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  1. #1
    WWPierre's Avatar
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    Default Evaluating Eyepieces Scientifically



    Klattu posted in another thread some suggested criteria to use for a more scientific evaluation of eyepiece performance than "it gives nice crisp views, but there is coma at the edge". I think it would be a good start for an eventual stickie at the top of this forum.

    Below are his suggestions, edited from his post; The list seems pretty thorough, but someone else may have something to add.

    .........What criteria do you use to evaluate an ep's performance on your scope, on any scope?

    Scatter? (Light around bright objects)

    Contrast? (also a function of mag and sky)

    Flat fied? (also very much tied in with particular scope type, but some ep designs more prone to curvature)

    Eye relief? (surely comfort plays a part, but too much er has it's own problems)

    Exit pupil? (not the end all but deserves mention)

    AFOV? (do you prefer wide over narrow, where and why?)

    Lateral color? (does it bother you if there?)

    Availability (some great ep's are very difficult to get)

    Cost (bang for buck and all that)

    Ok that's a partial list... how about kidney beaning and pincushion and smooth side vs. cutout and eyeguard/eyecup... and....
    Meade 16" LightBridge; Celestron G-8N Bird-Jones/motorized EQ5; Orion 127 Mak/go-to EQ5; Burgess 127f8 refractor; Sky-Watcher 5" F/5 collapsible dob; 90mm Mak/motorized EQ2; Royal Astro 76/910-GEM; Meade 60x700 refractor/alt/az; Zhumell 25x100 Coin Ops; GalilleoScope. Celestron 8mm-24mm zoom; lots of fixed EPs,some good, some..not so much. A small collection of surveying instruments; a forest of tripods; Canon Rebel Xti. Confirmed gadget junkie; Custodian of the Magnetic North Pole (Send $1.00 to Pierre each time you use a compass.)
    49-41-37.03N 123-09-29.61W Calculated magnetic declination: 17° 39' East

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    Default

    Without a standardized series of metrics, and standardized assignment of values on the various dimensions listed so thoroughly above, these mostly can't be more than subjective as we discuss them here. Each prospective user will have to wing it, essentially, or take it anecdotally from those who have used them.

    Eyepieces are costly if you want superior ones with good quality coatings on all surfaces, wide FOV, and quality ground lenses stacked more than three or four deep in a properly blackened and stopped inner tube.

    Eyeglass wearers won't see the same view as those whose eyelashes can wipe the top layer of glass. How well will an eyepiece show contrasty and sharp views with non-spurious colours if they have been coated with eyelash oil?

    Of course, the primary optics hosting the eyepieces would ideally be standardized, but that is highly unlikely to be possible here in any meaningful way.

    All this to say that we don't have much hope of a scientific comparison here, but we could discuss the various factors mentioned in the list and how they affect the view...assuming the novice looking for a gee-whiz improvement would really notice the improvements or the defects from eyepiece to eyepiece.

    -Crandell

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    Quote Originally Posted by Inkie View Post
    we could discuss the various factors mentioned in the list and how they affect the view
    Crandell:
    This is what I would be looking for in this thread. Your points about conducting metric-based scientific reviews are well stated. But even if subjective, I think the readership gains insight with eyepiece review information. I for one greatly value this type of information as it is extremely impractical for me to head out to star parties.

    I don't have enough experience to be able to evaluate many of the criteria Klaatu lists, but I sure would like to learn more about them. For example, kidney beaning: I dont think I have ever seen this; maybe the EP's in my collection don't suffer from this (?) Pincushioning? Maybe I have seen it and didn't know. I do know blackout now thanks to the only Hyperion in my collection.

    Regarding the assertions of previous posters that an amateur with very limited viewing experience will not be able to detect differences between, for example, the plossls that came with their scope and a Nagler, my own experience directly contradicts this notion as detailed in this performance review I conducted with only 3 months of telescope viewing experience: 13mm Nagler Type 6 Eyepiece: A Comparative Review In the review, I come clean up front about the very limited context of the study, refer the reader to more in-depth reviews, and focus solely on criteria (fine details) for which I can speak authoritatively based upon my observations.
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    Perhaps I should have titled the thread, "Evaluating Eyepieces Somewhat Scientifically."
    Meade 16" LightBridge; Celestron G-8N Bird-Jones/motorized EQ5; Orion 127 Mak/go-to EQ5; Burgess 127f8 refractor; Sky-Watcher 5" F/5 collapsible dob; 90mm Mak/motorized EQ2; Royal Astro 76/910-GEM; Meade 60x700 refractor/alt/az; Zhumell 25x100 Coin Ops; GalilleoScope. Celestron 8mm-24mm zoom; lots of fixed EPs,some good, some..not so much. A small collection of surveying instruments; a forest of tripods; Canon Rebel Xti. Confirmed gadget junkie; Custodian of the Magnetic North Pole (Send $1.00 to Pierre each time you use a compass.)
    49-41-37.03N 123-09-29.61W Calculated magnetic declination: 17° 39' East

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    Here are a couple of resources related to quantitative evaluation of eyepieces... the first is an article from Astromart's review section. It does a reasonable job of outlining and demonstrating the use of a procedural, and hybrid quantitative/qualitative method for evaluating eyepieces:

    Astromart Reviews - 5mm Shootout Using a New Standardized Approach

    I think the outlined method is fairly well-balanced, and it could be extended readily, as well as partially reduced or otherwise simplified.

    The second comes from one of the Willman-Bell texts, "Telescope Optics: A Comprehensive Manual For Amateur Astronomers". I have this text, and highly recommend it in general. In particular, Chapter 15 covers eyepiece design from a quantitative perspective, and a reasonable process for quantitative evaluation could be extracted from the material therein:

    Telescope Optics, A Comprehensive Manual for Amateur Astronomers by Harrie Rutten and Martin Van Venrooij

    I've always thought an interesting, though time-consuming project would be to obtain eyepieces of various manufacture and design, bench test them and record the results, then disassemble and "reverse engineer" them in a virtual fashion in OSLO or a similar design support system, using the result to compare the theoretical design performance against the bench data.

    Were I an astronomy professor, this might make a good boondoggle project for some graduate students and a chunk of department budget... alas, I am but a poor rancher...
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