Hi all,
I think I have figured out this little puzzle.
It was strange that the Zuiko 21/3.5 and 35~105 exhibited the same
phenomenon, when I was looking for a specific and different fault with the 21
only.
The phenomenon was paired hexagonal dark patches in areas of fairly
uniform colour. Both lenses have six aperture blades.
I had decided to combine the test of the 21 with a scoping test of a local
land(sea)scape from a cliff-top for a panorama image. The shot was to be
right into the sun to see if the chips on the rear of the 21 would cause flare,
and that's just where the sun was. Since the shot was over sea from a cliff-
top, there was ample plain colour in sea below and sky above, to show up
faults.
The paired dark patches are diagonally across the centre of the lens from the
sun position, and this is the clue to the origin of the phenomenon being due
directly to the sun. Of course in this position a lens shade is of no use
whatsoever. These patches did not show in either lens when I photographed
away from the sun. I don't understand why the patches show up as dark; I
would have thought lighter colour.
What has shown up is that both lenses are very resistant to flare showing as
patches of rainbow colour, but internal reflections (paired in these cases)
incorporating the outline of the hexagonal aperture have left an impression on
the image.
SO; conclusions: chips on the rear of this lens seem to have no effect on
image quality even shooting into the sun, AND both lenses are resistant to
flare anyway.
I had wondered if the sensor of the OM4 had been affected but now discount
that possibility :-))
Brian
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