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Thread: plossl or planetary eyepiece

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    Default plossl or planetary eyepiece



    Hello
    Can anyone explain me the difference between plossl, orthoscopic and planetary eyepieces?
    I thought planetary would be good for planets, but from what I'm researching they're good for more than just that?

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    Default Re: plossl or planetary eyepiece

    Plossl and orthoscopic are specific optical designs consisting of 4 glass elements. They are actually very good on planets but have narrow filed of view (40-55 degrees) and very short eye relief in short focal lengths range. This make them somewhat difficult to use at high magnifications required for planets in particular with manual mounts.

    To address these ergonomics issues EP makers came out with 'planetary' EPs. They are of different optical designs (typically 5 to 8 glass elements) but typically have good eye relief 15-20mm (which is also good for people observing with glasses) and wider FOV (55-70 degrees). Good planetary EPs should also provide sharp focus at high magnifications and good light scatter control.

    All these features make planetary EPs good 'all around' choice. They work well on all sorts of astronomical objects.
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    Default Re: plossl or planetary eyepiece

    I want to add that even though I have a large collection of both Explore Scientific 68 and 82 degree and Televue 82 degree eyepieces, I still often use my plossel eyepieces on planets and lunar. Less glass sometimes = more.
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    Default Re: plossl or planetary eyepiece

    Most of those eyepieces that say planetary are really only average or maybe a little better, all you get these days for $50 to $100. I went with used Televue Radians in 3-4-5-6mm's. About $150 each and these focal lengths give the higher powers in my scopes needed for planetary viewing, 200x to 400x. Hardly anything better unless you spend $275 and up.
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    Default Re: plossl or planetary eyepiece

    Hi El,

    If you are up for a little light reading, here is a link to the definitive optics reference manual that will explain nearly everything you wanted to know about telescope optics (the link leads to the EP section). Telescope Optics

    Cheers,
    JT
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