"John Hendry" wrote in message
news:intRc.52767$gE.21416@pd7tw3no...
----- Original Message -----
From: "Richard Knoppow"
Newsgroups: rec.photo.equipment.large-format
Sent: Thursday, August 05, 2004 4:25 AM
Subject: fog inside lens cell


snip
Cement is available from Summers Optical.
The easiest to use is probably their Ultra Violet curing
type UV-69 This will cure with a BL BLB UV lamp. The
technique is described on their web site.
http://www.emsdiasum.com/Summers/opt...ts/default.htm
snip

No experience with UV-69 but I know firsthand that J-91 also works well
and
cures with a black light fluorescent - 1min to set and 1 hour to cure. The
relative merits of these two isn't entirely clear from the website but
Summers are a helpful bunch on the phone. For separating cells I find
methylene chloride and patience (a day or so) is a low stress method that
works well.


One thing that has occurred to me in the past relates to alignment of the
cemented elements (I use two steel v-blocks). One generally assumes that the
elements have been ground individually with the optical centres bang in the
middle. On the last lens I did, I marked the orientation of the lens cells
with a diamond scribe (very light scratch on the ground edges) prior to
decementing so I could reorient them identically on recementing. I don't
really know whether the elements are rotated against one another in the
factory on an optical bench to minimise any slight relative eccentricity in
the grinding (slight off centre optical axes) to find the best orientation
for cementing. Can anyone confirm whether such a step is taken, or are
lenses factory cemented purely on physical alignment of the ground edges
with no regard for axial orientation? i.e. grinding stage is absolutely
perfect with centred optical axis. Having thought about it since I assume
this must be the case or you'd end up with very inconsistant quality as the
number of elements increased.