1 – Very Poor.


Star image 2x the diameter of the 3rd diffraction ring – Star image 13″ in diameter.

2 – Very Poor.


Star image occasionally 2x the diameter of the 3rd ring.

3 – Poor to Very Poor.


Star image about the same diameter as the 3rd ring (6.7″) and brighter at the centre.

4 – Poor.


Airy disk often visible. Arcs of diffraction rings sometimes seen.

5 – Fair.


Airy disk always visible. Arcs frequently seen.

6 – Fair to Good.


Airy disk always visible. Short arcs constantly seen.

7 – Good.


Disk sometimes sharply defined. Diffraction rings seen as long arcs or complete circles.

8 – Good to Excellent.


Disk always sharply defined. Rings seen as long arcs/complete circles, always in motion.

9 – Excellent.


Inner diffraction ring stationary. Outer rings occasionally stationary.

10 – Excellent/Perfect.


The complete diffraction pattern is stationary.