lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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Longtime reader first time poster here.
I have recently come into temporary possesion of a wonderful scope a hand built 8" F/15 Gregory Mak. The man who built this scope was a longtime member of my local small astronomy club. George died a few years ago. The scope was given to a member of our club and since he is not using it he agreed to loan me the scope so I could image with it. He said George would want that as he was a excellent astrophotographer.
My buddy Al and I have decided to restore the Mak to the best of our abilities. Also we plan to adapt a Moonlite focuser to the scope for automated focusing. The Mak currently has of course a moving primary which although has a small amount of image shift is better than any commercial SCT I have used.
Overall the scope is in excellent condition the meniscus coatings appear excellent, the primary though may need a recoat. The scope was finished in 1966 and I have been told that George had discussed the design by letters to Mr. Maksutov himself. We are currently trying to locate all of the notes and communications about this scope now. George was a perfectionist and a great man with great enthusiasm. With that in mind we hope to honor him with the restoration of this wonderful instrument. We also hope with any modifications we make that they are fully reversable so as to be able to put the scope back in it's original state.
Here is what we plan to start with:
First off adapting the scope for the Moonlite focuser with out doing any or little machining to the scope. I know little about Maks and wonder how an external focuser will affect image quality, focal ratio, SA? Second we need to make a Losmandy style dovetail to mount the scope on my AP900. I'll take some pics so that you folks can see what I mean and throw any suggestions my way that come to mind. I'm excited about brining this little piece of history back to life.
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Chris
A mount from Illinois
A scope from Japan
A camera from Cal-I-Fornia
A dog from Kentucky
A wife and kids from the "Twilight Zone"
The Geek Shed
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DAVIDG
Carpal Tunnel
Reged: 12/02/04
Posts: 1985
Loc: Hockessin, De
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There is only spacing of the primary to the meniscus lens that results in the best correction of spherical abberation. So setting that spacing and using an external focuser is a very good idea and will improve the optical performance of the telescope.
- Dave
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Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics
Engineering = Taking what you have and making what you need.
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lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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Thanks Dave. How do I calculate the optimal spacing? I'm sure that the spacing is gonna be off with the external focuser but I wonder how bad the SA will become.
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Chris
A mount from Illinois
A scope from Japan
A camera from Cal-I-Fornia
A dog from Kentucky
A wife and kids from the "Twilight Zone"
The Geek Shed
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DAVIDG
Carpal Tunnel
Reged: 12/02/04
Posts: 1985
Loc: Hockessin, De
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Chris,
A simple method is to use a ronchi screen in place of the eyepiece while looking at a star. The screen needs at 100 lines per inch, the more the better. Move the mirror until the lines are straight when only 3 lines are visible. Then switch to an eyepiece that is equal or shorter in focal length to F-ratio of the 'scope like 15mm or short and examine the diffraction pattern on each side of focus. Pull and push the eyepiece to focus don't move the mirror to focus and see if the pattern is the same on both sides. If not move the mirror a small amount and repeat and until you find the position of the mirror in which the patterns look to be the closest on both sides of focus. That is point of least spherical abberation.
- Dave
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Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics
Engineering = Taking what you have and making what you need.
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lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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Cool, thanks for your help. I'll need a Ronchi screen next then.
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Chris
A mount from Illinois
A scope from Japan
A camera from Cal-I-Fornia
A dog from Kentucky
A wife and kids from the "Twilight Zone"
The Geek Shed
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lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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The mounting plate is designed to fit George's home built mount. This will require a new design to fit a Losmandy type saddle. The other scope for this mount is a 6" F/5 newt that features a ZerodurŠ primary and a 3" m.a. quartz secondary. A rack-and-pinion focuser moves the primary mirror. This scope was a 1988 Stellefane award winner in the following three catagories: Optics, Workmanship and Design. You can see a low res pic of George and his observatory here: link
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Chris
A mount from Illinois
A scope from Japan
A camera from Cal-I-Fornia
A dog from Kentucky
A wife and kids from the "Twilight Zone"
The Geek Shed
|
lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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2
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Chris
A mount from Illinois
A scope from Japan
A camera from Cal-I-Fornia
A dog from Kentucky
A wife and kids from the "Twilight Zone"
The Geek Shed
|
lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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I have some doubts as to we will be able to fit a Moonlite back here?
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Chris
A mount from Illinois
A scope from Japan
A camera from Cal-I-Fornia
A dog from Kentucky
A wife and kids from the "Twilight Zone"
The Geek Shed
|
lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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Original 2" eyepiece holder.
