Lens shading/vignetting question

We put a lens on a big CCD chip and noticed a huge (2-to-1) drop off
in intensity near the edges, like dark vertical bands near the right
and left edges - not so much on the top and bottom edges. Now if I
remember my terminilogy correctly "vignetting" happens when the
optical stop actually occludes part of the optical path, which I don't
think was the case here (it happened even with iris wide open). (By
the way, there was no shading at all with the lens removed so it is
due to the lens.) The manufacturer calls it "lens shading" rather
than "vignetting" which I agree with. Would that be the more accurate
terminology? What causes this shading? Is it that there is more
glass to go through when the ray of light is traveling towards the
edge of the image and so it gets attenuated more, and so it's darker
there? Is that the right explanation, or is it something else?
Someone said try bigger 45 mm machine vision lenses rather than
standard lenses meant for 35 mm sensors to reduce the lens shading.
Anyone agree with that?
.

Relevant Pages

  • Re: Lens shading/vignetting question
    ... there was no shading at all with the lens removed so it is ... than "vignetting" which I agree with. ... standard lenses meant for 35 mm sensors to reduce the lens shading. ... Vignetting does not occur when the aperture stop occludes the optical path. ...
    (sci.optics)
  • Re: Lens shading/vignetting question
    ... in intensity near the edges, like dark vertical bands near the right ... there was no shading at all with the lens removed so it is ...  Is that the right explanation, ... standard lenses meant for 35 mm sensors to reduce the lens shading. ...
    (sci.optics)
  • Re: Internal ND filters on the XH-A1 affecting focus
    ... because they increase the length of the optical path. ... Unless the lens optics are moved to accommodate the filter thickness ... under the same conditions (as would using a higher shutter speed). ... the filters that the sharpness in the left 1/3rd or so isn't great, ...
    (rec.video.production)
  • Re: Internal ND filters on the XH-A1 affecting focus
    ... Internal filters actually do indeed affect the back-focus of the lens, ... because they increase the length of the optical path. ...
    (rec.video.production)
  • Re: Circles on Canon 350D
    ... They are shadows in the optical path. ... diffuse, blobs on the sensor, or, perhaps more likely, and judging from ... crud on the rear element of your lens. ...
    (rec.photo.digital.slr-systems)