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. |
|
|
Thread Tools | Display Modes |
|
#1
|
|||
|
|||
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
|
|||
|
|||
fog inside lens cell
"PGG" wrote in message newsan.2004.08.05.00.27.33.962000@NO_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
|
|||
|
|||
fog inside lens cell
"PGG" wrote in message newsan.2004.08.05.00.27.33.962000@NO_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
|
|||
|
|||
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. |
#5
|
|||
|
|||
fog inside lens cell
"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. |
#6
|
|||
|
|||
fog inside lens cell
"John Hendry" wrote in message news:jgyRc.55606$gE.30814@pd7tw3no...
"John Hendry" wrote in message news:intRc.52767$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. 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 |
#7
|
|||
|
|||
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 |
#8
|
|||
|
|||
"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 |
#9
|
|||
|
|||
"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. |
Thread Tools | |
Display Modes | |
|
|
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 |