A Photography forum. PhotoBanter.com

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » PhotoBanter.com forum » Photo Equipment » Large Format Photography Equipment
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

fog inside lens cell



 
 
Thread Tools Display Modes
  #1  
Old August 5th 04, 05:19 AM
Stacey
external usenet poster
 
Posts: n/a
Default fog inside lens cell

PGG wrote:


I bought a spanner wrench to remove a rear retaining ring from my
Ilex-Calumet 215mm f5.6 lens. This allow me to get to this cell, however
the fog is _inside_ the cell and not on the accessible surfaces. It is
pictured at the link below:


http://pg.photos.yahoo.com/ph/papago...&.dnm=3376.jpg

It looks like there are 2 pieces of glass sandwiched together somehow.

I don't think cement is used because I called my local repair shop, for
which I got a previous estimate of $78 to clean, and asked if they
uncemented/recemented cells to clean them. They said they do _not_ do
this, and that if they gave an estimate for my lens, then they are able to
clean it regardless. Unless they didn't realize the extent of the fog,
then I believe these glass pieces are attached some other way.

Any ideas?


They look cemented together to me, what else could be holding them together?
--

Stacey
  #2  
Old August 5th 04, 12:25 PM
Richard Knoppow
external usenet poster
 
Posts: n/a
Default fog inside lens cell


"PGG" wrote in message
news[email protected]_SP_A_Myahoo .com...

I bought a spanner wrench to remove a rear retaining ring

from my
Ilex-Calumet 215mm f5.6 lens. This allow me to get to

this cell, however
the fog is _inside_ the cell and not on the accessible

surfaces. It is
pictured at the link below:


http://pg.photos.yahoo.com/ph/papago...&.dnm=3376.jpg

It looks like there are 2 pieces of glass sandwiched

together somehow.

I don't think cement is used because I called my local

repair shop, for
which I got a previous estimate of $78 to clean, and asked

if they
uncemented/recemented cells to clean them. They said they

do _not_ do
this, and that if they gave an estimate for my lens, then

they are able to
clean it regardless. Unless they didn't realize the

extent of the fog,
then I believe these glass pieces are attached some other

way.

Any ideas? Should I give up and pay the $78?

-PGG

I replyed via e-mail about this. Its hard to tell from
the photo but it looks like a cemented lens. The Ilex lens
described is a "Plasmat type. These have two cemented
elements facing the outside of each cell and a single
element inside facing the stop. When some types of synthetic
cements begin to become degraded they look hazy. Sometimes
they even have an "orange peel" look when examined using a
strong loup.
Recementing lenses can be reasonably simple and done
yourself. Most cemented elements are made with precisely
ground edges, when the edges are lined up and clamped the
lens is aligned. 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

There are a few technicians who will recement lenses.
John van Stelten has been offering this service for a long
time and has a good reputation, however, he is expensive.
Some older lenses are not worth the cost of recementing
them.

The Focal Point
John Van Stelten
1017 South Boulder Road
Suite E-1
Louisville, CO 80027-0027
Tel.- 303-665-6640
Fax - 303-665-3803
http://www.411web.com/F/FOCALPOINT/


