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#1
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dismantling and rebuilding a cemented doublet
Hi all,
I have a small cemented doublet which has some staining between the elements. Is there a way to dismantle it for cleaning and how should I rebuild it afterwards? Thanks Robin |
#2
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"Robin Leadbeater" wrote:
I have a small cemented doublet which has some staining between the elements. Is there a way to dismantle it for cleaning and how should I rebuild it afterwards? My advice would be "don't!". However, I'm no optician. You might want to ask on sci.astro.amateur where a few refractor-makers hang out. Tim -- Foo. |
#3
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"Tim Auton" wrote in message ... "Robin Leadbeater" wrote: I have a small cemented doublet which has some staining between the elements. Is there a way to dismantle it for cleaning and how should I rebuild it afterwards? My advice would be "don't!". However, I'm no optician. You might want to ask on sci.astro.amateur where a few refractor-makers hang out. Hi Tim, Oh I am happy to submit this one for experimentation. I got it cheap from SurplusShed in the US. When I pointed out the flaw, they sent a replacement by return and told me to keep the old one. (Amazingly efficient and cheap too) Robin |
#4
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Robin Leadbeater wrote:
"Tim Auton" wrote in message ... "Robin Leadbeater" wrote: I have a small cemented doublet which has some staining between the elements. Is there a way to dismantle it for cleaning and how should I rebuild it afterwards? Worth thinking about that before you take it apart. You want something like DPX slide fixative or Canadian balsam - available from your friendly microscopy shop. Don't be tempted to use cyanoacrylate - it is clear and watery but it plates out wisps over optical surfaces as it cures. One of its other uses is for developing fingerprints. Not sure about clear epoxy - but I suspect bubbles will be an issue with any two part adhesive. My advice would be "don't!". However, I'm no optician. You might want to ask on sci.astro.amateur where a few refractor-makers hang out. Oh I am happy to submit this one for experimentation. I got it cheap from SurplusShed in the US. When I pointed out the flaw, they sent a replacement On the understanding that you may not be able to put it together again and ignoring the risks associated with aromatic solvents. Immersing in tepid xylene or toluene should encourage it to fall apart eventually (Hammerite paint thinner will probably do). But unless you can find suitable cement I wouldn't do it. Regards, Martin Brown |
#5
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Martin Brown wrote:
On the understanding that you may not be able to put it together again and ignoring the risks associated with aromatic solvents. Immersing in tepid xylene or toluene should encourage it to fall apart eventually (Hammerite paint thinner will probably do). But unless you can find suitable cement I wouldn't do it. Regards, Martin Brown IF its Canadian Balsam,then gentle heating, possibly in a double water bath, will part canadian balsam. at around 50-55 C. If its too hot to hold and hasn't parted, it ain't CB. Steve |
#6
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Presumably the refractive index of the cement matters too, if you
want to retain optimal freedom from colour. Martin -- M.A.Poyser Tel.: 07967 110890 Manchester, U.K. http://www.fleetie.demon.co.uk |
#7
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I had some success with a bino objective. I marked the edges to
re-orient them correctly, then heated it gently over a 100W bulb, presto it came apart and cleaned up ok. Then a blob of Canada balsam in between and reverse the process with gentle pressure, you don't need much balsam. jc -- http://mysite.wanadoo-members.co.uk/jc_atm/ --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.804 / Virus Database: 546 - Release Date: 30/11/2004 |
#8
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Most come apart with heat.
Clear Skies Chuck Taylor Do you observe the moon? Try http://groups.yahoo.com/group/lunar-observing/ Are you interested in understanding optics? Try http://groups.yahoo.com/group/ATM_Optics_Software/ ************************************ "Robin Leadbeater" wrote in message ... Hi all, I have a small cemented doublet which has some staining between the elements. Is there a way to dismantle it for cleaning and how should I rebuild it afterwards? Thanks Robin |
#9
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Why would you want to use an adhesive? You'd only get one chance and
have no idea of the adhesive's effect on the glass. Or it's own opacity over time. I cemented a few small hom-made (60mm) achromats with balsam cement many years ago. I believe I used meths to clean up the residue of the old cement which clung rather tenaciously. Those who have oiled their own achromats will know that only a tiny amount of liquid is necessary to fill the space between the elements. Have your glass spotlessly clean and handle the lenses only by the edges. The Pink Marigolds might come in handy at ths point. You place a blob of balsam cement in the middle of the concave surface. Then carefully lower your convex onto the blob (the right way round if it's a biconvex! You did mark the elements permamently before dismantling didn't you?) Now watch as the balsam expands magically to finally run stickily off the edges. So have plenty of paper towels beneath the doublet and meths handy to clean up the mess. Leave it to harden a bit before attacking ithe edges with too much meths covered tissue or cloth. Or you could find the meths creeping into the gap between the elements and have to start again! I also remember reading about loading weights onto the achromat to ensure a close seperation. But this may cause distortion. Balsam is not usually used for anything over 75mm if I remember correctly. Something to do with the strain the balsam would cause with changing temperature on a cemented doublet. The front element being in contact with the cold dew. While the rear element is warm and cosy in its sealed refractor tube. Chris.B |
#10
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wrote in message ups.com... Why would you want to use an adhesive? You'd only get one chance and have no idea of the adhesive's effect on the glass. Or it's own opacity over time. I cemented a few small hom-made (60mm) achromats with balsam cement many years ago. I believe I used meths to clean up the residue of the old cement which clung rather tenaciously. Those who have oiled their own achromats will know that only a tiny amount of liquid is necessary to fill the space between the elements. Have your glass spotlessly clean and handle the lenses only by the edges. The Pink Marigolds might come in handy at ths point. You place a blob of balsam cement in the middle of the concave surface. Then carefully lower your convex onto the blob (the right way round if it's a biconvex! You did mark the elements permamently before dismantling didn't you?) Now watch as the balsam expands magically to finally run stickily off the edges. So have plenty of paper towels beneath the doublet and meths handy to clean up the mess. Leave it to harden a bit before attacking ithe edges with too much meths covered tissue or cloth. Or you could find the meths creeping into the gap between the elements and have to start again! I also remember reading about loading weights onto the achromat to ensure a close seperation. But this may cause distortion. Balsam is not usually used for anything over 75mm if I remember correctly. Something to do with the strain the balsam would cause with changing temperature on a cemented doublet. The front element being in contact with the cold dew. While the rear element is warm and cosy in its sealed refractor tube. Chris.B Thanks Chris, Just the information I need. All I need to do now is find a friendly microscopist to give me a drop of balsam. (The sources I have found so far, although not unduly expensive, are more than the cost of this surplus optic!) Robin ----------------------------------------------------------------------- Robin Leadbeater 54.75N 3.24W http://www.leadbeaterhome.fsnet.co.uk/astro.htm ------------------------------------------------------------------------ |
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