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Old Jan 27, 2011, 1:35 PM   #1
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Default Newbie Lens Questions

This might be a dumb question, so dumb that I could't find an answer. I have never worked with any cameras/lenses... ever... Work decided to throw me a project upgrading our machine vision equipment (not their smartest move, but here I am). Specifically, I am looking at tube zoom lenses. But what does it mean when they say that the zoom modules they carry range from 7:1 to 16:1. Are they talking zoom, or magnification--what is the difference if any?

And also, what factors determine a lens' working distance? It seems common when looking through these types of lenses for me to find working distances that are quite small, 25mm-50mm, while 100mm+ would be ideal really.

(Note: we are looking at small pins that are ~1-3 microns in diameter, so we have to zoom in from afar while staying out of the way of the xyz stage that moves the specimen.)

If anyone can help educate me, it would clear up some confusion on my end that I've run into while researching.

Thanks!

Last edited by TheMech; Jan 27, 2011 at 2:22 PM. Reason: Clarity
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Old Jan 27, 2011, 8:17 PM   #2
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Quote:
Originally Posted by TheMech View Post
...
(Note: we are looking at small pins that are ~1-3 microns in diameter, so we have to zoom in from afar while staying out of the way of the xyz stage that moves the specimen.)
...
What are you using now to look at those in that situation? Likely the best answer is to attach a camera to that gear.
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Old Jan 27, 2011, 11:15 PM   #3
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'Upgrading machine vision' sort of implies cameras and lenses already in place.
I would guess video cameras and C-mount lenses. If the system has been in place for a while, it may be that you can do what you need with higher resolution cameras, using your existing lenses. (that was kind of a long way of repeating what Bill said)
If the lens resolution is the limiting factor, you will probably need larger diameter lenses as well as longer focal length. Check Wikipedia "Lens Resolution" for more info.

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Old Jan 28, 2011, 6:30 AM   #4
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It seems to me that what you've been asked to do is upgrade one small part of an entire system, and that's never a good idea. You might get higher resolution cameras and then find that the software that manages the images might not like the higher resolution. You might get lenses with higher zoom ratios and then find that the control software doesn't know how to use them.

What do your bosses want to happen?
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Old Jan 28, 2011, 10:10 AM   #5
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Likely an upgrade of whatever viewing gear you have will have the option of image capture. If not, talk to what the competitors have to offer.

What sort of gear are you now using? What is their web site?
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Old Jan 28, 2011, 6:43 PM   #6
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Alright, I think I can make it more clear what I am doing.

Current Equipment Setup:
There is currently a system in place. We are using 1.3 MP Pixelink PL-B741F camera (machine vision video camera) with C-mount OPTEM lens (part#: 39-95-10-000). We use it in conjunction with labview, which the two are highly compatible. The lens is a manual zoom, not motorized. In our lab what we are doing is there's an XY stage that moves a piece of material around while a Z stage plunges a 1-3 micron sized pin into the material. We capture the interaction on video/take still frames and analyze how well a certain plunging or scrubbing action works.

Now, the problem is... whoever set up the system made it so the lens has to be incredibly close to the sample in order to see it (roughly 35mm...) This does not leave us a lot of room to move our samples because we will end up running the stage into the lens.

My assumption after looking at different lenses was that the working distance is the deciding factor as to how far away from the object the lense needs to be to see it. So i was hoping to find something with similar magnification/resolution/depth of field and just a longer working distance. I am starting to think this assumption is wrong because I was able to get some specs from the avsupply company that the working distance is 89mm.... So no longer did my assumption make sense to me. I am now thinking that a greater magnification is necessary, as well as the greater working distance. Some other specs they told me was that it has Resolution: 75-240LP/MM, Magnification: 0.75x-5.25x.

Does this help?

Last edited by TheMech; Jan 28, 2011 at 8:03 PM. Reason: typo's
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Old Jan 28, 2011, 8:46 PM   #7
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The working distance may not be measured from the front of the lens, but from the camera sensor. If you subtract the length of the lens, do you come up with something close to the 35mm distance you measured? If so, then your assumption of needing increased working distance seem OK.
I'm guessing that you will need greater magnification in order to get better resolution, and to do that, the lens needs to be longer, so, to get the required distance from the stage, you may need another increase in working distance.
If I were in your position, I would let the vendor know what my requirements were re: resolution, distance from front of lens, etc., and let their engineers figure out the appropriate equipment. Saves having to reinvent the wheel every time.

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Old Feb 1, 2011, 11:49 AM   #8
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Thanks for the responses. I have been out sick and don't have a computer at my house currently (fried it with water.... blahh). I'm not sure where they are measuring the working distance from because the lens is roughly 10" long already (much more than 89mm). I put in an inquiry with a company and their engineers are hacking away to satisfy my needs. Hopefully they get back to me soon!

Thanks,

Dale
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