Lens quality control

Started Sep 24, 2013 | Discussions
parallaxproblem
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Re: Lens quality control
In reply to OpticsEngineer, Sep 26, 2013

OpticsEngineer wrote:

"Is lens design really so difficult these days? Don't you just need to pump a few reflective/refractive indexes into a MathCad model and out pops your answer? Optics is a very well established field and there are no 'mysteries' there and so I would imagine (I have never done it myself) optical design is just a case of chosing between compromises of cost/quality"

It is easy to analyze a design once you have it. To come up with a new design is considerably more difficult. Millions of combinations of variables.

But even then, it is somewhat easy to come up with a lens design that performs fantastic when everything is perfect. What is difficult is to design a lens that still performs well with variations in curvatures, tilts, decenters, thicknesses and variations in index of refraction. That process is known as tolerancing and it actually is 90% of the work in making a good lens design. You have to know many details of your process capability, sometimes making guesses that improvements are going to there when you need them. That is where I see Sony's move into short registration distance and small and light as being technical challenge. And when you tolerance, you need to know costs associate with increased tolerance levels.

I don't think anyone has been complaining that E-mount lenses are bad when they are perfectly made. There are great copies out there. It is the consistency.

Designing something versus making a few hundred thousand is a completely different thing. Completely different teams of people.

By the way, Mathcad would not be used by lens designer making lenses for a DSLR. Low end software is like Zemax. That is what I use, so real lens designers consider me an amateur. It cost $4000 and works forever. CODE V last time I checked was $25000 and expires yearly - requires $5000 a year to license. It has much better optimization routines than Zemax. Companies like Zeiss have their own lens design software that they continually are improving and in my conversations with them, I believe the Zeiss software is a step up in capability. They have Phd mathematicians working on it all the time. I assume companies like Nikon and Canon also use internally developed softwares but I do not actually know what they use.

Thanks for providing the insight from a knowledgable perspective

Sorry, the MathCad reference was a joke (though it is interesting to learn about the actual software you would use)

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OpticsEngineer
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Re: Lens quality control
In reply to parallaxproblem, Sep 26, 2013

"Sorry, the MathCad reference was a joke"

I was wondering if you were joking.  (I actually laughed)  But you would be surprised how many people graduate with an engineering degree of some kind and don't want to learn an industry standard software .. for instance insisting that they are going to write their own raytracing software.  (An absolute complete waste of time)

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ProfHankD
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Learning lens design
In reply to OpticsEngineer, Sep 26, 2013

OpticsEngineer wrote:

But you would be surprised how many people graduate with an engineering degree of some kind and don't want to learn an industry standard software

You know, I couldn't even find somebody on faculty here at the University of Kentucky who does lens design. Physics has people who look at an entirely different type of lens, and my department has an EM group that does lots of antenna design and analysis, but no optics per se. The closest is one of my fellow ECE faculty who is working on nanofabrication technologies.

How did you learn about optical design?  I definitely am not competent in optical design... I barely know enough to be dangerous.     Years ago, I helped improve a supercomputer-based program for design of diffractive optics, but I still haven't learned enough about lenses to support my research in computational photography.  Any suggestions on where to start?

Thanks.

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parallaxproblem
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Re: Learning lens design
In reply to ProfHankD, Sep 26, 2013

ProfHankD wrote:

OpticsEngineer wrote:

But you would be surprised how many people graduate with an engineering degree of some kind and don't want to learn an industry standard software

You know, I couldn't even find somebody on faculty here at the University of Kentucky who does lens design. Physics has people who look at an entirely different type of lens, and my department has an EM group that does lots of antenna design and analysis, but no optics per se.

I did a student placement in a department which designed millimeter band antennas (you can probably guess the application...). Even back in the 1980's everything there was based around mathmatical modelling (fortran running on HP1000's and microvax's ) of a very limited number of antenna design options. The specifics of the environment it was to be used in defined which of the designs was most appropriate (microstrip phased arrays generally being the most popular at that time) and then the design engineers would bang a few numbers into the appropriate modelling software and then the students would fabricate a pre-production model based on whatever numbers came out, for measurements on the test ranges

Everybody on my degree knew to avoid as much as possible the 'electro-optics' options in the final year if you wanted good final grades because they were so difficult, and to focus instead on the 'easy' digital electronics options...

