jean_marie_dederen Posted March 26, 2015 Share Posted March 26, 2015 <p>Borrowed a cron35 (goggled) 1959 vintage. Lens looked almost too good to be true: couldn't see any blemishes or cleaning marks or hairline scratches.... Took it out to do some BW landscape. After a closer inspection I can see why there is no damage to the coating: it doesn't seem to have any! (at least not on the front element). Hate to think what I will develop over the weekend!<br> I suppose that 1959 front element coating is of the kind that rubs off over the years? But surely it wouldn't rub off completely? How do you see that a lens has been repolished? </p> Link to comment Share on other sites More sharing options...
james_elwing Posted March 26, 2015 Share Posted March 26, 2015 <p>I don't believe the coating would have all come off through normal cleaning.<br> The older coatings were soft over soft glass. Once the coating on the front element had been progressively over-cleaned, the contrast declined. The prime option would have been to have the front element re-ground and recoated. As long as the damage to the actual glass was slight, there was an option to re-polish the surface to remove the remainder of the coating. I assume this could be re-coated, but the cheapest option was to polish this front surface alone.<br> The light reflected away from this surface would be around 4%. Little would be bounced around the lens interior, as all other coated surfaces remain intact, so contrast is not heavily compromised. Certainly it is more usable than an untreated lens.<br> I had a collapsible 1953 tm Summicron treated this way maybe 28 years ago. All other surfaces were clean, there is no obvious flare, and I still use it on my M9. </p> Link to comment Share on other sites More sharing options...
jean_marie_dederen Posted March 26, 2015 Author Share Posted March 26, 2015 <p>James - Thanks. I thought the coating was limited to the front and final back element only. Your early summicron would have had a light blueish coating, not much different from the coating that was put on uncoated prewar lenses in the late 40's and early 50's?<br> If this sample I borrowed was polished they sure did a good job, looks as good as new. I want to hold next to another summicron 35 so that I can see the difference.</p> Link to comment Share on other sites More sharing options...
winfried_buechsenschuetz1 Posted March 27, 2015 Share Posted March 27, 2015 <p>It IS possible to remove coatings without polishing. Some older coatings are so soft (or vulnerable) that they can be removed completely with mild acids such as concentrated vinegar. </p> Link to comment Share on other sites More sharing options...
jean_marie_dederen Posted March 27, 2015 Author Share Posted March 27, 2015 <p>Do they wear because of age? Fade because of exposure to light? What happens to the coatings inside?</p> Link to comment Share on other sites More sharing options...
james_elwing Posted March 27, 2015 Share Posted March 27, 2015 <p>If they are not affected by mould or cleaning marks, the internal coatings stay the same. We are used to more dramatic coating colours, so the coatings on 50's lenses look a bit faded.</p> Link to comment Share on other sites More sharing options...
Gus Lazzari Posted March 27, 2015 Share Posted March 27, 2015 <blockquote> <p>"What happens to the coatings inside?"<strong><em> Jean-Marie D.</em></strong></p> </blockquote> <p>Keep in mind that this version 8 element 35 Summicron lens series, has particularly soft coatings and is almost impossible to find a sample that doesn't have some coating issues. I've personally gone through 4 units and every one of them had coating issues. <br> <br> In addition to what was stated by <em><strong>James E.</strong>:</em><br> <em>"If they are not affected by mould or cleaning marks, the internal coatings stay the same" </em><br> Not quite, the <strong>inside</strong> air space coatings are also easily attacked by failed lubricant out-gassing, then with age turning acidic...</p> Link to comment Share on other sites More sharing options...
james_elwing Posted March 28, 2015 Share Posted March 28, 2015 <p>Fair enough. Since it wasn't an issue with my type 1 Summicron, 3.5 Summaron, 35mm Elmar or Summitar 50, I have little experience. I appreciate the 35 Summicron is a rare beast.</p> Link to comment Share on other sites More sharing options...
jean_marie_dederen Posted March 29, 2015 Author Share Posted March 29, 2015 <p>Gus, James:thanks; what exactly is 'lubricant regassing'?<br> Is each element coated? If I hold the lens up and stand under a tubelight, I see different colours: I thought the orange-yellow was caused by the glass type, and that only the violet/purple and blue were coatings: the latter seem to be limited tothe front and back elements only?<br> Lastly: one of the elements in front of the diaphragm seems to have a mark that runs along the barrel of the lens. What is going on there?</p> Link to comment Share on other sites More sharing options...
james_elwing Posted March 29, 2015 Share Posted March 29, 2015 <p>I think I recall a number of Canon TM lenses have somewhat straw coloured coatings, while some Russian tm lens coatings are a bright mauve. I think in some of the prettier modern coated lenses, the coatings are chosen to balance out to give neutral colour transmission. The lenses we are discussing are all delicately single coated.<br> Lubricant outgassing could be from excessive heat on a lubricant that is a mixture of lighter and heavier oils, such that the lighter evaporates, or the lubricant has undergone a chemical reaction, liberating substances which condense on the glass surfaces. It's not something I know much about. Clearly it is something Gus has had a fair bit of experience with.<br> The only experience of this kind I have had was with a Canon 35mm f2 tm, where an oil had condensed on two very close elements right in the centre. I didn't personally clean the lens, but whatever it was came off without any visible affect on the coatings. </p> Link to comment Share on other sites More sharing options...
