Thursday, April 24, 2014

Modifying a Logitech C310 HD webcam

As per William Steptoe's recommendation, I chose to augment my Oculus Rift DK1 with two Logitech C310 webcams, modified to have a wider FOV.

The C310s can be found easily on Amazon for around 40 bucks, with Prime shipping. Not too bad.

Steptoe also cannibalized two Genius WideCam F100. The F100s have an FOV of 120°, while the C310s only have an FOV of about 40°. Rather than spend an extra 80 dollars, I looked to sourcing my own lenses.

To achieve an FOV of 120°, a focal length of around 2.5 is needed. I promptly went onto Amazon, and picked up a pair of 2.8mm CCTV lenses. They arrived with my cameras, and I set to hacking.

My first issue arose when I found that the threads on the lenses I had ordered were the wrong size! CCTV cameras have a standard size, called the "S-Mount". S-Mounts have a 12mm thread with a 0.5 pitch (M12x0.5). The C310s have an M8x0.5 thread! I searched to no avail for the smaller size, and eventually modeled and printed a new lens adapter. This new lens adapter can be found on Thingiverse.

This worked! I swapped then lenses, and turned on my cameras to measure my FOV... and I was right around 60°.

What? With a 2.8mm lens, the FOV should be at LEAST 115°! A little more research brought me to my answer. The FOV is related to both the focal length of the lens, as well as the size of the camera sensor! The lenses that I purchased were meant for 1/3" sensor. I carefully measured the sensor on the C310 board, and used this helpful site to find my sensor size. Turns out that the C310 sensor is 3.6mm x 2.7mm, with a diagonal of 4.5mm. This corresponds to a 1/4" sensor!

There's not many lenses that are made for a 1/4" sensor... at least, not cheap ones. I found this site, which would allow me to convert my focal length between 1/3" and 1/4" sensors. To get an FOV of about 120° on a 1/4" sensor, I needed a lens with an FOV of about 160° on a 1/3" sensor.

After a fair amount of digging, I finally came across a reasonably priced 170° FOV lens. This should theoretically put me at about 130° FOV for the C310s... But who knows! When I get them I'll test them out.



Below are some random links. I don't remember why I pasted them here, but I'll leave them for posterity.

http://petapixel.com/2013/06/15/a-mathematical-look-at-focal-length-and-crop-factor/

http://www.peauproductions.com/blog/2009/07/23/m12-lens-and-distance-calculator-formulas/

2 comments:

  1. First of all, thanks for your great advice. Were you successful using the DSC-L1.8mm?

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    1. I haven't had a chance to really try the new lenses, unfortunately. The original lens mount design is a bit too long, and the new lenses can't quite get focused. I've been to busy with other projects to change the model and reprint the parts.

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