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Thread: Eyepiece(s) for viewing planets

  1. #1
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    Default Eyepiece(s) for viewing planets



    I've bought a new telescope recently it's an 8" dob 1200mm (f/6). I live in the suburbs and can only very rarely get away into darker skies so I enjoy spending most of my time viewing the planets, usually Jupiter, Saturn and Uranus. The telescope I've got came with 25mm, 10mm and 6.3mm plossl eyepieces giving me (48x 120x and 190x). I'm after one more step in terms of magnification (since planets in good seeing can be good high power targets) and I'm thinking about buying a 4-5mm eyepiece. The problem is I find the 6.3mm tough, but useable, due to the tight eye relief and I'm scared something like a 4mm would be even harder to use. My question is am I better off buying a barlow or new eyepiece(s) ?
    Last edited by Kumquat; 04-09-2013 at 10:48 AM.

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    Default Re: Eyepiece(s) for viewing planets

    Hi,
    You haven't said what sort of eyepieces you have, although if they came with the scope they are probably plossl's, and these usually have around 50 degree field of view and fairly low eye relief. If you are having problems with eye relief, there are many other types of eyepiece out there that have a lot more than the standard plossl.
    For example, Orion are now selling their "Edge-on", "Stratus" and "Long eye relief" types, all for around $100 in Australia, and each have 20mm eye relief, even for 5mm FL. 20mm eye relief is more than enough, even if you wear glasses.
    I don't think you would have any trouble at all using something like those. Long Perng sell similar "planetary" eyepieces to the Orion Stratus (probably just re-badged), as do Williams.
    I think you would be better off going for a new, long-eye-relief eyepiece of around 5mm FL and with a wider field of view than your plossls rather than trying a barlow with the ones you have already. The wider field makes things easier at high power with a dob, as you don't have to move it around as often.
    The barlow will increase eye relief a bit, but I suspect adding it to your 6.3mm would give you too much magnification except for very rare nights of exceptional seeing.

    All the best,

    Dean

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    12" home-made dob, Celestron 150 f5, Tak TSA102, TV 76, Celestron 800CPC, ETX 125
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    Default Re: Eyepiece(s) for viewing planets

    I agree with dean...about the 20 mm of eye relief...BUT to be honest you sure as the devil do not need OR WANT any wide field eyepiece...UNLESS you have problems keeping the planet in the fov of your dob....in which case then a 68 degree FOV should be more then sufficient ...

    I own a bunch of scopes and no matter which one I am using on any given night I tend to view planets between 120 and 200x so your 10 and your 6 puts you right in that range ...So to be honest I think I would look for another 6 or if you have a barlow I'd look for a 12 ... the barlow ...."may" be usable with the 10 on really good ..ok "fantastic" nights...

    Bob G
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    Default Re: Eyepiece(s) for viewing planets

    How well do eyepieces keep? If I was to spend a bit of money on it now how long do they last if I decide to upgrade the telescope in X years time?
    OZScopes 8"
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    Default Re: Eyepiece(s) for viewing planets

    Sorry Kumquat, you did say the eyepieces you had were plossls...

    And a typo: I meant the Orion "Edge-on" and the Long Perng "planetary" seem to be identical.

    I think Bob is right in that you would rarely be able to go over 200x (6mm eyepiece), especially in the city where there are lots of heat sources affecting seeing.
    I suggested you might try a 5mm because you already have a 6.3, and you said you wanted to go a step higher in magnification.

    Regarding field of view, the examples I gave have between 55 and 68 degrees fov. Some people love the wide-field experience of the expensive 82 degree and 100 degree eyepieces, but you have to move your eye around to appreciate the full field, and this is not to everyone's taste.

    Many people regard the classic orthoscopic design as giving the sharpest views for planetary work, and this design has a fov of around 40-45 degrees. The draw-backs are that you have to keep moving the dob to keep the object in the field at high power, and this makes it hard to get a good, steady look; and they typically have a very short eye-relief...

    If you are a member of an Astronomical Society (the AS of Victoria people I have met are friendly...), why not see if you can try someone's eyepiece, or go along to a members' night and check out what people are using.

    All the best,

    Dean

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    Default Re: Eyepiece(s) for viewing planets

    Thanks for the input guys it's got me thinking about things. I certainly only want to go 1 step higher with magnification above 190x. I do notice the image is dimmer in the 190x compared to the 120x so I am aware high magnification does not equal better image. Saturn is in a good position now and I've found that it responds well to high power however I don't think I'm the only one with that opinion/observation. I don't mind shifting the telescope around often to keep the target in view. I'll go out and try the 6.3mm again and if I'm comfortable with it i'll buy a 5mm, if not i'll barlow the 10mm.
    OZScopes 8"
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    Default Re: Eyepiece(s) for viewing planets

    YOU ASKED ....How long do eyepieces last ????

    Well... lol...that depends... ! I purchased my first scope in 1952 or 53 as a cub (not boy) scout with major big time financial held from my parents.. .. Got an expensive (to me) Sears and Robuck ..2 inch refractor ..

    So I have been in this hobby for decades and I'll tell you I still have (and use) some eyepieces that are at least 30+ years old... HOWEVER not a one of the eyepieces in my Eyepiece case I normally use is more then 15 years old... conversely none are newer then about 3 years

    Bob G
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    Default Re: Eyepiece(s) for viewing planets

    Get a 2x2 barlow. That would double the mag of your existing eyepieces.This is the one I bought:
    http://www.opticsmart.com/accessorie...sion-ring.html
    Last edited by mlk1950; 04-09-2013 at 05:17 PM.
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    Eyepieces: 9mm plossi, 30mm 68 degree, Explore Scientific 4.7, 6.7, 8.8, 11, 14, 18mm and 24mm /82 degree, Russell Optics 13mm Super Wide Konig XL, Apertua 2x
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    Default Re: Eyepiece(s) for viewing planets

    I agree with Bob G.

    EPs should last a long time with proper care. I have a 16.3mm Galoc UWA (for that time) purchased in 1971 that I still use regularly.

    I think your best and cheapest option for now is to get a good quality 2x barlow.

    Last thought: Contrary to previous opinions, I have a 9mm EP (that gives me 311x in my C11) I use every time I view the bright planets. It is my "seeing" tester EP. More often times than not I keep using that EP for the night.

    Clear skies,
    JT
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    Default Re: Eyepiece(s) for viewing planets

    There's a lot you can do to improve your view of planets without buying new glass. The set of eyepieces you have now should be fine. Once you go beyond a 1mm exit pupil (6mm eyepiece), you are not exposing any new detail, just magnifying existing details. At or around a 1mm exit pupil, you have reached the diffraction limit of the scope, so fine details no longer resolve as points, but rather as discs. This makes the image more and more blurry and difficult to focus as you go beyond a 1mm exit pupil.

    I have a 10" f/4.7, and my best planetary eyepiece (on perfect nights) is a 5mm orthoscopic. This gives me just over a 1mm exit pupil (your 6.3mm eyepiece would be the equivalent in your scope). On nights of pristine seeing conditions, I've occasionally tried using my 7mm orthoscopic in a 2x barlow (0.75mm exit pupil), but I've never actually seen "more" of the planet than I did with the 5mm only.

    Have a look at this post describing a whole host of things you can do to maximize your planetary views: A Treatise on Optimizing Planetary Views
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