Porro prism is a reflecting prism may be used to change the image direction. Omo light enters the prism, and then is irradiated on a roof, the roof through the whole two reflected light beams emitted by Omo again. The image rotated by 180 degrees by the Porro prism, but not reversed.

Focal length: ± 5mm - ± 1000mm ± 1%
OD: 5mm - 200mm ± 0.1mm
Center thickness tolerance: ± 0.05mm
Center deviation: ≤ 3 min
Surface accuracy: λ / 4 @
Surface quality: 40/20
Effective aperture: 90%
Coating: antireflection film, splitting film, reflective film