How to Calculate Arc Seconds Per Pixel

By Margaret Worthington

Calculate the arc seconds per pixel of your camera or telescope.
i refractor telescope image by Jim Mills from

The measurement of arc seconds per pixel is used when taking pictures of the sky for astronomical purposes. An arc second is a unit of measurement of the sky, and is equal to 1/360th of 1 degree. To get accurate photographs that are of good quality, it's important to find out how many arc seconds per pixel your camera equipment can record in. This measurement is easy to figure out, thanks to a simple formula.

Locate the pixel size and focal length of your camera in the required dimensions (microns and millimeters, respectively). This information should be in your camera's technical manual. If you don't have the manual, contact the camera's manufacturer for the information, since you will need to be exact in your calculations.

Multiply the pixel size of your camera in microns by the focal length of your camera in millimeters.

Divide this number by 206.265 to calculate the arc seconds per pixel resolution of your camera.