# Determining the CCD width of a camera [duplicate]

How can I determine the CCD (imaging area width) given image details such as focal length? I have images taken by cameras, but very little information about the cameras themselves (I have focal length and resolution). Given this, is there any way to determing the CCD width

• You can derive this from the field of view. Take a picture of an object of known size (ruler/scale works good) at a known distance. Commented Jan 18, 2020 at 17:40
• @Mattman944 The question seems to indicate the OP has a large number of images made using a large number of different cameras. It does not seem to imply that the OP has possession of the cameras themselves. Commented Jan 19, 2020 at 20:57

If you know the distance to the subject and the size of a subject that will exactly fill the frame, it is simple geometry.

Sensor_Width / Focal_Length = Subject_Width / Distance_to_Subject

or

Sensor_Width = Focal_Length * Subject_Width / Distance_to_Subject

Where the subject exactly fills the frame.

Here is a test on my camera, a Canon 7D:

Sensor Width = 50mm * 32.5"/72" = 22.57 mm

My actual sensor width is 22.3 mm, an error of about 1%

Note that this method is only valid for "normal" rectilinear lenses. It is not valid for fisheye or macro lenses.

For a compound lens, you will need to estimate the equivalent simple lens position, the "nodal" point. It is usually about in the middle of the lens. However, it can be outside the lens in some cases.

Note that the units of the distance to subject and subject width can be anything (as long as they are the same), they will cancel, it is the ratio that is important.

• It's also not perfectly valid for "normal" rectilinear lenses with very wide angles where magnification is greater at the corners/edges than in the center of the frame. Effectively, such lenses have longer focal length at the edge than at the center. It only works in a theoretically perfect way for theoretical "zero thickness" lenses that do not actually exist. Commented Jan 19, 2020 at 20:53