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
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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
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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
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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
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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
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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
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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
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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: 1221
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
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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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lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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Hey Mike,
Thanks for chiming in. I'm sure the scopes optical quality is pretty good, George would settle for nothing less I would like to know for sure though the optical quality, and have considered having it Zygo'd by whom ever does the recoating. BTW PM on the way.
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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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BTW I'm located in central PA.
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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 few pics of the primary and focusing mechanism. Notice the marking on the side of the primary that says "Top". It was not near the top of the OTA...George knew what it meant I'm sure  There are a few other marks as well. I noticed the silver ring around the baffle tube that is closest to the primary was loose this allowed the primary to turn around the baffle. I wonder now if "Top" is really supposed to be at the top? I pressed it down slightly and tightened the set screws. The image shift is eliminated...well at least at 120 power it is not noticeable.
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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 closer image of the focusing mechanism which is suprisingly positive and smooth.
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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 closer look at the baffle assembly shows 2 sets of pencil marks. I assume that one of them was marked for optimal spacing?
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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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And if I'm not already confused enough...another mark on the edge of the primary.
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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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I just found another bit of interesting history on this scope here. It's on the right hand side of page three under,"Letter from Joe Montani". It seems as though Mr. Montani is quite the accomplished asteroid hunter. Cool stuff.
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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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Can any one recommend a coater that will do both the primary and meniscus lens?
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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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Contact Jim Mulherin at Optical Mechanics. He is up in the top few best mirror coaters in the country, and I'm sure he could re-do your primary mirror and secondary spot. You might even see if he can do AR coatings in his vacuum equipment, that would give you a little more light.
And don't lose track of that mark on the side of the mirror. Look for a mark on the side of the corrector as well, they may be rotation alignment marks that give the best image quality.
Mike
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lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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Thanks again for the Help Mike. Which marks though, lol there are marks everywhere. Last night we removed the meniscus and it also had a "top" mark. This mark just happened to be at the top of the ota. So we thought that the primaries top mark should be the same???
About the coatings...The meniscus coatings are in excellent shape but both the secondary spot and primary could use a recoat. How does the recoating of the secondary spot go? In that I mean must it be done before the anti-reflective coatings are done on the meniscus? I've been told by one coater that to redo the meniscus AR coatings the existing once need to be polished off. I don't know if I wanna go that route? We got the Losmandy style dovetail mounted last night. I'll post pics later today.
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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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Here are a few pics from last night.
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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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Well had to make a few holes in the Losmandy dovetail and then drill and tap the half rings on the OTA.
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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 dovetail.
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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 dovetail installed.
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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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We disassembled the entire scope except for the meniscus cell. I don't really know why, but it was fun
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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 closer look at the focusing mechanism
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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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Is it possible to tell if this mirror is Zerodur? There were some numbers inscribed on the back of the mirror. If memory serves they where 339.186?
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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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And a final image of the back of the meniscus.
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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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We were happy to see that a Moonlite Newt focuser will work just fine. We will have to turn a new plate for the back of the scope though.
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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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It's not Zerodur - Zerodur has an amber-ish tint, as does Cervit and AstroSitall. Looks like it's Pyrex, although it could also be fused silica or even ULE.
Stripping the old secondary spot coating without harming the existing AR coating would be a little tricky. If it was originally done right, there should be no AR coating where the secondary spot is; that should have been masked off during coating. There should only be aluminum on the corrector shell glass where the secondary spot is. When stripping with PC board etchant, the AR coating would have to be protected to minimize risk of damage.
Jim would just make a mask with the secondary spot diameter opening, center it on the existing secondary spot after stripping, and vacuum deposit a new coating. Should be a no-brainer for him.
Mike
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lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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I have been in contact with Jim. He said he would be happy to work on this project with me and will give me more details once he returns from a trip. Thanks again Mike. As I siad the AR coatings appear to be in very good condition so if as you say it is possible just to aluminze the center spot and primary then that is good news which will save me $. I'm so excited about this project. I'm starting to wonder about mirror ventilation of some sort. I really don't want to make any modifications to the rear cell though. I wonder if I'll have issues with the closed tube reaching equilibrium?
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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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JohnH
professor emeritus
Reged: 10/04/05
Posts: 734
Loc: vancouver near the wilds of B...
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The numbers on the primary MAY be the secondary to primary spacing. 339.186mm would seem to be the right order of magnitude for this number.
Edited by JohnH (09/17/09 10:04 AM)
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lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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Interesting. Thanks John. Is there anyway to distinguish between quartz and pyrex easily?