I've recemented a number of lenses using Summers binary
(heat curing) cement. This worked well but the UV curing
stuff is easier to use. The UV-69 type has the advantage
that it is not considered a hazardous material for shipping.
The suggested method of decementing elements cemented
with synthetic cements is to boil them apart in a special
oil. The oil is also available from Summers and is not too
expensive but it must be shipped as a hazardous material
which about doubles the cost. Another method which works on
many lenses is to soak them in Methylene Chloride. This is a
common solvent used in paint removers. It may take days for
the solvent to penetrate. If this works its safer for the
lens because there is no danger of heat shock which can
cause chipping or even break the elements.
Very old lenses, cemented with Canada Balsam (the stuff
that turns yellow or brown at the edges) will come apart
with gentle heat. Its often suggested that they be heated on
a hot plate but I find they will come apart in heated water.
Put them in cold water and heat until they come apart. The
heat needed is well below the boiling point. Lenses
originally cemented with Canada Balsam should be recemented
with a modern synthetic.
The hardest part of recementing is getting the glass out
of "burnished" or "spun-in" mounts. These were made with a
thin lip of metal which was burnished down around the
periphery of the lens. This is an excellent mount as far as
accurate centering and protection of the glass but is
difficult to undo. I have had some luck in prying up the lip
so that it can be re-used but very often it will break or
become wrinkled. The usual technique is to machine it off in
a precision lathe, thread the back of the mount, and make a
back retaining cap. All fine if you are a skilled machinist,
I am not. It is also possible to reinstall the lens using
epoxy cement around its periphery. Most Tessar type lenses
have the back component mounted this way. Recementing the
elements is much easier than dealing with the burnished
mount.
When a lens is recemented the anti-reflection paint must
be removed. After cementing it must be replaced to prevent
total internal reflection from the edges (some single
elements do not need the paint). At one time an excellent
paint called Velvet was available but its been off the
market for many years. The best current paint is Krylon
Untra-Flat Black. This comes in spray cans. Its used by
spraying some into a small container and applying it with a
brush. Its also good stuff for painting the interiors of
lens cells and and generally on other surfaces which should
not reflect light. The paint also acts as a seal for the
cemented edges of the lens. I think one reason that some
brands of old lenses seem to be more prone to degredation of
the Canada Balsam cements is the variation of the
effectiveness of the sealing quality of the anti-reflection
paint. For instance, old Zeiss lenses seem to more resistant
to cement problems than old Bausch & Lomb lenses.
While the effect of oxidizing or crystalized Canada
Balsam is pretty familiar the effect of degraded synthetic
cements is less so. That is partly because they are much
more stable than Balsam but also because the effect may be
harder so see. Sometimes is appears to be large bubbles
between the elements, this is due to separation of the
cement and probably due to poor surface perparation or
curing problems during manufacture. Another effect, and one
that may be difficult to see if you don't specifically look
for it is the slight haziness the cement develops. This is
visible when a flashlight is shown directly into the lens.
Sometimes its more visible by reflected light than
transmitted light. The effect on lens performance is to
destroy contrast. Even a very slight haze has a surprizingly
large effect on contrast. When shopping for used lenses its
a good idea to carry a loup and a small flashlight with you.
These can show up cement problems, fine scratches, gouges,
haze, dirt, and fungus. While even a very clean lens can be
awful its also true that the best lens can be ruined by any
of the above.


--
---
Richard Knoppow
Los Angeles, CA, USA



  #3  
Old August 5th 04, 12:25 PM
Richard Knoppow
external usenet poster
 
Posts: n/a
Default fog inside lens cell


"PGG" wrote in message
news[email protected]_SP_A_Myahoo .com...

I bought a spanner wrench to remove a rear retaining ring

from my
Ilex-Calumet 215mm f5.6 lens. This allow me to get to

this cell, however
the fog is _inside_ the cell and not on the accessible

surfaces. It is
pictured at the link below:


http://pg.photos.yahoo.com/ph/papago...&.dnm=3376.jpg

It looks like there are 2 pieces of glass sandwiched

together somehow.

I don't think cement is used because I called my local

repair shop, for
which I got a previous estimate of $78 to clean, and asked

if they
uncemented/recemented cells to clean them. They said they

do _not_ do
this, and that if they gave an estimate for my lens, then

they are able to
clean it regardless. Unless they didn't realize the

extent of the fog,
then I believe these glass pieces are attached some other

way.

Any ideas? Should I give up and pay the $78?

-PGG

I replyed via e-mail about this. Its hard to tell from
the photo but it looks like a cemented lens. The Ilex lens
described is a "Plasmat type. These have two cemented
elements facing the outside of each cell and a single
element inside facing the stop. When some types of synthetic
cements begin to become degraded they look hazy. Sometimes
they even have an "orange peel" look when examined using a
strong loup.
Recementing lenses can be reasonably simple and done
yourself. Most cemented elements are made with precisely
ground edges, when the edges are lined up and clamped the
lens is aligned. 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

There are a few technicians who will recement lenses.
John van Stelten has been offering this service for a long
time and has a good reputation, however, he is expensive.
Some older lenses are not worth the cost of recementing
them.

