[rollei_list] Re: An Embarrassing Omission by the List Owner
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Wed, 7 Nov 2007 15:34:52 -0800
----- Original Message -----
From: "Eric Goldstein" <egoldste@xxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Wednesday, November 07, 2007 7:25 AM
Subject: [rollei_list] Re: An Embarrassing Omission by the
List Owner
The context of what low contrast means pre and post war is
important
to keep in mind...
Prewar, Sonnars were famous for their "bite" with
relatively few glass
to air surfaces but by post-war standards we would not
view them as
having good contrast. And yes Ed prewar, all fine lens
makers apotized
for resolution and not contrast, because contrast sans
coatings could
only be taken so far. This is why the Zeiss paper I
mentioned in a
previous post was such a turning point not only for that
marque but
most others who followed suite... the day contrast became
king...
Eric Goldstein
I suspect the low contrast is just plain flare due to
internal haze. It doesn't take much of this to destroy the
contrast of a lens. Fortunately, it cleans off with any
ordinary lens cleaner or alcohol, the problem is getting
access to the internal surfaces. Some lenses are pretty easy
to disassemble, some a bear. I don't know how the Sonnar is
assembled. Some Zeiss Tessars have back caps on the front
cell, these are very easy to get open. Others have a front
retaining ring. These need a friction wrench. Its possible
to make one from a bit of tubing the right diameter with a
ring of sticky rubber cemented to the edge. Either front of
back element will automatically center when the mount is
re-assembled.
I don't know the source of the haze but suspect it may
be something evaporated from the anti-reflection paint
inside the cell. I have also encountered some very old
lenses with what appears to be soot inside. This also
cleaned off easily and left no damage but I have no idea
what caused it.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
---
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