18 incher

This topic contains 11 replies, has 6 voices, and was last updated by  Brendan Martin 6 years, 2 months ago.

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  • #2763

    Austin Fitch
    Registered user
    0p

    Hi guys, I’ve managed to persuade my wife to let me make a scope. I’m going to make an 18 inch, getting the blank for christmas! So stand by for me pestering everyone for advice!! <img src=” title=”Smiley” /> see you soon.

    #3251

    Daniel kenealy
    Registered user
    0p

    thats cool me and barry are making a 16inch scope barrys already started hogging the blank out.

    #3252

    Austin Fitch
    Registered user
    0p

    Nice one! I think the thing that persuaded my missus, was the cost is so much lower. It’s going to be a steep learning curve, but can’t wait to get going. Just doing homework on different designs at the mo, I wonder if I should let my better half know that I can keep my 12 inch doing it this way? Better not!!

    #3253

    Austin Fitch
    Registered user
    0p

    Just had a look at blanks, thinkin 500mm is the way foreward… In for a penny, in for a pound!!

    #3254

    David Galvin
    Administrator
    2p

    Tell your wife that the 12 inch is going to be the finder scope.

    #3255

    Brendan Martin
    Administrator
    1p

    What F ratio you goin for Austin, now that you have decided on a 20″. Dont say below F4 <img src=” title=”Smiley” />

    #3256

    Graham Bell
    Registered user
    0p

    You’ll have to put some pics up Austin as you build. Should be a good project to watch

    #3257

    Austin Fitch
    Registered user
    0p

    Certainly will do, it will be a while before I start as i’m getting the blank as a christmas prezzie! Plenty of time to collect bits and bobs needed for the build though!

    #3258

    JULIE ORMONDE
    Registered user
    0p

    Our astronomy group ahve been taking about making our own scope but the costs of the mirror put us off…though we still hanker to do it.
    Where did you get your mirrror and how much did it cost?
    We were thinking of a retractable scope with the rods so it could come appart easily….at least that was/is the dream.

    #3259

    Brendan Martin
    Administrator
    1p

    Hi Julie, we actually make the mirrors usually out of 1″ plate glass as this helps keep the cost right down, details and pics can be found here
    http://datscope.wikispaces.com/20+inch+F4+Dobsonian
    cheers
    Brendan

    #3260

    JULIE ORMONDE
    Registered user
    0p

    It looks amazing…was it hard to do the mirror, and how did you overcome flaws in the mirror.  In other words could we do it, though we’d never made one before, or should we try polishing a small mirror first?  The telescope looks like a real crafmanship job…great work! I’ve always had the idea that  making your own telescope would really tune you into how a telescope really works…but I suppose you could say that about anything

    #3261

    Brendan Martin
    Administrator
    1p

    Hi Julie, there are lots of pro’s and con’s to making your own mirror, making a smaller mirror first would help, doing a large mirror at such a short focal length did pose many problems not least testing the figure. There are many books available on mirror making but one of the best is “The Dobsonian Telescope” by Richard Berry and David Kriege.
    cheers
    Brendan

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