Eyepiece and telescope pairing
Tele Vue 35mm Panoptic in the Sky-Watcher Flextube 300P (12-inch Dobsonian): magnification and field
What the Tele Vue 35mm Panoptic does in the Sky-Watcher Flextube 300P (12-inch Dobsonian), worked from the published focal lengths and apparent field.
Field of view
ring = 1.59 degrees true
dot = 7.1 mm exit pupil
- Magnification
- 43x1500 mm / 35 mm
- True field
- 1.59 degrees68 deg / 43x
- Exit pupil
- 7.1 mm305 mm / 43x
- Max useful mag
- about 610x2x aperture
Computed optics
- Barrel match
- 2 in eyepiece in a 2 in focuser
Works, but the 7.1 mm exit pupil is wider than a dark-adapted pupil of about 7 mm, so the outer light is wasted and the sky background looks brighter. Fine for framing, but a slightly shorter eyepiece uses the aperture better.
Magnification is the telescope focal length divided by the eyepiece focal length: 1500 mm divided by 35 mm is 43x. The true field of view is the eyepiece's 68 degree apparent field divided by that magnification, 1.59 degrees.
The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 305 mm over 43x, which is 7.1 mm. That makes this a low-power, wide-field and deep-sky setting.
The eyepiece to buy
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