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Aperture setting and calibration

The place for questions, problems, comments and tips regarding the camera calibration.

Aperture setting and calibration

Postby billyd » Fri Oct 02, 2015 8:36 pm

Hi guys this is my first post and I am getting great results with my SLS-2 in general. Love this product and it amazes me every time I use it.

But I am confused a little about light levels, calibration, software light control vs aperture setting.

I am scanning some fairly small things (from 50-200mm in size), and as a result I am often having to set the aperture higher than 16 on the camera. I just read in the manual, that I should avoid such a high number, and use the software to control the lighting instead and keep the aperture setting below 16 on the camera. But I have also read to avoid using the software to control the lighting in general. So it seems there is a little confusion there.

Also as I rotate the object I am scanning, I often see large variations in the light reflected. And as a result, in one position I may have perfect sine waves, in another I either get clipped waves or such low amplitude that it doesn't cross the dashed line, all in the course of scanning a single object.

So what is the best way to approach this? If I am already using the software to control lighting, it seems like the documentation warns about altering light levels once the calibration is done, but why not? It seems like many objects require a different amount of light as they are rotated. I am tempted to change the software light control for each subsequent scan of an object, since it seems like that should yield the most detail. What are the negatives from doing this? If it's just about maintaining accurate texture colors that's fine. I don't need color anyway, since I am largely doing this for 3D printing. Or will doing this also impact details and size accuracy negatively?

Thanks for any replys.
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Re: Aperture setting and calibration

Postby WalterMo » Sat Oct 03, 2015 1:23 pm

Hi billyd,
Welcome to the DAVID forum.

Normally a small aperture (high value) will increase the depth of field which is good for scanning. On the other hand diffraction can occur if the diameter of the iris becomes very small values: ... graphy.htm

For high-end photographs it could be a reason to avoid this. But also for 3D scanning? I don't know. But I think, not.
If the DAVID developers point to 'avoid aperture values > 16' there should be a reason why. Maybe structured light is especially sensitive to diffraction effects.

I am not a top expert in scanning, but to avoid effects which you mentioned when the object is rotated and the reflection becomes too high or too low, I carefully readjust the mechanical aperture. 'Carefully' means without to change any other setting of the camera lens or the camera position itself.

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Re: Aperture setting and calibration

Postby micr0 » Sat Oct 03, 2015 6:36 pm

Before scanning, I rotate the object and try to find the brightest and dimmest spots with the projector brightness set to one or two clicks below maximum brightness. I Then set the aperture somewhere around the average and adjust the projector brightness to give closest to optimal sine wave patterns. I also usually spray my objects with white chalk so they reflect very well and tend to be bright so I get aperture setting of F11-F16 for good depth of field.. In a perfect world I think doing it via the mechanical aperture is the better way of doing it,but you run the risk moving the camera or effecting the focus. Also I'm a bit lazy, and by adjusting the brightness in the software I can control everything while still sitting at the computer.

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