On Monday, August 11, 2003, at 06:56 PM, Mark Dapoz wrote:
On Mon, 11 Aug 2003, whunter wrote:
Now Sports Fans........ Take another look at the image by Dapoz.
(Mark - Can you shoot this again minus the distracting reflection in
the center right where the answer may lie??)
- I see, aside from the reflection, a disk of yellow with greatest
intensity in the center and extremely uniform falloff to the
periphery.
If true, this would be consistent with uniform yallering of the
glass
of a convex element. (????) with insignificant contribution from the
surface of the lens. i.e. If the surface contained the yaller, the
entire yaller area would be uniform yaller intensity. No??
Ok, I've re-shot it using outdoor ambient light instead of the cheesy
built
in flash. If we need better results then I'll have to switch to using
the
OM's rather than this digital P&S. There is indeed a higher insensity
of
yellowing in the centre than the edges. Here are the results:
http://olympus.dementia.org/misc/55mm_yellowing_front.jpg
http://olympus.dementia.org/misc/55mm_yellowing_back.jpg
It's more obvious when looking through the rear, but you can see it
both
photographs. I'd say the yellowing is being caused by the glass and
not
the coatings.
Mark -
Most interesting...... Certainly these images support the thesis of
yaller within the glass of a convex element. From the posted picture
I do not perceive a fall off in intensity from the center to the
periphery to the extent expected, but expectations are empirical given
the absence of thickness measurements. From the rear, the confines of
a single(?( element is evident. The two white/light spots would be
suspicious, but one is outside the perimeter of the affected element on
the rear view. Probably the most effective would be for you to take a
fairly strong loupe and examine directly for any focal defect within
the perimeter of the yellow. Given the difficulty of photography with
adequate magnification in this situation plus posting to the web, your
first hand observation is needed. There should be a way to rig this
lens to 'project' an image on a large white wall. That degree of
magnification could be enlightening.
Despite all the sniping and quoting of extraneous texts on this issue,
a good scientist asks the questions then searches for evidence to
support or modify the hypothesis. My focus is on this group of Zuiko
lenses produced in this time/technology frame. Extraneous and
voluminous documentation of 'radiation effects on materials including
glass', etc. are well known to those with experience in radiochemistry
but will not provide the desired proof unless Olympus has published
relevant data. Clearly (should I say 'yallerly'), your photos support
involvement of a convex segment of the lens with extremely uniform
changes within the glass. Radiation damage, chemically induced color
change from either the rare earth ingredient or a contaminant or both
remain equally suspect? The absence of any focal defects supports
chemically induced color change. Short of more definitive chemical
analysis, your photos support a non-destructive trial of 'sunlight'
or other UV treatment. Again, if my lens, would remove the involved
element for isolated Rx. If removed, a simple but definitive
assessment can be made from the 'feel' of the lens surface. Is the
surface smooth just like the other lens elements or rough like fine
sandpaper. The latter would be consistent with radiation induced
change in material structure; a smooth surface STRONGLY weighs towards
chemically induced color change.
Will be interested in your results.
Bill
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