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Thread: High mag, ultra-wide FOV EP question

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    Default High mag, ultra-wide FOV EP question



    Hi,

    I'm still waiting arrival of my first telescope, an XT8 Plus. It comes with a 2" 28mm EP, a 1.25" 10mm and a barlow. I'm interested in getting a couple of other eyepieces to fill out the range. I like the idea of the Q70 32 or 38mm for a low-mag wide FOV, but I also want a max-mag.

    To that end, I've been shopping for a 5-6mm eyepiece (or considering sticking with the 10mm + barlow). I came across the Explore Scientific 82* 6.7mm and 4.7mm pieces. My question is, how do these work to get such high magnification and also have such a wide FOV? How do they look, for example, when viewing planets, in comparison to a normal FOV 6mm EP?

    Thanks.

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    Default Re: High mag, ultra-wide FOV EP question

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    Default Re: High mag, ultra-wide FOV EP question

    Thanks. Is the magnification across the entire FOV? Given an EP that does not have abberations except on the far edge, why would one choose a narrow FOV over a wide FOV?

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    Default Re: High mag, ultra-wide FOV EP question

    A couple of reasons:

    1) They tend to be cheaper.
    2) They tend to be much better corrected across the FOV - if you want good correction across the entire FOV, be prepared to take out your wallet. If you have an SCT or a Mak, then its not that big a deal, as they're much less sensitive to mid to low quality EP's. For a Dob, you're off to Televue/ES at the low end of things.
    3) They inevitably require more glass, some planetary observers feel that ultimately detracts from contrast.
    4) There is a learning curve to using them - once you hit around 82, you need to get the head roll going, and some people don't like that. If you don't really use the head roll technique, you're not using the whole 80 degree + FOV, which kind of defeats the purpose of the eyepiece.
    5) Wide FOV eyepieces can be problematic for bino-viewing
    6) Weight, in general wide field eyepieces are heavy hunks of metal, especially in the 2" range
    7) Personal preference - not everyone needs or wants the so-called porthole into space view. If you're a lunatic, planetary observer, double star observer, or variable star observer, they really aren't all that necessary. If you observe from an urban environment, a wider FOV usually just means more darkness. You can barely pick up any additional stars anyways.
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    Default Re: High mag, ultra-wide FOV EP question

    Thanks! FOV aside, would the quality difference between the standard 10mm Sirius Plossl with a barlow and an ES 82* 6.7mm be worth the investment, or would the only reason to purchase the ES be the extra FOV? Is the 82* ES even recommended for planetary viewing?

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    Default Re: High mag, ultra-wide FOV EP question

    Just to be clear, you can use any eyepiece for planetary viewing, you just won't use that whole 82 degree fov, since you're only interested in the planet. For some people, the nice thing about a wider FOV eyepiece if you have a manual mount is that you have to readjust your dob slightly less. I still like keeping things roughly centered, so that doesn't make a huge difference to me.

    Do you find the 10MM eye relief for the Sirius Plossl objectionable? If not, just use it with a barlow, that gets you down to 5MM pretty easily, and that's probably the lowest exit pupil you want to go anyways. Your exit pupil is around .83, which I find to be a sweet spot for planetary viewing. Remember that you get 90-95% of your telescopes maximum resolution at magnification = diameter of your telescope in MM. You get 80% or so when your magnification = 1/2 x Diameter of your telescope.
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    Default Re: High mag, ultra-wide FOV EP question

    Great explanation Dio. Myself, I prefer that my head not roll so much, so I use Explore Scientific 68 degree models.
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    Default Re: High mag, ultra-wide FOV EP question

    Thanks very much for the advise. What is this head roll technique?

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    Default Re: High mag, ultra-wide FOV EP question

    Quote Originally Posted by msb View Post
    Thanks very much for the advise. What is this head roll technique?
    With 82 degree eyepieces and wider, can't see the entire field at once. To see the edges, you have to move your eye to the sides, as if looking around a corner. To move your eye, you have to roll your head. With 68 degree models, I can see the entire field at once.
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    Default Re: High mag, ultra-wide FOV EP question

    Quote Originally Posted by Raymondhow View Post
    With 82 degree eyepieces and wider, can't see the entire field at once. To see the edges, you have to move your eye to the sides, as if looking around a corner. To move your eye, you have to roll your head. With 68 degree models, I can see the entire field at once.
    This is why (for me) the 68*/70* EP's are perfect!
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