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Thread: Back to the zenit prisms on the refractors, and aberrations reduction

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    Default Back to the zenit prisms on the refractors, and aberrations reduction



    Hello all,

    back in the days, our John Baars has posted a report by Wolfgang Rohr about reducing the chromatic blur on a refractor by means of a zenit prism.
    In another discussion in Germany, I have retrieved the Rohr's measurements,
    astro-foren.com - A037A * Zeiss APQ # 96998 100/640 mit Glasweg verwenden
    on the Zeiss APQ 4" F=640mm refractor.
    This may explain, why Zeiss has used to deliver some of their refractors with the Zeiss zenit prisms.

    The reason for this retrieval is my not recalling exactly if this link refers to the same measurement, as the link John has posted before.

    Admitted, the 2" Wild Heerbrugg zenit prism cleans quite nicely the view through my 6" F/5 achro frac,
    allowing to magnify up to about 300x, without annoying color blur and contrast loss.

    Best,

    JG
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    Default Re: Back to the zenit prisms on the refractors, and aberrations reduction

    Thanks, JG, for this very useful post.
    I did not know that this phenomenon applies to the 150mm F/5 Achro too. Nice to know, since I have a 1.25" Baader prism with Zeiss specifications. So I will use the combi and a 30mm Eudiascopic, a 24mm Pan or my 25mm CZJ for the lowest magnifications and leave the zenit-mirror in the first instance at home. Gonna try the mirror too, of course.

    I think this is the topic (with several links) you referred to:
    Zenitprism or zenitmirror in Evostar?
    Telescopes in Schiedam : SW 150 F/5 Achromat, SW Evostar 120ED F/7.5, Vixen 102ED F/9, OMC140 maksutov F/14.3, SW 102MAK F/13 on Vixen GPDX.
    Binoculars: AusJena 10X50 Jenoptem, Swarovski Habicht 7X42, Celestron Skymaster 15X70, Swift Observation 20X80.
    Astronomical Rijswijk observatory telescopes: Astro-Physics Starfire 130 f/8 on NEQ6, 6 inch Newton on GP, C8 on NEQ6, Meade 14 inch SCT on EQ8, Lunt.
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    Default Re: Back to the zenit prisms on the refractors, and aberrations reduction

    Is any prism always going to perform better then a mirror diagonal?
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    Telescope: Mak; 127, Meade 8 LXD75, Fracs; ES127mmFcd100,ES80Essential, SW 100ED Evostar, Skychief 60mmF15. Mount: cg4, az/eq5, slt, lxd75, farpoint Para. EP: Doctor 12.5 UWA, Pentax 7-14XW, KK Ortho 4-25, Meade Plossl x3, TV 22Panoptic, Leitz 10X,12.5X, Leica 10X25 HC, Bits of other glass. Binoculars: 8x43 Pentax, 10X30 Swarovski, 25X100 Oberwerk.Cam;Nikon d90, Nikon d810.
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    Default Re: Back to the zenit prisms on the refractors, and aberrations reduction

    Quote Originally Posted by Don Quixote View Post
    Is any prism always going to perform better then a mirror diagonal?
    That is a "it depends" question, do a star test with the refractor and if you see a reddish color in the first ring you may benefit from a prism.
    If the ring is a neutral tone then you may do better with a mirror.
    Prisms tend to be very slightly under corrected so may cause aberrations if the telescope does not need one.

    Well manufactured prisms can be quite expensive as well.
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    Amici prism, 2" Stellarvue Dielectric, 2" TeleVue Everbrite
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    Default Re: Back to the zenit prisms on the refractors, and aberrations reduction

    JG,
    It seems to have been the HCQ115/1000 APO tested by Wolfgang Rohr, you were talking about?
    astro-foren.com - A091 HCQ APO Nr 4 - Mit Glasweg ein Super APO
    Telescopes in Schiedam : SW 150 F/5 Achromat, SW Evostar 120ED F/7.5, Vixen 102ED F/9, OMC140 maksutov F/14.3, SW 102MAK F/13 on Vixen GPDX.
    Binoculars: AusJena 10X50 Jenoptem, Swarovski Habicht 7X42, Celestron Skymaster 15X70, Swift Observation 20X80.
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    Default Re: Back to the zenit prisms on the refractors, and aberrations reduction

    Quote Originally Posted by John Baars View Post
    Thanks, JG, for this very useful post.
    I did not know that this phenomenon applies to the 150mm F/5 Achro too. Nice to know, since I have a 1.25" Baader prism with Zeiss specifications. So I will use the combi and a 30mm Eudiascopic, a 24mm Pan or my 25mm CZJ for the lowest magnifications and leave the zenit-mirror in the first instance at home. Gonna try the mirror too, of course.

    I think this is the topic (with several links) you referred to:
    Zenitprism or zenitmirror in Evostar?
    Hello John, hello all,

    yes, this is your thread, I am referring to.

