroPhysics does.

Other makers came and went: Tinsley, Vega, Max Bray, Quantum et al.

Two types can be made: Newtonian or Cassegrain versions. The Newtonian is easy as you simply make a spherical mirror, easy to do accurately and with a smooth figure. There is a subset, where you can use a sub-diameter corrector closer to focus, in some cases as a Mangin type mirror or even double pass.

The photo at top shows the results of my interest in getting the raw and  finished pieces for building Maksutov scopes.

On the case are slumped and molded blanks as they arrive from optical glass manufacturers or suppliers. To two at the outside left and right are the HUGE Hayward Glass of California’s 11 1/4″ X 1 3/8″ thick and the other really large one is a 10 3/4″ by Hayward as well.  This size allows the making of a variety of designs that use a 12″ or 12 1/2″ mirror blank for a complete telescope.

The two at the right middle are a 7 1/2 and a 5 1/2″ and the 4 smallest are the 4 1/2″ ones. 2 of the latter have had a start with rough grinding.

On the carpet are the semi-finished 6″ and 4 1/4″ Maksutov correctors and their mirrors.

Various publications exist for making these scopes, notably “Construction of a Maksutov” by Fillmore and “Bulletin C”, published by Sky and Telescope, as well as articles in Sky and Telescope.

 

MY first exposure to this niche of ATM was an old issue which had a 10.8″ version built by AAVSO member Howard Louth. He doesn’t give many details but it became apparent that he simply used “well established techniques” to arrive at the proper curves for his corrector.

 

 

 

 

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