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Joined on Nov 9, 2010

Antisthenes' recent activity

  • @stefpix
    > I am wondering if Sony's new lenses are designed by cutting
    > corners and they all focus shift

    Focus shift is essentially caused by spherical aberration (SA). A lens subject to...

  • @Rishi
    > The lens also stopped down even for AF-S/initial acquisition
    > if you pointed it a bright-ish scene - as if the camera is
    > afraid of letting in too much light, which makes no sense


  • .
    > That's a 50mm lens, a standard, boring focal length. [..]
    > it's something that you can put on the camera and take
    > everywhwre with no high expectations.

    The kind of fashionably dismissive...

  • Replied in compl-E-ment
    Simple Definition of compliment : a remark that says something good about someone or something Simple Definition of complement : something that completes something else or makes it better As to ...
  • Note that discussions about the aperture bahaviour of this lens based on Rishi's interesting, but necessarily quick hands-on are fairly irrelevant.

    Sony explicitly states that the A7R2 must be...

  • ../..
    As light field photography demonstrates, imaging systems are becoming, more and more, computational systems.

    An important theoretical limit of such systems is that the mapping mechanism...

  • Your assertion:

    "there exist bijections form R^3 to R^2, you did not have to go to countable sets"

    My reply:

    Such bijections are theoretical constructs — e.g. fractal — that are not computable,...

  • Your assertion:

    "On a more mathematical note, R^2 and R^3 are not isometric, and there is nothing we can do about that."

    My reply:

    As explained above, nothing prevents a 2D surface from being...

  • Your assertion:

    "There is no projection that would preserve distances - it is a trivial thing to figure out. All points on any radial way, for example, will be projected to one, which means zero...

  • Your assertion:

    "The same "distortion free" lens makes your head look like a head of a Martian near the edges and does not preserve angles or ratios of angles/sides not parallel to the image...

  • ../..
    Note that, say, a 24MP full-frame sensor has a pixel pitch of about 6 microns — i.e. about six thousand nanometers. As explained above, there exist optical systems that can project a picture...

  • Nope. It's you who are a bit out of your depth, as demonstrated by your shallow, sweeping statements.

    Your assertion:

    "there is no such thing as a distortion free lens or a lens with...

  • On a more mathematical note, a projection is a mapping. Furthermore, it's far from established that the fabric of the Universe has the cardinality of the continuum.
    At a microscopic scale — e.g....

  • The angles and distances of 3D objects can be preserved by photographing them using a bi-telecentric lens, as used e.g. in machine vision applications.

    With such a lens, given that the entrance...

  • ../..

    It's thus much more rational for a lens designer to allocate the "correction budget" — i.e. ther finite number of available lens surfaces and degrees of freedom in an optical design — to...

  • ../..

    Examples of well-corrected, essentially distortion-free lenses include e.g. the Apo-Nikkor photoengraving process lenses.

    Other examples include the reduction lenses in the scanners that...

  • Assume the subject is a 2D flat plane — e.g. a brick wall — and that the camera is parallel to said wall.

    Assume we choose, on this wall, four distinct points, which we'll name A1, A2, B1 and...

  • ../..

    Volume anamorphosis will NECESSARILY happen when mapping / projecting a 3D subject to a 2D surface, like a film or an image sensor.

    This is a bit similar to the "distorsion" which occurs...

  • Take a picture of a flat brick wall with a well-corrected — i.e. distortion-free — wide-angle lens, and the bricks at the edges of the picture should have the exact same size as in the center. ...

  • A simplistic opinion, which overlooks the fact that any decent, well-corrected photographic lens is typically constructed from glass elements and groups, assembled using positioning rings, shims,...

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