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Chris
A mount from Illinois
A scope from Japan
A camera from Cal-I-Fornia
A dog from Kentucky
A wife and kids from the "Twilight Zone"
The Geek Shed
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lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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A look down the baffle. My friend Joe who owns the scope said the secondary baffle had fallen off and he put it back on with some double sided tape. It appears to be slightly misplaced as I can see some light around the secondary spot.
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Chris
A mount from Illinois
A scope from Japan
A camera from Cal-I-Fornia
A dog from Kentucky
A wife and kids from the "Twilight Zone"
The Geek Shed
|
lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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6
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Chris
A mount from Illinois
A scope from Japan
A camera from Cal-I-Fornia
A dog from Kentucky
A wife and kids from the "Twilight Zone"
The Geek Shed
|
lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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7
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Chris
A mount from Illinois
A scope from Japan
A camera from Cal-I-Fornia
A dog from Kentucky
A wife and kids from the "Twilight Zone"
The Geek Shed
|
lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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The focus knob. I have an older picture of this scope which shows a different knob on it. Also in this pic the scope has a rack and pinion on the back end. We are currently looking for these parts as well.
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Chris
A mount from Illinois
A scope from Japan
A camera from Cal-I-Fornia
A dog from Kentucky
A wife and kids from the "Twilight Zone"
The Geek Shed
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lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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Looks to me the primary could use a recoat...what do you folks think?
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Chris
A mount from Illinois
A scope from Japan
A camera from Cal-I-Fornia
A dog from Kentucky
A wife and kids from the "Twilight Zone"
The Geek Shed
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lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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George made this diagonal including the flat. This puppy needs some TLC.
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Chris
A mount from Illinois
A scope from Japan
A camera from Cal-I-Fornia
A dog from Kentucky
A wife and kids from the "Twilight Zone"
The Geek Shed
|
lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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Battery box for the finders IR. Also note the date in pencil on the side. The notes on the top of the box are eyepiece focal length and resulting magnifications. I have repaired the battery box as there was a bit of corrosion from a leaking 9V battery. It works just fine now.
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Chris
A mount from Illinois
A scope from Japan
A camera from Cal-I-Fornia
A dog from Kentucky
A wife and kids from the "Twilight Zone"
The Geek Shed
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Darenwh
Pooh-Bah
Reged: 05/11/06
Posts: 1224
Loc: Covington, GA
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Quote:
Original 2" eyepiece holder.
It seems to me that if you either sent this to Moonlight or made good drawings and sent photo's that they should have no problem at all making an adapter plate that would fit in place of this holder.
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Daren
Covington, GA
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lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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Your right I have both good drawings and photos but...
My buddy Al who is working on this project with me is 1/2 of Moonlite  He has agreed to help me machine what ever I need but I have to do it. Ron and Al have agreed to supply me with the materials, anodizing and advice. I want to do this for both my own learning experience and satisfaction. The problem with the holder is the primary mirror knb. All of the Moonlite focusers will *maybe* be too big of a foot print. The plate is 4.25" in diameter and the minimum for the Moonlite is 3.94". As you can see the knob for the mirror intrudes on that space. We have thought about possibly using a Moonlite Newt focuser as one side of it is "open", and may provide enough clearance? Only time will tell on this.
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Chris
A mount from Illinois
A scope from Japan
A camera from Cal-I-Fornia
A dog from Kentucky
A wife and kids from the "Twilight Zone"
The Geek Shed
|
lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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I was just informed that the primary is thought to be Zerodur. I should soon have the notes that George made as he built the scope.
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Chris
A mount from Illinois
A scope from Japan
A camera from Cal-I-Fornia
A dog from Kentucky
A wife and kids from the "Twilight Zone"
The Geek Shed
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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I'm surprised Dave didn't suggest the good idea of using an autocollimating flat to set your shell/primary spacing. That would give you twice the sensitivity and accuracy in setting spacing compared to using star imagery, and would also show you the quality of the telescope overall figure, again doubled in magnitude. This of course requires a very smoothly figured flat mirror, preferably full aperture, to perform. Perhaps Dick Parker could give you a hand with it if you live up near him.
In the absence of a flat, Ronchi testing on stars to optimize the spacing would still work fine.
I think one of the Mak circulars or an S&T article would have the nominal design prescription for it which would include the nominal spacing. Of course that could be a little off considering real radii and thicknesses vs. nominal design values.
You could also just contact John G. directly, he'd probably be interested in hearing about it. PM me and I'll connect you two.
Mike
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56 mirrors, lenses, 16" f/6 Newt, 6" f/10 refractor, TOA-130S, Tinsley 5" f/15 Mak, 6" f/4 RFT, Coronado PST. Still to build: 24" f/10 Modified Dall-Kirkham, 10" f/26 Mak, 8" f/12 apo, spectrohelioscope, Herrig, Schupmann, and others.
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