    The other link you have provided refers to A091 HCQ APO Nr.4 and is about an APO which has been designed to be used with the prism and not without. The HCQ APO with the prism leaves with its extremely small C-e-F deviations in the range up to 10 micrometers the other APOs in a deep shadow.

    I can't give it you for granted that any glass prism will reduce (or sufficiently reduce) the spherochromatism, but it is certainly worth of trying.

    Please report your results with the Zeiss prism,

    JG
    Binoculars: Leica Ultravid 7x42, 8x42HD; Swarovski EL 8.5x42 Swarovision; Nikon 10x70 Astroluxe; Docter Nobilem 7x50 Porro; Jenoptem 7x50W, 10x50W; BA8: 10.5x70, 15x85; 25x100FB, AsahiPentax 8x40, Refractors: Sky-Watcher 150mm/750mm; Leica APO Televid 82mm (25x-50x WW ASPH); EPs:Baader Classic Orthos; Fujiyama ortho, Leica B WW, ultrawide zoom ASPH, Periplan GF, HC Plan S, L; DOCTER UWA; Wild UW mil; Tele Vue Delos, Nagler Zoom, Plössls; Swarovski SW; Pentax XW; ZEISS diascope B WW T*, Carl Zeiss E-Pl; Hensoldt mil; Filters: Astrodon, Astronomik, Baader (CCD), TS; Astrophotography: AstroTrac; Leica R7: Leica 2/50, 2/90mm, 2.8/180mm lenses
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    Default Re: Back to the zenit prisms on the refractors, and aberrations reduction

    Quote Originally Posted by Don Quixote View Post
    Is any prism always going to perform better then a mirror diagonal?
    Hello Mark,

    this is what we at the moment still do not know.

    It looks like the BK7 prisms mostly do the job both on the achromatic and APO refractors.
    As the secondary spectrum in the focus plane does not show the flip towards the sort of primary spectrum,
    my 2" prism does not seem to be oversized.

    (Rodenstock is using extra big prism about 85mm x 85mm to cancel the spherochromatism on the fast XR Helix,
    https://www.ebay.de/itm/Rodenstock-X...kAAOSw9wxbkM5S)

    I have so far tested the assembly through the Wild Heerbrugg)* 2" prism with the Leica and Zeiss spotting eyepieces,
    Pentax XW 3.5mm, and the Pentax XO 2.5mm
    And it is working to my full satisfaction.

    Wait on the results of John with his Zeiss prism, to get it confirmed.

    Best,

    JG

    PS: )* I am a particular fan of Swiss, and of anything which the Swiss call the Swissness
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    Default Re: Back to the zenit prisms on the refractors, and aberrations reduction

    Quote Originally Posted by j.gardavsky View Post
    (...)Please report your results with the Zeiss prism,
    JG
    Quote Originally Posted by j.gardavsky View Post
    (...)Wait on the results of John with his Zeiss prism, to get it confirmed.
    Best,
    JG
    Can't wait!
    Have to wait at least for a week or two, though.
    The first owner of my "new" 150mm SW Achro is still on holiday. But the purchase has already been concluded and paid for.
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    Default Re: Back to the zenit prisms on the refractors, and aberrations reduction

    Thank you for all of this.

    I have in the mail to me a mirror prism from Baader that I want to use on my my f6, f6.5, and my 7.5 refractors.
    I hope I have not made a mistake.
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    Telescope: Mak; 127, Meade 8 LXD75, Fracs; ES127mmFcd100,ES80Essential, SW 100ED Evostar, Skychief 60mmF15. Mount: cg4, az/eq5, slt, lxd75, farpoint Para. EP: Doctor 12.5 UWA, Pentax 7-14XW, KK Ortho 4-25, Meade Plossl x3, TV 22Panoptic, Leitz 10X,12.5X, Leica 10X25 HC, Bits of other glass. Binoculars: 8x43 Pentax, 10X30 Swarovski, 25X100 Oberwerk.Cam;Nikon d90, Nikon d810.
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    Default Re: Back to the zenit prisms on the refractors, and aberrations reduction

    Thank you Gabby. I have neutral color.

    This thread is of particular interest to me as I am presently reviewing my back end optics for possible improvement in my diagonal.
    Telescope: Mak; 127, Meade 8 LXD75, Fracs; ES127mmFcd100,ES80Essential, SW 100ED Evostar, Skychief 60mmF15. Mount: cg4, az/eq5, slt, lxd75, farpoint Para. EP: Doctor 12.5 UWA, Pentax 7-14XW, KK Ortho 4-25, Meade Plossl x3, TV 22Panoptic, Leitz 10X,12.5X, Leica 10X25 HC, Bits of other glass. Binoculars: 8x43 Pentax, 10X30 Swarovski, 25X100 Oberwerk.Cam;Nikon d90, Nikon d810.
    "The pendulum of the mind oscillates between sense and nonsense"
    "Gratuitus affermations of a dominant theory can mesmerize the unwary."

 

 
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