Optical tube binocular(20° inclined)Eyepiece(wide field) 10X (view field .87" DIA)Objective 0.8X~8X (zoom)Zoom ratio 1:10Infinity parallel optical system and 20° inclined optical tube reduce fatigue.Coaxial illumination is optical for deep holes that cannot be observed by ring light.Aperture diaphragm is optional for large depth for dield and high quality image.