Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 69,986   Posts: 1,523,978   Online: 859
      
Page 2 of 2 FirstFirst 12
Results 11 to 17 of 17
  1. #11

    Join Date
    Mar 2005
    Shooter
    Multi Format
    Posts
    3,329
    Quote Originally Posted by Ronald Moravec View Post
    Slower lenses are easier to control aberations and macro lenses will focus on a flat plane if they are designed to do so. Field flatness is not a design optimizarion with faster lenses usually.
    Oh, come on, Ronald, curvature of field is almost always undesirable. The big exception is lenses designed to image a subject of known curvature -- usually a CRT -- on a plane.

    The ideal lens is aberration free and so has no curvature of field. In practice, designers trade off aberrations against each other so may accept a little field curvature to get less of something else. But you can't tell me that they think curvature of field is ok.

    Cheers,

    Dan

  2. #12

    Join Date
    Sep 2007
    Shooter
    35mm
    Posts
    136
    Flatening?
    There is something "like" flatening around macro lenses. It does nothing with 2 dim and 3 dimension picture.
    Distance FILM-OBJECT AT CORNER of finder are larger than distance FILM-OBJECT AT CENTER of finder. So if one focus at center, corner is out of focus and will apper blur. Macro lenses are corrected to make both and center and corner "sharp" when we focus at center (or corner). It is caled "flat field", and again, does nothing with 3D od 2D.
    Hex
    Daniel OB

  3. #13
    AgX
    AgX is offline

    Join Date
    Apr 2007
    Location
    Germany
    Shooter
    Multi Format
    Posts
    8,352
    Daniel,

    Yielding a flat image plane is the goal of the calculating of all photographic lenses since the beginning. Might they be `macro´ lenses or those calculated for much smaller image scales. (With the exception of very special lenses.)

    However there are lenses such as `process´ or `lithographic´ ones, where the flatness of the image field is of even greater importance due the fact they are only intented to project flat object planes.

  4. #14
    AgX
    AgX is offline

    Join Date
    Apr 2007
    Location
    Germany
    Shooter
    Multi Format
    Posts
    8,352
    Something more on Field Curvature and Astigmatism:

    http://www.vanwalree.com/optics/astigmatism.html

  5. #15
    AgX
    AgX is offline

    Join Date
    Apr 2007
    Location
    Germany
    Shooter
    Multi Format
    Posts
    8,352
    And as macro lenses are intended for large image scales, the dof will be rather small; thus there will be less tolerance to any kind of spherical image. And thus there is the necessity to even more reduce these aberrations.
    To my understanding this will not gain a bettter image quality at infinity in comparison with lenses intended for smaller image scales.

  6. #16
    Ed Sukach's Avatar
    Join Date
    Nov 2002
    Location
    Ipswich, Massachusetts, USA
    Shooter
    Medium Format
    Posts
    4,520
    Images
    26
    Quote Originally Posted by AgX View Post
    Something more on Field Curvature and Astigmatism:

    http://www.vanwalree.com/optics/astigmatism.html
    This is a useful web site. Please note the emphasis on "oversimplification". Optical Design is, IMHO, one of the most complex of all sciences. It is NOT difficult, or unusual, in practice to find oneself out of the realm of "basics".

    Every characteristic in the design of an optical system has its tolerance. "Process" lenses are designed to have an *exceptionally* "flat" field ... and more compromises with other characteristics; lessening maximum aperture, or even eliminating variable apertures altogether, are common. Performance at other focusing distances than those expected, may not merit close consideration.

    It may come as bad news to some of us who are heavily anal, but lens Quality Control is not dedicated to the search for absolute perfection, but to limiting the acceptance of compromises, variations and imperfections involved - to produce a lens that is "good enough"!
    Carpe erratum!!

    Ed Sukach, FFP.

  7. #17
    Ole
    Ole is offline
    Ole's Avatar
    Join Date
    Sep 2002
    Location
    Bergen, Norway
    Shooter
    Large Format
    Posts
    9,281
    Blog Entries
    1
    Images
    31
    The "basic" design criterion for process lenses is absolutely minimal distortion. Sharpness, flatness of field, contrast, astigmatism and everything else is secondary to that. Performance at anything but optimum distance is not even considered.

    The fact that so many process lenses are quite usable for other photography is pure coincidence.
    -- Ole Tjugen, Luddite Elitist
    Norway

Page 2 of 2 FirstFirst 12


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin