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ultra and master primes


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#1 govind

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Posted 27 August 2009 - 01:19 AM

can you help me understand the difference between ultra primes and master primes.

and

2)difference between spherical and aspherical lenses ?
thank you
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#2 Stephen Williams

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Posted 27 August 2009 - 02:54 AM

Hi you need to change your name to your real name, it's a requiremnet here.

About 15 years, the Master Primes are far heavier, faster , sharper & twice the price.

can you help me understand the difference between ultra primes and master primes.



2)difference between spherical and aspherical lenses ?
thank you


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#3 John Sprung

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Posted 27 August 2009 - 03:18 PM

Lenses are made by precision grinding and polishing of glass. From the Renaissance up until about the 1960's, the only practical way to grind such a surface was to make it a constant distance from a center point, so the surfaces of lenses were always a small part of the surface of a sphere. With the computer age came the ability to design and grind surfaces that were different, aspherical. Computers made it practical to do loads more ray tracing than lens designers of the past could do "by hand". This allowed designers to correct some of the little errors they'd had to live with in the past, like spherical abberation.

At first, this was only done for things like high end astronomical telescopes. As technology got better, it also got cheaper. Today, most lens designs have at least one aspherical surface. (The cost effective way to go is to collect all the corrections into one surface).





-- J.S.
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#4 georg lamshöft

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Posted 28 August 2009 - 05:56 AM

@John Sprung
Great explanation! But I'll have to add that aspherical lenses are just a technology, a tool to improve possibilities in lens design. They're not a guarantee for better quality. There also various different technologies used to create aspherical surfaces, many consumer-lenses incorporate plastic-molds to create cheap aspherical lens-elements of low-quality/precision. Aspherical elements that truly enhance quality are extremely difficult to manufacture (many hours of CNC-polishing for one surface!) and to assemble (centration) into the final lens, that's why this is still high-end-technology and really expensive.
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