A Celestron Omni 9mm Plossl in the Orion SpaceProbe 130ST gives 72x, a 0.69 degree true field and a 1.8 mm exit pupil. The worked calculation and whether it sits in the useful range.

Updated 05 September 2026.

Eyepiece and telescope pairing

Celestron Omni 9mm Plossl in the Orion SpaceProbe 130ST: magnification and field

What the Celestron Omni 9mm Plossl does in the Orion SpaceProbe 130ST, worked from the published focal lengths and apparent field.

Field of view

ring = 0.69 degrees true
dot = 1.8 mm exit pupil

Computed optics

Magnification
72x650 mm / 9 mm
True field
0.69 degrees50 deg / 72x
Exit pupil
1.8 mm130 mm / 72x
Max useful mag
about 260x2x aperture
Barrel match
1.25 in eyepiece in a 1.25 in focuser
Fits

Good fit. In the Orion SpaceProbe 130ST the Celestron Omni 9mm Plossl gives 72x with a 0.69 degree true field and a 1.8 mm exit pupil, inside the telescope's useful range.

Magnification is the telescope focal length divided by the eyepiece focal length: 650 mm divided by 9 mm is 72x. The true field of view is the eyepiece's 50 degree apparent field divided by that magnification, 0.69 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 130 mm over 72x, which is 1.8 mm. That makes this a medium-power general setting.

The eyepiece to buy

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Related

Orion SpaceProbe 130ST130 mm f/5
Celestron Omni 9mm Plossl9 mm, 50 deg
Best eyepiece for the Orion SpaceProbe 130STexit-pupil match

Questions and answers

Celestron Omni 9mm Plossl in the Orion SpaceProbe 130ST: magnification and field?

Good fit. In the Orion SpaceProbe 130ST the Celestron Omni 9mm Plossl gives 72x with a 0.69 degree true field and a 1.8 mm exit pupil, inside the telescope's useful range.