The telescope generally captures images through a distal-mounted objective lens. The image is then relayed through a rod-lens system to a proximal-mounted ocular lens that magnifies it for the surgeon. The resolution of any optical system is limited by diffraction—point objects are converted into spots, and the size of those spots is determined by the optical aperture, image magnification and light wavelength. Generally, larger telescopes with lower magnification generate smaller spots, meaning higher resolution. Nevertheless, lens design and production quality are critical factors in determining resolution since suboptimal quality can reduce image quality.

The lens diameter is a primary factor determining resolution. For example, a professional HD video camera with a 70mm lens and a 10 times larger optical aperture provides significantly higher resolution images compared with the 10mm lens of an endoscope. The larger lens is capable of transmitting a much larger bandwidth of information. Larger telescopes with lower magnification generate small spots, resulting in higher resolution. Such optical characteristics mean that the perceived visual benefits of HD versus standard definition (SD) endoscopy are quite subtle for many surgical specialties, though even smaller endoscopes displaying a full-circle image on a monitor may show a noticeably better image with an HD camera.