Viewing limits

Here is a table to try to determine the probability or detection of an object.
You will note, while the probability gets lower the faint object just might be seen by a smaller aperture.
Floyd
Telescope Limiting Magnitude
Aperture Probability of Detection
Inches 98% 90% 50% 20% 10% 5% 2%

1 9.7 10.2 10.7 11.2 11.7 12.4 13.2
2 11.2 11.7 12.2 12.7 13.2 13.9 14.7
3 12.1 12.6 13.1 13.6 14.1 14.8 15.6
4 12.7 13.2 13.7 14.2 14.7 15.4 16.2
5 13.2 13.7 14.2 14.7 15.2 15.9 16.7
6 13.6 14.1 14.6 15.1 15.6 16.3 17.1
7 13.9 14.4 14.9 15.4 15.9 16.6 17.4
8 14.2 14.7 15.2 15.7 16.2 16.9 17.7
10 14.7 15.2 15.7 16.2 16.7 17.4 18.2
12.5 15.2 15.7 16.2 16.7 17.2 19.9 18.7
14 15.5 16.0 16.5 17.0 17.5 18.2 19.0
16 15.7 16.2 16.7 17.2 17.7 18.4 19.2
18 16.0 16.5 17.0 17.5 18.0 18.7 19.5
20 16.2 16.7 17.2 17.7 18.2 18.9 19.7
22 16.4 16.9 17.4 17.9 18.4 19.1 19.9
24 16.6 17.1 17.6 18.1 18.6 19.3 20.1
30 17.1 17.6 18.1 18.6 19.1 19.8 20.6
36 17.5 18.0 18.5 19.0 19.5 20.2 21.0

Well, I guess I will have to inform the makers of scopes to increase the light grasp specs on their products. For example, the "limiting" visual magnitude for an 8" is listed as mag 14 while for a 10" it is 14.5, as per manufacturing specs. I would stress these are maximum theoretical achievable magnitudes as stated by the maker(s). Most scopes don't achieve max performance for a variety of reasons so it's unlikely that the stated maximums will be achieved at all.

I think this graph has been posted before, but I found it interesting. I just took the first column of your data (98%)and plotted it against the aperture.

The first few inches really make a big difference. (Extrapolate 6 mag at 7mm aperture)

I would like to see another chart that shows the typical number of galaxies visible, plotted against aperture.

Any takers

David Simons

Attached Image:

Viewing Limits from my backyard in Houston:

In 98% 90% 50% 20% 10% 5% _ 2%
1 . GL... GL... FM... FM... FM... FM... HM
2 . GL... GL... FM... FM... FM... FM... HM
3 . GL... GL... FM... FM... FM... FM... HM
4 . GL... GL... FM... FM... FM... FM... HM
5 . GL... GL... FM... FM... FM... FM... HM
6 . GL... FM... FM... FM... FM... HM... HM
7 . GL... FM... FM... FM... FM... HM... HM
8 . GL... FM... FM... FM... FM... HM... HM
10+ CSM CSM CSM. CSM. CSM CSM CSM

Legend:
GL = Good Luck
FM = Full Moon
HM = Half Moon
CSM = Cloudy Skies and Mosquitos

And yet I still drag the scope out there at every opportunity.

Ed