gypsy
member
Reged: 10/29/08
Posts: 57
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Hello everyone
1. I have acquired an old Celestron "green tube" Richfield 80 f5 (I think) scope. The optics are made in Japan and seem to be well coated. However, it has a few issues.
1. There are what appear to be three spacers at the edge of the lens assembly between the lenses that have migrated toward the center about a quarter of an inch. The retaining ring that holds the lens in the cell won't budge. Is there a simple tool that I can fabricate that would facilitate removing the ring?
2. The tube is very short, and could be remedied by converting to a two inch focuser/back to allow all of the light to pass through. Has anyone tried this?
3. There are no collimating screws on the lens cell. I am not sure whether it would be worth the expense of fabricating a new push/pull lens cell for the objective.
Any ideas or opinions would be appreciated.
John
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gypsy
member
Reged: 10/29/08
Posts: 57
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here is another pic
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neo
professor emeritus
Reged: 02/12/08
Posts: 618
Loc: Iasi, Romania
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Hi John!
You could get a good little scope from this one, I believe.
About the objective...you'd need a spanner wrench to take the retaining ring off (you can find one of those cheap from ebay). Than you can reset the 3 spacers between the lenses.
For the other tweaks....it depends on how much do you want to spend on this project. You could redesign it entirely: a new high end focuser, a good machined lens cell with a collimation system.
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Russian 15x50 binos
Home made 8" f/5 Newton on eq mount
Home made 70mm f/6 (Rodenstock Rotelar lens) Apo refractor
www.astronomy.ro
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gypsy
member
Reged: 10/29/08
Posts: 57
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I've read that the lens were made by vixen, as far as the execution of the rest of the scope leaves something to be desired. By my calculations, the visual back cuts into the light path, reducing the aperture. The tube itself is machined well, the visual back screws into the tube. baffles would certainly help cutting down stray light.
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stevie
Spiderman
Reged: 12/07/03
Posts: 3282
Loc: Belgium
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I use needle nose pliers to remove the retaining ring .
The tips of the are grinded so they fit in the cuts of the retaining ring .
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WE MUST STOP MANBEARPIG !!
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gypsy
member
Reged: 10/29/08
Posts: 57
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Thanks Stevie,
I got it off...
John
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neo
professor emeritus
Reged: 02/12/08
Posts: 618
Loc: Iasi, Romania
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If it's a Vixen lens, than it will worth the trouble building something solid. It will make a very nice RFT.
From what I see in the picture you could very well change the focuser with a more reliable one, 2" GSO for example if you still want to keep the price tag low.
For starter you can change the focuser, see how it performs and then if you don't like collimating the scope from the foucuser side (from what I know GSO let you do that), you can make a new lens cell with a push&pull system.
Can you detach the focuser from that visual back?
Alex
--------------------
Russian 15x50 binos
Home made 8" f/5 Newton on eq mount
Home made 70mm f/6 (Rodenstock Rotelar lens) Apo refractor
www.astronomy.ro
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gypsy
member
Reged: 10/29/08
Posts: 57
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No, the back and focuser are one piece.
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neo
professor emeritus
Reged: 02/12/08
Posts: 618
Loc: Iasi, Romania
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Ok, then you'll have to check the new focuser you'll buy that the base will fit on your OTA, if not I guess you'll have to build a custom made one.
--------------------
Russian 15x50 binos
Home made 8" f/5 Newton on eq mount
Home made 70mm f/6 (Rodenstock Rotelar lens) Apo refractor
www.astronomy.ro
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gypsy
member
Reged: 10/29/08
Posts: 57
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I will have to measure the opening and see if there is anything that would fit. The other option is to replace the tube with a longer one.
The focal length is 400mm or 15.75 inches. The lenth of the optical tube from the front of the objective to the visual back is 7 inches. When I draw a triangle from the outsides of the objective lens to the focal plane (15.75 inches), the visual back intrudes into the light path. Am I calculating this correctly or am I missing something?
According to my calculations, I would have to add at least 3 inches to the tube to be able to use the stock focuser or replace it with a two inch focuser to eliminate vignetting.
John
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