Eyepiece and telescope pairing
Tele Vue 7mm Nagler Type 6 in the Sky-Watcher Classic 250P (10-inch Dobsonian): magnification and field
What the Tele Vue 7mm Nagler Type 6 does in the Sky-Watcher Classic 250P (10-inch Dobsonian), worked from the published focal lengths and apparent field.
Field of view
ring = 0.48 degrees true
dot = 1.5 mm exit pupil
- Magnification
- 171x1200 mm / 7 mm
- True field
- 0.48 degrees82 deg / 171x
- Exit pupil
- 1.5 mm254 mm / 171x
- Max useful mag
- about 508x2x aperture
Computed optics
- Barrel match
- 1.25 in eyepiece in a 2 in focuser
Good fit. In the Sky-Watcher Classic 250P (10-inch Dobsonian) the Tele Vue 7mm Nagler Type 6 gives 171x with a 0.48 degree true field and a 1.5 mm exit pupil, inside the telescope's useful range.
Magnification is the telescope focal length divided by the eyepiece focal length: 1200 mm divided by 7 mm is 171x. The true field of view is the eyepiece's 82 degree apparent field divided by that magnification, 0.48 degrees.
The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 254 mm over 171x, which is 1.5 mm. That makes this a high-power lunar, planetary and double-star setting.
The eyepiece to buy
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