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  1. #1
    Mustafa Umut Sarac's Avatar
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    Sagittal Tangential Petzval Terms

    I want to clarify these terms in my mind. Erwin Putts tells that an image is a combination of these three. I saw at MTF tests , first two but not the third one. Do all aberrations spread in to these three or does it spread on more on one or two ? How do them to form a combination for better plasticity ?
    Is there any computer simulation examples for each image characteristics to understand them better ?
    Is there any way to effect each one to create a different combination ? Is there a way to separate each one ?

    Umut

  2. #2

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    "Sagittal" and "Tangential" are terms relating to astigmatism . http://www.astrosurf.com/luxorion/re...errations3.htm

    "Petzval" is a type of portrait lens, http://www.antiquecameras.net/petzvallens.html or the Petzval sum, http://books.google.com/books?id=kS9...%20sum&f=false

    Mustafa, do you ever try to look things up yourself?
    Last edited by E. von Hoegh; 06-22-2013 at 11:12 AM. Click to view previous post history.

  3. #3
    Mustafa Umut Sarac's Avatar
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    I found the same at wikipedia. Does it mean MTF tests only explain the amount of astigmatism ?

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    Quote Originally Posted by Mustafa Umut Sarac View Post
    I found the same at wikipedia. Does it mean MTF tests only explain the amount of astigmatism ?
    No. MTF = Modulation Transfer Function. Think of it as a combination of resolution and contrast, since all aberrations effect both. http://spie.org/x34298.xml

    If I could google this, so can you.

  5. #5
    Mustafa Umut Sarac's Avatar
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    But MTF tests have two curves , tangential and sagittal and we found that two relates to astigmatism. But your latest post and I have read in books says MTF shows the combination of all aberrations.

    Whats going on ? I could not get it. Is it telling the aberrations in astigmatism ? By the way , I found a reference about the authors who got their prescriptions from ELCAN archive and conduct tests on Summilux , f:1 one and Summicron 50 f:2. They analysed mandler designs and the double gauss ones.

    All they found , there is virtually no aberration record at summicron , but for others all aberrations are so low but one single abnerration is 10 times more. I never heard that one in any book.

    IMHO , If they would put under MTF test , they would be worse than Zeiss or Nikon. But it does not say the all story.

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    Two of the Seidel aberrations are closely related, namely field curvature and astigmatism.

    Field curvature is where the best focus of the image lies not on a plane but on a curved surface.

    Astigmatism is where the tangential rays and sagittal rays do not focus at the same point. The tangential rays focus on a curved surface and the sagittal rays focus on a different curved surface.

    There is an equation that provides a relationship between the radii of these three surfaces. I don't recall what the formula is, but it can be found on line. However, as I recall, one consequence of the formula is that it is impossible to correct for astigmatism unless one also corrects for field curvature.

    There is also a theorem that relates field curvature to the refractive indexes and curvatures of the lens surfaces.

    One other thing. Astigmatism contributes to the MTF curves, as do the other aberrations. As a result, the MTF curves in two directions are not equivalent, so one needs to MTF curves.

  7. #7
    Mustafa Umut Sarac's Avatar
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    Can We say or not ,the balance between sagittal and tangential curves responsible for plasticity ?



 

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