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Thread: Prism diagonal comparison

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    Default Prism diagonal comparison



    Last time I did a thread on diagonals it was about how the cheapo Celestron 1.25" prism diagonal beat my $100+ mirror diagonal on the planets with a 4" achro and a 4" apo. Just got a Baader T-2 with a Zeiss prism. But is it worth $272 with no screw on ends? The other prisms are the Baader T-2 that costs around $170 with ends and the good old Celestron for around $35.

    The planets are the best for testing optics because of all the fine details. Only have Saturn and Mars now. Scope used: William Optics 5" f/7 fpl53 triple. Eyepiece used" Televue 3mm Delite for 273x power.

    Saturn was too low even just after sunset and could only use a 6mm Delos for 150x. Could not see any differences between the 3 prisms.

    Moved over to Mars. Right off could see that the Zeiss prism was the best. The small ice cap was sharply defined. The centered dark area of Syrtis Major had more contrast against the surrounding lighter areas.

    The big surprise was the cheapo Baader and the Celestron were nearly equal. At times the Celestron looked better. However these 2 could not define the central dark areas like the Zeiss could. This Zeiss T-2 prism is one of the last made in Germany, it is not the BBHS prism. Almost all manufacturing has been moved to China and there have been grumblings about lesser quality now.

    The larger 2" prisms do not work so well with f/7 and shorter apo's. With the current 2" APM prism could see residual colors around Mars. None visible with T-2 prisms because of the smaller prism and shorter light path.

    The Celestron 1.25" prism diagonal is the real winner. Not because it has the better optics but because everybody dismisses it as junk, it only costs around $35 new. Maybe it is great because they have been making it so long it is now perfected.
    AbbN, Doug James, DeanD and 2 others like this.
    Newtman but some refractors allowed.

  2. The Following 6 Users Say Thank You to tomjones For This Useful Post:

    AbbN (11-04-2018),Bigzmey (11-02-2018),burris (11-02-2018),Gabby76 (11-02-2018),John Baars (11-02-2018),SpyderwerX (11-02-2018)

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    Default Re: Prism diagonal comparison

    Thanks for your report.
    As you experienced before some refractors have a better marriage with a prism. Manufacturers constructed them that way. Other refractors blossom with mirror- diagonals. Those too are constructed that way.

    So it seems to me that your conclusion is maybe bit too drastic. The conclusion I would draw is that your 5 inch refractor works best with the Zeiss prism, secondly the Celestron and thirdly the Baader T-2. It is like finding out which diagonal X ( prisms or mirrors) works best with telescope Y, like 4Mentalastro already stated in your previous thread about this issue.

    I am quite curious how the "looser mirror diagonal" from you previous report acts in this refractor?
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    Default Re: Prism diagonal comparison

    Quote Originally Posted by John Baars View Post
    Thanks for your report.
    As you experienced before some refractors have a better marriage with a prism. Manufacturers constructed them that way. Other refractors blossom with mirror- diagonals. Those too are constructed that way.

    So it seems to me that your conclusion is maybe bit too drastic. The conclusion I would draw is that your 5 inch refractor works best with the Zeiss prism, secondly the Celestron and thirdly the Baader T-2. It is like finding out which diagonal X ( prisms or mirrors) works best with telescope Y, like 4Mentalastro already stated in your previous thread about this issue.
    ...
    Hello John,

    I agree with you!
    It depends also on the material of the prism (BK7, or anything else?),
    and on the planarity, like up to λ/10, or better than λ/12, or even λ/20.

    There is one top 2" prism manufactured by Wild Heerbrugg (Switzerland) and matched to the ultrawide Wild eyepieces, on the way to my hands.
    Attached is the Wild ultrawide, I already have.

    Thank you for your input,

    JG
    Attached Images Attached Images
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    Default Re: Prism diagonal comparison

    Before I got the Baader Zeiss the regular Baader prism was my best planetary diagonal. Other diagonal bested by the cheapo Baader
    w.o. enhanced 2 inch
    W.o. dielectric 1.25
    Televue enhanced 1.25
    Televue regular aluminum very old 1.25.
    Prisms seem to work best for all achromats and apo f6.5 and longer.
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    Newtman but some refractors allowed.

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    Default Re: Prism diagonal comparison

    Nice comparison. Thanks for reporting. Coincidentally, I needed to shorten the light path in my 80ED scope, which reignited my interest in prisms. In the past I also was pleasantly surprised with performance of the Celestron prism so I decided to pick it for now over non-Zeiss version of T2.