Gus Lazzari Posted March 29, 2015 Share Posted March 29, 2015 <blockquote> <p>"what exactly is 'lubricant regassing'?" <strong><em>Jean-Marie D.</em></strong></p> </blockquote> <p>"<strong>out-gassing</strong>" is one of the properties of <strong>failed</strong> lubricant.<br /> As when the inside glass of your fairly new 'dark' colored car <strong>gets hazy</strong>. <br /> The out-gassing of the interior materials due to the combo of heat build-up & age; plastic, vinyl, rubber, paint, leather etc. <br /> <br /> The other main property of lube failure would be thickening/stiffening.</p> <p>"<em>mark that runs along the barrel of the lens. What is going on there?</em>" <strong><em>Jean-Marie D.</em></strong><br /> Accumulation can "stick" to contamination.</p> Link to comment Share on other sites More sharing options...
jean_marie_dederen Posted March 29, 2015 Author Share Posted March 29, 2015 <p>Thank you James and Gus. Pity there is so little data available on coatings in the Leica literature.Zeiss, pioneering coating technology, including multi coating, was quite verbose about it. The Japanese manufacturers who were eager to imitate, I mean compete, made it a selling point in their adverts. Leitz just never made it much of an issue.</p> Link to comment Share on other sites More sharing options...
james_elwing Posted March 30, 2015 Share Posted March 30, 2015 <p>I am sure there are a number of articles about their coatings in old copies of 'Leica Fotografie', with a bit of technical information related to then current techniques.</p> Link to comment Share on other sites More sharing options...
jean_marie_dederen Posted March 31, 2015 Author Share Posted March 31, 2015 <p>James - You're right. Just started checking and found a reference to a discussion of lens coatings in the 1983/1 issue. Any comments on the following thread:<br> <em>Some vintage (prior to WWII) lenses that left the factory uncoated but because of age and oxidation during these years have developed "bloom" which acts somewhat like a coating. Regarding lenses with a "bloom", I seem to remember reading that the idea for deliberately putting coatings on lenses happened when it was observed that old lenses with such a "bloom" tended to perform better than new lenses without one. Some types of optical glass develop some superficial corrosion over time. And sometimes this layer of corrosion has optical properties similar to that of coating. In some cases, intentional "forced" surface corrosion was used instead of coating.</em><br> <em> </em></p> Link to comment Share on other sites More sharing options...
jean_marie_dederen Posted March 31, 2015 Author Share Posted March 31, 2015 <p>Pics with repolished lens came out normal by the way. Maybe my multicoated ND4 helped.</p> Link to comment Share on other sites More sharing options...
jean_marie_dederen Posted March 31, 2015 Author Share Posted March 31, 2015 <p>Had no idea oxidation inspired lens coating:<br> Harold Dennis Taylor, <em>A Method of Increasing the Brilliancy of the Images Formed by Lenses.</em> United Kingdom Patent #GB29,561 (1904); granted 23 November 1905. (from Wikipedia)<br /></p> Link to comment Share on other sites More sharing options...
jean_marie_dederen Posted March 31, 2015 Author Share Posted March 31, 2015 <p>Whoops, forgot this one:<br> <em>It was noticed by Dennis Taylor in 1896 that some lenses with glass tarnished by age counterintuitively produced brighter images. Investigation revealed that the oxidation layer suppressed surface reflections by destructive interference.</em></p> Link to comment Share on other sites More sharing options...
evan_dong1 Posted April 2, 2015 Share Posted April 2, 2015 <p>Gus,<br> For these "out-gassing", can they be cleaned up? I believe that I have such an issue on my Rolleiflex MX-EVS Type II. It has a "Cloudy" appearance when viewed through a bright light source. I was hoping on having it cleaned up, but was not sure whom to use. Do you do any lens servicing when a camera comes in for a CLA?</p> <p>Evan</p> Link to comment Share on other sites More sharing options...
Gus Lazzari Posted April 2, 2015 Share Posted April 2, 2015 <p><em><strong>Evan</strong></em>, any good TLR camera repair technician during a C L A, should address a fog/haze contaminated "taking" lens.<br> Thank you for asking, but my shop is currently overflowing and up to capacity with repairs.<br> Instead, try an often recommended TLR specialist: <a href="http://www.rolleirepairs.com/cla.htm">Harry Fleenor</a> <<< <em>click</em></p> Link to comment Share on other sites More sharing options...
evan_dong1 Posted April 3, 2015 Share Posted April 3, 2015 <p>Gus,</p> <p>I did check with Harry. He is currently about 4-6 months backlogged. I will check with Paul Ebel about the lens. Hopefully he might be able to do something for me</p> Link to comment Share on other sites More sharing options...
steve_rasmussen Posted April 6, 2015 Share Posted April 6, 2015 <p>"I thought the orange-yellow was caused by the glass type"<br> This is highly unlikely, as designers know that any color in the glass is going to block the opposite color on the color wheel to some degree. <br> It was discovered many years ago that a lens element made of high index glass was more reflective that those made from low index glass. So there is more of a tendency to coat high index elements. Anti reflection coatings are all low index materials.<br> </p> Link to comment Share on other sites More sharing options...
jean_marie_dederen Posted April 12, 2015 Author Share Posted April 12, 2015 <p>Thanks Steve - I only knew about the blue and purple coatings on the pre 1970's lenses.</p> Link to comment Share on other sites More sharing options...
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