The Focal Point
John Van Stelten
1017 South Boulder Road
Suite E-1
Louisville, CO 80027-0027
Tel.- 303-665-6640
Fax - 303-665-3803
http://www.411web.com/F/FOCALPOINT/


I've recemented a number of lenses using Summers binary
(heat curing) cement. This worked well but the UV curing
stuff is easier to use. The UV-69 type has the advantage
that it is not considered a hazardous material for shipping.
The suggested method of decementing elements cemented
with synthetic cements is to boil them apart in a special
oil. The oil is also available from Summers and is not too
expensive but it must be shipped as a hazardous material
which about doubles the cost. Another method which works on
many lenses is to soak them in Methylene Chloride. This is a
common solvent used in paint removers. It may take days for
the solvent to penetrate. If this works its safer for the
lens because there is no danger of heat shock which can
cause chipping or even break the elements.
Very old lenses, cemented with Canada Balsam (the stuff
that turns yellow or brown at the edges) will come apart
with gentle heat. Its often suggested that they be heated on
a hot plate but I find they will come apart in heated water.
Put them in cold water and heat until they come apart. The
heat needed is well below the boiling point. Lenses
originally cemented with Canada Balsam should be recemented
with a modern synthetic.
The hardest part of recementing is getting the glass out
of "burnished" or "spun-in" mounts. These were made with a
thin lip of metal which was burnished down around the
periphery of the lens. This is an excellent mount as far as
accurate centering and protection of the glass but is
difficult to undo. I have had some luck in prying up the lip
so that it can be re-used but very often it will break or
become wrinkled. The usual technique is to machine it off in
a precision lathe, thread the back of the mount, and make a
back retaining cap. All fine if you are a skilled machinist,
I am not. It is also possible to reinstall the lens using
epoxy cement around its periphery. Most Tessar type lenses
have the back component mounted this way. Recementing the
elements is much easier than dealing with the burnished
mount.
When a lens is recemented the anti-reflection paint must
be removed. After cementing it must be replaced to prevent
total internal reflection from the edges (some single
elements do not need the paint). At one time an excellent
paint called Velvet was available but its been off the
market for many years. The best current paint is Krylon
Untra-Flat Black. This comes in spray cans. Its used by
spraying some into a small container and applying it with a
brush. Its also good stuff for painting the interiors of
lens cells and and generally on other surfaces which should
not reflect light. The paint also acts as a seal for the
cemented edges of the lens. I think one reason that some
brands of old lenses seem to be more prone to degredation of
the Canada Balsam cements is the variation of the
effectiveness of the sealing quality of the anti-reflection
paint. For instance, old Zeiss lenses seem to more resistant
to cement problems than old Bausch & Lomb lenses.
While the effect of oxidizing or crystalized Canada
Balsam is pretty familiar the effect of degraded synthetic
cements is less so. That is partly because they are much
more stable than Balsam but also because the effect may be
harder so see. Sometimes is appears to be large bubbles
between the elements, this is due to separation of the
cement and probably due to poor surface perparation or
curing problems during manufacture. Another effect, and one
that may be difficult to see if you don't specifically look
for it is the slight haziness the cement develops. This is
visible when a flashlight is shown directly into the lens.
Sometimes its more visible by reflected light than
transmitted light. The effect on lens performance is to
destroy contrast. Even a very slight haze has a surprizingly
large effect on contrast. When shopping for used lenses its
a good idea to carry a loup and a small flashlight with you.
These can show up cement problems, fine scratches, gouges,
haze, dirt, and fungus. While even a very clean lens can be
awful its also true that the best lens can be ruined by any
of the above.


--
---
Richard Knoppow
Los Angeles, CA, USA



  #4  
Old August 5th 04, 12:25 PM
Richard Knoppow
external usenet poster
 
Posts: n/a
Default fog inside lens cell


"PGG" wrote in message
news[email protected]_SP_A_Myahoo .com...

I bought a spanner wrench to remove a rear retaining ring

from my
Ilex-Calumet 215mm f5.6 lens. This allow me to get to

this cell, however
the fog is _inside_ the cell and not on the accessible

surfaces. It is
pictured at the link below:


http://pg.photos.yahoo.com/ph/papago...&.dnm=3376.jpg

It looks like there are 2 pieces of glass sandwiched

together somehow.

I don't think cement is used because I called my local

repair shop, for
which I got a previous estimate of $78 to clean, and asked

if they
uncemented/recemented cells to clean them. They said they

do _not_ do
this, and that if they gave an estimate for my lens, then

they are able to
clean it regardless. Unless they didn't realize the

extent of the fog,
then I believe these glass pieces are attached some other

way.

Any ideas? Should I give up and pay the $78?

