Coona Skies


Star Trail Sizes

You can use this table to determine two things.

1) the size of star trails produced by a motionless or non-tracking camera.
2) the maximum exposure that can be used with a non-tracking camera without producing trailing stars in the image.
  • The following table displays the star trail size in microns for lenses of different focal lengths.
  • The left hand column displays the focal length of the lens being used.
  • The column headings indicate the length of exposure in seconds in bold and the amount in arc seconds that the earth has rotated in that period of time.
The star trail size is given for an angular position of 90 degrees from the pole. If you are imaging closer to the pole, multiply the figure by the sine of the angular distance from the pole. These figures do not take into account any atmospheric perturbations caused near the horizon.

focal length 1 sec
(15 arcsec)		 2 sec
(30 arcsec)		 3 sec
(45 arcsec)		 4 sec
(60 arcsec)		 5 sec
(75 arcsec)		 8 sec
(120 arcsec)		 10 sec
(150 arcsec)		 15 sec
(225 arcsec)		 20 sec
(300 arcsec)		 30 sec
(450 arcsec)
15 mm 1.1 2.2 3.3 4.4 5.5 8.7 10.9 16.4 21.8 32.7
20 mm 1.5 2.9 4.4 5.8 7.3 11.6 14.5 21.8 29.1 43.6
24 mm 1.7 3.5 5.2 7.0 8.7 14.0 17.5 26.2 34.9 52.4
28 mm 2.0 4.1 6.1 8.1 10.2 16.3 20.4 30.5 40.7 61.1
30 mm 2.2 4.4 6.5 8.7 10.9 17.5 21.8 32.7 43.6 65.4
35 mm 2.5 5.1 7.6 10.2 12.7 20.4 25.5 38.2 50.9 76.4
40 mm 2.9 5.8 8.7 11.6 14.5 23.3 29.1 43.6 58.2 87.3
50 mm 3.6 7.3 10.9 14.5 18.2 29.1 36.4 54.5 72.7 109
55 mm 4.0 8.0 12.0 16.0 20.0 32.0 40.0 60.0 80.0 120
60 mm 4.4 8.7 13.1 17.5 21.8 34.9 43.6 65.4 87.3 131
70 mm 5.1 10.2 15.3 20.4 25.5 40.7 50.9 76.4 102 153
75 mm 5.5 10.9 16.4 21.8 27.3 43.6 54.5 81.8 109 164
80 mm 5.8 11.6 17.5 23.3 29.1 46.5 58.2 87.3 116 175
85 mm 6.2 12.4 18.5 24.7 30.9 49.5 61.8 92.7 124 185
90 mm 6.5 13.1 19.6 26.2 32.7 52.4 65.4 98.2 131 196
100 mm 7.3 14.5 21.8 29.1 36.4 58.2 72.7 109 145 218
120 mm 8.7 17.5 26.2 34.9 43.6 69.8 87.3 131 175 262
150 mm 10.9 21.8 32.7 43.6 54.5 87.3 109 164 218 327
180 mm 13.1 26.2 39.3 52.4 65.4 105 131 196 262 393
200 mm 14.5 29.1 43.6 58.2 72.7 116 145 218 291 436
250 mm 18.2 36.4 54.5 72.7 90.9 145 182 273 364 545
300 mm 21.8 43.6 65.4 87.3 109 175 218 327 436 654
350 mm 25.5 50.9 76.4 102 127 204 255 382 509 764
400 mm 29.1 58.2 87.3 116 145 233 291 436 582 873
450 mm 32.7 65.4 98.2 131 164 262 327 491 654 982
500 mm 36.4 72.7 109 145 182 291 364 545 727 1091