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Lens Angle

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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

GreyhoundZero wrote:Also, a couple of threads on here mention attaching something like the following

( http://www.amazon.com/C-mount-Adapter-E ... B004ILSMD4 )

to the new created housing of the webcam. I can see how this would allow me to attach a C-mount lens, but don't we mostly use CS-mount lenses for this? Will this adapter allow a CS-mount lens to be attached? (I know almost nothing about cameras other than what I've learned from these forums.)


Create the housing of your modified C615 in a way that it can be used with both kind of lenses, C- and CS-mount. The difference between both kinds is only a 5mm "bigger" distance for the C - mount one from the lens mounting plane to the photo sensor plane. These are the measures for a CS-mount lens modification:
download/file.php?id=7320&mode=view

If you like to use a C-mount lens you simply have to screw an additional 5mm adapter into the glued-in ring. So best is to buy two of these adapter rings:
One fixed (glued) at the camera housing and the second to make a C-mount cam of your CS-mount cam.
You don't need two lenses for scanning of small and very small objects. Simply change the distance. Often lenses can focus sharp at a minimal distance of only about 30cm or bigger. In this case you have to put something, e.g. the flat side of a coin between lens and camera. More professional are of course extension adapter rings, like these:
http://www.theimagingsource.com/en_US/p ... ics/tubes/
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Re: Lens Angle

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

WalterMo wrote:
GreyhoundZero wrote:Also, a couple of threads on here mention attaching something like the following

( http://www.amazon.com/C-mount-Adapter-E ... B004ILSMD4 )

to the new created housing of the webcam. I can see how this would allow me to attach a C-mount lens, but don't we mostly use CS-mount lenses for this? Will this adapter allow a CS-mount lens to be attached? (I know almost nothing about cameras other than what I've learned from these forums.)


Create the housing of your modified C615 in a way that it can be used with both kind of lenses, C- and CS-mount. The difference between both kinds is only a 5mm "bigger" distance for the C - mount one from the lens mounting plane to the photo sensor plane. These are the measures for a CS-mount lens modification:
download/file.php?id=7320&mode=view

If you like to use a C-mount lens you simply have to screw an additional 5mm adapter into the glued-in ring. So best is to buy two of these adapter rings:
One fixed (glued) at the camera housing and the second to make a C-mount cam of your CS-mount cam.
You don't need two lenses for scanning of small and very small objects. Simply change the distance. Often lenses can focus sharp at a minimal distance of only about 30cm or bigger. In this case you have to put something, e.g. the flat side of a coin between lens and camera. More professional are of course extension adapter rings, like these:
http://www.theimagingsource.com/en_US/p ... ics/tubes/


Wait, do C-Mount and CS-Mount lenses have the same mount, just a different distance from the sensor? I was under the impression that "C" and "CS" referred to the thread and/or the diameter of the lens.

If I'm not using a C-Mount lens do I not have to worry about the second adapter? And would using multiple CS-mount adapters accomplish the same thing as the extension adapter rings?

(Sorry for how basic my misunderstandings are, I am approaching this project with no prior optics or photography knowledge.)
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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

Thank you for your help. I'm having some difficulty understanding this paragraph:

fred_dot_u wrote: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.


Would you mind explaining this?
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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

GreyhoundZero wrote:@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...?)

The main reason for me to modify a C600 was its “built-in” IR cut-off filter. Not the Logitech driver.

Regarding the focal length of a lens: If the camera and the projector are mounted close together, maybe at one frame, both should circa have the same opening angle of their lenses.
If you use a “normal” projector and not a short throw one, the focal length of the cam's lens should have about 12mm (If mounted at the same distance to the object). Under the just mentioned condition you can zoom in with a zoom lens to longer focal lenghts until only the 6 rings of both patterns are visible for the camera. These 6 rings are necessary for DAVID for a (successful) calibration. But in so doing you would give away a lot of the projector's resolution.
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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

Okay, I've played around and had some fun with the lens by itself (not with the projector), and with some practice using the lens I've re-read the posts in this thread and I understand nearly everything that's been explained to me.

I still have a few questions, though (so sorry and thank you both so much for helping me):

WalterMo:
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.


I understand that adding extra space beyond the 12.5/17.5 required between the sensor and the lens will allow it to zoom in closer, but I'm having difficulty understanding the phrasing used in the bolded sentence. Are you just pointing out that the extra space would have to be reduced again if I switched to larger scans? If so, I understand.

WalterMo:
If you use a “normal” projector and not a short throw one, the focal length of the cam's lens should have about 12mm (If mounted at the same distance to the object). Under the just mentioned condition you can zoom in with a zoom lens to longer focal lenghts until only the 6 rings of both patterns are visible for the camera. These 6 rings are necessary for DAVID for a (successful) calibration. But in so doing you would give away a lot of the projector's resolution.


Is this not relevant to me currently because I'm adding an additional zoom lens on the projector? The image it projects, with the added lens, is very small and not projected very far, making it effectively a short throw projector (if I understand the terminology correctly).
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Re: Lens Angle

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

WalterMo wrote: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.


I have another question about this post: the link you posted includes long extension tubes as well as rings. It's just the spacer rings that I need to increase the distance for zoom, right? In what circumstance would I need the much longer tubes, if any?
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