Quoting Larry Colen <[email protected]>:
On Mar 23, 2012, at 2:07 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.
My first thought is that maybe something is delaminating inside of it.
I'd be interested to see how it looks photographing a linear grid to
see if there is any distortion. Is it the 90/2.5 macro? If so,
then maybe some photos of graph paper. Also, does it make a
difference if the subject is back lit?
I also can't tell how much of the frame that really is, can you show
one that isn't a 100% crop?
What it almost looks like is shooting through a drop of water.
Yeah, exactly. But there were no drops of water present.
Here's the full frame version of the previous crop:
http://dl.dropbox.com/u/1370864/_IGP3904a-full.JPG
And here's where I first noticed the problem. I was trying to
photograph some tiny mushrooms growing within an old log. I couldn't
get enough light onto them so the photo is beyond crap, but it does
show the issue clearly:
http://dl.dropbox.com/u/1370864/_IGP3895a.JPG
(both of these are about 4MB each)
--
Cheers
Brian
++++++++++++++++++++++++++++++++++
Brian Walters
Western Sydney Australia
http://lyons-ryan.org/southernlight/
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