# How can I know the focal length and sensor size of my webcam?

I have this webcam: QHM495LM WEB CAMERA and I need to know its focal length and its sensor size, but in the specs of the webcam, it only gives me this information:

• Inbuilt sensitive microphone and Image Sensor High Quality CMOS Sensor

• Image Resolution 16 Mega Pixels (Interpolated); Light sensor to switch on 8 lights automatically when in dark

• Image Control Color saturation, brightness, sharpness and brightness is adjustable; Snap shot switch for taking still pictures

• Anti-flicker 50Hz, 60Hz or outdoor; Resolution Hardware: 500K pixels; Image Quality: RGB24 or I420

• Exposure: Auto or manual and Angle of view: 58 Degree; Interface: USB2.0; Frame Rate: 30 fps (MAX)

• Lens: f=6.0 F=2.0

• Focus Range 4cm to infinity

For the focal length, the webcam has printed in it: "f=3.85mm", but I know it changes depending on the zoom and I was wondering if the point that says "Lens: f=6.0 F=2.0" refers to range of focal length the webcam has.

And for the sensor size I don't know if I can find it in this information.

I would really appreciate your help in this, I cannot go any further in my project without this information.

Thank you for the answers in advance.

It seems your question has been asked earlier but seperately..

Here, this will tell you how to find the focal length.

And this might help in finding sensor size.

Hope this helps.

• This works with a webcam too? Apr 10 '15 at 15:55

Calculation goes as following. Angle of view will define effective (in 35mm sense) focal length of the lens. 58 degrees of angle of view will give you roughly 39mm focal length (if angle is measured diagonally).

Your lens is (let's say) 6 mm by spec, that is 39/6=6.5 times smaller. Which means that sensor has crop factor of 6.5 (consider 1.5 for Nikon's DX). That means that sensor size (if it is 3:2 ratio) is 36x24mm / 6.5 = 5.5x3.7mm rectangle.

Final thought. I believe your camera has about 500K real pixels, which means that single pixel area is about (6.4um)^2, which seems reasonable for CMOS sensors.