Table of Instruments Limiting Magnitude

Instruments Limiting Magnitude

Aperture (in ")	Aperture (in mm or cm)	Limiting magnitude (NSO Sacramento Peak (1))	Limiting magnitude (Clay Sherrod (2))	Limiting magnitude (usual formula (3))
2.4 "	60.9 mm	8.5	na	11.4
2.5 "	63.5 mm	8.59	10.5	11.5
2.8 "	71.1 mm	8.84	na	11.8
3 "	76.2 mm	8.9	na	11.9
3.5 "	88.9 mm	9.33	11.4	12.2
4 "	101.6 mm	9.62	11.7	12.5
5 "	127 mm	10.10	12.8	13
6 "	152.4 mm	10.50	13.2	13.4
7 "	17.78 cm	10.83	13.6	13.7
8 "	20.32 cm	11.12	13.9	14
9.25 "	23.49 cm	11.44	na	14.4
10 "	25.00 cm	11.59	na	14.5
11 "	27.94 cm	11.8	na	14.7
14 "	36.56 cm	12.4	na	15.3

(1) back figures from a National Solar Observatory, Sacramento Peak page. The author states these values for a reasonably dark night, and for instruments of a quality equal to that of his common 7x50 binoculars, using this formula: limiting magnitude = -0.4 + 5 times LOG aperture in mm, or limiting magnitude = 6.6 + 5 times LOG aperture in inches. These values may be underestimated

(2) back figures from "Telescope Performance I - Limiting Magnitude by Clay Sherrod. The author made an average of several formulae and found that these values are very closely fitting his 32 years actual practice of observation

(3) back figures computed with the usual formula (limiting magnitude = 7.5 + 5 times LOG aperture in cm). These values are the theoretical value obtained with one of the usual formulae computing limiting magnitude