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  1. #1
    47Tuc's Avatar
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    Question Which EPs meet these parameters?



    My new scope is a 190mm Mak-Cass, f2700, F/15.
    Please name any high quality EPs you know of which meet all of the following:
    The widest possible TFOV.
    1.25" barrel only.
    Must have 20mm eye relief (or more).

    The best I can think of at the moment is the Baader Aspheric 36mm which would give a True Field of 0.67 degrees. Can anyone better that?

    Thanks.
    Paul
    36.85 S 174.57 E
    12" GSO Dobsonian
    Orion 180mm Maksutov-Cassegrain, 8" Richey-Chretien, HEQ5Pro mount
    Explore Scientific 30mm, Baader Hyperion 24mm, 17mm & 8mm, Pentax XW 10mm, TV 2x Barlow

  2. #2
    kencrowder's Avatar
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    I'm not sure what you are looking for. That is a good scope and with f/15 isn't sensitive to most ep problems. There are several "brands" of eps with apparent FOV's in the 70 degree and up range. There are also the generics which are made by the same manufacturer. I doubt you can tell the difference between them with an f/15.

    I have a super plossl from OPT that has a 70 degree aparent FOV, 15 mm fl and 20 mm eye relief. On my f/10 sct it works very well.

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  4. #3
    47Tuc's Avatar
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    Quote Originally Posted by kencrowder View Post
    I have a super plossl from OPT that has a 70 degree aparent FOV, 15 mm fl and 20 mm eye relief. On my f/10 sct it works very well.
    It's a wide TRUE field of view I want. The eyepiece you mention has a TFOV of only 0.39 degrees. A wider TFOV will allow me to see more of large deep sky objects.
    Paul
    36.85 S 174.57 E
    12" GSO Dobsonian
    Orion 180mm Maksutov-Cassegrain, 8" Richey-Chretien, HEQ5Pro mount
    Explore Scientific 30mm, Baader Hyperion 24mm, 17mm & 8mm, Pentax XW 10mm, TV 2x Barlow

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    47Tuc's Avatar
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    My scope is 180mm aperture, not 190 which I mistakenly wrote.
    Paul
    36.85 S 174.57 E
    12" GSO Dobsonian
    Orion 180mm Maksutov-Cassegrain, 8" Richey-Chretien, HEQ5Pro mount
    Explore Scientific 30mm, Baader Hyperion 24mm, 17mm & 8mm, Pentax XW 10mm, TV 2x Barlow

  6. #5
    kencrowder's Avatar
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    Use a 0.5 focal reducer on the ep I mentioned. It doubles the FOV and still gives a 5 mm exit pupil. Or go with TeleVue or the one you mentioned.

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    I've not run the numbers for you, but you probably should visit Tele Vue's site and run their calculator. The Ethos eyepieces are excellent and have a wide FOV.

    Ethos, though, has only 15mm of ER. For the 20mm you may need to look at Ethos. I think some of the Naglers are at 19mm. My 35mm Panoptic has an ER of 24mm?

    I think Explore Scientific now has a 120 degree AFOV eyepiece. It is probably very good as well - and I think I saw one on OPT for about $1,000. Not sure about the ER.
    Last edited by OleCuss; 12-08-2011 at 08:15 PM.

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  9. #7
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    You're going to be limited by the 1.25" barrel requirement. If you could go to 2" you should be able to go wider.

  10. #8
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    Hi Paul. What about the 68* Explore scientific 24mm. It is 1.25 and probably in the best price range for what you are looking for.
    15 inch Obsession
    Low Power: ES 28mm ~60x @1.1° : Televue Delos 17.3mm ~100x @.72°
    Medium Power: ES 14mm ~122x @.82° : Televue Delos 10mm ~170x @.42°
    High Power: Televue Delos 6mm ~285x @.25° : ES 4.7mm ~365x @.22°

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  12. #9
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    Default

    I'd skip the widest FOV stuff with the scope - I am assuming its a Skymax 180. The FOV is very tight with the scope anyway and widefield EPs may end up producing vigenttes anyway.

    There are only a handful of objects that wont fit in the FOV of that scope with a bog standard Plossl in about 32mm and the ones that wont fit wont fit no matter HOW wide your EP FOV is because they are limited by the scope.

    I kind of see where your coming from because getting a decent wide view with the 180 was one of my concerns. In actual use I mostly used a Hyperion 13mm for high power and a 32mm Vixen NPL (Plossl) for low power views.

    Something to bear in mind with that scope is its FL is so huge you have to redefine your EPs.

    For instance being used to a 1000mm FL on my other two scopes meant I was always thinking in terms of EPs being...
    5mm powerful ( x200)
    13mm mid power (x76)
    32mm low power (x31)

    Whereas with the massive focal length of the Mak 180 your more like

    5mm Forget it - its way too powerful unless your in Arizona (x540)
    9mm Massive power (x300)
    13mm Still very powerful ( x207) almost at the limit of UK seeing conditions on MOST nights
    32mm medium power (x84)
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