    This also brings me to the next question. When you have a chance could you check how different is focuser travel between Celestron, Baader T2 and Baader T2 with Zeiss?
    Scopes: Celestron: 8" SCT F10, Omni 150R Achro F5, Onyx 80ED F6.3, Mak 127mm F12; ES: 127mm CF F7.5 APO; Meade: ST80 F5. Mounts: ES Twilight I, Bresser EXOS2, SW SkyTee2, AzGTi, UA MicroStar. Binos: Orion 15x70, 10x50, Nikon 8x40. EPs: Pentax: XWs; TeleVue: Delites, Plossls & barlows; ES: 68s; Vixen: SLVs; Baader: BCOs, Aspherics, Mark IV; Meade: UWAs & Plossls. Diagonals: Baader: BBHS mirror, Zeiss Spec prism, Clicklock; TeleVue: Evebrite. Filters: Lumicon, Baader, Astronomik. DSO tally: 1333 (Completed: M110, H1, H2. In progress: H3: 115, H2,500: 962, S110: 73). Doubles: 772, Comets: 11, Asteroids: 59

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    Default Re: Prism diagonal comparison

    While searching for the best prisms for planetary targets came across this mirror type with best specs ever seen:
    2" dielectric, fused quartz, 1/12 wave, comp brass ring, SCT size threads on screw on ends for maximum inside diameter to fully illuminate 2" eyepieces, made in Taiwan, part number ends in 2Q. Bought one but it did not match cheapo Baader on planets. Hi-Point Scientific has them in USA.

    https://www.teleskop-express.de/shop...12-lambda.html
    Gabby76 likes this.
    Newtman but some refractors allowed.

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    Default Re: Prism diagonal comparison

    The Celestron eats up less of your back focus than the others. On the T2 diagonals I used screw on ends direct from China off eBay. Much less than Baader screw ons. Both ends for around 30 dollars shipped but they are longer than the Baader stuff.
    Bigzmey likes this.
    Newtman but some refractors allowed.

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    Default Re: Prism diagonal comparison

    These are amazing: Diagonals
    A bit expensive so I will stick with my Baader and Astro Physics Maxbright in the meantime.
    DeanD, SpyderwerX and Bigzmey like this.
    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: Prism diagonal comparison

    About 10 years ago Baader sold a 2" Zeiss prism in a Baader body which was approximately €700
    46mm clear aperture and designed for high power planetary work. Outstanding views!
    Unfortunately they must have been a bit to expensive as they only sold this version for a few years.
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    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 Diagonals: 2" Astro-Physics MaxBright, 2" Zeiss/ Baader prism, 2" Baader Herschel Wedge (Photo Version), 2"
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    Amici prism, 2" Stellarvue Dielectric, 2" TeleVue Everbrite Eyepieces: A-Z

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    Default Re: Prism diagonal comparison

    Quote Originally Posted by tomjones View Post
    While searching for the best prisms for planetary targets came across this mirror type with best specs ever seen:
    2" dielectric, fused quartz, 1/12 wave, comp brass ring, SCT size threads on screw on ends for maximum inside diameter to fully illuminate 2" eyepieces, made in Taiwan, part number ends in 2Q. Bought one but it did not match cheapo Baader on planets. Hi-Point Scientific has them in USA.

    https://www.teleskop-express.de/shop...12-lambda.html
    William Paolini compared two high-end diagonals with the Baader BBHS. Very nice reading.
    https://www.baader-planetarium.com/d..._w_paolini.pdf

    You may distrust specified surface details, for no manufacturer specifies whether the measurements were done before of after applying the multiple dielectric layers. Measuring before applying gives more positive results than doing so afterwards. Surface accuracy is far more important than 95% or 99% reflectivity. The first one can be seen, the second one not.




    Quote Originally Posted by Bigzmey View Post
    (...)
    This also brings me to the next question. When you have a chance could you check how different is focuser travel between Celestron, Baader T2 and Baader T2 with Zeiss?
    I found this. Page 5. Don't know if you have seen it before.
    https://www.baader-planetarium.com/d...sm_diagonal_co
    Telescopes in Schiedam : SW Evostar 120ED F/7.5, Vixen 102ED F/9, OMC140 maksutov F/14.3, SW 102MAK F/13 on Vixen GPDX.
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    Astronomical Rijswijk observatory telescopes: Astro-Physics Starfire 130 f/8 on NEQ6, C8 on NEQ6, Meade 14 inch SCT on EQ8, Lunt.
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