Lens Focal Length

Similar triangles: sensor / f = FOV / working distance. The ideal focal length is almost never a stocked one, so the useful part is the second half — what field you actually get with the nearest real lens, and how far back you would have to move to keep the field you wanted.

Enter the sensor dimension along the axis you are measuring (a 2/3" sensor is 8.8 mm wide, 6.6 mm tall). Thin-lens model — real lenses shift the principal planes, so confirm against the vendor’s working-distance chart.