Quoting Darren Addy <pixelsmi...@gmail.com>:
It is described often as "CCD flare". I'm guessing that between the
little microlenses over the pixels on the sensor and the flat spot on
the back of the sensor you get a little light that bounces off the
sensor, and back off the flat lens element to effectively overexpose
that little circle.
So the effect may be more noticeable on some sensors rather than
others, meaning that you might see it on some cameras and not others.
It was never a problem (that I have seen reported) on film cameras.
The good news is that there is probably nothing newly wrong with your lens.
I suppose that's good news.....
Checking out the link you mentioned in an earlier post, I think you're
right. It does seem to be a known problem with this lens on some (but
maybe not all?) digital SLRs.
The interesting thing is that I've used this lens almost exclusively
on my *istDS and looking back closely at those images, there's no
obvious indication of the 'hot spot'. The latest case that prompted
my post was using the lens on a K200D and I can't positively identify
any previous images taken with that lens/camera combination.
I'll fire up the DS tomorrow and see whether I can reproduce the
problem with that camera.
Another suggestion that was made was to use the lens with Tamron's
dedicated 2X adapter, which has a curved rear element. It might be
clutching at straws but I have one of those, so I'll give that a try
as well.
--
Cheers
Brian
++++++++++++++++++++++++++++++++++
Brian Walters
Western Sydney Australia
http://lyons-ryan.org/southernlight/
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