Fixed aperture telephoto lenses

Discussion in 'Photography Equipment & Products' started by Patrice, Mar 25, 2011.

  1. Patrice

    Patrice No longer a newbie, moving up!

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    Astronomic telescopes are easily mounted unto most dSLR's. They make pretty decent telephoto lenses since they are corrected for chromatic and spherical aberrations. A couple of the ones shown have low dispersion glass elements incorporated in the lens cell. They are connected to the camera with a $50 camera adaptor and a $25 t-ring. Some designs may also require an optical field flattener.

    These not only work as astronomic instruments but as terrestrial lenses as well, not as handy or compact as purpose made camera lenses but very useful none the less. The image quality is tied to the quality of the elements in the optical path.

    Of course they are manual focus and of fixed aperture.

    Below (mine) are a 1500 mm f10 catadioptric scope, a 1000 mm f5 reflector, a 900 mm f9 refractor with ED lens, and a 400 mm f5 refractor also with an ED lens.

    If you have a telescope, give it a try as a telephoto lens, you might be surprised at the result.

    [​IMG]


     
  2. c.cloudwalker

    c.cloudwalker TPF Noob!

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    Mirror lenses are fixed aperture telephoto lenses. There are some very cheap ones that are pretty nasty IQwise but the quality ones can be quite nice while not that expensive and much lighter than an equivalent in the non-fixed aperture world.

    I don't know what focal length mirror lenses go up to but the most common ones are the 500mm. I had a 250mm myself that was about the same size and weight as my 50mm.

    Some people hate the bokeh on those...
     
  3. Bitter Jeweler

    Bitter Jeweler Been spending a lot of time on here!

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    Patrice, can you post any pictures taken through any if those?
     
  4. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    Here's a couple taken through a Celestron CPC 2000mm f/8:

    [​IMG]




    17 stacked images..... I cheated!:

    [​IMG]
     
  5. Patrice

    Patrice No longer a newbie, moving up!

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    Here is one from 30 minutes ago. 900 mm f10 refractor. Used d200 and set non cpu lens data to the nearest defaults: 1000 mm at f11. Matrix metered.


    View to across the bay from my back porch, about 2 1/2 miles away. A little bit of chroma but not bad. Dull overcast and windy.

    [​IMG]
     
  6. usayit

    usayit No longer a newbie, moving up!

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    Minus the electronics that many telescopes come equipped, is there an advantage to using letsay a 500mm refracting telescope over a 500mm photographic lens? keep in mind I know zilch about telescopes but just recently sparked an interest. Probably be a long while before the interest weighs in enough to invest in a real telescope.

    1950s 500mm f4.5 lens on a 2x crop camera
    [​IMG]
     
  7. soylentgreen

    soylentgreen TPF Noob!

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  8. djacobox372

    djacobox372 No longer a newbie, moving up!

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    One side-benefit of Mirror lenses is that they produce little to no CA, which makes them great for telescopes.
     
  9. Forkie

    Forkie Been spending a lot of time on here!

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    I miss my telescope :sad anim:

    I had to sell it a couple of years ago, along with all my eyepieces because I had no more space for it. Worst mistake ever. I should've chucked the bike out. :banghead:
     

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