MtnGoat
scholastic sledgehammer
Reged: 02/18/07
Posts: 917
Loc: Columbia Gorge, WA
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I've had no luck whatsoever coming up with a tube that fits my Surplus Shed 80mm objective. Everything is either too small or too large.
I've looked at PVC both plumbing and conduit, and every danged tube shaped thing at Home Depot and the local scrap yard. (I did find a sweet 10" steel flange at the scrap yard to make a pier top for a Cave GEM, but that's another thread).
If you know of some common tube size in pipe I haven't seen yet..(irrigation pipe or something?) or have any ideas, fill me in. Heck, you may have a length of the perfect size to trade me or sell me. With a 400mm FL, I don't need much. After that, the search will be on for a cheap but servicable focusser...and reading up on just how to figure exactly where to put it. Haven't done any refractors before.
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"Ignorant people think it's the noise which fighting cats make that is so aggravating, but it ain't so; it's the sickening grammar they use." Mark Twain
Edited by MtnGoat (07/14/08 01:12 PM)
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zjc26138
Post Laureate
Reged: 02/24/05
Posts: 4439
Loc: Mingo Junction, Ohio
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This place has a good selection of tubes to buy.
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SCOPES:
Custom Meade AR5
Zhumell Z10
Orion ED80
MOUNTS:
Meade LXD500
CAMERAS:
DSI Color
Canon Rebel XT
Clear, dark skies everywhere,
-Zachary
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MtnGoat
scholastic sledgehammer
Reged: 02/18/07
Posts: 917
Loc: Columbia Gorge, WA
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Holy *BLEEP*...$25 bucks a foot for 3.5" thin wall? This project may languish a while at those prices! heck, by the time I got paid that plus shipping, plus a focusser plus shipping, it would almost be cheaper to buy someone's used short tube Orion 80mm!
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"Ignorant people think it's the noise which fighting cats make that is so aggravating, but it ain't so; it's the sickening grammar they use." Mark Twain
Edited by MtnGoat (07/14/08 02:08 PM)
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Greyhoundman
sage
Reged: 11/20/07
Posts: 283
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Reverse the lens group in the cell. Then you can use 4" PVC pipe. The finned end will then slide in with a little to spare.
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http://www.flickr.com/photos/greyhoundman/
http://greyhoundman.blogspot.com/
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MtnGoat
scholastic sledgehammer
Reged: 02/18/07
Posts: 917
Loc: Columbia Gorge, WA
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Dang, you're one of them smart ones...why didn't I think of that. Duhh!
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"Ignorant people think it's the noise which fighting cats make that is so aggravating, but it ain't so; it's the sickening grammar they use." Mark Twain
Edited by MtnGoat (07/14/08 02:50 PM)
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MtnGoat
scholastic sledgehammer
Reged: 02/18/07
Posts: 917
Loc: Columbia Gorge, WA
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Who's selling cheap focussers these days? I guess I'll check telescope warehouse and SS first, maybe put a wanted ad up on the buy-n-sell forum.
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"Ignorant people think it's the noise which fighting cats make that is so aggravating, but it ain't so; it's the sickening grammar they use." Mark Twain
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MtnGoat
scholastic sledgehammer
Reged: 02/18/07
Posts: 917
Loc: Columbia Gorge, WA
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well, there's a crapload of stuff at the warehouse these days...a meade plastic R&P with 5" of travel and 1.25" size for ten bucks, and a diagonal for another ten. not the greatest, but not bad. I'm sure the diagonal is OK since that merely requires a decent mirror..but concerned about the focusser considering the side load of a DSI on it.
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"Ignorant people think it's the noise which fighting cats make that is so aggravating, but it ain't so; it's the sickening grammar they use." Mark Twain
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ken scharf
sage
Reged: 02/09/08
Posts: 393
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I'm using that focuser and it's ok but you might want to drill out the field stop in the middle of the draw tube.
BTW I've used a drum sander in a drill press to machine PVC parts to fit the SS lens cells. You can reduce the ID or OD of a 'close but no cigar' PVC fitting to match the cell. The fluted end of the cell required filing to make 'slots' for the flutes in the fitting and the OD had to be reduced to fit under the cell flange. I have have a perfect friction fit but allowed a little wiggle room to align the cell square with the focuser.
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MtnGoat
scholastic sledgehammer
Reged: 02/18/07
Posts: 917
Loc: Columbia Gorge, WA
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Thanks for the tips, Ken. That sounds workable. have you done one of these 80mmF5's? I'm wondering how long to make the tube considering I'll be using it for visual as well as a spot of imaging if it looks OK.
I guess my one end of the baseline is that the CCD surface needs to be able to reach the 400mm mark for prime focus when all barrel margins and focuser parts are included, but I don't know much about how eyepiece focal length impacts the length requirements for the visual use case.
I'm guessing that for a 25mm eyepiece, the total system length is 425mm to the field lens, with variations around this from eyepiece to eyepiece related to differing barrel lengths and relative depths of the field lenses.
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"Ignorant people think it's the noise which fighting cats make that is so aggravating, but it ain't so; it's the sickening grammar they use." Mark Twain
Edited by MtnGoat (07/14/08 07:11 PM)
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ken scharf
sage
Reged: 02/09/08
Posts: 393
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I actually have the 90mm SS objective, but the cell is similar.
