1. Point the binoculars at the bright white wall, let the eyes view about 10cm from the eyepiece, the exit pupil brightness of good telescope is coordinated and uniform, the display is dark color around.
If there are bright light shadows around the pupil, which appear to be square, it means the prism of the telescope is not good, allowing more light to reflect into the tube, resulting in astigmatism.

2.with binoculars to observe the distant scenery of 3 meters, if the image is clear, that is good quality, if it looks like the image is very hazy. As if covered with a layer of yarn, feeling dizziness, the quality of the telescope is poor.

3. if you see the TV from the telescope double, shows that the optical axis of the two mirror cylinder is not parallel, the optical axis is not mostly because of the prism offset, the inferior brand telescope in the prism fixed bracket some will cut corners, leading to the prism movement.