07-07-2013, 11:22 AM
I don't own the lenses and haven't tested it so far, so I can only guess: technically the explanation could be quite pronounced field curvature. You could find out by carefully focusing manually "through the newspaper".
But shapito also has a point: another explanation could be an optical defect, like fungus. You should carefully check the lens for that. Best approach is to fully open the aperture (you can do so manually with the lever at the mount), point the lens towards a light source and carefully inspect it by looking through from the other and. Make sure the light comes in at a slight angle... and slowly adjust that angle while inspecting the lens.
-- Markus
But shapito also has a point: another explanation could be an optical defect, like fungus. You should carefully check the lens for that. Best approach is to fully open the aperture (you can do so manually with the lever at the mount), point the lens towards a light source and carefully inspect it by looking through from the other and. Make sure the light comes in at a slight angle... and slowly adjust that angle while inspecting the lens.
-- Markus
Editor
opticallimits.com
opticallimits.com