Nope. Focal length is how far the light has to travel, diameter is the aperture, or how big the opening is to collect light. The XT8 telescope I references has

Nope. Focal length is how far the light has to travel, diameter is the aperture, or how big the opening is to collect light. The XT8 telescope I references has an 8 inch aperture, and a 1200mm focal length