Suffice to say that brief exposure was enough to frighten me off both those areas for life!

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GaryW
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Re: Lens quality control
In reply to parallaxproblem, Sep 27, 2013

parallaxproblem wrote:

forpetessake wrote:

Poor quality control on part of Sony and other manufacturers opens a business opportunity for third parties to test lenses and sell them at a premium. I wonder why we don't hear about companies reselling lenses with full DXO test data and making some profit from this. Why should a poor quality lens cost the same as a good one? I think many consumers would prefer paying 10% extra for known quality rather than buying a pig in a poke.

Nice idea but I think the main companies would be very unhappy with this as it implies that there might be sub-par lenses in the supply chain - we know there are, but the main manufacturers don't want this to be 'common knowledge', not just from a sales point of view but also from a support point of view when dealing with customers who think their lens might be sub-par

If Sony can't satisfy you under warranty repair, your beef is with them, not your fellow posters.  But, I think you're right -- if they're not going to spend time to Q/A to exacting enough standards at the factory, they don't want to draw attention that some lenses are going to underperform.

Even on this forum there are a small number of posters who refuse to believe there are quality issues with some of Sony's lenses.

That's being a bit disingenuous.

Of course there are "quality issues", not just with Sony, but with all brands.  Now how do you narrow down just what percentage of lenses are sub-par?  And by whose standards?  Most consumer-grade lenses have sample variation.  When I shopped for used A-mount lenses, I'd often run into reviews that would say things like, "It's a good lens,depending upon getting a good sample" or other such comments.

In the general buying public there are probably only a very small percentage of customers who know about the possibility of sample variation in lenses

The variation might be small enough for the vast majority of cases where no one notices a problem.

The problem that you and another poster showed seemed much more severe than average.

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Jefftan
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Re: Lens quality control
In reply to GaryW, Sep 28, 2013

http://www.photozone.de/sony_nex/829-sony1018f4ossUnfortunately, and that's a bit of a tradition in the local Sony test history, we experienced significant centering defects in the two samples that we tested. The first sample delivered miserable results throughout the range whereas and the 2nd sample showed a very soft output on the left image side. Honestly, we consider two samples to be enough so the resolution observations reflect the results from the 2nd sample (based on the center and right image side).

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YuriS
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Re: Lens quality control
In reply to nevada5, Sep 29, 2013

Guys! Let’s stop talking about QA and QC. Just to be clear – all these things are POST MORTUM. That means some things by-design have higher chance to be manufactured well, but some things - have not. We have a good mantra for such occasion: It can be made but cannot be manufactured. And we call it manufacturability. The article There is no perfect lens is a very good example of it. It looks like SEL1628 by design had higher in-process variability. And one important note: the lens with higher elements number has higher change to be manufactured wrong. So Tessar and Triplet lenses supposed to be high manufacturability lenses… Which was proved in a past…

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GaryW
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Re: Lens quality control
In reply to Jefftan, Sep 29, 2013

Jefftan wrote:

http://www.photozone.de/sony_nex/829-sony1018f4ossUnfortunately, and that's a bit of a tradition in the local Sony test history, we experienced significant centering defects in the two samples that we tested. The first sample delivered miserable results throughout the range whereas and the 2nd sample showed a very soft output on the left image side. Honestly, we consider two samples to be enough so the resolution observations reflect the results from the 2nd sample (based on the center and right image side).

That's an expensive lens.  At least with the 16mm, it was the least-expensive Sony-manufactured Nex lens -- maybe still is.

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Gary W.

