How do I convert focal length from mm to pixels?

Hello,

I used the Exif data to determine the focal length of an image. and i get it with measure unit (mm) and in need to convert it to pixels

How do I convert focal length from mm to pixels??

Answer 1

[bym]

Does the Exif data contain the CCD width information? If so, use: focal length in pixels = (image width in pixels) * (focal length in mm) / (CCD width in mm)

[Amr]

Thanks for your reply

i didn't find the CCD width in the Exif data bout i searched for my camera model in site samsung (Camera Model : Samsung ES30) and i found Image sensor Type 1/2.3″ (Approx. 7.81mm) CCD

can i use 7.81 mm ?

[bym]

no, that is actually an aspect ratio. I saw a web site that actually gave common ccd sizes. I'll try to find it again a post link here

[bym]

here is the web site http://www.dpreview.com/learn/?/key=sensor%20sizes

looks like you should be using 6.16 mm

Answer 2

[George Abrahams]

Let F be the focal length in mm, be the focal length in pixels, and be the pixel size in mm.

Then, and .

The values for should be available in, or derivable from, the camera's technical specifications.