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Mark EON 80 - Twilight 2 | C11 - iEQ45 | Astro Physics 175EDF - 900GTO
Quote:I wonder if anybody has ever compared an inexpensive 1.25" prism diagonal with a premium unit. Hope Bill conducts more experiments , so that we get more info on it George
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David-------David Lukehurst UP 20" f/4, Orion Optics ODK12, CFF 180, Borg 125SD, Wiliam Optics FLT98, Borg 71FL, TS 50EDLunt LS60THa + LS60FHa
“I am the only person to ever ace a 1951 USAF resolution test. My 'to observe' list says 'done'. I do not use charts or atlases when I starhop; men do not use maps. One of my sketches won an SBIG deep sky imaging contest. I am the life of star parties I have never attended. I never say anything looks like a faint fuzzy - not even a faint fuzzy. Pilots aim green laser pointers at me. Don Pensack proofreads my CN forum posts.” - The Most Interesting Astronomer in the Universe
Quote:Bill, in some older CN threads it was mentioned that Prism diagonals are not suitable for shorter focal length telescopes (f10 and faster) due to refraction effects when light enters at an angle creating chromatic aberration. I noticed that you used a f8 refractor and it did not seem to be an issue. Might it be more of an issue with 2 inch diagonals and lower magnification? I would appreciate your insight.Thank you, Ulrich
Quote:I do not have experience with either diagonal. Could the observed difference be just the higher optical quality of the Tak diagonal compared to the Astrotech diagonal. Would you still see an improvement if it was compared to an AP, TV or Baader dielectric diagonal? I would assume that a Zeiss prism diagonal should be of similarly high quality as a Tak Diagonal and would also show a similar improvement as a Tak.
Quote: +1 on Chuck's reply, David. Amici prisms (90 degree) and Schmidt prisms (45 degree) both have a "roof" with an edge in the center of the field. This roof portion of the prism reverses right and left to give a fully corrected image. Diffraction of light hitting the "roofline" creates a horizontal spike visible both directions from every bright object. Better quality correct image prisms have a finer edge and so a fainter spike, but all have it. Regular right angle prism astronomical diagonals show an erect image but it is reversed right and left - no roof in these, hence there should be no spike. - Bill
C10NGT, Z8, 150 Rumak, XLT 150, C6, C5, SW5 Newt, 4.5 Ball, C102GT, C90, ST80, A70LF; 15x70, 25x100; Burgess BV; Paracorr II; T6 2.5, XO 2.58/5.1, Ethos-SX 3.7, Delos 4.5, TV Plossl 7.4-26, BCO 10, Hutech HC 12.5, Sterling 12.5-25, ES100 14, CZJ H 16/25, CZJ O 16, M5k UWA 24, T5 31, Ultrascopic 35, Titan-II 40; Bino Pairs M5k UWA 6.7, Baader Zoom 8-24, M5k SWA 24, TV Plossl 26, RKE 28.7; Zooms NZ 2-4, NZ 3-6, Leica ASPH 8.9-17.8, Baader 8-24; Baader Zoom Barlow, VIP Barlow
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"Dancing all around it, we have been, which gives me pause, and license, to speculate with mind experiments, to illuminate this stuff, this Dark Energy" Mindjog 2011
Quote:Just wondering how many CNers have been Googling "1.25 prism diagonal reviews" since Bill started this subject. I know I have. George
Blog: Astronomy & Living by Hernando
Quote:Bill, in some older CN threads it was mentioned that Prism diagonals are not suitable for shorter focal length telescopes (f10 and faster) due to refraction effects when light enters at an angle creating chromatic aberration. I noticed that you used a f8 refractor and it did not seem to be an issue. Might it be more of an issue with 2 inch diagonals and lower magnification? I would appreciate your insight.
Thank you, Ulrich
Quote:If I upgrade to a better prism diagonal I will use it mostly in my f/10+ SCT's and Maks for moderate to high magnification. IMO, it would make more sense to get a 1.25" diagonal.
Which is the best 1.25" prism diagonal? Which ones are almost as good?