fisheye

Discussion in 'Photography Beginners' Forum' started by quat, Apr 8, 2009.

  1. quat

    quat TPF Noob!

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    at what focal length do you start to get the rounded fish eye look. I have my 18mm - 55mm lens and I want to take a panorama but dont want everything to look warped.
     
  2. dcclark

    dcclark TPF Noob!

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    It's not just a matter of focal length. Most normal lenses are designed to be "rectilinear," meaning that they keep straight lines straight. (Lens designers are always using crazy optical tricks to keep their lenses from curving lines, but you still see a little of it -- in the form of barrel and pincushion distortion which people talk about so much). On the other hand, fisheye lenses are NOT designed that way -- their optical elements deliberately DO distort straight lines into that wonderful curved effect.

    So, to summarize, it's the design of the lens, not the focal length, which determines whether it's fisheye or not.
     
  3. TJ K

    TJ K No longer a newbie, moving up!

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    if you want fisheye buy a fisheye lense otherwise no fisheye with the 18-55
     
  4. Moon Baby

    Moon Baby TPF Noob!

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    You gain distortion at focal lengths under 17mm but it also depends on how the lens is built. 17mm on AF-S type lenses are considered Ultra Wide Angle and some fisheyes start at 15mm under.
     
  5. TUX424

    TUX424 TPF Noob!

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    It would have to be 17mm on Full Frame, AF-S has to do with the build in focusing motor and nothing to do with the size of the sensor.
     
  6. Moon Baby

    Moon Baby TPF Noob!

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    True true, I was referring to AF-S because of their 1.6x magnification factor on crop cameras. On full frame I would have said 24mm as it's close to 17mm on 1.6x sensors, which they can't fit AF-S lenses.
    I assumed the op uses a 1.6x or 1.4x crop camera..

    Edit: there's a chart out there on the web that refers to focal lengths on 35mm equivalent cameras.
    i.e. 17mm = fisheye/wide angle, 50mm = standard focal length (human eye) 80mm = telephoto (ideal portrait length)
     
  7. Dwig

    Dwig TPF Noob!

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    dcclark posted a good explanation of what constitues a "fisheye". To add, in general most manufacturers design all lenses to avoid the barrel distortion characteristic to fisheyes as much as is practical except in lenses that they intend to be fisheyes.

    When intentionally making a fisheye lens, they only make them in focal lengths that yield at least 150 degrees, and most commonly 180 degrees, of angular coverage. This is measured either diagonally from corner to opposite corner in what is commonly called a "full frame" fisheye or across the circular images somewhat smaller than the frame in what some call a "true" fisheye.

    Each fisheye lens has an intended format. Full frame fisheyes intended for 35mm full frame or digital equivalents (e.g. Nikon FX format) are generally in the 15-17mm range. The spherical, or "true", fisheyes are generally 7-8mm. When the intended format is an APS-C format (e.g. Nikon DX format, 1.5-1.6x "crop factor") the focal lengths are in the 9-10mm and 4-5mm range respectively.

    To make good panoramas, you need software that will unbend images if you intend to use a fisheye. There are a number of special panorama software packages that can do this allowing a 360 panorama in two or three shots. Most people simply use a common wide-angle in the 24-35mm range on 35mm/FX or 16-24mm range on APS-C formats. You need to take more pictures, but the results are good. The better software packages will remove the subtle barrel distortion common in ordinary wide angles.
     
  8. quat

    quat TPF Noob!

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    [​IMG]

    This is what I was talking about. It has some roundness to it. It was shot at 18mm.

    I had planned to use my kit lens to do the pano. and then stitch it together with PS.
    I have a 50mm lens as well, would that be better suited for a pano?
     
  9. dcclark

    dcclark TPF Noob!

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    Are you talking about the vignetting, perhaps? (The rounded, dark spots around the outside)?

    Now you've got me really confused, because I don't understand what you're talking about -- fisheyes are unrelated to your 18-55mm, and they are also basically never used for panoramas (because of the crazy distortion, you can't stitch together different frames).

    What are you trying to do?
     
  10. quat

    quat TPF Noob!

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    no I am talking about how the proportions of the car and bike are slightly distorted. The vignetting is due to the hood I was using. Unless the vignetting causes an optical illusion that makes the photo seem rounder?


    I am trying to take a series of four photos to stitch together. I guess the question should be, should I use my 50mm 1.8/f, my 18-55mm 4.5/f, or my 55-250mm 4.5/f?
     
  11. DavidElliot

    DavidElliot TPF Noob!

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    if i understand quat right, he's trying to make a stitch a series of photos together to make a panoramic image at his lens widest without having any barrel distortion affecting the shot. is that the gist of it? or did i totally read your post wrong?
     
  12. bakkie

    bakkie TPF Noob!

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    Take the 18-55mm but do not zoom out full (maybe 25-30mm) and shoot more slices.
     

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