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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, 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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    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, 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/
    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. - Jon Isaacs (CN)

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    Default Re: Type of lens needed for refractor

    kanadalainen 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"
    To view links or images in signatures your post count must be 5 or greater. You currently have 0 signatures.
    Amici prism, 2" Stellarvue Dielectric, 2" TeleVue Everbrite Eyepieces: A-Z

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

    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. - Jon Isaacs (CN)

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    kanadalainen (02-13-2019),michael131313 (02-12-2019)

 

 

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