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