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parallaxproblem
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Re: Lens quality control
In reply to YuriS, Sep 29, 2013

YuriS wrote:

Guys! Let’s stop talking about QA and QC. Just to be clear – all these things are POST MORTUM. That means some things by-design have higher chance to be manufactured well, but some things - have not. We have a good mantra for such occasion: It can be made but cannot be manufactured. And we call it manufacturability. The article There is no perfect lens is a very good example of it. It looks like SEL1628 by design had higher in-process variability. And one important note: the lens with higher elements number has higher change to be manufactured wrong. So Tessar and Triplet lenses supposed to be high manufacturability lenses… Which was proved in a past…

Er... the people in this forum are nex owners and are buying nex lenses.  Sony are not replacing faulty lenses, as I have shown, so isn't qc rather an important issue here?  Why should we stop talking about it ?t

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parallaxproblem
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Re: Lens quality control
In reply to GaryW, Sep 29, 2013

GaryW wrote:

Jefftan wrote:

http://www.photozone.de/sony_nex/829-sony1018f4ossUnfortunately, and that's a bit of a tradition in the local Sony test history, we experienced significant centering defects in the two samples that we tested. The first sample delivered miserable results throughout the range whereas and the 2nd sample showed a very soft output on the left image side. Honestly, we consider two samples to be enough so the resolution observations reflect the results from the 2nd sample (based on the center and right image side).

That's an expensive lens. At least with the 16mm, it was the least-expensive Sony-manufactured Nex lens -- maybe still is.

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Gary W.

It is a 300 dollar lens, or at least was - that is a significant amount of money, particularly when you look at the strip down and see how little is in it.  Having to throw away 300 dollars is an issue for most people!

This issue seems trivial to you.  I'm very interested in hearing what you think somebody who ends up with a poorly assembled lens from Sony should do with it?  Please remember that Sony are not replacing these lenses as my experience demonstrates, and shops outside of the usa do not have such generous returns policies as you are used to

Should that person be as unprincipled as Sony and try to sell that defective lens to an unsuspecting person on Ebay or similar?  My morality is superior to Sony's (which makes it interesting that you take their side in this matter) and I was not prepared to behave in such a way and so that money I spent is literally lost and I have a lens I cannot use and which cannot be resold - I might as well put it in the bin and wave goodbye to that money (and in my case I have a second bad copy so I lost even more money).  What about somebody who spends 1000 dollars and gets a bad Sony 'Zeiss' lens which Sony will not replace?

QC is a serious issue for all NEX users and 'apologising' for Sony will only bring closer the day you end up with one of these decentered lenses!

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YuriS
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Re: Lens quality control
In reply to parallaxproblem, Sep 29, 2013

parallaxproblem wrote:

YuriS wrote:

Guys! Let’s stop talking about QA and QC. Just to be clear – all these things are POST MORTUM. That means some things by-design have higher chance to be manufactured well, but some things - have not. We have a good mantra for such occasion: It can be made but cannot be manufactured. And we call it manufacturability. The article There is no perfect lens is a very good example of it. It looks like SEL1628 by design had higher in-process variability. And one important note: the lens with higher elements number has higher change to be manufactured wrong. So Tessar and Triplet lenses supposed to be high manufacturability lenses… Which was proved in a past…

Er... the people in this forum are nex owners and are buying nex lenses.  Sony are not replacing faulty lenses, as I have shown, so isn't qc rather an important issue here?  Why should we stop talking about it ?t

Ha! Please do not understand me wrong…  QA/QC is effective when checks 100% of the product. I’m sure, that each and every lens checked electrically. And (if I’m not mistaking) there is no complains for electrical functionality. But I’m not sure that each and every lens checked optically. And if it checked – what specification limit of MTF  or other parameters were applied? So we (I’m a NEX owner as well) can continue to talk about QA, but I think quality deviation is just within the internal Sony spec. So design is a root cause, not QA/QC.

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OpticsEngineer
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Re: Lens quality control
In reply to walkaround, Sep 29, 2013

"The challange for Sony is cost: how to make a good enough and small enough lens in China for as little money as possible. This is not the pure engineering problem you are making it out to be."

