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fun with optics

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  • fun with optics

    After experimenting with my zoom lens and the digital camera, I ended up with the following performance:
    - minimun distance where focus is possible at full zoom, including camera at full zoom, is 50 inches.
    - a closer focus is possible to 40 inches if I focus with the added achromat between zoom lens and camera, otherwise this lens has a fixed position.
    - from 15 ft and farther from subject, the focus doesn't alter much over the zoom range.
    - the camera must be zoomed at least x2 to keep pincushioning from being very obvious, and to prevent vignetting.
    - the camera will auto focus except where closer than 15 ft from subject, but manual focus will work right up to 50 inches, and closer with adjusting of the intermediate lens.
    - at minimun zoom, the image I get is about 30% smaller than with the camera alone, without adjusting the camera's zoom. When I used an eyepiece instead of the simple lens, this image was even smaller. There are no specs on the eyepiece or the simple lens I used, so I can't identify them in optical terms.
    This zoom lens is a Canon, has a zoom range of 20-100, focus range from 6 ft to infinity, has a 35 mm lens.
    If anyone can make some sense of what I've said, and would care to indulge me a bit, I'd appreciate your comments, or if you can suggest what I might do to improve anything, that's what I'm looking for. TIA.
    By the way, my project for the day was a mount for this that allows the camera to hinge away from the zoom, for an instant reversal to camera only, and I have it so it will all mount on a tripod, or I can carry it with a strap around my neck. It's obvious that I can't hold it still enough by hand to take good pictures, so now I need to make a sturdy but lightweight tripod so the whole mess is still backpackable.

    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2

    Just a couple of ideas. I made an adapter for an old zoom lense I have that allows the use of a standard 1 1/4" telescope eyepiece. Makes a nice compact telescope. I also made an adapter that allows the use of a web cam on the lense. Using software such as Astrostack makes web cam photography very high quality. The same principle can be applied to any image, not just astrophotography. That is how they identified the make of backpack that had the bomb in it at Atlanta. Here is an image that is a composite of six images. Each of those six images is a stack of 40 individual images put together with Astrostack. Total number of images was 240. The webcam has a resolution of only 640X480 but the stacking process effectively increases the resolution greatly.

    This was taken with my six inch scope.

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    • #3
      Thanks, Evan. That's an impressive result from stitching 240 images together. My welding of 3 images in a panorama isn't nearly as seamless.
      We have an astronomy buff in our outdoor club, maybe I'll have a chat with him, possibly borrow some optical pieces to test with.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


      • #4
        Just think what you could do if you stacked inages from a good lens/camera.

        Paul A.
        Paul A.
        SE Texas

        Make it fit.
        You can't win and there is a penalty for trying!