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  1. #1
    szaki's Avatar
    szaki Guest

    Default SCT, FR and wide field 2" eyepieces

    What 2" wide field eyepiece works on SCT telescopes using focus reducers?
    I have a 2" Pentax 40 mm 65 FOV and it don't work with SCT focus
    reducers installed. I had the C.6 FR lens before, now I have the
    Denkmier Starsweaper. Later don't have vignetting problem, but stars
    badly distorted.

  2. #2's Avatar Guest

    Default SCT, FR and wide field 2" eyepieces

    If you had read the manual (Celestron's) you'd know that it expressly
    says not to use wideangle 2" EPs with the FR installed, due to
    vignetting and field correction issues. You can still use shorter focal
    length 2" EPs, from 16mm downward they're little affected.

    Andrea T.

  3. #3
    RMOLLISE's Avatar
    RMOLLISE Guest

    Default SCT, FR and wide field 2" eyepieces wrote:

    Many wide angle eyepieces will work just fine with the 6.3.

    Original poster:

    It's true that when you get over about 20 - 25mm, you'll begin to
    notice some vignetting. How much of a problem this is depends on you. I
    find the view of the Pleiades with an 8 inch SCT, a 35 Panoptic, and a
    6.3 reducer splendid. Yes, there's vignetting, but that is outweighed
    by the ability of this combo to put almost all the Pleiads in one

    Hint? In astronomy, when someone tells you "can't," use a piece of
    equipment "that way," it often pays to try it for yourself. ;-)

    Rod Mollise

  4. #4's Avatar Guest

    Default SCT, FR and wide field 2" eyepieces

    Apparently the original poster wasn't too happy of the combo 2" EP
    (long focal length) and SCT+FR. The manual says why and off the top of
    my head I seem to remember that from 32mm 2" EPs shouldn't be used with
    FR, thereby confirm the "experimental" result of te original poster.
    IOW, you're just wasting glass, costly glass. Let's be frank, SCTs
    field correction is poor as they are, don't need a FR to reduce it


    Andrea T.

  5. #5's Avatar Guest

    Default SCT, FR and wide field 2" eyepieces

    A F/10 to F/6.3 focal reducer takes a 2" <pre>image from the optical
    path and makes a 2"/<f/10>*<f/6.3> = 2" * 6.3/10 = 1.26" circle of
    illumination! In effect the FR takes a 2" FoV and smashes it down to a
    1.25" FoV which coincidentally is the size of the typical eyepiece
    (will wonders never cease).

    Any eyepiece that has a wider field stop than 1.26" will vignette.
    Therefore, a Focal Reducer is a device that enables one to avoid buying
    2" eyepieces. The old Lumicon BIG reducer was/is a device that takes a
    ~3" image and creates an ~2" image and can be used with big eyepieces
    with the 10" and larger SCTs.

    However, the focus sharpness of the extended field from the main optics
    is "not all that good", and you end up with a big field where the
    center is acceptably focused and the outer ring of fuzz is anoying.



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