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Thread: Type of lens needed for refractor

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    Default Type of lens needed for refractor



    Hi all.

    So I'm toying around with making a refractor. I took my 700/60 apart and found 2 lenses which I believe are an achromatic double.

    I tested the focal length of the front lens with a torch and found it to be 350mm to show a sharp image on a piece of paper.

    Would this work as a set up as I'd like to make a refractor with a larger apature so this is my tester?

    Also does the second lens, flint glass I think, have to be butted up to the front lens or can they have a gap?

    I'm a complete novice at this and don't want to throw money at something I cant make work.

    Many thanks in advance.

    Carl
    j.gardavsky likes this.

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    Default Re: Type of lens needed for refractor

    You need to test the two lenses together, normally a doublet will have a slight air gap and you will need to test the setup using a artificial star or doing a star test to find out what the spacing should be.
    A good starting point would be two layers of tin foil as a spacer, you may have to add more. Make the spacers 1/4"x1/4" and place them 120° apart from each other.
    If you look in my album refractor tweaks there is a green coloured chart there showing what a proper star test should look like.
    Refractors: Antares 105 f/15, Bresser 102XL f/13.2, Celestron 102 f/6.5, 2-150 f/8, Stellarvue NHNG 80 f/6.9, TAL 100RS f/10, TS 102 f/11, Vixen SD115s f/7.7
    Mounts: Manfrotto 028B/ 055PRO, Celestron SLT, Celestron CG-5/ Argo Navis, Stellarvue M2C, Vixen SXP Binoculars: Celestron 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)

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    Default Re: Type of lens needed for refractor

    Thank you Gabby76. I looked at your album picture and to be honest I'm not sure how to replicate this test. I'm starting to think I may be wasting my time believing I can do this. Will keep trying to learn for a little longer though.

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    Default Re: Type of lens needed for refractor

    If you can verify the doublet focal length you can do a "stick build" by placing the doublet with the focuser spaced behind. A bit like a tubeless refractor.
    Refractors: Antares 105 f/15, Bresser 102XL f/13.2, Celestron 102 f/6.5, 2-150 f/8, Stellarvue NHNG 80 f/6.9, TAL 100RS f/10, TS 102 f/11, Vixen SD115s f/7.7
    Mounts: Manfrotto 028B/ 055PRO, Celestron SLT, Celestron CG-5/ Argo Navis, Stellarvue M2C, Vixen SXP Binoculars: Celestron 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.

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    Default Re: Type of lens needed for refractor

    kanadalainen likes this.
    Refractors: Antares 105 f/15, Bresser 102XL f/13.2, Celestron 102 f/6.5, 2-150 f/8, Stellarvue NHNG 80 f/6.9, TAL 100RS f/10, TS 102 f/11, Vixen SD115s f/7.7
    Mounts: Manfrotto 028B/ 055PRO, Celestron SLT, Celestron CG-5/ Argo Navis, Stellarvue M2C, Vixen SXP Binoculars: Celestron Eyepieces: A-Z

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    The weakest link in the optical chain is the large nut located directly behind the
    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    / camera. - Gabrielle

    Ya gotta keep this Apo/
    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    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.

    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.

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