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  1. #1
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    Default Ethos 3.7mm for Orion ed80t cf??



    I've just received my new ed80 t and am wondering about purchasing the Ethos sx 3.7 to use primarily with this scope. I've got two other scopes but the 3.7 wouldn't be very useful in the sct. I could likely use it in the xt8i, but am thinking primarily for the ed80t. Visual use only of course. Just curious if this is going to be a good pairing or not, if anyone had experience with this or a similar setup I'm proposing? I don't have any stores anywhere near me so I only have mail order as an option, so no try before you buy unfortunately. This combo would provide 130x which is nearing the suggested useful high end of 160 magnification. Any thoughts or opinions? Thank you.
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  2. #2
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    Default

    If you like immersive views I'd be betting you end up liking that quite a bit.

    I'm not sure you will get to use it all that often, however. You'd probably have to have pretty good seeing to make much use of it - and that is a lot of money to tie up in an eyepiece if you are not going to get to use it very often.

    FWIW

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  3. #3
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    Default

    Quote Originally Posted by OleCuss View Post
    If you like immersive views I'd be betting you end up liking that quite a bit.

    I'm not sure you will get to use it all that often, however. You'd probably have to have pretty good seeing to make much use of it - and that is a lot of money to tie up in an eyepiece if you are not going to get to use it very often.

    FWIW
    That's kinda where I'm at. But, I was thinking that even though it's a 3.7, at only 130x isn't that well within the realm of average seeing for most nights? Or is it more a function of being near the scope limit, which would require excellent seeing conditions?
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    Default

    Both the ed80t and the xt8i are f/6 scopes, so it would be a bit over-powered for both of them. Not terribly over-powered, so in really good conditions, it would be usable. But in average conditions, the view probably won't be as good as you'd like.

    TBH, I think that huge field of view is wasted on a high magnification eyepiece. Most of the time, you'll be concentrating on the tiny object at the centre that needs the magnification, and that wide FOV will just be a distraction.

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  6. #5
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    Default

    Thanks KeithBC. I know I'm nearing the ideal limits, but thought that the max useful magnification was more the limiting factor than the med/fast f ratio. Maybe my knowledge is the limiting factor here!

    And yes, the idea was for more wide field viewing of clusters etc... But thought the odd time would be nice to zoom in at one of the planets.
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    Quote Originally Posted by Guest234 View Post
    Thanks KeithBC. I know I'm nearing the ideal limits, but thought that the max useful magnification was more the limiting factor than the med/fast f ratio. Maybe my knowledge is the limiting factor here!
    The limiting factor is diffraction. The diffraction limit can be expressed either as a magnification or as the eyepiece size that will give you that magnification. Very conveniently, both can easily be determined. The limiting magnification is equal to your aperture in millimetres. If you calculate the eyepiece size that will give you that magnification, you will find that it is equal to the focal ratio.

    The focal ratio itself and whether the scope is fast or slow doesn't matter much in this case. However, the number in the focal ratio tells you what the eyepiece is for maximum magnification. In this case, an f/6 scope means that a 6mm eyepiece will give you the maximum magnification.

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  8. #7
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    Quote Originally Posted by KeithBC View Post
    The limiting factor is diffraction. The diffraction limit can be expressed either as a magnification or as the eyepiece size that will give you that magnification. Very conveniently, both can easily be determined. The limiting magnification is equal to your aperture in millimetres. If you calculate the eyepiece size that will give you that magnification, you will find that it is equal to the focal ratio.

    The focal ratio itself and whether the scope is fast or slow doesn't matter much in this case. However, the number in the focal ratio tells you what the eyepiece is for maximum magnification. In this case, an f/6 scope means that a 6mm eyepiece will give you the maximum magnification.
    I can follow that, thanks.
    So if using a 6mm eyepiece then (focal length) 480 / 6mm = 80x max useful mag? Even though the stated max mag is 160x according to Orion? Does this imply that most days 80x is likely the optimum, and on a perfect day 160x is absolute max?
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    Quote Originally Posted by Guest234 View Post
    I can follow that, thanks.
    So if using a 6mm eyepiece then (focal length) 480 / 6mm = 80x max useful mag? Even though the stated max mag is 160x according to Orion? Does this imply that most days 80x is likely the optimum, and on a perfect day 160x is absolute max?
    Pretty much, yes. Manufacturers are fond of quoting the absolute max as the "practical maximum", double the diffraction limit.

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    So, beyond the diffraction limit, the image will start to break down, and any further magnification will become less and less beneficial. Sticking with an eyepiece that would provide the diffraction limit for the given telescope is the way to go.
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