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Thread: One star with diffraction spikes using a refractor

  1. #11
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    Default Re: One star with diffraction spikes using a refractor



    This is why I bought a refractor too - I want my stars to look like glowing orbs. However, the UK supplier sent me this forum link: https://stargazerslounge.com/topic/3...-type-pattern/ to show me, saying "William Optics, Takahashi etc., they all suffer from this to one extent or the other – it's a fact of lens spacing, rather than the manufacturer itself." And from that thread on SGL:

    Quote Originally Posted by ollypenrice
    I've read several explanations for the refractor 'inverse light house beam' effect, blame being laid variously on lens clips and pinching. Since it is more than normal in most Takahashis and other high end refractors, and since it doesn't send spikes flying half way across the image, I've never let it bother me.
    Nevertheless, I watched a Youtube video by Trevor from astrobackyard where he processed an image with his carbon fiber version of the same ES telescope (mine is aluminium). I looked at his stars carefully throughout the process and I can see no 'inverse lighthouses', so I don't believe this artefact is inevitable. So I think I probably will release the shipping screws slowly, releasing 90 degree turns on 3 bolts at a time and then waiting for a viewing session to see the effect. (I could send it back - but it's probably better that I develop these skills myself.)

  2. #12
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    Default Re: One star with diffraction spikes using a refractor

    I would get ES to do the adjustment, that is what the warranty is for.
    There are also many discussions about this issue on CN and they have had them operating properly once they have been returned.

    If this is the triplet model I would not adjust them yourself as you may throw the lens out of center or tilt making it worse.
    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
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    Default Re: One star with diffraction spikes using a refractor

    I thought I should provide an update in case anyone else with an ES telescope has these same problems.

    1. After a lot of hesitation, I decided I was unhappy with the lens spacer artefacts and wanted it fixed.
    2. I spoke with the UK supplier about this, the risk of misalignment, and my concern about doing it myself. Their view was basically that I had nothing to lose by trying this myself. The telescope was still under warranty and if I messed up the alignment, they'd take it back and either repair it or send me a new one. But they did want me to try it myself first.
    3. I roughly followed the instructions here to ease off the shipping screws with some extra precautions: (i) Telescope in upright position (with lenses horizontal). (ii) The shipping screws are arranged in 3 rings of 3 screws. They are the ones without sealant in them. I assume the other sealant-filled set adjusts the lenses themselves and I didn't touch these. I eased off the shipping screws ring in batches of 3 (one ring at-a-time), loosening each by just one 90-degree turn. Then I let it 'rest' until the next clear night for testing. I repeated this 3 times, moving to the next ring of screws with each subsequent adjustment. So I actually loosened every shipping screw by 90 degrees in total by the end. (I did not remove them entirely as per the instructions.)
    4. On the 3rd round of testing, the 'inverted lighthouses' from the lens spacers were completely gone and the rings from the star diffraction ring test were still completely concentric. I don't know if I'd be able to detect any other degradation in optical performance. I did ask the UK supplier about this, but didn't really get a clear answer. Certainly the images I'm getting with this telescope are incredible and I'm happy.

    I collected a few hours of data last night. I haven't processed it yet, but from my first look, it looks really nice. Hopefully I can really start enjoying this telescope properly now without all these niggling concerns about it.

    And thank you Gabby for your advice!
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    Default Re: One star with diffraction spikes using a refractor

    It is good to hea that your telescope is operating properly now.
    Good luck with the imaging
    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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    The weakest link in the optical chain is the large nut located directly behind the
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    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: One star with diffraction spikes using a refractor

    It's a collimation issue with your lens. My Esprit 80 has the same issue and is going back for tuning. Can't post any links yet but if you look on my Flickr page you'll see it clearly.

 

 
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