About this tool
The CCD Pixel Scale Calculator tells astrophotographers how much sky each pixel of their camera covers on a given telescope, and how large the whole frame is. Image scale is the number that decides whether a rig is over- or under-sampled for the seeing conditions.
Pixel scale = 206.265 × pixel size(µm) ÷ focal length(mm), in arcseconds per pixel. So a 3.8 µm pixel behind a 1000 mm focal length images 0.784″ per pixel. The field of view along each axis = pixel scale × number of pixels ÷ 3600, giving degrees (also shown in arcminutes) for the sensor width and height you enter.
The 206.265 constant is the number of arcseconds in one radian divided by 1000, which lets the formula mix micrometres and millimetres cleanly. As a rule of thumb, 1–2″/px suits most deep-sky imaging under typical backyard seeing; much smaller than that and you are over-sampling. Enter pixel size, focal length and sensor dimensions and everything is worked out locally in your browser.