Learning about telecentric lenses

I see far too many vision applications that should use telecentric lenses but don’t. I imagine this is because: (a) telecentric lenses are expensive, and (b) not many people understand what telecentric imaging can do for them. I can’t do anything about (a) but I can help with (b).

Opto-Engineering have on their website a telecentric tutorial titled, “TELECENTRIC LENSES: BASIC INFORMATION AND WORKING PRINCIPLES” (the capitals are theirs). This does it exactly what it says, so I suggest everyone take a few minutes to expand their knowledge by clicking on that link.

I may set a test, so study hard!

Saying “No” to North Korean lenses

In case you didn’t read the comment from Navitar, “Where is that lens from?” (MachineVision4Users, May 15^th, 2013,) let me make it absolutely clear: Navitar do NOT source components from North Korea. Not at all. Never have, probably never will.

Apparently my misunderstanding stemmed from a poorly-written statement on the Navitar website. As an amateur hack myself, I know how difficult it is to proof-read. As they say, “English, she is a difficult master.”

Seeing the potential in 3D

3D imaging and inspection seems to be the new frontier in terms of machine vision innovation. There’s lots of application work going on, and on the back of that, there’s quite a bit of Mergers and Acquisitions activity too.

Most recently (May 8^th, 2013,) LMI announced their purchase of white light scanner company 3D3 Solutions. That’s interesting for two reasons. First, it broadens LMI out beyond their laser triangulation base, and second, LMI is itself part of AVT parent, Augusta Technologie. So Augusta are clearly very serious about being a force in machine vision. (And it’s probably their financial muscle that has allowed LMI to launch a slew of new and improved products.)

In the same vein, although it’s hardly news, back in November of 2011 measurement specialists L.S. Starrett acquired laser profile company Bytewise, adding their products to the Starrett range.

So it seems to me I need to launch my 3D business quickly, then start a bidding war between those who are getting left out. Anyone care to join me?

Sources for Telecentric Lenses

Announcing new telecentric lenses for 12k and 16k sensors, Italian lens manufacturer Opto-Engineering reminded me that they are “the telecentric company!”

Curious about this claim, I scrolled through my favorites for other providers of telecentric lenses. Melles Griot, Schneider Optics, and Navitar all showed up, and I’m sure there are other vendors/manufacturers too.

That got me wondering: how big is the global market for telecentric lenses? It can’t be above a couple of thousand units a year, can it? And if you figure the median price of a telecentric lens is say, $3,000, then you’re looking at a global market of $6M.

Not exactly huge is it? Although I suspect it is rather profitable.

Where is that lens from?

I’ve always considered Germany the center of optics expertise, with Asia challenging at the lower cost end of the market. Japan, China and South Korea all have lens manufacturers, but North Korea?

It was this note on Navitar’s home page that had me scratching my head:

“Navitar is confident that our various suppliers located in and near North Korea will provide us adequate insurance in the event that a war breaks out.”

Fortunately the tension seems to have been dialed-back since that was posted in mid-April, but it still made me think: so Navitar get optical components from North Korea? Buy a Navitar lens and you’re enriching Kim Jong-un? I doubt that’s the case, but the simple statement on the Navitar website cries out for more explanation.

Taking advantage of polarization

The math of polarization gets pretty hairy, but you don’t need to know it to put the technique to work. Just take a look at these two images.

These show the same bar code label fixed to the same piece of bright steel and were acquired with the same camera, lens and light. In both cases there was a polarizing filter over the lens, but the image on the left also had a polarizer over the light. In other words it was throwing polarized light on the target.

The polarizing filter was turned at 90 degrees to that over the light, so only light that changed polarization when it bounced off the target could reach the camera’s sensor. That’s why the metal looks black: no light is returned from this region.

Usually light becomes polarized when it reflects off a surface, like water, but that doesn’t happen when metal is the reflecting surface. In the example above the label was paper and so changed the polarity of the light, which was then captured by the sensor.

I don’t pretend to follow all the math of polarization, but I think this effect is pretty cool. Expect to see it in an application near you very soon.

Does LED size matter?

The machine vision industry is pretty small, so when it comes to developing new technology we tend to hang on to the coattails of the big boys. Lighting is a good example. I think I’m right in saying that no one is developing LEDs for machine vision. Instead, the vision lighting companies have to utilize what’s being churned out for the higher volume applications, like industrial and residential lighting.

These days it seems LED manufacturers are working on ever bigger LEDs, and many are finding their way in to machine vision lights, like the Monster series from Spectrum Illumination. The problem I have with these is that they are prone to creating hot spots. Interestingly, judging by the lens optics diagrams on their website, smartvisionlights has recognized this problem and tries to shape the light to reduce the problem.

Some engineers I work with take the view that a sufficiently thick diffuser is all that’s needed to smooth out the light, but in my view that wastes photons by reducing the total output. I would rather see a higher density of small LEDs, which is the approach taken by CCS in most of their lights. You might notice though that even they’ve jumped on the high intensity – big LED bandwagon.

Now I appreciate that mounting LEDs takes time, which it probably why CCS’s lights are among the more expensive, but I’ve also found the light they put out to be some of the most uniform. I guess you get what you pay for, and I’m willing to pay extra to get more even illumination from a higher quantity of lower output LEDs.