-PGG

I replyed via e-mail about this. Its hard to tell from
the photo but it looks like a cemented lens. The Ilex lens
described is a "Plasmat type. These have two cemented
elements facing the outside of each cell and a single
element inside facing the stop. When some types of synthetic
cements begin to become degraded they look hazy. Sometimes
they even have an "orange peel" look when examined using a
strong loup.
Recementing lenses can be reasonably simple and done
yourself. Most cemented elements are made with precisely
ground edges, when the edges are lined up and clamped the
lens is aligned. 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

There are a few technicians who will recement lenses.
John van Stelten has been offering this service for a long
time and has a good reputation, however, he is expensive.
Some older lenses are not worth the cost of recementing
them.

The Focal Point
John Van Stelten
1017 South Boulder Road
Suite E-1
Louisville, CO 80027-0027
Tel.- 303-665-6640
Fax - 303-665-3803
http://www.411web.com/F/FOCALPOINT/


I've recemented a number of lenses using Summers binary
(heat curing) cement. This worked well but the UV curing
stuff is easier to use. The UV-69 type has the advantage
that it is not considered a hazardous material for shipping.
The suggested method of decementing elements cemented
with synthetic cements is to boil them apart in a special
oil. The oil is also available from Summers and is not too
expensive but it must be shipped as a hazardous material
which about doubles the cost. Another method which works on
many lenses is to soak them in Methylene Chloride. This is a
common solvent used in paint removers. It may take days for
the solvent to penetrate. If this works its safer for the
lens because there is no danger of heat shock which can
cause chipping or even break the elements.
Very old lenses, cemented with Canada Balsam (the stuff
that turns yellow or brown at the edges) will come apart
with gentle heat. Its often suggested that they be heated on
a hot plate but I find they will come apart in heated water.
Put them in cold water and heat until they come apart. The
heat needed is well below the boiling point. Lenses
originally cemented with Canada Balsam should be recemented
with a modern synthetic.
The hardest part of recementing is getting the glass out
of "burnished" or "spun-in" mounts. These were made with a
thin lip of metal which was burnished down around the
periphery of the lens. This is an excellent mount as far as
accurate centering and protection of the glass but is
difficult to undo. I have had some luck in prying up the lip
so that it can be re-used but very often it will break or
become wrinkled. The usual technique is to machine it off in
a precision lathe, thread the back of the mount, and make a
back retaining cap. All fine if you are a skilled machinist,
I am not. It is also possible to reinstall the lens using
epoxy cement around its periphery. Most Tessar type lenses
have the back component mounted this way. Recementing the
elements is much easier than dealing with the burnished
mount.
When a lens is recemented the anti-reflection paint must
be removed. After cementing it must be replaced to prevent
total internal reflection from the edges (some single
elements do not need the paint). At one time an excellent
paint called Velvet was available but its been off the
market for many years. The best current paint is Krylon
Untra-Flat Black. This comes in spray cans. Its used by
spraying some into a small container and applying it with a
brush. Its also good stuff for painting the interiors of
lens cells and and generally on other surfaces which should
not reflect light. The paint also acts as a seal for the
cemented edges of the lens. I think one reason that some
brands of old lenses seem to be more prone to degredation of
the Canada Balsam cements is the variation of the
effectiveness of the sealing quality of the anti-reflection
paint. For instance, old Zeiss lenses seem to more resistant
to cement problems than old Bausch & Lomb lenses.
While the effect of oxidizing or crystalized Canada
Balsam is pretty familiar the effect of degraded synthetic
cements is less so. That is partly because they are much
more stable than Balsam but also because the effect may be
harder so see. Sometimes is appears to be large bubbles
between the elements, this is due to separation of the
cement and probably due to poor surface perparation or
curing problems during manufacture. Another effect, and one
that may be difficult to see if you don't specifically look
for it is the slight haziness the cement develops. This is
visible when a flashlight is shown directly into the lens.
Sometimes its more visible by reflected light than
transmitted light. The effect on lens performance is to
destroy contrast. Even a very slight haze has a surprizingly
large effect on contrast. When shopping for used lenses its
a good idea to carry a loup and a small flashlight with you.
These can show up cement problems, fine scratches, gouges,
haze, dirt, and fungus. While even a very clean lens can be
awful its also true that the best lens can be ruined by any
of the above.


