Focusing with LK002 lenses
Published by derossi on
- July 5, 2020 at 3:13 pm #24847
I bought the LK002 low-distortion lens kit from your Amazon store to use with the B0031 camera and a Raspberry Pi Zero W. I have both still images and video streaming working. The FOV with the default B0031 lens was too narrow for my purpose.
In the LK002 kit, both the 65 degree (LN015) and 90 degree (LN014) lenses will only focus to a distance of about 10mm, and that’s with the lenses screwed all the way into the 7mm lens holder as far as it will go (with care not to damage the sensor). I cannot focus on anything beyond 10mm.
The 70 degree FOV lens (LN013) works better and can focus to a much wider range of distances. It may be good enough for my needs, but it looks like there may be a problem getting the entire image in focus.
My requirement is to image a full US Letter page 216 x 280 mm (8.5 x 11 inches) from a distance of approximately 235mm. I can compensate for lens distortion in software, so low distortion is nice, but not essential. If you have a better camera/lens combination you can recommend for this setup, even if it requires a different interface or controller (e.g. USB, ESP32, etc.) I would appreciate your suggestions.
For the focus problems with the 65 degree and 90 degree lenses from the LK002 kit, please let me know if this is expected or if I should be able to focus beyond 10mm with the B0031 camera.
- July 6, 2020 at 12:45 am #24871
Looking at the BFL row of the following table, we can see that the 65 degree lens and 90 degree lens are respectively 1.6mm and 1.19mm, which are much shorter than the other three.
The BFL – back focal length – basically shows how far the back (bottom) of the lens is from the image sensor when it’s in perfect focus. Therefore, those two lenses should be closer to the sensor than the others.
To conclude, the focus problems are expected, but are also fixable by further screwing the lens into the holder. We can try the 65-degree lens first, which are supposed to be 1.6mm from the image sensor and less likely to damage the sensor. So please just try slowly with a little extra force to thread the lens in, and do that while previewing the video feed.
- This reply was modified 1 month ago by Lee Jackson.
- July 10, 2020 at 4:50 am #25012
Thanks for the response and the explanation of BFL.
I was able to set the focus by putting the lens into the holder (with a lot of force) before installing the holder on the camera board, and then make small adjustments when everything was fully mounted.
I appreciate the help. However, I am unable to get the entire page into focus at once given the requirements of my environment. It does not appear that I’ll be able to clearly image a full page from the distance I need. I’ve looked at your options for auto-focus and software controlled focus cameras, but none of them have the required FoV. It seems I have overconstrained my requirements.
- July 12, 2020 at 7:11 pm #25046
- July 31, 2020 at 1:53 pm #25832
- August 2, 2020 at 5:24 pm #25843
- August 2, 2020 at 5:51 pm #25762
Here’s the best I was able to get. This uses the 65 degree FoV low distortion lens. Sorry about the shadow; I haven’t yet installed all the lights.
The center is in good focus, although I can probably improve it very slightly. As you get further to the left and right, the image is more out of focus.
As I mentioned above, my specific situation doesn’t allow me to move the camera further from the paper, which is why the FoV was so critical.
- August 2, 2020 at 5:51 pm #25776
Here’s a picture from the camera with the best focus I could get. The center is pretty well focused (and I can probably do slightly better), but the further to the edges, the more out of focus.
My situation does not allow me to move the camera further from the page. That’s why the 65-degree FoV was so critical.
- August 2, 2020 at 5:51 pm #25801
I’ve tried to attach a picture to reply several times, but it doesn’t appear. So let’s try a link instead.
This is the best focus I could achieve with the 65-degree FoV low-distortion lens. I do not have the ability to move the camera further away in my setup. You can see the center is in very good focus (but I could probably make it slightly better), but it gets more out of focus further left and right in the image.
- August 3, 2020 at 6:07 pm #25953
It seems that the forum automatically put the replies with links or images into pending states, and I have just fixed that.
Looks like your application requires not only low distortion and high resolution, but also good conformity of the focus quality at a relatively short distance. Currently, the lenses are more for the surveillance end and less for the industrial-level. Perhaps I might have to consult our lens partner for possible customization because it’s already above average.
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