Eyepiece and telescope pairing
Tele Vue 35mm Panoptic in the Sky-Watcher Classic 250P (10-inch Dobsonian): magnification and field
What the Tele Vue 35mm Panoptic does in the Sky-Watcher Classic 250P (10-inch Dobsonian), worked from the published focal lengths and apparent field.
Field of view
ring = 1.98 degrees true
dot = 7.4 mm exit pupil
- Magnification
- 34x1200 mm / 35 mm
- True field
- 1.98 degrees68 deg / 34x
- Exit pupil
- 7.4 mm254 mm / 34x
- Max useful mag
- about 508x2x aperture
Computed optics
- Barrel match
- 2 in eyepiece in a 2 in focuser
Works, but the 7.4 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: 1200 mm divided by 35 mm is 34x. The true field of view is the eyepiece's 68 degree apparent field divided by that magnification, 1.98 degrees.
The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 254 mm over 34x, which is 7.4 mm. That makes this a low-power, wide-field and deep-sky setting.
The eyepiece to buy
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