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Doofer

Focussing board cameras

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I always struggle to be satisfied setting up board camera lenses for best focus: I'd like to use a nice printed target with fine lines on it, but of course I also want this target to be at infinity.

In practice, setting max contrast of tree branches at a distance (for example) seems to change depending upon what % of the image is sky. I feel I'm fighting a lot of DSP, and the fact that the images are blurred pixels, rather than a pin-sharp optical image doesn't help.

It's about finding the right compromise: Does anyone out there have any tips/tricks they use to get this right?

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I do it comfortably at home with a nice big screen, targeting something that has enough detail at about 2-3m away.

With the focal length of the lenses we commonly use, 50cm is already infinity anyway. Better have a nicely detailed target tather than a tree branch needlessly far away and that shows as just a couple of pixels...

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Thanks, part of the question is undoubtedly "Where is infinity for these lenses/sensors?" and "What is the depth of field?".

My impression is that infinity is a little further than 2-3m, even for these cameras, but I guess that could be because things at 3m are things in my room, indoor lit, and things at 10+m are outside in sunlight.

I will certainly try a big screen...

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I made up a little board to plug into my camera lead that powers it and connects to the video out that I plug into my main TV, then I point it out the window (open) at some distant houses and adjust the lens.

Terry

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Yes, that's what I've been using, but the 'best focus', especially for high contrast things like branches, seems to vary depending on how much sky is in the frame (and how bright the sky is)...

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That's because if you have a large bright area (like the sky), it will tend to "bleed" onto small details. That's what happens with branches, and why it's not a good focus indication.

The indoor scene is much better as the exposure level is much more regular.

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