Eyepiece and telescope pairing
Explore Scientific 18mm 82 Degree in the Sky-Watcher Flextube 300P (12-inch Dobsonian): magnification and field
What the Explore Scientific 18mm 82 Degree does in the Sky-Watcher Flextube 300P (12-inch Dobsonian), worked from the published focal lengths and apparent field.
Field of view
ring = 0.98 degrees true
dot = 3.7 mm exit pupil
- Magnification
- 83x1500 mm / 18 mm
- True field
- 0.98 degrees82 deg / 83x
- Exit pupil
- 3.7 mm305 mm / 83x
- Max useful mag
- about 610x2x aperture
Computed optics
- Barrel match
- 1.25 in eyepiece in a 2 in focuser
Good fit. In the Sky-Watcher Flextube 300P (12-inch Dobsonian) the Explore Scientific 18mm 82 Degree gives 83x with a 0.98 degree true field and a 3.7 mm exit pupil, inside the telescope's useful range.
Magnification is the telescope focal length divided by the eyepiece focal length: 1500 mm divided by 18 mm is 83x. The true field of view is the eyepiece's 82 degree apparent field divided by that magnification, 0.98 degrees.
The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 305 mm over 83x, which is 3.7 mm. That makes this a medium-power general setting.
The eyepiece to buy
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