Eyepiece and telescope pairing
Celestron Omni 4mm Plossl in the Orion SkyQuest XT4.5 Classic Dobsonian: magnification and field
What the Celestron Omni 4mm Plossl does in the Orion SkyQuest XT4.5 Classic Dobsonian, worked from the published focal lengths and apparent field.
Field of view
ring = 0.22 degrees true
dot = 0.5 mm exit pupil
- Magnification
- 225x900 mm / 4 mm
- True field
- 0.22 degrees50 deg / 225x
- Exit pupil
- 0.5 mm114 mm / 225x
- Max useful mag
- about 228x2x aperture
Computed optics
- Barrel match
- 1.25 in eyepiece in a 1.25 in focuser
Good fit. In the Orion SkyQuest XT4.5 Classic Dobsonian the Celestron Omni 4mm Plossl gives 225x with a 0.22 degree true field and a 0.5 mm exit pupil, inside the telescope's useful range.
Magnification is the telescope focal length divided by the eyepiece focal length: 900 mm divided by 4 mm is 225x. The true field of view is the eyepiece's 50 degree apparent field divided by that magnification, 0.22 degrees.
The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 114 mm over 225x, which is 0.5 mm. That makes this a high-power lunar, planetary and double-star setting.
The eyepiece to buy
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