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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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afrancis
Vendor - MoonLite
Reged: 01/26/08
Posts: 164
Loc: Central PA
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Chris,
I am glad you are restoring this scope and am happy to be playing a small role. George would be very pleased to see it updated and used. Keep posting your progress.
Mike, Dave and John, thank you for your valuable contributions.
As far as my new avatar Chris, sorry, I couldn't resist 
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Al
TSA 102, G-11, ST-2000XCM
MoonLite Telescope Accessories
Geek Shed Observatory
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JohnH
professor emeritus
Reged: 10/04/05
Posts: 734
Loc: vancouver near the wilds of B...
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Quartz and Pyrex are hard to tell apart. Both are tough to grind, with quartz being soemwhat harder. Quartz is usually completely colorless, and Pyrex various tinges of yellow-clear. It also has swirl marks inside it from the casting porcess.
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lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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Thanks John. I'm going to assume this primary is quartz then. It appears colorless.
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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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Chris,
Just a thought - did George leave any notes indicating what 8" f/15 design he made? I have looked through the various 8" f/15 designs published (S&T, Mak circulars, etc.), and there's enough variation in them that we don't really know at this point what design was actually fabricated. I doubt even John Gregory would know exactly what design George built to unless they collaborated on it. Having the radii and corrector shell thickness would make it easy to reverse engineer the proper spacing and back working distance.
If this data isn't available, ask Jim Mulherin if he could measure R1 and R2 and the thickness on the corrector shell and the primary ROC while the parts are up at OMI for re-coating. Jim and his team know how to put a spherometer or depth gauge on finished optics without scratching them.
Another thought: Jim has a nice autocollimation setup there. He could bypass measuring radii and thicknesses and simply set your optimum spacing for you on his optical bench if you send the tube assembly along with the optics. He can also do an interferogram of the finished system for you. You'd have to contact him for any extra cost over and above doing the coatings.
Side note: Corning Pyrex had the pale yellowish tint. International Glass sheet Pyrex 7740 was colorless. You couldn't tell 7740 from BK7 from fused silica unless you set a polished blank up in schlieren testing, where the 7740 would show loads of internal inhomogeneity (swirls, straie, etc.) and the BK7 and fused silica would not. George sounds like the kind of perfectionist that would use fused silica, though.
Mike
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lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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Mike,
I am still waiting on word of George's notes. Ihave been told he took detailed notes on all of his projects. I'm still waiting to hear back from Jim as well. Hopefully Jim and I can get together on this project soon. FWIW I put the scope on a few stars last night and while well collimated the SA is obvious to my untrained eye. I hope to hear soon about the notes. Again thanks for your help.
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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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Ok got the notes tonight including 6 or so pages of notes done as the grinding and polishing took place. A couple of the images I am going to post were pretty interesting.
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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 Zemax drawing from John Gregory.
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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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Some notes.
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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 letter from "Dick"...it's all Greek to me.
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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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Page one of a design? I assume the initials are John Gregory's? Also George has John's phone number and name written on the back of some notes. I guess George sought advice from John. Cool stuff.
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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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continued.
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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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Knife edge drawing?
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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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From looking at these notes, it looks like George may have had a problem when he first assembled the telescope and the image was focusing in front of the primary. It looks like John Gregory ran a Zemax analysis of the design to see what might be the problem. John is telling George that the spacing between the primary and menicus would have to be long by 0.425" to cause the focus problem so look for error in the spacing between the primary and meniscus.
The specs for the telescopes are listed under surface data:
Corrector
R1 = 8.776 convex (front surface)
Thickness = 0.694"
R2 = 9.184 convex (rear surface)
The seperation between the corrector and the primary is
16.14"
The primary has a concave radius of 39.23"
The distance from the spot on the corrector to the focal plane is 25.225"
So the focal plane is 9.085" behind the front surface of the primary mirror.
I hope this helps.
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 for helping me to understand that Dave. Going through all of these drawings and notes is pretty fun. George has a detailed drawing and some notes of an 11" F/4.2 Mak Newt that he built.
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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,
I entered that data into OSLO and here is the spot diagram. The small black circle is the size of the Airy disk. There is a good amount of energy outside the airy disk so I can understand why you said that spherical abberation is visible in the image.
- 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.
