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Thread: DIY Long Focal Length 6” refractor

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    Default DIY Long Focal Length 6” refractor



    One of my long time wishes is to make a long focal length refractor with 4-6” aperture.
    As a boy i used to make simple cardboard tube telescopes with DCX lenses upto 100 mm FL and 50mm aperture (the longest and biggest lenses i could get then).

    Now I found a couple of interesting objective lenses here:


    https://www.surplusshed.com/pages/item/L3855D.html

    https://www.surplusshed.com/pages/item/L3920D.html

    https://www.surplusshed.com/pages/item/L3854D.html

    https://www.surplusshed.com/pages/item/L3919D.html

    I know these are not achromats nor coated, but the 2500mm and 4000mm FL and a 150mm aperture seems too good to pass up at $25-$26 each! ( Who has not dreamed of owning a 14 foot long telescope ?). Two of them are PlanoConvex (PCX) two or Positive Meniscus (PMN)

    Assuming i can workout the mounting problems with tube that is 10 to 14 feet long, is this worth trying?
    Has anyone used simple PCX objectives before?
    I don’t know the pros and cons of the PCX vs PMN lenses with regards to being used as an objective.
    Does anyone have any experience or wisdom they would like to share.

    Thank you for reading!
    refractordude likes this.

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    Default Re: DIY Long Focal Length 6” refractor

    I read in other thread that at F/20 or greater, the image will be very dim to even see. So this maybe a stupid idea of mine, but thought i would check. Thanks

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    Default Re: DIY Long Focal Length 6” refractor

    You should have read further into that thread
    The refractor would work fine though it would be a very long tube.
    I use a 150mm f/15 on a regular basis, the views are not dim nor were they in my 102mm f/13.2
    bladekeeper likes this.
    Refractors: Antares 105 f/15, Celestron 150 f/8, Stellarvue NHNG 80 f/6.9, TAL 100RS f/10, TS 102 f/11, UR 70 f/10, Vixen SD115s f/7.7
    Mounts: Celestron SLT w/ pier mod & EQ-3 tripod, Celestron hypertuned CG-5 w/ tracking motor & Argo Navis, Manfrotto 028B w/ Stellarvue M2C, Manfrotto 055PRO w/ 128RC, TAL-1 HD EQ, Vixen SXP w/ HAL-130 SXG & half pier
    Diagonals: 2" Astro-Physics MaxBright, 2" Zeiss/ Baader prism, 2" Baader Herschel Wedge (Photo Version), 2"
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    Amici prism, 2" Stellarvue Dielectric, 2" TeleVue Everbrite
    Eyepieces: A-Z

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    The weakest link in the optical chain is the large nut located directly behind the
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    / camera. - Gabrielle

    Ya gotta keep this Apo/
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    thing in some balance of perspective. Apos are awesome, but long focus Achros aren't that far behind them - Siriusandthepup (CN)

    Refractors kick arse precisely because they don't hide behind excuses. That is, they have no obstructions to hide behind. - Jon Isaacs (CN)

 

 

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