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Thread: Ultra Wide Field of View

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    Default Ultra Wide Field of View



    I have heard Al Nagler speak of the Ethos 100° & 110° Apparent Field Eyepieces giving you a space walk experience.

    I often see people in this forum talking of refractors with a great field of view. Orion ST-80 for example.

    If wide field of view is the primary goal I would be interested in hearing from the group their opinion on the best scope / eyepiece combination both ideally and balancing the fact that the scope should be available for routine observing also.

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    Default Re: Ultra Wide Field of View

    For LOW powered wide field viewing I usually use my f/6 100 mm very inexpensive Orion Astroview refractor...it excels on open clusters under low power.. No CA at all, and has a nice bright wide FOV with a wide field good eyepiece . ( I use a 35 mm Pan in the scope usually)..17 or so X which is not much greater then binoculars but a lot more comfortable to use...

    However it is NOT worth a heck of a lot for general observation (visual) ...the only thing it is good at are those open clusters...and that is the only reason I own it... On a normal night I can not push that sucker up to 100x (say bye bye to splitting most doubles) on The moon it has absolutely awful CA even with a minus violet filter which makes viewing any good detail on the moon frustrating..

    Bottom line I only purchased this scope to use on open clusters and for that purpose it was worth the small amount of money I spent on it... For general use I do not need ... nor do I want... a very wide FOV ...I want ample magnification for the type of target I am looking at and I want that object to fill up most of the FOV ..

    Bob G


    Bob G

    I do have a Orion Short tube 80 piggybacked on my CPC1100 in my observatory that I use for the same purpose after I finish my planned session just to sit back and relax .and look around...
    CPC1100 housed in a slotted domed observatory (Exploradome) 4 and 5 inch refractors for use from the lawn, a 8" Sct (NS 8i) for star parties...
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  3. #3
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    Default Re: Ultra Wide Field of View

    I have an F/6 AT72ED refractor, Skywatcher 120ST refractor, APM100ED binocular telescope, Garret Optical BT70/90 70mm binocular telescope with 90° oculars, AT152 F/5.9 short tube refractor.

    These all do really great at low power widefield observation.

    Check out some of these size comparisons to the moon and you might get a good idea of why low power widefield is great:

    Deep Sky Sizes - Imgur

    I also have a iOptron mak 150 at F/12 and the mak just can't get all of these objects in view framed correctly. I get pieces of it.

    Milky Way sweeping is pretty spectacular with richfield viewing.

    Lots of reasons to like it besides just clusters.

    Having enough instruments to cover both types of viewing is nice. Certain instruments like the Orion 180mm Mak-newt or David Levy Comet Hunter, Omni XLT 150 newt, etc will cover both low power and high power viewing very well.

    If I want high power with my AT152 I put a filter in to block CA spectrum of the scope.

    Most of the time I'm viewing in Narrowband Ha with image intensifiers which also blocks CA

    UHC and OIII filters readily block CA.

    Sometimes I attach a 50mm F1.2 camera lens to my image intensified eyepiece, with 3nm Ha filter in front of the lens to view things like Barnards loop which is entirely too big to fit in view of any scope I have.

    If you can experiment with an ST80, it's a great way to view widefield objects. Pleiades is 2°

    In summer time, I can get both M8 and M20 in the same view or go up. A little and get M16, M17 in the same view.

    I can view all of the North American Nebula in Ha
    I can get both Eastern and Western Veil in full view in narrowband Ha

    My short scopes allow for all that.
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    Default Re: Ultra Wide Field of View

    This is a topic where nothing beats going to a star party and trying out different gear. Failing that, often astronomy clubs can give you ideas. My sweet spot is 82 deg, but everybody has their own favourite.
    Dave
    Dobsonian Apertura AD12, TV N5 Nagler 31mm, ES 82deg 18mm, TV plossl 15mm, 11mm, 8mm, TV Delos 8mm, UO HD Abbe Orthoscopic II 6mm, Telrad.
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  5. #5
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    Default

    For wide true fields, fast refractors tend to be the obvious choice (along with binoculars).

    Very widest true field is probably the astronomical version of opera glasses - only about 3x but huge true field.

    Binoculars come next (for true field)

    Then fast refractors - for a 2" eyepiece, my fs60 is about as wide as it gets (60mm, f5.9).

    For imaging, the widest is probably Tak's FSQ106ED (530mm, f5, with an 88mm image circle for a 9.4° photographic field). It also works great visually, though with a 2" eyepiece the shorter focal length of the fs60 will give you a wider true field... But if you allow bigger eyepieces, the 92mm focuser and 88mm image circle should make for some really wide views - the 3" ES eyepiece and diagonal would probably be impressive .

    For apparent field of view, that's down to the eyepiece design rather than the scope, but you can easily max out what fits in a 2" barrel - around 40mm for a 65-70° AFOV, 31mm for 82°, and shorter for the 100°+ ones.

    Note that with high magnifications, you can still have a huge AFOV but with a small TFOV - apparent field is the size of the circle you see the image in - up to around 70° or so it's obviously a circle on a dark background, at 80° or more the circle is big enough that the edges are much less noticeable; that's where the spacewalk effect comes from.

    True field of view is how much of the sky you see - this increases as the AFOV increases, or as you reduce the magnification.

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    Default Re: Ultra Wide Field of View

    Not to take away from the original post, but the FS60 is awesome. I want one. Ok, back to regular programming.
    "To confine our attention to terrestrial matters would be to limit the human spirit."
    Stephen Hawking

    A varied hodgepodge of observing gear,

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