finding focal length of mobile camera

Hi, I want to get specification of my camera e.g., focal length of lens etc.I made a picture of known distance. By measuring pixel difference of known 3D distance, how can I proceed further? I also know how many Mega pixel camera I have. Regards,

Answer 1

[Ivan van der Kroon]

The magnification of a positive lens is M=f/(f-v) (see wikipedia), with f the focal length and v the distance of the center of the lens to the object. So if you can find the magnification with your pixel difference and know distance to the lens, you can find it with this formula.

It is also written on the lens in 99% of the cases.

[shah baba]

But how can I find (camera-object) distance?. I can roughly know it. But I know only length of table.

[Sean de Wolski]

According to the above formula you have to know M,f.