The focal ratio of a telescope, denoted as f-number, is the ratio of its focal length to aperture diameter. It determines the telescope's light-gathering ability and resolution. A lower f-number indicates a wider aperture, offering brighter images and better for observing dim objects, crucial in astrophotography and stargazing.

The Critical Focus Zone (CFZ) of a telescope is the range within which the focus is acceptably sharp for astrophotography. Determined by the telescope's focal ratio, the CFZ is narrower in faster (lower f-number) telescopes, demanding precise focusing to capture clear, detailed images of celestial objects.

Pixel scale, crucial in astrophotography, measures the sky area each camera sensor pixel covers. Expressed in arcseconds per pixel, it influences image resolution and detail capture, depending on the telescope's focal length and camera's sensor size, guiding astronomers in matching equipment for optimal celestial imaging.

The Telescope Camera FOV Calculator, essential for astrophotographers, determines the visible sky area based on telescope focal length and camera sensor size. It guides equipment choice, ensuring detailed celestial captures, making it key for astronomical observation and exploration.