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 |
Limiting Magnitude |
| 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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by Matt Oltersdorf