AstroLAB's Interesting Tables        
Telescope Limiting Magnitude      
Aperture Probability of Detection    
" mm 98% 90% 50% 20% 10% 5% 1%
       
1.0 25.4 9.7 10.2 10.7 11.2 11.7 12.4 13.2
2.0 50.8 11.2 11.7 12.2 12.7 13.2 13.9 14.7
3.0 76.2 12.1 12.6 13.1 13.6 14.1 14.8 15.6
4.0 101.6 12.7 13.2 13.7 14.2 14.7 15.4 16.2
5.0 127.0 13.2 13.7 14.2 14.7 15.2 15.9 16.7
6.0 152.4 13.6 14.1 14.6 15.1 15.6 16.3 17.1
7.0 177.8 13.9 14.4 14.9 15.4 15.9 16.6 17.4
8.0 203.2 14.2 14.7 15.2 15.7 16.2 16.9 17.7
10.0 254.0 14.7 15.2 15.7 16.2 16.7 17.4 18.2
12.5 317.5 15.2 15.7 16.2 16.7 17.2 17.9 18.7
14.0 355.6 15.5 16.0 16.5 17.0 17.5 18.2 19.0
16.0 406.4 15.7 16.2 16.7 17.2 17.7 18.4 19.2
18.0 457.2 16.0 16.5 17.0 17.5 18.0 18.7 19.5
20.0 508.0 16.2 16.7 17.2 17.7 18.2 18.9 19.7
22.0 558.8 16.4 16.9 17.4 17.9 18.4 19.1 19.9
24.0 609.6 16.6 17.1 17.6 18.1 18.9 19.3 20.1
30.0 762.0 17.1 17.6 18.1 18.6 19.1 19.8 20.6
36.0 914.4 17.5 18.0 18.5 19.0 19.5 20.2 21.0
source: http://members.efn.org/~mbartels/aa/visual.html