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alfi1966
super member
Reged: 08/24/09
Posts: 119
Loc: norway
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hello people
im looking at the possibility of buying one of Istar`s 4 lens lenscells, and build a ota for it myself.
the problem is how to find any diagrams or drawings that show me how to make the calculations for it?
i have read all over the net, but all i find is about newtons, and mirrors.
the lenscell is a 152mm f/7.5, and i think i would use a moonlite focuser.
are there anyone that can give me any tips on where to find up to date info on how to calculate the ota and focuserflange?
any tips appreciated.
alfi
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skywatcher 200mm f/5 newt, 150mm f/8.3 refractor w/ moonlite upgrade, Skywatcher EVOSTAR ED80 Pro DS,Meade Series 5000 80mm Triplet, eq6 pro synscan, eq5, canon 450d unmodded, canon 1000d modded, TS duomount and LVI Smartguider.
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GlenM
Vendor
Reged: 05/20/07
Posts: 1741
Loc: Lancashire UK
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I'm still new at this Alfi so bare with me.
I would draw a full size light cone for the lens that you are going to use. This will help in figuring out all the dimensions of the tube you need. Also the adapter for the lens/tube,baffle system and whatever else you're going to put in the light path. It's what I did anyway.
HTH and good luck.
Glen.
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Glen
www.lyraoptic.co.uk
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plyscope
sage
Reged: 11/23/06
Posts: 327
Loc: Perth, West Australia
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Glen is right Alfi. Start with drawing the light cone. The focal length is 152 x 7.5 = 1140mm. Draw a line 1140mm long. At the lens end draw a perpindicular line of 76mm (radius of lens aperture). At the focuser end draw a perpendicular line of 23mm (radius of field stop for 2 inch eyepiece). Now draw a line between the two radius ends and you have a half cone. Wherever you place a baffle along the length you can measure off the radius of the baffle aperture. When you get your focuser, diagonal, adaptors etc., deduct their lengths from the focal length and what is left will be the length of your tube plus the amount of focus extension you want.
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Andy
6" f15 refractor
90mm f16.7 refractor
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alfi1966
super member
Reged: 08/24/09
Posts: 119
Loc: norway
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hi
thank you very much for your advice, i will do that, it seems like a really simple way to do it, and understandable for a noob.
alfi
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skywatcher 200mm f/5 newt, 150mm f/8.3 refractor w/ moonlite upgrade, Skywatcher EVOSTAR ED80 Pro DS,Meade Series 5000 80mm Triplet, eq6 pro synscan, eq5, canon 450d unmodded, canon 1000d modded, TS duomount and LVI Smartguider.
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PJ Anway
Pooh-Bah
Reged: 06/04/03
Posts: 1141
Loc: Michigan's U.P.
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Alfi,
In building refractors I've used this method as a guide for baffle placement: http://www.berfield.com/baffles.html . I feel that it has worked fine for each of the six I've built.
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PJ
_________________
Lookum Observatory
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alfi1966
super member
Reged: 08/24/09
Posts: 119
Loc: norway
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hi
thank you for that PJ.
i have orded the lenscell, and countercell from Ales now, and a baader steeltrack 3" crayford.
my plan is to calculate the baffles, attach them to 3-4 bars running the lenght of the tube, flock the tube and the baffles, and slide the baffle assembly into the tube.
does this sound as a good way to do it?
i will have to see if i can find a way to calculate how far back in the lightcone i will put the focuser, so i can reach focus with binowievers, cameras and eyepieces.
i have seen some refractors where you take of part of the tube, to reach focus with binowievers, but i dont know if this is something i need to do?
alfi
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skywatcher 200mm f/5 newt, 150mm f/8.3 refractor w/ moonlite upgrade, Skywatcher EVOSTAR ED80 Pro DS,Meade Series 5000 80mm Triplet, eq6 pro synscan, eq5, canon 450d unmodded, canon 1000d modded, TS duomount and LVI Smartguider.
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rwiederrich
Goldfinger
Reged: 11/17/05
Posts: 8334
Loc: Bremerton Washington
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Quote:
hi
thank you for that PJ.
i have orded the lenscell, and countercell from Ales now, and a baader steeltrack 3" crayford.
my plan is to calculate the baffles, attach them to 3-4 bars running the lenght of the tube, flock the tube and the baffles, and slide the baffle assembly into the tube.
does this sound as a good way to do it?
i will have to see if i can find a way to calculate how far back in the lightcone i will put the focuser, so i can reach focus with binowievers, cameras and eyepieces.
i have seen some refractors where you take of part of the tube, to reach focus with binowievers, but i dont know if this is something i need to do?
alfi
Don't worry about flocking. Tt the focal length you're talking about you won't need it.IMV.
Take a look at my homemade refactor forum on Yahoo...an see what I did for my 10"f/15 refractor.
Just check the photo link on the left side and follow to the gallery.
The group link is located at the bottom of my sig line.
Good luck...
Rob
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www.goldmtobservingcenter.com
A great place for amateur astronomers, and ATM's to come and enjoy their hobby.
http://tech.groups.yahoo.com/group/HomemadeRefractorTelescopes/ My homemade refractor group.
www.vimeo.com/6014031
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plyscope
sage
Reged: 11/23/06
Posts: 327
Loc: Perth, West Australia
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Thats a good link PJ. Thank you.
If you have the baffles you probably don't need to be concerned with flocking Alfi. Just matt black paint. Your plan to mount the baffles on bars is good.
Depending on how much focuser travel you have will determine the need for a removable focuser extension piece. If you intend to use a binoviewer and sometimes a 2" eyepiece as well then it is probably a good idea to design a removable extension piece equivalant to the optical length of the binoviewer or thereabouts.
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Andy
6" f15 refractor
90mm f16.7 refractor
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alfi1966
super member
Reged: 08/24/09
Posts: 119
Loc: norway
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hi
thank you for the tips.
i will look into the possibility of making a removable extension, but it may make the build overly complicated, but i will see what i will come up with.
alfi
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skywatcher 200mm f/5 newt, 150mm f/8.3 refractor w/ moonlite upgrade, Skywatcher EVOSTAR ED80 Pro DS,Meade Series 5000 80mm Triplet, eq6 pro synscan, eq5, canon 450d unmodded, canon 1000d modded, TS duomount and LVI Smartguider.
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