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Thread: Eye pieces for a dobsonian

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    Default Eye pieces for a dobsonian



    The more you learn, the more you realize your ignorance. I paid a lot of attention to telescope choice, but until recently I thought eye piece choice was purely a matter of incremental quality (along with price) for one's magnification and FOV needs. I now understand that it's a matter of matching the design to the type of scope. Thanks again to Alex (mental4astro) for a neat short course in this in another one of my threads.
    I bought the Celestron Luminos in 19 mm based on good reviews, and the picture is awesome, except that the periphery of the field gets pretty badly distorted in a reflector. I thought that was unavoidable, but apparently it's just that it's poorly matched to reflector designs. Having recently bought a dob (it's actually on the way! The Skyline 8" from Orion, newly back among their offerings), I'm revisiting my eye piece options. I can probably return the other Luminos I have just bought, again, because I really like the image in the 19, except for the periphery distortion, which I thought was part of the game.

    So, staying with the same reasonable price range, what are some good options? I know the Tele Vue at 500 a pop would solve my problem, but they are not an option financially. I have heard that the Meade Series 5000 are better in this regard (they are the same price more or less as the Luminos series). Are those a good upgrade? Or do I need to save up and go to the ES 82║ series, for which the consensus seems to be that they are the way to go among the reasonably priced pieces?
    Alternatively, is the slightly longer focal ratio (f/6 compared to f/5 in my previous reflector) likely to improve things enough that I don't need to rush?
    Thanks!
    Last edited by rocdoc; 02-14-2018 at 01:39 PM.
    Properly collimated cornea-lens-vitreous optical apparatus, projecting on retinal sensor slightly limited by deuteranomaly, feeding through stock optic nerves into functional primary cortex, processed through frequently misfiring and buggy integrative cortex.
    Other instruments: Skyline 8" Dobsonian; Celestron Omni XLT 120 w upgraded focuser and diagonal on Stellarvue M2C mount; Oberwerk 25x100 IF; Celestron SkyMaster 8x56. Main EPs: ES 82║ 24mm and 11mm, Celestron Luminos 19mm, Meade UWA 14mm, Meade HD-60 6.5mm. Filters: UHC, 13%, blue. Finders: RACI, Telrad, RDF, reticle.

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    Default Re: Eye pieces for a dobsonian

    Thanks for the post, look forward to answers you get.
    Mostly wanted to subscribe to the thread. I know that can be accomplished through thread tools without posting but that wouldn't
    sate my own buggy integrative cortex
    Great sig line rocdoc
    rocdoc likes this.
    Moving on.......

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    Default Re: Eye pieces for a dobsonian

    1) Televue is not $500 a pop unless you're talking the 41mm Panoptic which you don't want. TV can be more or less.

    2) Price depends on what AFOV you can tolerate with wider AFOV costing more.

    At f6 you get better performance than f5, but you still need very well corrected eyepieces. I don't think that I'd consider any of the Meade Series 5000 except the HD-60s which I know are good at f5. The others are not keepers at all. I use mine with an 0.5x reducer in my VMC100L at effective f5 and its sharp to the edge. A Newt would have different field curvature though.

    If I were designing a basic eyepiece set, and putting aside my dislike of the 80 degree AFOV for the moment I would start with Televue and if necessary compromise on price with ES.

    You're at f6 (so unless you are very young and have 7mm pupils) the maximum exit pupil is in the 5-6mm range so that puts the maximum focal length at 30-36mm.

    100 degree AFOV? I wouldn't bother. Too gimmicky, you see the eyepiece not the sky. Ditto on 90 degree AFOV.

    80 degree AFOV?
    For a finder eyepieceTV 31mm Nagler type 5 is $666, perhaps the ES clone at 30mm is a good economy measure at $256.

    For a wide field eyepiece you want a ~3-4mm exit pupil ~18-24mm focal length. My favorite Nagler is the 17mm type 4 at $398. Again the ES clone at 18mm and $214 might be a decent compromise.

    For maximum contrast and resolving power you need a 2mm exit pupil so 12mm. I would be extremely reluctant to compromise on price here. Either the 11 or 13mm type 6 Nagler would be fine at ~$320. ES has an 11mm at $160 but specs on the TV are tighter and the somewhat better performance can teach me to observe better so unless the chancellor of the exchequer were pointing a loaded gun at my head....

    For high magnification 1mm exit pupil. 6mm fl. TV 5 or 7mm type 6 Nagler at $320 or the ES 6.7mm at $160.

    For max magnification 0.5mm exit pupil, a 2x Barlow or TV type 6 2.5 or 3.5mm or, well, ES doesn't have an offering close enough.

    At 70 degree AFOV things are less pricey and optical quality (orthoscopy, freedom from pincushion distortions) is better. Following the same logic w.r.t exit pupils...

    TV Panoptics 35mm ($390), 24mm ($321), Delos 12mm ($352), Delos 6mm ($352), Delos 3.5mm ($352). But the Panoptics barlow really well so one do without the shorter two Delos if you've got decent barlows. Anyway I have Orthoscopics and Pseudo Masuyamas for short fls.

    ES has 34mm ($208), 24mm($140), 16mm($140) not quite right fit but necessary to Barlow shorter fls.

    60 degree AFOV? I think you get the idea.
    Last edited by not_Fritz_Argelander; 02-14-2018 at 03:36 PM.

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    Default Re: Eye pieces for a dobsonian

    PS

    ES has some packages that resemble remarkably well the recommendations above. I guess they've heard of exit pupils.

