Introduction

Tonight In the Sky

• Planisphere Late Evening
• Planisphere Midnight
• Planisphere Early Morning
• Lunar/Solar Calendar

Telescopes

• Optical Terms and Characteristics of Telescopes
• Optical Aberrations
• Light Grasp Table
• Refracting Telescopes
• Newtonian Reflecting Telescopes
• Catadioptric Telescopes

Mounts

Applications

• Night Time Observing
• Solar Observing
• Daytime use of Astronomical Telescopes
• Photography
• Digital Imaging

Eyepieces

• Eyepiece Calculator
• Telescope Calculator
• Light Grasp Table

Filters

• Planetary Neutral Density and Polarizing Filters
• Nebular Filters
• Solar Filters

Collimation

Astronomy Product    Websites

The following table shows common scope apertures listed, both in inches and millimeters, with the associated Light Grasp, Magnification limits and Limiting Visual Star Magnitudes.

Aperture in Inches Aperture in Millimeters Light Grasp Lowest Magnification Highest Magnification Limiting Visual Magnitude assuming transparent dark skies 0.98 25 13 4 40 9.7 1.26 32 21 5 51 10.2 1.57 40 33 7 63 10.7 1.65 42 36 7 66 10.8 1.97 50 51 8 79 11.2 2.36 60 73 10 95 11.6 2.76 70 100 12 111 11.9 2.99 76 118 13 120 12.1 3.15 80 130 13 126 12.2 3.35 85 147 14 134 12.3 3.5 88.9 161 15 140 12.4 3.54 90 165 15 142 12.5 3.94 100 204 17 158 12.7 3.98 101 208 17 160 12.7 4 101.6 210 17 161 12.7 4.02 102 212 17 161 12.7 4.13 105 225 18 166 12.8 4.33 110 247 18 174 12.9 4.49 114 265 19 180 13.0 4.5 114.3 266 19 181 13.0 4.72 120 294 20 190 13.1 4.92 125 319 21 198 13.2 5 127 329 21 201 13.2 5.12 130 345 22 205 13.3 5.91 150 459 25 237 13.6 6 152.4 474 25 241 13.6 7 177.8 645 30 281 13.9 7.87 200 816 33 316 14.2 8 203.2 842 34 321 14.2 9.25 234.95 1126 39 371 14.6 10 254 1315 42 401 14.7 11 279.4 1592 47 441 14.9 12 304.8 1894 51 482 15.1 12.5 317.5 2055 53 502 15.2 14 355.6 2578 59 562 15.5 16 406.4 3368 68 642 15.7 20 508 5262 85 803 16.2