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Thread: Cheap low power

  1. #1
    Johansson's Avatar
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    Default Cheap low power



    How would this ep do in my Nexstar 8se ?
    Or should i go with the 40mm ?

    GSO 32mm RK 55 fov.

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    Default

    What do you want it to do?

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    Let me see star clusters and galaxies.

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    Default

    What scope will you be using it in? What aperture and focal ratio?

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    C10-N/C14+Losmandy G11; Portaball 12.5"; NexStar 6SE; Meade ETX125; Stellarvue F80
    Meade HD-60 9mm, 6.5mm; 56mm; University Optics Orthoscopic 12.5mm, 9mm, 7mm, 5mm;
    ES 70° 15mm, 20mm; ES 82° 30mm, 18mm; ES 100° 9mm; Baader Hyperion 24mm; TV Nagler T6 13mm
    William Optics Binoviewer; GSO 2" 2x ED barlow; 5x APO barlow, Parks 2.5x APO barlow
    Filters: Orion Ultrablock, Thousand Oaks OIII

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    Default

    The GSO 32mm Plossl should work fine in your 8SE as a low power eyepiece. The actual FOV between the 40mm and the 32mm will be basically the same due to the smaller apparent FOV of the 40mm plossl. An 8" SCT is limited with its FOV capabilities because of the opening at the end of the tube (entrance to the focuser). However, a focal reducer which reduces the focal length of the scope to f/6.3 would help to increase the FOV by reducing the magnification. You're never going to get more than about 1.5 degrees of actual FOV from an 8" SCT.
    Regards,
    Clay

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    Im kind of new to these things so i dont really know what way to go.
    Right now i have the Baader hyperion zoom and a WO 2" diagonal.
    With these things im not able to get for example the pleiades in my fov.
    Is there a way to get the entire pleiades and more into my fov like i can with a simple binouculars ?

    Should i get a Baader aspheric 31mm or 36mm or use my hyperion zoom with a focal reducer ?

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    The GSO eyepieces are more than good enough for your 8se. It IIRC is a F10 telescope making the optics somewhat slow. You don't need high end eyepieces to get awesome viewes out of a slow SCT.

    I have a Celestron C9.25 and using my GSO 42mm and a 6.3 focal reducer, I come no where close to getting the Pleiades in the fov. I'm not sure if you can in a C 8 either.

    You can buy a Celestron/ Orion ST80mm guide scope for the price of a good focal reducer. I have one attached to my C 9.25 and use it for wide field viewing as well. Its kinda cool to look at an object in the SCT then see what it looks like in the ST80. Works great as a guide scope too if you ever venture down the dark path.

    Jim
    Celestron C9.25. Atlas EQG mount. Canon 500D unmodded, Celestron ST80 guide scope, SSAG, Meade 6.3 FR, Thousand Oaks dew control with Dewnot straps. Zhumell 8/24mm Zoom, 2"Gso Superview 42mm, Meade 2"QX wide angle 30MM, Meade 1.25 EP and filter set. Tasco 10x50 Zhumell 20x80 bino and a few other odds and ends.
    Now where did I put that clear sky button!

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    Default

    Quote Originally Posted by Johansson View Post
    Im kind of new to these things so i dont really know what way to go.
    Right now i have the Baader hyperion zoom and a WO 2" diagonal.
    With these things im not able to get for example the pleiades in my fov.
    Is there a way to get the entire pleiades and more into my fov like i can with a simple binouculars ?

    Should i get a Baader aspheric 31mm or 36mm or use my hyperion zoom with a focal reducer ?
    It sounds like you want to know how to compute the fov. If so, consider a 10x50 bino with f/5 lens design. The fl would be 250 mm and the magnification is 10x. That tells you the ep is 25 mm.

    Other numbers give the fov. For example it might say 100 yards at 1000 yards. That is 0.1 radians which can be converted to degrees. Divide 0.1 by 0.01745. That would be the fov of the binos.

    Every ep has an apparent fov given in the specs. Divide that by the magnification to get the true fov. Plossls tend to be about 50 degrees, GSO designs tend to be about 70 degrees. Televue and others are offering much larger apparent fovs.

    In a telescope, however, consider the size of the exit pupil. That is the aperture, 200 mm, divided by the magnification. It should be 7 mm or less.

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    Default

    If no ep can make it get the pleiades in the fov i might by a 10x50 finder instead.

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    Default

    The Pleiades are about 2 degrees in diameter. From there, it's a reasonably straight shot to figure out what size eyepiece you want.

    The NexStar 8SE has the following specs:

    Aperture: 203.2 mm
    Focal Length: 2032 mm
    Focal Ratio: f/10

    You can go to this site to plug in specs for various eyepieces to see which one gets you to 2 degrees TFOV. Since your scope is an f/10, you can't practically achieve a 2 degree FOV -- you'd need something like a 55mm Plossl in a 1.25" barrel (which nobody makes) or a ~40mm Ethos (100 degree AFOV), which again I don't think anybody makes, especially in a 1.25" format.

    What it boils down to is that your scope, with the widest field eyepiece I could find (granted I didn't hunt particularly long) -- Baader 31mm Hyperion Aspheric 2"-1.25" Eyepiece - Free Shipping - OPT Telescopes -- gives you just over 1 degree of field.

    You might look at getting a focal reducer, which would reduce the effective focal length and could give you a wider FOV. Or, as mentioned, you could get a nice 9x50 finder and use it for observing very large objects.

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    C10-N/C14+Losmandy G11; Portaball 12.5"; NexStar 6SE; Meade ETX125; Stellarvue F80
    Meade HD-60 9mm, 6.5mm; 56mm; University Optics Orthoscopic 12.5mm, 9mm, 7mm, 5mm;
    ES 70° 15mm, 20mm; ES 82° 30mm, 18mm; ES 100° 9mm; Baader Hyperion 24mm; TV Nagler T6 13mm
    William Optics Binoviewer; GSO 2" 2x ED barlow; 5x APO barlow, Parks 2.5x APO barlow
    Filters: Orion Ultrablock, Thousand Oaks OIII

 

 
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