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Refractor question

Discussion in 'Telescopes and Mounts' started by Nebula, Mar 28, 2023.

Refractor question

Started by Nebula on Mar 28, 2023 at 8:36 AM

16 Replies 2684 Views 0 Likes

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  1. Nebula

    Nebula Well-Known Member

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    Nebula, Mar 28, 2023
    #1
    Hello I have this question for you, we often see short refractors for sell, like F5 and faster. My question, is it the same thing as with a Newtonian regarding the coma situation for short tubes? Is it as bad?

    Should a person buy a longer refractor, something like F6?

    I am talking about something affordable on a manual mount for visual under a dark sky, something around 102mm.

    @Mak the Night you must know a lot about this, you recommended one the other day, I think it was a Altair.

    Thanks.
     
  2. Mak the Night

    Mak the Night Well-Known Member

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    Mak the Night, Mar 28, 2023
    #2
    TBH there isn't much noticable difference between F/5 and f/6. Any longer than those and the OTA starts to become unwieldy.

    [​IMG]

    My ST102 is f/4.9 there is no coma, just a wider FOV.
     
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  3. Nebula

    Nebula Well-Known Member

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    Nebula, Mar 28, 2023
    #3
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  4. Mak the Night

    Mak the Night Well-Known Member

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    Mak the Night, Mar 28, 2023
    #4
    Not sure what that diagonal is on Amazon, looks like a 45 degree Amici. I have a 2" Baader and TV dielectric mirrors, although I prefer the twistlock of the Altair dielectric. The focuser is a MoonLite and was a lot more expensive than the OTA!

    [​IMG]

    The stock focuser grease is a bit dodgy. I used to have a GSO focuser on the ST102,

    [​IMG]

    I replaced it with a Long Perng, which is now on my 80ED.

    [​IMG]

    80ED with Long Perng focuser, Takahashi diagonal and Takahashi eyepiece.
     
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  5. Nebula

    Nebula Well-Known Member

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    Nebula, Mar 30, 2023
    #5
    You tried many different focusers on these telescopes, I don't see the moonlite?
    They must be crazy expensive to import to UK :eek:
     
  6. Mak the Night

    Mak the Night Well-Known Member

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    Mak the Night, Mar 30, 2023
    #6
    Oh, sorry Neb:

    [​IMG]
    [​IMG]
    [​IMG]

    The MoonLite was two and a half times more expensive than the OTA. It's beautifully made though and worth every penny!
     
    Last edited: Mar 30, 2023
  7. Mak the Night

    Mak the Night Well-Known Member

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    Mak the Night, Mar 30, 2023
    #7
    Brave now have a search engine.

    [​IMG]
     
  8. Nebula

    Nebula Well-Known Member

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    Nebula, Mar 31, 2023
    #8
    Ahh it's the green one from the first picture., ok very cool!

    Brave search it's not that new, I have been using it for about 1 year now maybe even more. But it's similar to DuckDuckGo, both are biased on the side of the left which is unfortunate for a person in the center or leaning to the right a bit.

    Nowadays websites that are not aligned with the liberal view, have their own registry of websites because they can't rely on search engine to have normal visibility. This is taking form, I like it.

    Have you tried the chat bots, Bard and ChatGPT so far?
     
  9. Mak the Night

    Mak the Night Well-Known Member

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    Mak the Night, Mar 31, 2023
    #9
    I'm a bit of a Commie so that suits me fine. Although I'm sceptical about right-wing claims of woke-bias. It's an invention and subjective ideological ontology invented by the paranoid right-wing. :rolleyes:

    Chat bots, they sound a bit uncanny valley to me.

    Liberal has a very different meaning in the UK.
     
    Last edited: Mar 31, 2023
  10. Nebula

    Nebula Well-Known Member

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    Nebula, Apr 7, 2023
    #10
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  11. Nebula

    Nebula Well-Known Member

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    Nebula, Apr 7, 2023
    #11
    @Mak the Night have you looked at Venus lately with your refractors?
     
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  12. Mak the Night

    Mak the Night Well-Known Member

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    Mak the Night, Apr 9, 2023
    #12
    I worry about Dave. I have a feeling he's brown bread.
     
  13. Mak the Night

    Mak the Night Well-Known Member

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    Mak the Night, Apr 9, 2023
    #13
    Unfortunately ill-health has prevented me from taking a scope out. Ever since the recent TIA my balance, previously good, is now gone. Best time is early twilight with polarising filters.

    [​IMG]

    60ED set up for twilight Venus last year.
     
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  14. Nebula

    Nebula Well-Known Member

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    Nebula, Apr 9, 2023
    #14
    I am very sorry that it's so difficult to get the scope out right now. I really hope that things will improve for you, at least if you can get out with something small and enjoy this for many years, you deserve it for your love of astronomy.

    The balance will be back, keep the faith.

    Cool 60ED instrument must be awesome for Venus and even Mercury, the sharpest view possible. What kind if ideal power will you use for the planets with that one?

    I myself tried a couple of filters on Venus but no good result with the Moon 13% (I don't have a polarizing filter)

    GSO 23a light red: Will greatly improve cloud shades. (8" and 12")
    GSO 47 Violet: Will greatly improve cloud shades (12" only)
    GSO 56 Green: Will greatly improve cloud shades. (Even a bit better then 23a)
    GSO 80a blue: Will define the disk + comfortable amount of light coming in, but will not improve cloud shades
    GSO #21 orange: Like 23a, will improve cloud shades but less.
    Orion 13% moon: No enhancements
    Lumicon 82a light blue: No enhancements
    Baader Neodymium: No enhancements

    The winners for me are #47 with the 12" mirror and #56 with the 8" mirror. I never had good result with either of these filters in the past, violet is too dark for the 8" and I never had results with #56 on Venus, it's good for sun observation with white light. The Orion 13% was very disappointing on Venus last evening.

    GSO filters rocks this year!!
     
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  15. Mak the Night

    Mak the Night Well-Known Member

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    Mak the Night, Apr 11, 2023
    #15
    Not all polarising filters are expensive.

    [​IMG]
     
  16. Mak the Night

    Mak the Night Well-Known Member

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    Mak the Night, Apr 18, 2023
    #16
    You don't need much power for Venus and Mercury, although around 150x should allow cloud detail to be seen on Venus. You can go lower with Mercury as you can only really see the phase.
     
  17. Gabby76

    Gabby76 Well-Known Member

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    Gabby76, Aug 6, 2023
    #17
    To the original question about coma in a fast refractor.
    Coma is unusual in a refractor but with faster optics such as f/6 and faster, if you do see what looks like coma check the alignment of the focuser.
     
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