Hate your yaller lens, but not me in my mailbox plez........
OK - - - Mark just supplied some info to a 'logic' question which woke
me in the wee of the night. Let me present as "trying to find the
answer without first asking the question is like reading in the DARK" -
- or should I say "shooting through a yaller lens!!". Anyway, here
goes:
Key Question:
1. Is the yaller primarily confined to the surface (coating, cement,
dust, film, whatever) or is it primarily in the body of the glass?
- McEwen: "Yes - cutting a section through the lens shows that the
discoloration is homogenous throughout the glass, not restricted to the
surface."
- Conditions of this cut and method of examination to exclude surface
effects not provided. (Anyone who has looked at 'flash glass'
understands the issues.)
- Dapoz provided some interesting data, but what does it mean in
terms of cause and effect? Additionally, he provided an image through
a yaller lens:
http://olympus.dementia.org/misc/55mm_yellowing.jpg
- Slow brain registered the image, but not the implications.
Then........ cross examine this logic
A. If yaller is primarily confined to the surface, the color should be
reasonably uniform across any lens or element
B. if yaller is primarily confined to the glass of a biconvex or
plano-convex element, yaller intensity should be more intense in the
center and fall off uniformly towards the edges
C. if yaller is primarily confined to the glass of a biconcave
element, the yaller intensity should form a ring at the periphery.
- Somewhere in all this morass, believe someone posted a note that
the yaller was confined to one element?? configuration of that element??
- Mark Marr-Lyon just provided some answers to the effect that it is
most likely a single convex type element whence the glass thickness is
greatest in the center.
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??
Maybe we are getting somewhere?? Now the next question is WHY? Is
this primarily because of chemical coloration from a rare earth
(something they are purposely employed to effect) or is it primarily
glass degradation from ionizing radiation???? (Again, just because
'counter' activity is detected does not link radiation damage to the
yaller.) One 'next step' thought in this regard. Yes, very uniform
color changes proportional to the thickness of the glass (as the
picture implies) could be rendered by radiation damage. But...... my
limited experience in examination of radiation altered glassware
suggests inhomogeneities are always present when the damage is from
ionizing radiation (i.e. not chemical induced color change). Dapoz,
can you acquire a magnified view of the central region of this lens
image to look for 'bubbles' or other tiny focal defects characteristic
of radiation damage???
And Sherlock said, "Watson, the answer often lies in what is missing
rather than what you see."
Carry on...
Bill
On Monday, August 11, 2003, at 02:23 PM, Thomas Haegin wrote:
Out of curiosity I also put pretty much all my lenses
face-down on the little "light tablet" (tray) I have
for viewing slides.
These were the lenses I checked:
mm f S/N Coat Ring
---------------------------------------
50 1.8 136xxx SC Silver nose
50 1.8 887xxx SC Black nose
50 1.8 5.7 Mio MIJ Black nose
50 1.4 145xxx SC Silver nose
28 2.8 333xxx MC Black nose
100 2.8 202xxx MC Black nose
Here is what I found:
There was only one lens that actually was REALLY white
: the 50/1.8 with serial 887xxx. Interesting this was
my very first lens I obtained in 1979. It has always
been with me... no idea why it refuses to change
color.
The 50 MIJ had a slight tilt towards reddish and
warmer, as had the 100/2.8 MC.
The early 1.8/50 S/N 136xxx was darker/warmer than the
S/N 887xxx, but not as red/warm as the 100mm.
The 1.4/50 had a tilt towards greenish-greyish. With A
LOT OF goodwill one could see a little bit of yellow
in it as well. Certainly the taint on the 1.4 was
different in color than on the other lenses.
The 2.8/28mm was also warmer than white, about as the
100mm.
What does that all mean? I have no idea.
IMO we could probably ask all 200 members about their
600+ lenses and results will be all over the place...
This would show to me that Bill Hunter's assessment
that there are multiple factors, internal and
external, that contribute to changing the color of
glass must be quite correct, and yellowing is only one
possible variation among many.
I was quite surprised to see the differences so
clearly when putting them side-by-side. However, I
would not consider the color bias in any individual
lens as problematic. At least I never noticed
pronounced color shifts when looking at printed or
projected pictures of mine.
FWIW,
Thomas
--- Mark Marr-Lyon <markml@xxxxxxx> schrieb: > Mark
Dapoz wrote:
Lens Serial Colour Cast
- --------- ------- -----------
55mm f1.2 100584 severe yellowing
50mm f1.4 109257 minor yellowing
50mm f1.4 118622 minor yellowing
50mm f1.8 108622 no yellowing
50mm f1.8 114234 no yellowing
50mm f1.8 121253 no yellowing
35mm f2.8 103931 slight yellowing
35mm f2.8 108255 no yellowing
100mm f2.8 102159 slight yellowing
Very interesting! My 35/2.8 with SN in the high
109k's doesn't show any yellowing either. I would
be very curious to know if either the early 35/2.8
or 100/2.8 are radioactive too!
Mark
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