Limiting
Magnitude
DISCLAIMER: The larger the aperture, the more light a telescope
will gather and the fainter the object you can see. Here is a range of magnitudes
you might expect to see. Given excellent sky conditions and good optics, a well trained
eye can sometimes add up to 0.8 magnitude to these values.
Limiting Magnitude depends on much more than the instruments aperture.
Factors include:
seeing, the transparency of the atmosphere, the quality of the
telescopes optics, their cleanliness, magnification, and observers experience and use of
averted vision.
If ANY of the conditions are not met, expect to see less!
Two formulas are provided to give a representative range of possible magnitudes. One
formula is for aperture in inches the other is for aperture in millimeters. They are NOT
equivalent formulas - if they were, no range would result.
~ The differences in the columns reflect differences in initial
assumptions about sky conditions, visual acuity and others. ~
Aperture
(inches) |
Aperture (mm) |
Limiting
Magnitude
ML= 3.7 + 2.5 * Log10(D2)
D = aperture in mm |
Limiting
Magnitude
ML= 9.5 + 5.0 * Log10D
D = aperture in inches |
1/4 |
6 |
7.5 |
6.3 |
.31 |
8 |
8.2 |
6.9 |
2 |
50.8 |
12.2 |
11.0 |
3 |
76.2 |
13.1 |
11.8 |
4 |
101.6 |
13.7 |
12.5 |
5 |
127.0 |
14.2 |
12.9 |
6 |
152.4 |
14.6 |
13.3 |
8 |
203.2 |
15.2 |
14.0 |
10 |
254.0 |
15.7 |
14.5 |
11 |
279.4 |
15.9 |
14.7 |
12 |
304.8 |
16.1 |
14.8 |
14 |
355.6 |
16.4 |
15.2 |
16 |
406.4 |
16.7 |
15.5 |
17 |
431.8 |
16.8 |
15.6 |
18 |
457.2 |
17.0 |
15.7 |
20 |
508.0 |
17.2 |
16.0 |
22 |
558.8 |
17.4 |
16.2 |
24 |
609.6 |
17.6 |
16.4 |
30 |
762.0 |
18.1 |
16.8 |
32 |
812.8 |
18.2 |
17.0 |
200 |
5080 |
22.2 |
21.0 |
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Magnification Calculator
by Matt Oltersdorf |