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Thread: 2" Mirror Diagonal vs. f/6.3 Focal Reducer: final decision... maybe

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    Default 2" Mirror Diagonal vs. f/6.3 Focal Reducer: final decision... maybe



    Hello!

    I will be stepping up to a 9.25" SCT from a Nexstar 4SE very soon and plan to immediately upgrade to a 2" mirror diagonal, the Baader Hyperion Mark IV 8-24mm zoom eyepiece for general higher power viewing, and the Orion 2" Q70 26/32/38mm eyepiece set for lower power/wider views. Quite a few assumptions went into making this decision, so I would really appreciate any feedback on if and where I may be going wrong.

    This will be a general use visual scope, mostly DSO, but planetary and lunar fun too, essentially no AP.

    I really like the idea of the Baader zoom's ability to quickly find the balance between brightness and power, so here is assumption 1: The view quality of the Baader eyepiece will be at least as good as the standard Celestron kit Plossl eyepieces in comparable focal lengths (8,13,17,25mm). Assumption 2: The view with the Baader will be better with the 2" diagonal than with the supplied 1.25" diagonal. Assumption 3: The Baader can be used with a Barlow.

    Noticeably absent from my planned setup is the f/6.3 focal reducer, which many people seem to think is the best upgrade you can make to a 9.25" SCT. More assumptions... 4: The Orion Q70's without a focal reducer will give a better "wide" field view than 1.25" eyepieces (including the Baader) with a focal reducer. 5: Paying more for higher-end wide FOV 2" eyepieces gains very little in a scope this slow (f/10). 6: There is no point using a focal reducer with the Q70's because of likely vignetting. and... 7: I will use all three Q70's. (Will one or two be enough? Which one or two?)

    Are these assumptions reasonable? Or would I be just as well off with the focal reducer only, and sticking with the supplied diagonal and the 1.25" eyepieces (6,8,13,17,24,24,32,40mm Plossls) I already have?

    Thanks so much for your thoughts!

    Mike

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    Default Re: 2" Mirror Diagonal vs. f/6.3 Focal Reducer: final decision... maybe

    1) The view should be a bit better than kit eyepieces
    2) Yes, upgrading the diagonal even to a better 1.25" always adds to the view.
    3) Yes in can be but at 8-25mm you would only get detailed views using it on the longer settings. To low and you trade image scale for detail.
    4) That would depend on the focal lengths/ AFOV. The 38mm Q70 will give you a 1.12° TFOV which is just about the maximum without a FR
    5) If you were a dedicated visual observer than you may want to pay for the extra 5% or so but if just starting out save the money and buy cheaper good quality for now.
    6) The focal lengths you picked will vignette but changing the focal length will change the eyepieces you pick also. Six of one...
    7) Between the 32mm and the 38mm you are only changing magnification by 9x so really nothing noticeable on the low magnification. The 32mm is .95° TFOV and the 38mm is 1.12° TFOV

    Personally I am not a fan of reducers, I would buy an SCT because it was an f/10 scope, if I wanted shorter focal length I would get a Newtonian and buy good eyepieces. (My skewed opinion only)
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    Default Re: 2" Mirror Diagonal vs. f/6.3 Focal Reducer: final decision... maybe

    Hmm.... I use the f6.3 reducer along with a 2" diagonal in my N11GPS. I don't notice any obvious vignetting with a 2" 65 degree 40mm or a 2" 28mm 82 degree eyepiece.
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    Default Re: 2" Mirror Diagonal vs. f/6.3 Focal Reducer: final decision... maybe

    I was doing the numbers in my head
    The 38mm at f/6.3 will have 1mm to spare using a 2" diagonal so all good!
    PS: The FS of a 28mm 82° is 6.5mm smaller than a 38mm Q70
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    The weakest link in the optical chain is the large nut located directly behind the eyepiece/ camera. - Gabrielle
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    Default Re: 2" Mirror Diagonal vs. f/6.3 Focal Reducer: final decision... maybe

    Not the way I would go with the exception of going to 2" which I definitely would do. I would get the focal reducer. I would skip the zoom, the Baader is the nicest of these but would only be useful with a Barlow at the shortest focal lengths. I would skip the Q70s. I would invest in the ES 82s. The views with these would be significantly better than the plossls you currently have and much wider. And while the Q70s will work fairly well in the SCT, they will not with some other scopes. The costlier ES EPs will work well with any scope (you may want another at some time) and will be wider than the Q70s, the SCT is narrow and you want to widen that with focal reducer and WIDE EPs. Considering the cost of the Baader and Q70s, you can get the focal reducer and some ES 82s and be better off.
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    Default Re: 2" Mirror Diagonal vs. f/6.3 Focal Reducer: final decision... maybe

    The less glass you add in the optical train - the better. The urge to have a huge range of focal lengths covered leads to a huge collection of eyepieces that can add up to a lot of spending. I would carefully catalogue your uses of your current eyepieces and see how often you use which eyepieces on which targets, and see if you really need every focal length. Note also with your very complete range of Plossls where you really want more magnification and where the Plossls are perfect and just need a wider field.

