Pages: [1]   Go Down

Author Topic: Adjusting Curvature of Field  (Read 3176 times)

Dick Roadnight

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 1730
Adjusting Curvature of Field
« on: June 05, 2009, 01:33:29 pm »

There is a rumor that the top lens manufacturers now see Curvature of Field (COF) as an asset rather than an aberration, and are planning to give their users the ability to adjust their COF, so that an F2 lens can take a portrait with the nose and ears in focus, and then take an interior shot with three walls at right angles all in focus.

Unintentional curvature of field is caused by incorrect separation of elements in lens-board lenses, so adjusting this separation adjusts the COF... saving the trouble of DOF merge... which does not work very well in portraiture anyway.

P.S. can I patent this?
Logged
Hasselblad H4, Sinar P3 monorail view camera, Schneider Apo-digitar lenses

brianc1959

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 53
    • http://
Adjusting Curvature of Field
« Reply #1 on: June 05, 2009, 06:52:49 pm »

Quote from: Dick Roadnight
There is a rumor that the top lens manufacturers now see Curvature of Field (COF) as an asset rather than an aberration, and are planning to give their users the ability to adjust their COF, so that an F2 lens can take a portrait with the nose and ears in focus, and then take an interior shot with three walls at right angles all in focus.

Unintentional curvature of field is caused by incorrect separation of elements in lens-board lenses, so adjusting this separation adjusts the COF... saving the trouble of DOF merge... which does not work very well in portraiture anyway.

P.S. can I patent this?

True field curvature, called the Petzval Sum in lens design circles, cannot be altered by altering the separation between lens elements.  What you can do is to change the amount of astigmatism, which interacts with the Petzval Sum to give the apparent field curvature of a lens.  The problem is that really good lenses designed for a flat image plane will have very low astigmatism *and* a very small Petzval Sum.  For a portrait lens, which is allowed to have poor aberration correction, you might get away with some intentional astigmatism which you could vary by moving elements around.

Minolta marketed a variable "field curvature" lens back in the 1970s, but I don't think the idea really caught on.

You can undoubtedly patent a variable astigmatism lens if it has some unique features, but I don't think it would be a very broad patent.  Simply adjusting the cell spacing of a board-mounted lens is not patentable at all, as many manufacturers use cell spacing to compensate for small manufacturing errors during assembly.
Logged

Geoffrey

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 69
Adjusting Curvature of Field
« Reply #2 on: June 06, 2009, 06:57:33 pm »

so.... does a typical lens have a curved field of focus (constant length arcs from a single point at the center of the lens), or are they corrected to give a "flat field" of focus, where everyone 10' from the lens, as measured in coordinates, not radially, are in focus?

I thought it was the former, with only a few projector lenses or macro lenses corrected for the latter. Is this the case?
 
Geoff
Logged

Dick Roadnight

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 1730
Adjusting Curvature of Field
« Reply #3 on: June 07, 2009, 07:29:18 am »

Quote from: Geoffrey
so.... does a typical lens have a curved field of focus (constant length arcs from a single point at the center of the lens), or are they corrected to give a "flat field" of focus, where everyone 10' from the lens, as measured in coordinates, not radially, are in focus?

I thought it was the former, with only a few projector lenses or macro lenses corrected for the latter. Is this the case?
 
Geoff
Lens manufacturers try to achieve a flat (co-planar) plane of sharpest focus... especially for copying flat work, projection, etc.
Logged
Hasselblad H4, Sinar P3 monorail view camera, Schneider Apo-digitar lenses

EricWHiss

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2639
    • Rolleiflex USA
Adjusting Curvature of Field
« Reply #4 on: June 07, 2009, 02:02:07 pm »

Anyone know how the human eye is with respect to focus plane?

Logged
Rolleiflex USA
Pages: [1]   Go Up