Quoting "P. J. Alling" <[email protected]>:
Damn, I've never seen anything quite like that problem before. Are
you sure there's no visible blemishes on the lens surfaces annwhere?
Well, none that I can see, although it's difficult to eliminate all
extraneous reflections on the various elements when I'm trying to look.
Darren has an explanation that it may be a 'feature' of the lens on
digital. I'm looking in to that.
Cheers
Brian
++++++++++++++++++++++++++++++++++
Brian Walters
Western Sydney Australia
http://lyons-ryan.org/southernlight/
On 3/23/2012 5:07 PM, Brian Walters wrote:
My Tamron 90 mm 2.5 has been one of my favourite lenses for decades
but it has developed a problem.
I was using it a week or so ago and when I downloaded the images I
noticed an out of focus blob right in the middle of the frame. A
dirty sensor was my first thought but the same thing happened when
I tried it on a second camera.
The problem is that the lens looks almost completely clear. I can
see a few small specs of dust but no fungus or haze that would be
causing the issue. The 'blob' is not especially noticeable at
large apertures but as I normally use it stopped down, it is a real
problem.
Here's a couple of test shots (100% crops):
f16: http://dl.dropbox.com/u/1370864/_IGP3904a.JPG
f8: http://dl.dropbox.com/u/1370864/_IGP3905a.JPG
Bugger! :-(>
I'm at a loss to know what's causing this but at least I have the
Pentax f4 35-70 A zoom to fall back on and it can get nice and
close to subjects. At a pinch my Konica Hexanon 55mm macro will
work on my Pentax DSLRs if I attach it via a short extension tube.
Unfortunately, neither of these gives me the working distance of
the Tamron.
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