    I would suggest the 2 inch diagonal for its better quality as well as its potential for wider views. Then for the budget you are allocating for the Baader Zoom and the Orions, you could buy three premium eyepieces with the focal lengths and fields best suited for you. The Baader is a good zoom and is only bettered by the much pricier Leica Aspheric, but the zoom still has a lot of glass and minor but noticeable angular distortions. If you are convinced that the convenience of the zoom is an imperative for your viewing preferences, it is not a bad choice, but on a purely optical consideration better views can be had for an equivalent expenditure.

    I agree with Gabby that for visual use a reducer is just another piece of glass added to the optical train. The slightly over 2 meter focal length is well served by the current standard range of available eyepieces. With the reducer for DSO's it still won't gather light like a comparably priced larger mirrored f/4.5 or f/5 Dob. Equally, the Dob won't give the sharp high magnification views of the SCT.

    Premium eyepieces are also habitually well cared for and represent excellent value on the used market. You can resell them for close to the price that you buy them at if you change your preferences in the future.
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    Default Re: 2" Mirror Diagonal vs. f/6.3 Focal Reducer: final decision... maybe

    I agree with Gabby and Trombatissimo on no reducer. I have the reducer, but do not use it with my 8" SCT.

    Q70s should work well in your SCT, but they are not spaced far enough to justify purchase of all 3. I would suggest to get instead GSO Superview 30mm and 42mm. They also a bit better corrected than Q70.

    2" Telescope Eyepieces - Wide Angle Eyepieces | AgenaAstro.com

    Instead of Baader zoom I will suggest to invest in 2-3 fixed FL EPs. With F10 scope you don't need EPs below 10mm, so ~10mm and ~20mm should cover your needs.

    I would suggest ES 82 degree 11mm and ES 68 degree 20mm.

    And definitely yes on better quality 2" diagonal. Celestron SCT 2" diagonal works fine for me, but there are also other good options.
    Last edited by Bigzmey; 08-24-2017 at 01:47 AM.
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    Default Re: 2" Mirror Diagonal vs. f/6.3 Focal Reducer: final decision... maybe

    Wow, everyone! Thanks so much for the quick, thoughtful and thorough responses. There's a lot of info here- all good!

    So, long story short, I'm likely now to heed all this advice and go with two ES EP's (those suggested by Bigzmey seem ideal) and one 2" widefield EP somewhere between 30-50mm (Suggestions?) for now, and then build from there later. And of course the 2" diagonal.

    Thanks again, everyone. You've been most helpful.

    Mike
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    Default Re: 2" Mirror Diagonal vs. f/6.3 Focal Reducer: final decision... maybe

    Quote Originally Posted by Mike McComick View Post
    Wow, everyone! Thanks so much for the quick, thoughtful and thorough responses. There's a lot of info here- all good!

    So, long story short, I'm likely now to heed all this advice and go with two ES EP's (those suggested by Bigzmey seem ideal) and one 2" widefield EP somewhere between 30-50mm (Suggestions?) for now, and then build from there later. And of course the 2" diagonal.

    Thanks again, everyone. You've been most helpful.

    Mike
    Going with one 2" EP is sensible decision. I have 8" SCT and use just one 2" EP most of the time. I tested a few 2" EPs and Baader Aspheric 36mm provided the best balance between optical performance, size, price and weight in SCT. In the low price bracket I would suggest GSO SuperView 42 mm. Since you like me have F10 scope going to high priced EPs will have diminishing returns. Also, consider that those TeleVue and ES 68/82 2" glass pineapples could weight up to a few lbs.
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    Default Re: 2" Mirror Diagonal vs. f/6.3 Focal Reducer: final decision... maybe

    I have the GSO SV42, and I agree with Bigzmey that it works quite well with my 8" SCT (it is OK at f10, but it doesn't like my f5 dob, and I think it wouldn't be great at f6.3 either.). For very little expenditure it is a nice wide-field addition. A good choice if you have a limited budget or you want to put more money elsewhere. You should also check whether there is enough room for the bigger "pineapple" eyepieces at high viewing angles, in case they get caught on the mount.

    With regard to the zoom eyepiece: I have the Williams 7.5-22.5 and it does the job nicely (great for public viewing!); but remember that with zooms the lower the magnification, the smaller the AFOV. The AFOV reduces from around 60° at high power to around 45° at low power. If you want a wide-field, low power view then you need a dedicated wide-field eyepiece.

    I also put the GSO 2" Qtz diagonal on my SCT, and it made a huge difference vs the supplied one: nice stars that look like the theoretical ones that you should get from a good quality SCT instead of fuzzy blobs! I don't know why Celestron even bother with that diagonal; it detracts from their optics so much.

    I have the 6.3 reducer too, but I never use it...

    All the best with the decision making.

    - Dean
    Last edited by DeanD; 08-26-2017 at 03:03 AM.
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