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Re: Long focal length eyepieces at f/15 MCTs

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  • Mark Rieck
    I avoided the specifics of my 715 since the focus of the discussion was the eyepieces themselves, and namely the Paragon. Mine is built with a 29% CO, thereby
    Message 1 of 2 , Jul 10, 2008
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      I avoided the specifics of my 715 since the focus of the discussion
      was the eyepieces themselves, and namely the Paragon. Mine is built
      with a 29% CO, thereby providing a larger illuminated field size.


      --- In tmboptical@yahoogroups.com, "Guilherme de Almeida"
      <guilhermedealmeida@...> wrote:
      > Hi, Mark Riek
      > Good report about that eyepieces.
      > However, testing some 40 mm >65 degrees apparent field eyepieces,
      in a Intes-Micro M715 telescope, I reported the illumination drops to
      zero before the true edge of field of that eyepieces. That is, you
      will have zero light at more than 5degrees from the true edge. I
      tested the Aleph Lab 40 mm 70 degrees, the SWAN 40 mm 72 degres. I
      found the field stop of these eyepeieces is far greater than the
      illumination of the focal plane. There is not the case of only 60%
      illumination at edge, or so, of field. No, ist is trully ZERO. Also
      it is NOT a defect of these wonderful telescopes.
      > I have found we have only two sollutions about the M715 telescope
      with long focal lenght eyepieces:
      > a) For a 70º eyepiece, the maximum focal lenght is about 32 mm or
      33 mm.
      > b) For a 40 mm eyepiece focal lenght, the apparent field cannot
      be greater than about 55º.
      > c) To have 54x magnification available with the M715 telescope (50
      mm focal lenght eyepiece), it is uselless to have a wide angle
      eyepiece, because you will not see nothing at edge of field (or close
      to the edge of field). We will not benefit from the greater field.
      > For 50 mm focal lenght I choosed the Vixen LV 50, with only 45
      degrees apparent field. The field stop is about 39 mm diameter. It
      may seem a bad choice, or a peep hole eyepiece, but it is the only
      way to have a low magnification of 54x, for special low magnification
      views, wh the turbulence is a little greater..The focal reducers get
      worser results.
      > Did you also see this ???
      > Very best regards, my friend
      > Guilherme de Almeida
      > ----- Original Message -----
      > From: Mark Rieck
      > To: tmboptical@yahoogroups.com
      > Sent: Wednesday, July 09, 2008 6:44 PM
      > Subject: [tmboptical] Re: Paragons vs. the Empire
      > I just finished picking one up not long ago, along with a UO 40mm
      > to compare them against each other. My goal was to choose my
      > for use in f/15 Maksutovs. As would be expected, both exhibit
      > relatively poor edge of field correction in faster scopes such as
      > f/4.5 Newtonian I used them with. What surprised me is both
      > relatively poor edge of field correction in an f/6 MakNewt as well,
      > which provides great edge of field correction in itself, so the
      > was most definitely the eyepieces.
      > The same rang true with focal ratios when using refractors. Where
      > did perform admirably was in the scope they were obtained for use
      > an f/15 MakCass. Image quality was quite similar between the two
      > regarding contrast, clarity, and light throughput. I found I
      > the Paragon due primarily to it being one of the lightest 40mm
      > widefields made and an edge in comfort(since the UO I have does not
      > have an eyecup).
      > I have compared many of the less expensive widefields in the 30-
      > focal length range, and found none have the edge of field
      > the Naglers do at faster focal ratios. I must note I have not tried
      > side by side comparison with the 41 Panoptic. Other possible
      > in the 40mm range being comparable in price, weight, and
      > also include the Pentax(XL and XW) and Celestron Axiom. Every one
      > perhaps 4-5 budget priced widefields have fared even worse. YMMV
      > tolerance for edge of field correction varies.
      > Mark
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      > [Non-text portions of this message have been removed]
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