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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...

Lens Angle

Postby GreyhoundZero » Sat Aug 01, 2015 4:36 pm

Basic optics question, I guess:

Projectors project at an upwards angle rather than straight ahead so that they can be placed closer to the ground and not block our view of the projected image.

It seems like every time a person adds a lens to a projector for SLS, the lens is attached parallel to the projector's included lense, not at an upward-facing angle. Why isn't the lens angled upwards, perpendicular to the projected image's travel path?
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Re: Lens Angle

Postby WalterMo » Sat Aug 01, 2015 5:17 pm

Of course it's also possible to mount the lens at a tilted upwards angle. In any case, DAVID will eliminate eventual distortions during the calibration process.

I have done it in parallel to the original lens because the additional lens was easier to fix:
download/file.php?id=5283&mode=view
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Re: Lens Angle

Postby GreyhoundZero » Tue Aug 04, 2015 10:24 pm

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Re: Lens Angle

Postby WalterMo » Wed Aug 05, 2015 12:07 pm

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Re: Lens Angle

Postby GreyhoundZero » Wed Aug 05, 2015 6:53 pm

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Re: Lens Angle

Postby WalterMo » Thu Aug 06, 2015 12:15 pm

The C 915 seems to be very unpopular. I cannot find something useful on the web (in English or German). Mainly I was pointed at the C615. The latter is also well known on this forum, e.g.:
viewtopic.php?f=6&t=5863&hilit

I wouldn't try to replace the original lens of a projector. And I am dead certain that a C/CS- mount lens will not work. Better is to put an additional lens just in front of the built-in lens.

Edit: I think the easiest Logitech webcam to modify is the C600 because you don't have to take care about its IR cut-off filter: It's directly mounted in front of the photo sensor:
viewtopic.php?f=6&t=3727
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Re: Lens Angle

Postby GreyhoundZero » Thu Aug 06, 2015 7:04 pm

So sorry, I actually meant C910, not C915.

I started out with a C615 but accidentally destroyed it while taking it apart. I have the 910 taken apart and It looks very similar inside but there's a gap between the sensor and the closest that an added lens could get to it, which concerns me.

I found some jeweler's eyeglass attachment lenses that seem to work very well with the projector, though.
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Re: Lens Angle

Postby fred_dot_u » Thu Aug 06, 2015 7:35 pm

Just to toss a nickel's worth in here... I've modified a Logitech Pro 9000 with a CS mount lens. I did have to purchase separately the IR filter and add it over the sensor, as the original Pro 9000 has the filter as part of the lens that is removed. The lens I purchased to fit the CS mount works great, manual iris, adjustable focal length. I've not recently done any work with the David system, however, so I can't give you a long term reference.

I am interested in learning more about your projector modification. Do you have a representative link for the eyeglass attachment lenses you find to work well?
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Re: Lens Angle

Postby GreyhoundZero » Thu Aug 06, 2015 7:41 pm

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Re: Lens Angle

Postby fred_dot_u » Thu Aug 06, 2015 8:35 pm

Interesting use of the magnifiers. I have two sets of those "somewhere," although I have been unable to locate them last attempt. Inexpensive enough to purchase another set and not lose them!

The filter I located came from here:

and was purchased as a "sample" item for US$17.50, a bit pricey but necessary for the Pro 9000.

The only method I know to determine if you need one is to install the CS mount and lens and observe the fidelity of the image viewed by the camera. Color accuracy will be very poor, especially for outdoor images if you have a lens without IR filtering. The intensity of the projector, even at a low setting is likely to be quite high in IR content and will interfere with calibration as well as color in your scans.
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Re: Lens Angle

Postby GreyhoundZero » Sun Aug 09, 2015 10:13 pm

I'll get the IR if necessary since it's still cheaper than buying another C615, but I still have a concern about whether the 910 will work.

My concern, as seen in the attached pictures, is that instead of being on a single board, the 910 has two separate boards, so the lens has to be several additional mm away from the lens. Is this unacceptable?

And does this seem like the lens I should be using: http://www.ebay.com/itm/2-8-12mm-CS-1-2 ... tkn=maOaX2 ?
Attachments
logitech1.jpg
logitech2.jpg
logitech3.jpg
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Re: Lens Angle

Postby fred_dot_u » Sun Aug 09, 2015 10:34 pm

There is quite a bit of difference between the Pro 9000 board and yours. I would not be the one to suggest that you could make it work, unless you find someone else who has done so. My lens is 6-15mm focal length, so your 2.8 - 12 mm lens seems a bit out of ordinary range.
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Re: Lens Angle

Postby GreyhoundZero » Sun Aug 09, 2015 10:50 pm

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Re: Lens Angle

Postby fred_dot_u » Sun Aug 09, 2015 11:55 pm

The range of zoom would, in your case, be 2.8mm to 12mm, while the distance from the lens to the sensor is determined by the mount. My CS mount placed over the sensor resulted in the lens being at the proper distance from the sensor to permit clear images. You can find single figure lenses, i.e., 15mm focal length. This implies no zoom capability and a fixed magnification and fixed field of view (angle of view) somewhat limiting your ability to use different size calibration panels.

The lower number (2.8mm) means you have a low magnification and a wide field of view. The higher number (12mm will provide greater magnification and a narrower field of view.

It has been months since I have turned on my David, so I cannot recall that level of zoom I used with my lens. I do recall that I rarely used the wider setting, lower number.

The lens you linked has a manual iris which is good, and a relatively high speed lens (f-rating) which lets in more light than a slower lens.
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Re: Lens Angle

Postby GreyhoundZero » Fri Aug 21, 2015 11:14 pm

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