Edited by DAVIDG (09/20/09 01:43 PM)
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lineman_16735
Tak-o-holic
Reged: 12/04/04
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Loc: Central PA
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I assumed that the SA I was seeing was caused by the primary to meniscus spacing being off. I'm sure it was quite a bit off using the scope visually, as I assume it was intended for planetary film photography. I also assume the numbers you plugged into OSLO were best case scenarios based on the numbers supplied by Gregory?
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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,
I started with the numbers supplied by Gregory and they match the letter from Dick. I got the exact same back focus as Gregory calculated. I then let OSLO find the best spacing from the primary to meniscus which was 15.895" unfortunately it didn't improve things by much.
I'm assuming spherical curves so maybe George aspherized the front surface of the meniscus and/or the primary to achieve a diffraction limited image or these are not the real numbers ?
- 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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dougspeterson
Pooh-Bah
Reged: 09/01/04
Posts: 1041
Loc: Murrieta, CA
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I believe the Gregory F15 version was indeed aspherized at the corrector to remove a fifth order residual, and the F23 version left all spherical. That residual however visible in the star test may not be image destroying, like the lower order SA3 would be. Given the residual from Zemax, the Strehl could be calculated, it may well be high.
Also there is a small adjustment to the radii of the mak correctors to turn the tiny amount of primary color into secondary, discussed in Rutten, etc., Telescope design.
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18" Dob
12" SCT
8" TMB F6 + Chromacor
6" F6 APM/LZOS Fluorite triplet, 32", 32lbs
2ea. 6mm singlets, one blind
"--Granted, that's a worse case scenario. The destruction might in fact be ... limited to our own galaxy."
Edited by dougspeterson (09/23/09 02:13 PM)
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George Kiger
member
Reged: 05/19/06
Posts: 29
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I recall a response from John Gregory saying that the f/15 design did not need aspherizing, but that the need might arise when the curves did not match the design closely enough or the surfaces were not smooth enough. Also, I think the original spec and the spec modified for moving color correction to the 70% zone were for 6-inch scopes. Would the OSLO results change significantly if the scope was 6 rather than 8 inches.
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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These are the spot comparisons for George's 8" f/15 Greg Mak at 0.25 and 0 deg. off axis and a wavelength range of 435-656nm. All-spherical performance is poor, and George must have had to aspherize either R1 or the primary to achieve good on-axis performance.
There is no real difference in the on-axis performance by aspherizing either R1 or the primary. Aspherizing R1 at 546nm gives slightly smaller off-axis spots, however. This makes sense as R1 is the system aperture stop.
The only way to know what George really did would be to test R1 and the primary and see which surface has the asphere.
The airspace between the corrector and primary I'm getting with R1 aspherized is 16.14" and BWD=9.25". Maximum R1 departure from sphere is about a half wavelength.
Mike
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lineman_16735
Tak-o-holic
Reged: 12/04/04
Posts: 2604
Loc: Central PA
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Thanks again Mike. I think I just need to send the entire scope to Jim at OMI and have him test it. Hopefully he will get back to me with a ball park quote soon so we can get this project moving in the right direction.
--------------------
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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Jim from OMI got back to me with a quote. $340 to recoat the mirrors, and an additional $280 to test and align the scope. I'm kind of at a crossroad here. I have no doubt OMI will do a bang up job on the scope. On the other hand I have no idea how well the scope is going to perform? I hate to spend too much money on the scope if it isn't going to be as good as it should be. On one hand I think I should just get the coatings done, and see how it goes. On the other hand I think that I may not get all the scope can offer if I neglect to have the testing and alignment done by a pro? The adapter that we made should be anodized soon and then the Moonlite focuser can be installed. I may have the meniscus and primary cells anodized or powder coated as well. The tube is some sort of plastic so I guess I will just have to paint it? On a side note, if you recall I mentioned earlier that the baffle tube had what appeared to be a 3 reference marks. I measured from the secondary spot to the center of the primary and adjusted the focuser until it was very close to 16.14 inches. This brought the the baffle tube to the center mark of the 3 reference marks. One of the other 2 marks would require the mirror to be moved towards the meniscus by about 1/4" and the other mark would require I move the primary away from the meniscus about 1/8" or so from the center mark. So I think these marks were made by George as he tested the scope. Which one is correct if any I dunno?
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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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I would put the scope back together with mirror at the 16.14" position then using the new focuser on the back,at least a 15mm eyepiece, and star test it. Keep moving the mirror about 1/8" at a time until you hopefully find a place were the star test shows equal or nearly equal patterns on each side of focus indicating good correction. If you find this spot then you know the 'scope will perform well when recoated if not then it's time to do more testing to determine what the problem is before you spend the money.
- 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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