Image scale and field of view, without the confusion
See how focal length, sensor dimensions, and pixel size affect framing and angular sampling.
Sampling is not resolving power
Image scale describes the angle covered by one pixel. With 3.76 µm pixels and 640 mm effective focal length, the result is approximately 1.21 arcseconds per pixel. This value alone says nothing about atmospheric seeing, tracking, focus, aperture, or achievable detail.
Sensor size controls the frame
For each sensor dimension, field angle is 2 × atan(dimension / (2 × focal length)). A 23.5 × 15.7 mm sensor at 640 mm focal length gives approximately 2.10° × 1.41°. Shorter focal lengths give wider framing. Pixel size can change sampling without changing the field of view if sensor dimensions stay constant.
An image circle is only a nominal boundary
Compare the sensor diagonal with the published image circle for the corrector or telescope in use. A diagonal inside the circle is only a geometric check. Baffles, filters, adapters, off-axis aberrations, and manufacturer definitions can still limit illumination or image quality.