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Gene Hunter
super member
Reged: 12/29/07
Posts: 194
Loc: SC
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What inside diameter and what length are you looking for. I may be able to help.
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Clear Skies
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MtnGoat
scholastic sledgehammer
Reged: 02/18/07
Posts: 917
Loc: Columbia Gorge, WA
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The OD I need is about 3.6". That's the ID of the cell where it accepts the tube. with a 400mm focal length plus focuser travel, I'd guess I need no more than 16" of tube, probably 10" but I'm being conservative.
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"Ignorant people think it's the noise which fighting cats make that is so aggravating, but it ain't so; it's the sickening grammar they use." Mark Twain
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Siderea
Astronomess
Reged: 11/21/05
Posts: 1637
Loc: Novato
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Hi Mt Goat
How about and old Stanley Thermos? Take your objective to the Secondhand store and cruise the kitchenware section!
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Clear skies and pumpkin pies!
lc Carol
60mm Telescope Club
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MtnGoat
scholastic sledgehammer
Reged: 02/18/07
Posts: 917
Loc: Columbia Gorge, WA
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now that's an idea! thanks..good one.
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"Ignorant people think it's the noise which fighting cats make that is so aggravating, but it ain't so; it's the sickening grammar they use." Mark Twain
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Gene Hunter
super member
Reged: 12/29/07
Posts: 194
Loc: SC
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If I can make you one out of Carbon Fiber would you be interested. I need to know the exact inside diameter though in order for a perfect fit. I need to know what you want the ID of the tube to be. outside is irrelevant to fitting assuming the cell fits on the inside. If your cell fits on the outside then that would be different.
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Clear Skies
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Raven911
Pooh-Bah
Reged: 03/12/05
Posts: 1433
Loc: New Mexico
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I used a piece of acrylic plastic tube I got off of Ebay.
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http://smg.photobucket.com/albums/v287/Raven911/Astrophotos/
http://www.eye-of-the-raven.blogspot.com/
Celestron SC6
IM M66 Mak-Newt
100mm F6/76mm F4.5/80mm F5/SV NHII 80mm F6 Achros
Canon 300D/DSI Pro Mono/Starshoot DSCI
8 inch F7 Newt on Edmund EQ
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1168
Loc: Tampa, FL
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MtnGoat, this may not be helpful at all but I didn't know what kind of tools or workshops you may have access to. Currently I'm fussing over the exact same lens which is about to become my new guidescope. For lack of ready-made tubing that will fit the cell perfectly I am machining a new one from 6061 aluminum so it can mount in 4" aluminum tube from Hastings. The same goes for my GSO focuser which needs a custom adapter ring for mounting.
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Curt
8" F5 Newtonian Astrograph (under construction)
Orion 80ED CUSTOM
80mm F5 guidescope (under construction)
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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GlennLeDrew
professor emeritus
Reged: 06/18/08
Posts: 572
Loc: Ottawa, Ontario, Canada
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A little off-topic, but seeing as you mentioned a focuser...
Beware a too-long focuser tube! At f/5, the distance from the focal surface to the innermost part of the drawtube must be no greater than the f/ratio X the drawtube's I.D. In your case, let's say 5 X 1.13" = 5.65". So a 5" travel implies lots of extra tube (2.5-3"?) that must remain within the ficuser unit, so the item you mentioned should either have its drawtube shortened or be discarded for this project.
How often have I seen short-tube 'scopes with reduced effective apertures (down to ~60mm!!) because of excessively long drawtubes?
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Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV
Mediocre minds discuss people. Good minds discuss events. Great minds discuss ideas.
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Glenhuon
member
Reged: 10/01/07
Posts: 55
Loc: New South Wales, Australia
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90mm stormwater PVC is a close fit for 80mm SS cells.A few thou slack but I used some brass shim to pad it out. A few strips from a plastic drink container would do as well. For a dew shield, look for a 100mm Pad repair fitting. Its sized so it fits inside a 100mm pipe one end and and over at the other. Narrow end slips nicely over the spigot on the cell and put a 100mm stormwater cap on the other as a dust cap. I'm pretty sure thats a GSO focuser, fits nicely in the tube with no mods.
Bill
Edited by Glenhuon (07/24/08 09:09 AM)
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MtnGoat
scholastic sledgehammer
Reged: 02/18/07
Posts: 917
Loc: Columbia Gorge, WA
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wow, getting some good stuff here!
thanks for the tips on focuser travel, i hadn't considered that problem at all. I picked up a 2" one so I may get away without problems on that front.
90mm stormwater PCV, i'll look for some of that! I love the name of your scope...very clever.
back to the focuser travel...having not set up a refractor before, i'm not sure how to calculate tube length vs travel requirements. I'd like to do diagonalless prime focus photos with my DSI, but still be able to put on a diagonal for visual use.
How do I account for the FL of my various eyepieces plus diagonal and simultaneously maintain access to the prime focus distance? right now I'm assuming that the CCD use should be very near the closest to the objective i'll ever need to go.
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"Ignorant people think it's the noise which fighting cats make that is so aggravating, but it ain't so; it's the sickening grammar they use." Mark Twain
Edited by MtnGoat (07/24/08 01:17 PM)
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