Problem with the other camera not focusing properly

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wilbur
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Joined: 14 Mar 2016, 06:03
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Country: Sweden

Problem with the other camera not focusing properly

Post by wilbur »

Hi!

I am desperately in need of advice how to solve my problem with my scanner and with its cameras. The problem is that when I am scanning the other camera gets out of focus for some unknown reason. This problem occurs only in one camera at a time, never simultaneously.

The only thing that seems to help with this issue is to reboot both cameras. Sometimes I can scan 50-100 pages beautifully but then the blurring problem hits again?

I'm using a scanner that I bought from Lusis.eu. My hardware is following:

* 2 Canon Ixus 160 cameras
* Raspberry Pi 2

I am also using the Spreads software running on Raspberry Pi 2.

Is this a common problem and does it have something to do with my camera settings? :cry:

Many thanks in advance!
duerig
Posts: 388
Joined: 01 Jun 2014, 17:04
Number of books owned: 1000
Country: United States of America

Re: Problem with the other camera not focusing properly

Post by duerig »

I have tested and used ELPH 160 cameras extensively. This occasional blurring problem is something that seems to happen periodically on some of the cameras with or without CHDK. So it seems to be a flaw with the cameras themselves.

The good news is that we don't really need the autofocus when scanning using and Archivist or similar model. The distance between the camera and the page remains exactly constant as you scan. So once you get the focus right once, you can lock it in.

In Spreads, there is an autofocus_once option that you can set. This will autofocus the first time you take a picture but lock the focus there and not use the autofocus after that. So after taking that first autofocus picture, check the image and if it looks good, you can scan with confidence thereafter. If you use Pi Scan, this autofocus-once workflow is what you do by default.

BTW, there is a bug in Spreads white balance when using the ELPH 160 cameras. You will want to pick the option just below 'Tungsten' to get the correct white balance.

-D
wilbur
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Joined: 14 Mar 2016, 06:03
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Country: Sweden

Re: Problem with the other camera not focusing properly

Post by wilbur »

Thank you very much for your input Duerig.

Few ideas and questions popped to my mind as I read your answer.

I am wondering why it is always the other camera, not both, that starts blurring images or gets annoyingly out of focus as my workflow in Spreads progresses? Otherwise everything works pretty well but it is not particularly fast method to work and constantly reboot the cameras to get them work correctly.

I am using the "initial_focus" option as I figured that it determines the focus setting by the first image taken and keeps it until the end of the workflow? Nevertheless the blurring problem reappears after 10-20 pages, no matter what I do?

Also playing with white balance opetions does not seem to help, nor adjusting the zoom level or DPI?

Should I start looking for a better set of cameras? :lol:
duerig
Posts: 388
Joined: 01 Jun 2014, 17:04
Number of books owned: 1000
Country: United States of America

Re: Problem with the other camera not focusing properly

Post by duerig »

Hmm. It is possible that the autofocus_initial isn't working properly in Spreads. You might give it a try with Pi Scan. Take a look at the project page for a download link:

https://github.com/Tenrec-Builders/pi-scan

It works a bit differently so you might want to watch the linked video to get a sense of how the whole process comes together. If you use Pi Scan and this problem recurs, then let me know and I can try to help you debug it. The experience I've had with this lose-focus issue has always been that if you lock the focus then it doesn't happen.

-D
rkomar
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Re: Problem with the other camera not focusing properly

Post by rkomar »

For a fixed geometry, you might try taking a series of pictures at different focal lengths, see which looks the best, and then always set the focal length to that value and lock it prior to each session. Relying on autofocus is hit and miss, depending on what is being photographed.
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