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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to Magnification Calculator
by Matt
Oltersdorf |