History of Lens Glass

[jenkins]

<p>I would like to know?<br>

How is a lens made, as in the production?<br>

I have no idea. How long does it take, tools, materials, what sort of glass?<br>

Why is certain glass better than others?<br>

Why are lenses so expensive, is it because production is a very slow precise process which i know it has to be.<br>

Just some history, i am genuinely interested.<br>

Thanks<br>

Simon.</p>

<p> </p>

[jonathan_lui]

<p>Canon has published online a book called <a href="http://www.canon-europe.com/Support/Documents/digital_slr_educational_tools/en/ef_lens_work_iii_en.asp">EF Lens Work III</a> . Some of the chapters explain the technologies involved in the design and production of Canon's lenses. It may not answer all of your questions, but it might interest you nonetheless.</p>

 

[jenkins]

<p>Something from the heart Jonathan, maybe an old guy that has good knowledge, not a physics lesson, just common language, i am a Plasterer by trade and in the past a printer on a 5 colour Heidleberg Printing Press for 15 years, i would be able to put into words not links if asked a question, there was no internet at one time for answers, just experience.</p>

[MichaelChang]

<p>Simon, have a look at this video:<br>

<a href="http://ca.youtube.com/watch?v=X7_wL0ZZi6k">http://ca.youtube.com/watch?v=X7_wL0ZZi6k</a></p>

[MichaelChang]

<p>Also - Canon lens production:<br /> Part 1 - <a href="http://ca.youtube.com/watch?v=OkWsk9rXpcU">http://ca.youtube.com/watch?v=OkWsk9rXpcU</a> <br /> Part 2 -<a href="http://ca.youtube.com/watch?v=7T7BDeMU_Ks">http://ca.youtube.com/watch?v=7T7BDeMU_Ks</a><br>

Part 3 - <a href="http://ca.youtube.com/watch?v=KpkAWZTwqI4">http://ca.youtube.com/watch?v=KpkAWZTwqI4</a></p>

[colin carron]

<p>Simon, here is a wikipedia article on photographic lenses :</p>

<p><a href="http://en.wikipedia.org/wiki/Photographic_lens_design">http://en.wikipedia.org/wiki/Photographic_lens_design</a></p>

<p>Here is a brief article on the history of optical glass :</p>

<p><a href="http://www.applet-magic.com/opticalglass.htm">http://www.applet-magic.com/opticalglass.htm</a></p>

<p>Why is it all so complicated? The nature of glass is to act as a prism, separating white light into its distinct rainbow colours. This tendency can be countered by combining lenses made with glass of different properties so that the prism-type effects cancel each other out. You will see a lot of talk about CA (chromatic aberration) which is the degree to which a lens fails to create a single image from all the separate colours of light.<br>

You then also have the geometric properties of the lenses particularly the effect of spherical lens surfaces. These tend to produce various distortions of the image such as the barrel distortion and pin cushion distorton. <br>

This ends up with a modern zoom lens with a dozen or more elements, each made out of high grade optical glass with very specific properties of refractive index and dispersion. And each lens s ground to a very specific shape, mostly with spherical surgaces but some with complex aspherical surfaces. And then al the glass-air surfaces are multi-coated to reduce reflections. I find it surprising they work as well as they do!</p>

[Ed_Ingold]

<p>Here are a couple of links you should find interesting. The Zeiss page has several links to illustrate the manufacturing process. The Leica link presents an excellent history and outline of glass and lens development. Enjoy!</p>

<p><a href="http://www.zeiss.com/C12567A8003B58B9/Contents-Frame/C4B1A59613632D9DC1257226005F6AB7">http://www.zeiss.com/C12567A8003B58B9/Contents-Frame/C4B1A59613632D9DC1257226005F6AB7</a></p>

<p><a href="http://us.leica-camera.com/assets/file/download.php?filename=file_1750.pdf">http://us.leica-camera.com/assets/file/download.php?filename=file_1750.pdf</a></p>

 

[Ed_Ingold]

<p>The achromatic lens, which uses two elements with different dispersion to reduce chromatic aberation, was invented nearly 280 years ago by an English barrister. In order to protect his invention, he contracted with a separate optician for each element. The opticians, however, subcontracted their work to the same lens grinder, who quickly surmised the application and filed for a patent.</p>

<p>This patent was in litigation for more than 200 years. And they say Americans are lawyer-happy :-)</p>

[jenkins]

<p>Absolutely fascinating its hard to imagine how anybody was able to achieve making a lens before all this hi tech equipment, $1000 a kilo for optical glass, now i see why they are so expensive, its all a lot slower than i imagined, thanks for this info.<br>

It hard to imagine why there is any quality difference in lenses, must be the raw optical glass they buy in at the start of the process.</p>

<p> </p>

[sarah_fox]

<p>Edward, what a great piece of trivia!</p>

[alex_lofquist]

<p>This reminds me of the girl who after she had a couple of "glasses" would make a spectacle!</p>

[Ed_Ingold]

<p>It is a lengthy but technically simple job to grind a parabolic telescope mirror to an accuracy of about 1/2 a millionth of an inch. Do you wonder why it's called a "Newtonian" telescope?</p>

<p>Lenses are a little more difficult because you two sides to grind and polish and the curvature is much more pronounced than a Newtonian mirror, but precise spherical surfaces are simple. </p>

<p>Precise flats are more difficult. The trick is to grind three surfaces at once - as two surfaces become curved, the third will correct both and you end up with three flats.</p>

[oskar_ojala]

<p>The glass needs to be very uniform in structure and have the right properties. Then a very careful grinding takes place. After that, the lens needs to be assembled carefully. And of course the previous steps won't help if the design is not good begin with. Recently I read an article about the creation of a new, superlarge European space telescope where the ESA literally had to look for the best mirror material and the best grinder in the world in order to make it, fascinating stuff.</p>

[Ed_Ingold]

<p><em>It hard to imagine why there is any quality difference in lenses, must be the raw optical glass they buy in at the start of the process.</em><br>

<em></em><br>

Actually, it starts with the design. Even though we have replaced a platoons of mathemeticians with ray-tracing software, lens design is a long process, as much art as science (q.v., the Leica link I provided above). After the lenses are ground, polished and coated with extreme care, they must be assembled precisely. Zeiss (q.v., the Zeiss link above) centers and spaces the elements within 0.02 mm. That's about 1/6th the width of an human hair.</p>