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  1. #1
    NickN89's Avatar
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    Default First Eyepiece Help



    Hey guys i just joined the forum and i could use your help on buying my first eyepiece. (I mean other than the ones provided with the scope)

    The telescope is a 114/900mm, f7,9 reflector. (1.25" eyepieces) It came with 3 eyepieces: An H20, an H12,5 and an SR4. From what i read online these eyepieces are not that good and i can see that they don't give clear images especially on high magnification (SR4)

    I already did a fair amount of reading on eyepieces and with the formulas i found i can see that the maximum practical magnification for my scope is around 250x. (Please correct me if i'm wrong)
    Since the magnification is the telescope's focal / eyepiece focal in my understanding anything more than 4mm would be an overkill.

    I'm interested in (but not only) planetary observations so i'm thinking of getting an eyepiece at around 6-10mm which can be theoretically doubled using my 2x Barlow lens (which i also believe is not of great quality). From what i read i understand that Plossl eyepieces are pretty good for the price tag and i already found some online at pretty good prices ($30-$40). I also noticed that the Celestron X-Cel eyepieces (at the same price range) get good reviews too.

    These are just some ideas and my mind is not made up yet.
    Do you think i should get a fairly cheap Plossl eyepiece at around 6-10mm and see how that goes or save some money and go for something like the Celestron Ultima line?

    Of course i'm not interested in just one brand so any suggestions would be very useful. I would appreciate your help very much on choosing the best eyepiece for my telescope. Feel free to let me know if my thinking or understanding of telescopes/eyepieces is far off

    Nick

  2. #2
    AndreaF's Avatar
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    Default

    Well, in my experience 250x for a 114/900 are too much, I think 180x - 200x are enough for that telescope (expecially cause the mount)... an 4-5mm ep would be optimal and plossl are great eyepieces but short focal have short exit pupil and tend to be uncomfortable... I'd buy a planetary series like BO/TMB or William Optics SPL or something like that... they have a good 60° fov too

  3. #3
    NickN89's Avatar
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    Default

    Thanks for the input AndreaF. Don't you think that 4mm would be too much since it would give a 225x magnification? And since i have a 2x Barlow shouldn't i go for more than 6-8mm?
    Nick

  4. #4
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    Default

    Also consider your seeing conditions. I live in NW Ohio. Typicaly I can only use 100x to 180x, even with an 8" scope.
    I agree that the EP's that came with your scope are probably not the best. I would start with a decent EP ( probably $40 to $50) that provides a magnification of 75 to 100x.
    The problem you have with the 4mm is probably a combination of things; 1. seeing conditions, 2. scope apperature or quality, and 3. the 4mm EP quality. All IMO; Don T.

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  6. #5
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    Default

    Since i'm on a tiny island in the middle of the Mediterranean i'll need to order the eyepiece online. Do you guys have any experience buying eyepieces from websites like ebay? Or have any other websites to suggest?

    Nick

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  7. #6
    AndreaF's Avatar
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    Default

    I agree with Don Trinko... usually we think that 2x aperture in millimeters is the maximal magnification we can reach but this is true only with good seeing, good scopes and good eps... that's why I tend to underestimate the maximum attainable magnification, you can buy good instruments but not a good seeing

    If you have a good barlow you can easily use it in combination with an eyepiece without quality loss... for example in my 12" f/5 there isn't noticeable difference in image quality between pentax xw 10mm + televue 2x and the simple pentax xw 5mm

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  9. #7
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    Default First Eyepiece

    Hi Nick and welcome to the Astronomy Forum. As a first eyepiece I would recommend something in the 15mm to 16mm range, perhaps a TeleVue Plossl (under $80). The 15mm TV Plossl would give 60x magnification, a 0.83deg field of view, and a 1.9mm exit pupil. A 16mm EP (if you can find a suitable model in your price range) would be about perfect giving you 56x with a 2.0mm exit pupil. Exit pupil describes the size of the light cone exiting the eyepiece and is a measure of how much "usable " light you are getting in your dark-adapted pupil. 2.0mm is generally considered ideal to get the most out of a specific telescope/eyepiece combination.
    Here are some things to remember: You often get the best contrast at exit pupils of 1 to 3 mm, 50x per inch of aperture inch is the magnification limit for scopes (roughly 200x to 225x in your case), the typical usable exit pupil range for most people is 0.5 to 6 mm (the pupil of dark adapted eye typically opens to 6 to 7 mm for young folks and declines as one gets older), and if the exit pupil is larger than your dark adapted eye you'll lose light (not necessarily a big deal really).
    So my recommendation would be a 15mm Plossl (I cannot think of anyone who makes a 16mm Plossl) which are available from Meade, Celestron, Skywatcher, Vixen, and (best of all!) TeleVue for roughly $30 at the low end to the very nice TeleVue for $75 at the high end. Orion makes a 16mm in their Edge On series with a wider field of view that looks interesting at $105 list. Great deals can often be found in the used markets. Combine one of these with a 2x Barlow and you have a lot of capability. Hope this helps...Clear Skies, Brian
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  11. #8
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    Default

    AAAHHH I made a mistake! in my first post I wrote exit pupil instead of eye relif... plossl eps have short eye relif not short exit pupil... sorry!

  12. #9
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    Default

    Thanks everyone for the help.

    I decided to get a 9mm and a 15mm both Plossl. I hope to get good images from them and hopefully the Barlow eyepiece that came with the telescope is good enough to provide good higher magnification images.

    Nick

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  13. #10
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    Default

    Hey, Nick. Welcome to the forum. If your barlow is metal, it is probably pretty good. I have a $30 Seben barlow and a $60 Meade, and there is no difference, (at least to my 64yo Mark I eyeball.) I once compared the Seben to a plastic one, and, yeah, there was a barely discernable loss in clarity and contrast.

    I haven't experienced any of the the high-end, 3 element barlows, but I would expect any improvement to be in the single digits, percentage-wise. Probably less than my eye could detect.

    Your scope F/L is middle-of-the-road, and reasonably cheap plossls EPs should perform well.

    I recently purchased a 40mm plossl from these folks in Hong Kong, and I am very pleased with it's performance in my 127mm Orion Mak and my 8" Celestron G-8N. Their prices are reasonable, and shipping is free on some items.

    They auction some items, but I suspect that they bid them up at the end of the auction to close to the buy now price. I think this practise is common among eBay retailers.

    Anything below 8mm-10mm, and you are going to start losing clarity anyway, as pointed out above, unless you have exceptional seeing.

    If I were you, I would consider a zoom. I have a Celestron 8-24, and it is my most used EP. I did a head-to-head comparison with the zoom barlowed at 24mm and a 12mm plossl, and the only difference was a slight loss of contrast......very slight.

    You should think about augmenting your EP collection towards the lower magnification end; longer F/L EPs. Once you have seen Saturn, Jupiter and Luna, there is a great "wow factor" in wide starfields and open clusters. You don't have quite enough aperture to hunt down the more distant galaxies and faint nebulae. You need 8" (200mm) and up for that.

    This eBay retailer also has pretty good stuff, but doesn't ship free. Keep an eye on shipping costs when buying on eBay.
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