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8 or 10 inch refractor project

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#1 jimegger

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Posted 30 November 2010 - 08:52 PM

Hello all. I am wanting to fabricate my own refractor lens doublet in at least 8 inch range but would go for a 10 inch if feasible. I would like to go with ED glass as the lens would be in the f/10 area if possible. I have made a beautifully performing 6 inch refractor with the classic doublet. My question is , where does one go to get lens blank material for such a project. If the price is out of my league for ED glass I would opt for a longer focal length doublet. I have contacted Newport Glass and United Lens. Is there anyone else out there who supplies glass ? I used Palomar Optical supply once but when I called a number for them listed on the web I got a no service reply. Any suggestions would be appreciated.

#2 Mike I. Jones

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Posted 01 December 2010 - 12:09 AM

Try Glass Fab at http://www.glassfab.com/.

10" "ED" glass blanks like FK01, S-FPL52, S-FPL53, FK51, etc. are really going to be pricey, several thousand $$$. Good luck and get ready for sticker shock!
Mike

#3 Jeff B

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Posted 01 December 2010 - 10:01 AM

Try Glass Fab at http://www.glassfab.com/.

Good luck and get ready for sticker shock!
Mike


Especially if you want the blanks certified for quality!!

#4 jimegger

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Posted 01 December 2010 - 11:50 AM

Thanks Mike and Jeff ! I'll look into it further. I knew the ED glass would be more that's why there is a plan "B" for a classic lens design with the usual glass. Newport Glass was pretty reasonable on the classic doublet with the F series glass in the 8 inch size.

#5 mikey cee

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Posted 01 December 2010 - 01:44 PM

Jim.....Not to rain on anybodies' parade here but you do realize the expense and size of a good mount. Kiss any desire of portability out the window if you want jiggle and wobble free performance. Were talking at least 2-1/2" shafts and heavy castings to achieve that. But semi "portability" has been accomplished here by several with lesser sized mounts. :smirk:Mike

#6 rwiederrich

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Posted 01 December 2010 - 01:55 PM

Jim..I agree with Mike the *rain maker*. You're gonna need a substantial mount.....one of which I just happen to have for sale. A heavely modified 2.5" shaft Cave Observatory series GEM with a Byer's drive.

Just so you know.

Rob

#7 jimegger

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Posted 01 December 2010 - 02:10 PM

Thanks Mike and Rob.
I planned to make a mount for it when the scope is done. I run Aeroquest Machining so the mount and drives are no problem. The six inch refractor I made in the mid nineties is actually able to be used on my EQ5 mount from Skywatcher but it is maxed out as such. I figure the 8 or ten inch (whichever I go with) will need some beef so I am planning to build a conical German style mount head with 11.5 inch worm gears. It would be in the "heavy" portable class".

#8 Dick Parker

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Posted 01 December 2010 - 02:21 PM

Jim -

Been there, looked into that. I built a very successful 6 inch f/15 refractor and thought WOW on to an 8 inch. Color was not what I wanted. I priced glass for an APO doublet and there went that dream. I considered Rolands mid spaced triplet. Glass no longer available. So, I now have glass for a 9 inch Schuppmann. For anything larger than 6 inches, I suggest you consider the Schuppmann.

Dick Parker

#9 waynet

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Posted 01 December 2010 - 02:25 PM

Can I just toss in a beginner's question? Does "doublet" mean you have 2 lenses? And does that mean grinding 4 sides?

#10 jimegger

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Posted 01 December 2010 - 06:21 PM

Thanks for the advice Dick. It would appear that ED glass would be out of my range but I would still like to go with at least an 8 inch design, I have the urge to push some glass again and you all know how that feels. I have made many reflectors and just the one 6 inch f/11 refractor. I had a great time doing it. It was intimidating at first but once the work started it all fell into place and wasn't all that much more difficult than a good mirror , just more surfaces to play with. The newer more exotic glasses seem to be difficult to get much less at a (ATM'ers) reasonable price. The f/14.1 8 inch lens from Newport Glass was available as a kit with generated surfaces and tooling for $695. That doesn't seem too bad for the usual doublet. I am still pondering......

#11 rwiederrich

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Posted 01 December 2010 - 06:54 PM

Can I just toss in a beginner's question? Does "doublet" mean you have 2 lenses? And does that mean grinding 4 sides?


Welcome..yes doublet means 2 elements make up the objective.

And yes..again..you will have to figure 4 surfaces.

Rob

#12 rwiederrich

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Posted 01 December 2010 - 06:58 PM

Thanks Mike and Rob.
I planned to make a mount for it when the scope is done. I run Aeroquest Machining so the mount and drives are no problem. The six inch refractor I made in the mid nineties is actually able to be used on my EQ5 mount from Skywatcher but it is maxed out as such. I figure the 8 or ten inch (whichever I go with) will need some beef so I am planning to build a conical German style mount head with 11.5 inch worm gears. It would be in the "heavy" portable class".


Indeed you would need some mount for that 8~10".

My 10"f/15 homemade refractor is mounted on my 4" shaft custom made GEM with 12" ring gears' It needs to be heavy to keep that amount of moment steady.

Good luck

Rob

#13 Old Will

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Posted 01 December 2010 - 09:33 PM

If you fold it, the weight of course would be about the same, but the reduced leverage of a shorter tube would make it much easier to mount. As to the glass, I bought 8" & 9.5" sets of crown & flint on ebay from a Canadian, he got them from Canadian military surplus. His ebay name is blacklincoln. I see his stuff on ebay once in a while.

#14 jimegger

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Posted 01 December 2010 - 09:37 PM

Thanks Rob. How did things go with your scope ? Did you grind and polish your own objective ?

I did not use auto collimation with a flat for testing my 6 inch. What I did was use my 12.5 inch reflector to make a collimated beam with a pinhole image at the focal plane. I tested with the focault tester and also a high power eyepiece to check the image of the pinhole. The trick was to figure out which surface was the one that needed to be worked on. I had one concave surface with the other three convex. Without a lot of trouble I got it right and ended up with a really nice f/11 objective. I got the glass from Palomar Optical supply for around $300.00 back in the 90's. They were just the flat blanks with flat tools so I started from Scratch more or less.

How does your scope perform Rob ?

#15 Mert

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Posted 02 December 2010 - 03:10 PM

Interesting project Jim, hope to read more of
your progress on this.
I'd also like to see the surely very nice mount
you're gona machine for that beauty!

#16 jimegger

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Posted 02 December 2010 - 03:14 PM

Thanks Old Will for the advice. I'll be looking around for any deals as always with we ATM'ers. I just put out some info to get quotes on different glass types for both an 8 inch and 10 inch objective. I'll let you all know what comes of that if and when the quotes come in.

#17 Old Will

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Posted 03 December 2010 - 09:51 AM

You may get more response from suppliers if you fax them. Seems that a fax is a more serious inquiry than an email.

#18 Old Will

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Posted 03 December 2010 - 10:11 AM

I was given enough glass to make a dozen 4" to 6" achromats, (BSC2 & F2) I also bought the surplus for an 8" & 9.5". Having only made mirrors before, I am starting out small. I currently am fine grinding a 6" f/17. After gaining experience I am planning on f/18 for the 8" then f/20 for the 9.5". They will have to be folded down to under 5 feet long.

Anyone have experience making large folded refractors?

8" Newt, 5" f/15 achromat






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