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TeleVue flattener with Megrez

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  • danieldgj
    I ve just had my first night photographing with the TeleVue TRF-2008 field flattener attached to the Megrez 80 (I was too impatient to wait for the flattener
    Message 1 of 1 , Mar 11, 2003
      I've just had my first night photographing with the TeleVue TRF-2008
      field flattener attached to the Megrez 80 (I was too impatient to
      wait for the flattener William Optics says they'll make). The
      TeleVue flattener, like the proposed WO flattener, also is a 0.8x
      photo reducer.
      Despite the different manufacturers, it seems to be a useful
      combination. Using the Megrez without the flattener, only about the
      central 50% of a 35mm film frame has usable, pinpoint stars. Outside
      that, they're oval. Still, you can cover a lot of sky with that much
      film, and the Orion Nebula shot in my folder did not use a flattener.
      With the flattener, the usable part of the frame is expanded to
      about 85% (dim stars look pinpoint to the very edge of the frame,
      though brighter ones are a bit elongated at the corners, and
      vignetting would make faint nebulae invisible in the outermost
      corners--hence not 100% of the frame is usable if bright stars or
      faint nebulae are there). The drawback is vignetting. Without the
      flattener (as well as with it), there's practically no vignetting in
      that central 50% of the film. You'll have to do some digital
      processing to even out the vignetting if you want the full 85% (or
      100% if all you want to show in the corners is dim stars). The
      Megrez also needs a violet-reduction filter if there are any halfway-
      bright stars present (I sometimes use the IDAS light-pollution filter
      instead, but I have limited experience with it yet).
      One benefit and one drawback--for it is both--is the 0.8x
      reduction. For very extended sky areas, you'll get more on the
      film. However, for objects at the lower end of the Megrez's
      photographic size range (such as the Horsehead), 0.8x reduction means
      that the small objects now cover only 64% as many pixels. So you
      gain more sky area (significantly) and also photographic speed, but
      lose detail in some small objects because they're on a smaller-than-
      ever part of the film. Then again, for the small objects you can
      just remove the flattener.
      A photographic example with the field flattener is my "Orion's
      Belt" photo in the group's photo section. The compression used by
      Yahoo! robs the Horsehead of some detail in the web version.
      --Daniel Johnson
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