Of course you are correct. It is all about cost. Tighter tolerances cost money. I see my post did not bring out that important point.

In thinking about why that did not come across, I realize that in the context of working for a large company, if something does not meet the cost constraints, it simply gets lumped into "not manufacturable."

In contrast, one particular metrology lens I have personnel knowledge of is actually made in low quantities (a few a year) assembled at night by the designer who has a Phd optics.   The assembly is done at night so vibrations from traffic don't wash out the fringes on the interferometer used to align each element.  It can be made, but in my company it would be considered "non-manufacturable."

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OpticsEngineer
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Re: Learning lens design
In reply to ProfHankD, Sep 30, 2013

"How did you learn about optical design? I definitely am not competent in optical design... I barely know enough to be dangerous. Years ago, I helped improve a supercomputer-based program for design of diffractive optics, but I still haven't learned enough about lenses to support my research in computational photography. Any suggestions on where to start? Thanks."

It has taken me a little while to think of a hopefully useful response. In my case I have separate masters degrees in Optical Engineering and in Electrical Engineering so the "where to get started" answer is a bit elusive to me. A lot of the nuts and bolts about optical design I learned on the job from older engineers/physicists. And a lot of it I learned in lab work, fielding instruments, or from customers. Also optics has a lot of mechanical engineering to it so I have learned a lot from mechanical engineers as well and from my father who has degrees in Electrical and Mechanical Engineering. Considering your specific question of "knowing enough about lenses to support research in computational photography" There are three books I think might be useful.

Warren J Smith and Robert E Fischer Modern Optical Engineering McGraw Hill Has a good chapters on "basic optical devices"

Robert E Fischer / Bijana Tadic Galeb Optical System Design McGraw Hill good chapters on tolerancing, manufacturability, cost, case studies on optimization, rules of thumb, bloopers and blunders, and an explanation of exactly went wrong on the Hubble Space Telescope (which matches what I heard from people that worked in the facility that made the mirror).

Warren J Smith and Genesee Optics Software Modern Lens Design A Resource Manual McGraw Hill The figure that is a map of lens types of field angle and aperture brings a tremendous amount of understanding and organization into understanding the different lens types. Then lots of examples of lenses.

When I was in college 25 years ago, my professors would apologize for how poor the available books were for teaching the trade of optical engineering. A lot was taught just from their notes with no good textbooks as references. Since that time, many good texts have come out. It is a lot easier to learn the trade from books than it used to be.

Then also The University of Arizona I believe has an online degree program in optics.

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ProfHankD
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Re: Learning lens design
In reply to OpticsEngineer, Sep 30, 2013

OpticsEngineer wrote:

It has taken me a little while to think of a hopefully useful response. In my case I have separate masters degrees in Optical Engineering and in Electrical Engineering so the "where to get started" answer is a bit elusive to me.

Fair enough. My PhD is in Computer Science from an Electrical Engineering department (what we'd now call Computer Engineering), but I began as double major between Electrical and Mechanical Engineering. The only optics I've seen in courses were in Physics, and I don't recall ever putting two elements together.

A lot of the nuts and bolts about optical design I learned on the job from older engineers/physicists. And a lot of it I learned in lab work, fielding instruments, or from customers.

That's what I suspected. Rather like what happened in the Power Engineering field... Optics seems to be one of those fields that slowly became less of an emphasis in university settings although it is still much needed in the real world.

I'll check out the books you mentioned.

Any lens design software that is free (open source) and not total junk? I have a large supercomputing facility in my lab, so software that I can tweak to run on my clusters would be highly desirable... I might not know the right questions to ask, but have tons of compute hardware to spend on optimization.

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franzel
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Re: Learning lens design
In reply to ProfHankD, Oct 1, 2013

Interesting question .

Matter of fact, SEL lenses have so far never been proven to suffer from sample variation issues , even though there probably are some .

However, no single proper test or proof of SEL lenses re- that matter, only lots of repitious claims based on nothing .

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