Fields of view redux

Revisiting my field of view musings, some stats.

  • Binoculars
    10×50: 4.3° = 258′
    30×50: 2.2° = 132′
  • 8″ Dobsonian
    25mm Plössl: 1.1° = 66′
    25mm + 2x Barlow: 0.5° = 30′
    7.5mm Plössl 0.33° = 20′
    7.5mm + 2x Barlow: 0.17° = 10′

M31 (Andromeda) is 109′ x 62′: no wonder I couldn’t see the oval shape! I should try again in the binoculars. And I’m amazed I was able to make out M57 (Ring Nebula) in the 25mm; at 1′ it was less than 2% of my scope’s width.

I was thinking of looking for M52 tonight. It’s about 12′ across, so will fit comfortably in the 7.5mm eyepiece. Also thinking of NGC 7789, 16′ or about the same size.

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