    BTW in designing a set of eyepieces for a scope exit pupil rules not magnification or AFOV. Exit pupil determines how the scope will interface with the eye and how the eyepiece will function. The sticky threads have various bits of good advice and I think Gabby had an exit pupil article a while back? Exit pupil is an essential concept that a mature observer must come to grips with at some point.

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    Default Re: Eye pieces for a dobsonian

    Thanks, that is a wealth of good information.
    It seems that for a true upgrade I would need to spend more than I was planning at the moment. I may just go ahead with the current setup for a bit and see where it takes me for now, and then decide on further moves once the scope comes. But I'll check the ES packages you mention.
    Properly collimated cornea-lens-vitreous optical apparatus, projecting on retinal sensor slightly limited by deuteranomaly, feeding through stock optic nerves into functional primary cortex, processed through frequently misfiring and buggy integrative cortex.
    Other instruments: Skyline 8" Dobsonian; Celestron Omni XLT 120 w upgraded focuser and diagonal on Stellarvue M2C mount; Oberwerk 25x100 IF; Celestron SkyMaster 8x56. Main EPs: ES 82║ 24mm and 11mm, Celestron Luminos 19mm, Meade UWA 14mm, Meade HD-60 6.5mm. Filters: UHC, 13%, blue. Finders: RACI, Telrad, RDF, reticle.

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    Default Re: Eye pieces for a dobsonian

    Quote Originally Posted by rocdoc View Post
    Thanks, that is a wealth of good information.
    It seems that for a true upgrade I would need to spend more than I was planning at the moment. I may just go ahead with the current setup for a bit and see where it takes me for now, and then decide on further moves once the scope comes. But I'll check the ES packages you mention.
    The 82 degree package is here:
    https://www.highpointscientific.com/...ase-epwp82-kit

    The 68 degree package is here:
    https://www.highpointscientific.com/...ase-epwp68-kit

    I implore you to not go cheaper than the ES. It's more expensive in the long run. A good set of eyepieces is forever. Scopes come and go.
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    Default Re: Eye pieces for a dobsonian

    I would wait until the 8" Dob arrived because its eyepieces may not be bad at all. I splurged once on a 24 mm ES eyepiece (well it was a rare old model and only $180) but frankly I can't see much improvement over the 30 mm GSO that came with my Z12. Frankly, I would have put my money in a 10" or 12" Dob not in an expensive eyepiece for a consumer 8" - maybe for prime optics it would be different.
    ... Henk. Telescopes: 6" Mak-Newt (Comet Hunter), ES ED127CF, ES ED80, Zhumell Z12, Coulter Odyssey 10, AT6RC, Venture RX-7, Celestron Skymaster 20x80, Mounts and tripod: Losmandy G11S, AVX, LXD55, Tiltall, Cameras: Fuji X-a1, Canon SX40, Xt, XSi, T6, ELPH 100HS, DIY: Dob and camera barndoor trackers, afocal adapter, Dob with foldable base and Az/Alt setting circles, Accessories: SSAG, Plossls, Barlows, Telrad, laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: DSS, ImageMagick, PHD, Nebulosity, Photo Gallery, Gimp, CHDK

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    Default Re: Eye pieces for a dobsonian

    Quote Originally Posted by CamelHat View Post
    I would wait until the 8" Dob arrived because its eyepieces may not be bad at all.
    Could well be the case.

    I splurged once on a 24 mm ES eyepiece (well it was a rare old model and only $180) but frankly I can't see much improvement over the 30 mm GSO that came with my Z12. Frankly, I would have put my money in a 10" or 12" Dob not in an expensive eyepiece for a consumer 8" - maybe for prime optics it would be different.
    The expense of the telescope bears no relationship to the expense of the eyepieces though. A FAST telescope even in commercial grade OTAs demands highly corrected pricey eyepieces. Premium OTAs at f8 can get by with very inexpensive eyepieces.

    rocdoc's new toy is f6 so the supplied eyepieces (a 30mm "Erfle" and a 9mm Plossl) might be fine. Plossls should be good down to f4. The "Erfle" if it is an Erfle is good to f4.

    Best just check it out with and look to upgrade if the outer fields are fuzzy.

    I use a Pracorr Panoptic and Delos on my AT 8" f4 and that gets the most out of this fast scope.
    Last edited by not_Fritz_Argelander; 02-14-2018 at 04:44 PM.

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    Default Re: Eye pieces for a dobsonian

    I would look at some ES 82 degree eyepieces. The 18mm is my most used piece of glass.
    Michael
    Obsession 18" f/4.2, Zhumell Z10 f/4.9, ES AR 152 refractor f/6.5, Celestron Skymaster 15x70's , Bushnell 10x50's
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    Default Re: Eye pieces for a dobsonian

    Quote Originally Posted by rocdoc View Post
    Thanks, that is a wealth of good information.
    It seems that for a true upgrade I would need to spend more than I was planning at the moment. I may just go ahead with the current setup for a bit and see where it takes me for now, and then decide on further moves once the scope comes. But I'll check the ES packages you mention.
    Yes, a good plan. Use the ones that come with and wait and save to get the upgrades as your eye tells you. If you find something irritating fix it. With the 30mm "Erfle" (which I suspect is a GSO SV and therefore a Konig ) and a 9mm Plossl I'd suggest using those and filling in at the wide field (18mm) or max resolution (12mm) first then branching out. Folks who are primarily DSO observers would favor the 18mm. But an 8" f6 should be a very capable planetary scope so 12mm might be just the ticket if you do lunar/planetary. I use the 2mm exit pupil every time, every object.

    I hear a rumor that Mars is going to be in opposition sometime soon....
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