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Thread: Kellner v Plossl?

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    Default Kellner v Plossl?



    I know a little about EPs, but not enough. Back when I started in astronomy I had cheap nasty EPs with my cheap nasty Tasco 60, and its only now that I have a scope that uses a proper EP mount (1.25")
    My scope comes with 2 Kellners, a 9 and a 20mm. No idea of their exit pupil or FOV.(scope is 700/70)
    But what's the difference between a Kellner and a Plossl? I'm guessing theyre different designs of EP.
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    Default Re: Kellner v Plossl?

    Quote Originally Posted by Cyclops View Post
    I know a little about EPs, but not enough. Back when I started in astronomy I had cheap nasty EPs with my cheap nasty Tasco 60, and its only now that I have a scope that uses a proper EP mount (1.25")
    My scope comes with 2 Kellners, a 9 and a 20mm. No idea of their exit pupil or FOV.(scope is 700/70)
    But what's the difference between a Kellner and a Plossl? I'm guessing theyre different designs of EP.
    Try reading this thread diff between kellner and plossl?
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    Default Re: Kellner v Plossl?

    Thanks dagadget!
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    Default Re: Kellner v Plossl?

    Ay 700/70, that would make your scope f10 focal ratio. The 9mm would give a 0.9 exit pupil, the 25mm a 2.5mm exit pupil in that scope.

    The Kellner and Plossl are indeed two different eyepiece designs. http://www.handprint.com/ASTRO/ae5.html#kellner While I have seen some Kellners deliver great images in slower focal ratio scopes, generally the modern design Plossl's will greatly outperform them, depending on the quality of the Plossl, many times it's not even a close comparison.
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    Default Re: Kellner v Plossl?

    A well made Kellner can have some advantage over a Plossl in detecting very faint contrast differences. But they are limited in use to slow scopes like yours. A Plossl will work in fast scopes as well as in slow.
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    Default Re: Kellner v Plossl?

    Quote Originally Posted by SpyderwerX View Post
    Ay 700/70, that would make your scope f10 focal ratio. The 9mm would give a 0.9 exit pupil, the 25mm a 2.5mm exit pupil in that scope.

    .
    Sorry Spyderwerx, my mistake I should have put 400/70. By my reckoning that makes the scope a f5.7, so....95.7=exit pupil of 1.57? Which is weird because the eyepiece exit pupil looks much bigger than that!
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    Default Re: Kellner v Plossl?

    Ahh, yes, that would be f5.7. The size of the exit pupil won't really be noticeable in image size as the FOV of the EP is fixed, but more so in image brightness. This may help explain it much better than I can. Starizona's Telescope Basics and also https://www.youtube.com/watch?v=JI-DljZ8unY
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    Default Re: Kellner v Plossl?

    I am with not_Fritz on the Kellners,

    Quote Originally Posted by not_Fritz_Argelander View Post
    A well made Kellner can have some advantage over a Plossl in detecting very faint contrast differences. But they are limited in use to slow scopes like yours. A Plossl will work in fast scopes as well as in slow.
    as a high quality grade Kellner is the eyepiece of last resort on the low surface brightness nebulae and galaxies.
    That's why I am keeping this Carl Zeiss Jena series A Kellner since decades in my arsenal, see the attached picture.

    Today, you can find this CZJ A Kellner 12,5x (f=20mm) on the eBay for about 25 bucks,
    https://www.ebay.de/itm/1x-Mikroskop...-/312079778939
    and to beat it, you might spend 10 times more on the second hand Leica HC Plan S,
    or even more on a discontinued second hand "hyped" Carl Zeiss E-Pl, changing the hands for up to 1,500 USD.

    Best,

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    Default Re: Kellner v Plossl?

    I have a 15mm and a 9mm Kellner in a Celestron power seeker kit and they are tremendous when I look at the moon or planetary views. Very nice indeed especially in my 114 reflector and in the 80mm frac.
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    Default Re: Kellner v Plossl?

    Hi JG,

    Thank you for that input and example. I suppose my statement before derives from the experience that many of the supplied 'kit' Kellner's are not of the best quality and suffer from many aberrations. But I do totally agree that a top grade, well designed Kellner will indeed perform amazingly, especially in slower ratio systems. I have a couple of older volcano top design Japan Kellner pieces (25 & 40mm) which are beautiful to view through. I should have elaborated more thoroughly in my previous post.
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