--
---
Richard Knoppow
Los Angeles, CA, USA



  #5  
Old August 8th 04, 06:26 PM
John Hendry
external usenet poster
 
Posts: n/a
Default fog inside lens cell

----- 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.




  #6  
Old August 9th 04, 12:00 AM
John Hendry
external usenet poster
 
Posts: n/a
Default fog inside lens cell


"John Hendry" wrote in message
news:[email protected]
----- 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.



  #7  
Old August 9th 04, 12:00 AM
John Hendry
external usenet poster
 
Posts: n/a
Default


"John Hendry" wrote in message
news:[email protected]
----- 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.



  #8  
Old August 10th 04, 03:07 PM
Richard Knoppow
external usenet poster
 
Posts: n/a
Default fog inside lens cell

"John Hendry" wrote in message news:[email protected]
"John Hendry" wrote in message
news:[email protected]
----- 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.



The elements are precision ground so that the edges are exactly
concentic and coaxial with the axis. If the lens were to be rotated as
you suggest it would mean that the entire cemented lens could be
mis-centered. Since even slight decentering can cause a rather large
degradion of the image its important that the cemented lenses be very
carefully centered when made.
The type of mounting commonly used for spherical surface elements
automatically centers the surfaces in the mount. The mount clamps the
lens between two rings, the minimum distance is when the surfaces is
centered. Cementing procedures must rely on the precision of the edge
grinding for alignment.
The old method of centering is still used with some
modification. The traditional method was to fasten the lens to the end
of a thin walled tube wtih flexible cement. A point sourc of light is
then reflected from the surfaces and observed through a telescope. The
lens on the tube is slowly rotated and the reflections observed. If
the lens is not centered the reflection will trace a circle. The lens
is pushed around on the soft cement until the reflections from both
surfaces are absolutely steady. A second tube is then clamped down to
hold the lens in this position and the edge ground. Modern lens making
machines probably use lasers to provide a more sensitive measure of
eccentricity but the method is still essentially the same. When the
elements are cemented they are held in something like a V block. If
the edges are correctly ground the lens will be properly centered.
Some lenses, for instance the Schneider Angulon (not Super Angulon)
have elements of different diameters cemented. The edge is still the
reference point. It is likely that some pre-war multiple cemented
element lenses were never correctly centered. The Turner-Reich lens,
which has five cemented elements is an example. Getting these centered
correctly practically means re-grinding the edges. Not worth the
effort for the T-R.
A correction to my original post partly quoted above. The cement I
am currently using is Summers UV-74. This is a UV curing cement which
does not have to be shipped as a hazardous material. The shipping cost
for some of the cements exceeds the price of the cement. UV-74 cures
fine with a type BLB black light bulb and should also cure fine with a
BL type. The difference between these is that the BLB has an envelope
of Wood's glass to eliminate visible light, the UV produced by both
lamps appears to be the same.

Richard Knoppow
Los Angeles, CA, USA

  #9  
Old August 12th 04, 05:51 AM
John Hendry
external usenet poster
 
Posts: n/a
Default fog inside lens cell


"Richard Knoppow" wrote in message
om...

snip good stuff

Thanks very much for the very complete and interesting background info
Richard. I was talking to a chap working in a camera store recently who said
he had toured the Sigma plant in Japan. Sounded like a fascinating place to
check out.

Regards,
John




  #10  
Old August 12th 04, 05:51 AM
John Hendry
external usenet poster
 
Posts: n/a
Default


"Richard Knoppow" wrote in message
om...

snip good stuff

Thanks very much for the very complete and interesting background info
Richard. I was talking to a chap working in a camera store recently who said
he had toured the Sigma plant in Japan. Sounded like a fascinating place to
check out.

Regards,
John




 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Digital vs Film - just give in! [email protected] Medium Format Photography Equipment 159 November 15th 04 04:56 PM
White specks on lens. Steve Lee Digital Photography 26 August 8th 04 04:24 PM
hyperfocal distance leo Digital Photography 74 July 8th 04 12:25 AM
New Leica digital back info.... Barney 35mm Photo Equipment 19 June 30th 04 12:45 AM
swing lens cameras and focussing distance RolandRB Medium Format Photography Equipment 30 June 21st 04 05:12 AM


All times are GMT +1. The time now is 12:13 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2022, Jelsoft Enterprises Ltd.
Copyright 2004-2022 PhotoBanter.com.
The comments are property of their posters.