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DAVID-Laserscanner Forum • View topic - Lens Angle
Dear DAVID Community,

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Lens Angle

Which camera works? Where can you buy an adequate laser? And more...

Re: Lens Angle

Postby fred_dot_u » Fri Aug 21, 2015 11:31 pm

You would not want to use a 2.8 to 12 mm lens as it would reduce the magnification and make your objects appear smaller than could be useful. If anything, you should aim for higher numbers. Look for 12mm and above.

I can't advise regarding the C to CS mount adapter, not having had enough experience with such things.

The 2.8 to 12mm lens you have should work for your larger shells, perhaps as large as your fist?

Look also for "fast" lens speed, measured in f-speed. A lens with f-1.6 will be faster/better than a lens with f-4.0 and the faster lens can be better managed with a manual iris control as well.
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Re: Lens Angle

Postby WalterMo » Sat Aug 22, 2015 11:38 am

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Re: Lens Angle

Postby GreyhoundZero » Sat Aug 22, 2015 7:35 pm

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Re: Lens Angle

Postby WalterMo » Sat Aug 22, 2015 8:01 pm

To your question 1: Yes, C - and CS-mount lenses have the very same thread. Only the distance to the sensor differs for 5 mm.
Question 2: If you have built your modified webcam as a CS-mount cam you can use it as it is with a CS-mount lens. With a C-mount lens you must attach a 5 mm adapter ring.
To solve the problem of non-focussing sharp at a very short distance of an object you need adapter rings of only 2mm, maybe 3mm. I think 5mm is too much. Test it.

Another way not to need an extension ring is this:
Build your cam as a CS-mount cam and buy a CS-mount lens. But increase the distance inside the housing by mounting the sensor board some millimeters back. Normally the distance is 12.5 mm. Try it first with about 14 mm and then find an optimum.
Of course in so doing you cannot focus sharp with the lens at maybe 2 m or more. It's only a compromise.
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Re: Lens Angle

Postby GreyhoundZero » Sat Sep 05, 2015 9:46 pm

@WalterMo, I just noticed your earlier admonition to use the C600 rather than the C615 because it does not require an additional IR filter component. Is this the only reason? (In a post on another thread it sounds like there might be some differences regarding drivers...?)

@fred_dot_u / @WalterMo, I actually haven't purchased any lenses for the camera yet as I'm quite scared of purchasing the wrong one.

The "focal speed" is one part I'm especially having difficulty understanding. If a lens is labeled "1:1.4", does that mean the focal speed is f-1.4 or is it completely unrelated?

Are the lenses below closer to what I need than the last one I asked about? The "mm" range seems quite high; does that mean they will work for a wider range of object sizes, a wider range of distances from the object, both, or neither?

http://www.ebay.com/itm/Fujinon-TV-Zoom ... 2033486797

http://www.ebay.com/itm/FUJINON-1-2-8-5 ... 2054968002
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Re: Lens Angle

Postby fred_dot_u » Sun Sep 06, 2015 2:00 am

You are correct about the lens speed. An f-1.4 lens could also be described as a 1:1.4 lens. The two you've linked are f-1.2, which is faster/better than a 1.4 by a small amount. It's not so much that 1.4 would be a bad choice, but that 1.2 opens up that little bit more range if you require it. The first lens appears to be more restrictive at the focal length you may find useful and has a substantial zoom, while the second will "open" to 8.5mm (wide angle) and yet provide a reasonably high zoom level at the other end of the range. 8.5mm is likely to be more wide-angle than is generally useful, but it's akin to the 1.2/1.4 discussion in that you have that much more range as needed.

The high zoom level can be useful for small objects but only if you can modify your projector to provide the necessary calibration marks within the selected field of view. At 8.5mm, you'd have a wide field of view, suitable for large objects with a large calibration panel set. On the other end of the zoom, you'd want an appropriate match for the calibration panel.

Quite a challenge to pick, but I like your second choice very much.
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Re: Lens Angle

Postby GreyhoundZero » Sun Sep 06, 2015 4:22 am

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Re: Lens Angle

Postby fred_dot_u » Sun Sep 06, 2015 12:18 pm

Let's say that you have an item that measures less than one inch in all directions. With a 12mm lens, for example, your field of view could be eight inches (imaginary number, not measured in real life) and your panels could be about the same size. When you place the item to be scanned, it is such a small proportion of the entire scan field that your results are poor resolution.

Using the zoom feature to perhaps a 40mm setting, the item now fills the field of view nicely. The calibration markers do not appear in sufficient quantity, however, so the projector output has to be adjusted and a smaller panel implemented. I have not attempted to modify my projector, as others have, by adding lenses, but I understand that it can be done. You can move a projector closer to the panels and to the item, but focus is lost after a certain point, hence the need for additional lenses.

Computer projectors are created to provide large area images, to enable many viewers of a single "screen" while the scanning process is somewhat opposite to that. A smaller image presented on the calibration panels and on the scanned item requires that the image projected be reduced in size appropriate to the item.

If this is yet unclear, please ask specific questions.
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Re: Lens Angle

Postby WalterMo » Sun Sep 06, 2015 12:23 pm

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Re: Lens Angle

Postby GreyhoundZero » Wed Sep 16, 2015 10:33 pm

I purchased the 1.2/8.5-51mm lens and the diameter of the lens is much larger than I expected and, I believe, much larger than the one shown in this thread viewtopic.php?f=6&t=5863&hilit=c615

Will this create problems?
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Re: Lens Angle

Postby GreyhoundZero » Thu Sep 17, 2015 12:00 am

Not sure how to edit my previous post. The reason it's larger is because it's a C-Mount (I think?), so it's fine, although I'll have to add some support to hold it without depending on glue alone since it's quite heavy.
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Re: Lens Angle

Postby WalterMo » Thu Sep 17, 2015 9:20 am

A big (input) diameter of the lens will not create problems. The opposite is true: By means of the large input field more light can come into the lens system.
Some time ago I had disassembled my old Super 8 movie camera to use its light sensitive zoom lens for a Logitech C600 webcam:
viewtopic.php?f=6&t=3418&p=18642&hilit

The visible diameter (of the first lens) at front is 42mm.
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Re: Lens Angle

Postby fred_dot_u » Thu Sep 17, 2015 2:56 pm

With respect to the weight of the lens. My lens is about five times (or more) the weight of the camera board. I had a friend machine a lens clamp with a tripod socket that secured to a non-moving portion of the lens. The lens supported the camera board with no difficulty. Would your circumstance work in that manner?
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Re: Lens Angle

Postby GreyhoundZero » Sun Sep 20, 2015 10:54 pm

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Re: Lens Angle

Postby GreyhoundZero » Thu Oct 01, 2015 10:52 pm

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