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Thread: Meade 5 element eyepiece, claims its a plossl.

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    Default Meade 5 element eyepiece, claims its a plossl.



    This isn't a very major post just something I'm curious of.

    I have these two 60 degree Meade eyepieces, older eyepieces. A 40mm and a somewhat harder to find 26mm version. I love these things.

    However out of curiosity, why did Meade claim they are plossl designs? If they have FIVE elements why were they engraved as plossl and marketed as such? Wouldn't they be classified as erfle?

    I'm thinking this was a marketing idea or maybe I am not understanding something.. Let me know!

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    Default Re: Meade 5 element eyepiece, claims its a plossl.

    The 5th lens is usually added to increase eye relief and widen the AFOV a bit.
    Most are of a symmetrical plossl design though with the extra lens positioned between the two doublets.
    Some manufacturers use the term Super Plossl to signify a "new and improved" plossl though it is just a regular 4 element.
    The 5 element design is usually an offshoot of the Zeiss Astroplanokular design.
    Refractors: Antares 105 f/15, Celestron 150 f/8, Stellarvue NHNG 80 f/6.9, TAL 100RS f/10, TS 102 f/11, UR 70 f/10, Vixen SD115s f/7.7
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    Default Re: Meade 5 element eyepiece, claims its a plossl.

    These are an older 5-element (modified) plossl design that was made for Meade by JOC. They didn't do very well in the market place and were discontinued. It seemed to be an attempt on their part to stretch the AFOV of the typical plossl design from about 50° to 60°. However, it didn't work out very well for them. In slower scopes, say approaching f/8 or more, they would do ok. But in faster optical designs they got soft towards the edges. Had they just stayed at around 50° AFOV, I am sure they would have been fine. The newer Meade HD60 series is much better corrected at the edge of the field.

    The original idea of a plossl was indeed four elements, but that has somewhat evolved over the years, with some designers trying to stretch the limits of the design by slapping in an extra element. But in reality, a standard plossl will provide a cleaner view across the field when it sticks with the original idea of about a 50° AFOV. The biggest problem for them is that in the shorter focal lengths they get really, really stingy with eye relief.
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    Default Re: Meade 5 element eyepiece, claims its a plossl.

    Quote Originally Posted by Gabby76 View Post
    The 5th lens is usually added to increase eye relief and widen the AFOV a bit.
    Most are of a symmetrical plossl design though with the extra lens positioned between the two doublets.
    Some manufacturers use the term Super Plossl to signify a "new and improved" plossl though it is just a regular 4 element.
    The 5 element design is usually an offshoot of the Zeiss Astroplanokular design.
    Gabby, isn't the idea of a "super" plossl basically an Erfle design?
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    Default Re: Meade 5 element eyepiece, claims its a plossl.

    The lens curves follow closer to the Astroplanokular than the Erfle design though many do consider them as modified Erfles.
    Refractors: Antares 105 f/15, Celestron 150 f/8, Stellarvue NHNG 80 f/6.9, TAL 100RS f/10, TS 102 f/11, UR 70 f/10, Vixen SD115s f/7.7
    Mounts: Celestron SLT w/ pier mod & EQ-3 tripod, Celestron hypertuned CG-5 w/ tracking motor & Argo Navis, Manfrotto 028B w/ Stellarvue M2C, Manfrotto 055PRO w/ 128RC, TAL-1 HD EQ, Vixen SXP w/ HAL-130 SXG & half pier
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    Ya gotta keep this Apo/
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    Default Re: Meade 5 element eyepiece, claims its a plossl.

    Quote Originally Posted by Gabby76 View Post
    The lens curves follow closer to the Astroplanokular than the Erfle design though many do consider them as modified Erfles.
    That makes more sense. Now that you mention it, I do recall seeing the term "modified" Erfle. Regarding plossls, I still don't get, with the prevalence of 2 inch focusers, why the manufacturers don't make their 40mm plossls with a 2 inch barrel so you can take full advantage of the AFOV instead of being restricted to about 43°. I guess some old habits just don't change.

    Apologies to Mooninite, didn't mean to side-track your thread.
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    Default Re: Meade 5 element eyepiece, claims its a plossl.

    I'll bet Mooninite didn't care. I imagine he learned as much as I did just listening to you and Gabby.
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    Default Re: Meade 5 element eyepiece, claims its a plossl.

    Quote Originally Posted by Lowjiber View Post
    I'll bet Mooninite didn't care. I imagine he learned as much as I did just listening to you and Gabby.
    Thanks John. Sometimes I don't know if what I am saying makes sense or is even right - or just the senile ramblings of an old coot!
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    Default Re: Meade 5 element eyepiece, claims its a plossl.

    I was going to add more info on going above 1 radian with the Plossl design but I am still learning that point of needed information and the audience is now asleep!
    Refractors: Antares 105 f/15, Celestron 150 f/8, Stellarvue NHNG 80 f/6.9, TAL 100RS f/10, TS 102 f/11, UR 70 f/10, Vixen SD115s f/7.7
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    Default Re: Meade 5 element eyepiece, claims its a plossl.

    Hello all,

    according to the AFOV of 50°, the "Super Plössls" is 'numerically' close to the Zeiss Astroplan (1955), orthoscopically corrected for long EP focus lengths, where the classic orthos would have eye relief behind the observer's ear, ha, ha.
    The still popular astronomy Erfles are the Zeiss Erfle (65°) and the Rodenstock Erfle (70°), priced as discontinued items for about 350 EUR.

    The 2-1-2 lenses design is not enough to conclude what the Super Plössl really is,
    the typical glass materials prescription for the Erfles used to be SF2, PSK3, FK5, SF10, so even if looking symmetric, there is no materials symmetry inside.

    Hoping this helps,

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