# Optical Quality Assurance by LensRentals.com



## Canon Rumors Guy (Feb 8, 2016)

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Roger over at LensRentals.com has written great article on optical quality assurance and what goes into making sure you get a lens that works as intended.</p>
<blockquote><p>After we published a number of posts about copy-to-copy variation, people were quick to say that this company or that needs to ‘just’ improve quality control. I totally agree but realize most people don’t have a clue what ‘improving quality control’ would really look like. I think they have some vague idea of hiring a guy named Joe to sit at the end of the assembly line, check all the lenses, and reject all the bad ones. Optical quality control for lenses is way, way more complicated than that.</p>
<p>Before we start, let’s get a couple of things out of the way.</p>
<ol>
<li> If you expect that the lens you buy has the exact same MTF that the manufacturer published, then don’t read this. You’ve got too much reeducation to do.</li>
<li> If you ever say, “for that kind of money I expect perfect” please don’t read further. Perfect doesn’t exist. For $20,000 and up you can get pretty close. For $2,000 you should be able to get reasonably close.</li>
</ol>
<p>On the other hand, a reasonably expensive lens should have reasonable quality control and minimal copy-to-copy variation.  We know it can be done; some manufacturers are already doing it. Others totally suck. But when they suck, sticking Joe at the end of the assembly line won’t really fix things. If you want to read this pretty long article, I’ll explain why, and also explain some of what can be done. <a href="http://www.lensrentals.com/blog/2016/02/optical-quality-assurance" target="_blank">Read the full article</a></p></blockquote>
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## Mt Spokane Photography (Feb 8, 2016)

I've been thru that with many manufacturers of precision parts, but optics is the most difficult. Sometimes its impossible to measure a part directly to see if its accurate enough. 

We ran into that with fiberoptic connectors. Each one has a lens in it, and the tolerance for the alignment required is so small that we could not find a way to directly measure it, not anywhere in the world. What was eventually done was a clever way of creating a "Gold" standard which was nearly perfect. We were doing something that had never been successfully done before, and our competition said it would never work. 

Then during the assembly process, parts were checked against the standard using the same clever method that quickly picked up any that were out of tolerance. This happened at a early assembly stage and weeded out bad components before they were assembled into a very expensive product.

We amazed everyone when the final production items came in well under specification. That seldom happens in the real world. They also made Canon lens prices look like chicken feed  The cost was well worth it, because a multi million dollar system needed every bit of performance possible.


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## neuroanatomist (Feb 15, 2016)

Insightful post by Roger, as usual. 

Reading the title of the CR post, I briefly hoped it meant LensRentals was launching a lens testing service for individuals.


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## Mt Spokane Photography (Feb 15, 2016)

neuroanatomist said:


> Insightful post by Roger, as usual.
> 
> Reading the title of the CR post, I briefly hoped it meant LensRentals was launching a lens testing service for individuals.



He keeps mentioning it, but for now, buying a used one is one way to get a tested lens. I seem to remember that buying a new one thru a partner company also qualified for a test.


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## RGF (Feb 21, 2016)

Mt Spokane Photography said:


> neuroanatomist said:
> 
> 
> > Insightful post by Roger, as usual.
> ...



who is the partner company? And what would you pay for testing? Also lens can go bad of time. It would be nice to be able to test a lens after it is repaired.


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## kaihp (Feb 22, 2016)

RGF said:


> Mt Spokane Photography said:
> 
> 
> > neuroanatomist said:
> ...



Lensrental's used lenses (and bodies) are sold through LensAuthority.com. I am not aware of any other partner companies.


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## martti (Feb 28, 2016)

Wouldn't it be logical to sell the batch of not-so-excellent lenses to a gray exporter who can apply different politics in his post-sale services than the official agent?


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