NexStar 8SE Eyepiece Calculator
The NexStar 8SE is a 203mm f/10 Schmidt-Cassegrain with a long 2032mm focal length. The stock 25mm gives 81x, which is already more than many owners want for finding objects. This page loads the 8SE so you can check magnification, exit pupil, and field for any eyepiece, including 2-inch ones.
- Telescope
- Celestron NexStar 8SE: 203mm aperture, 2032mm focal length, f/10
- Max useful magnification
- ~406x (2 × aperture in mm). Celestron lists 480x. Most nights the atmosphere allows ~200–250x.
- Min useful magnification
- ~29x (7mm exit pupil)
- Widest true field
- 0.76° with 1.25" eyepieces, 1.04° with 2" (limited by the ~37mm rear baffle)
| Eyepiece | Magnification | Exit pupil | True field | Moon widths | Best for | Notes |
|---|---|---|---|---|---|---|
| 25mm (50°) | 81x | 2.5mm | 0.62° | 1.2 | Deep sky, Moon | – |
| 18mm (60°) | 113x | 1.8mm | 0.53° | 1.1 | Moon, Planets | – |
| 12mm (60°) | 169x | 1.2mm | 0.35° | 0.7 | Moon, Planets | – |
| 9mm (60°) | 226x | 0.9mm | 0.27° | 0.5 | Planets, Double stars | – |
The 8SE numbers
| Aperture | 203mm |
|---|---|
| Focal length | 2032mm (f/10) |
| Eyepiece(s) in the box | 25mm (81x) |
| Max useful magnification | ~406x by the 2 × aperture rule; Celestron lists 480x |
| Min useful magnification | ~29x |
| Widest field, 1.25" eyepieces | 0.76° |
| Rear baffle opening | ~37mm (fields wider than 1.04° vignette) |
Specs from Celestron’s product page, checked 2026-10-07.
What’s different about the 8SE
- The narrowest field in the SE line. Through any 1.25" eyepiece the 8SE tops out at about 0.76° (27mm field stop ÷ 2032mm). That’s 1.5 Moon widths, and too tight for big clusters like the Pleiades.
- A 2-inch diagonal is worth it here, up to a point. Celestron gives the C8 rear baffle as about 37mm. A 2" SCT diagonal with a ~35–40mm 2" eyepiece reaches roughly 1.0–1.1°. Field stops much beyond 37mm (like a 46mm) will vignette.
- More aperture, higher ceiling. Celestron lists 480x; the 2 × aperture rule gives about 406x. Seeing still caps most nights at around 250x, which is a 8mm eyepiece on the 8SE.
- Everything shifts one step longer than on a 6SE. An 18mm gives 113x (a 6SE needs a 13mm for that). A 12mm gives 169x, a planetary power on the 8SE.
Common eyepieces on the 8SE
Typical focal lengths and apparent fields. Your exact eyepiece may differ slightly; enter it above for its numbers.
| Eyepiece | Magnification | Exit pupil | True field | Moon widths | Best for | Notes |
|---|---|---|---|---|---|---|
| 32mm (50°) | 64x | 3.2mm | 0.76° | 1.5 | Deep sky, Moon | – |
| 25mm (50°) | 81x | 2.5mm | 0.62° | 1.2 | Deep sky, Moon | – |
| 18mm (60°) | 113x | 1.8mm | 0.53° | 1.1 | Moon, Planets | – |
| 15mm (60°) | 135x | 1.5mm | 0.44° | 0.9 | Moon, Planets | – |
| 12mm (60°) | 169x | 1.2mm | 0.35° | 0.7 | Moon, Planets | – |
| 9mm (60°) | 226x | 0.9mm | 0.27° | 0.5 | Planets, Double stars | – |
| 7mm (60°) | 290x | 0.7mm | 0.21° | 0.4 | Planets, Double stars | Most nights the atmosphere limits useful power to about 200–250x. Save this for very steady nights. |
With a 2-inch diagonal
Two-inch eyepieces need a 2" SCT diagonal. The widest useful field is about 1.04°, set by the 37mm rear baffle. Field stops shown are typical published values.
| Eyepiece | Magnification | Exit pupil | True field | Moon widths | Best for | Notes |
|---|---|---|---|---|---|---|
| 40mm (50°, 2") | 51x | 4mm | 1.3° | 2.6 | Deep sky, Moon | Wider than this scope's ~37mm rear baffle passes cleanly (~1.04°): expect darker edges (vignetting). |
| 35mm (68°, 2") | 58x | 3.5mm | 1.09° | 2.2 | Deep sky, Moon | – |
| 30mm (82°, 2") | 68x | 3mm | 1.18° | 2.4 | Deep sky, Moon | Wider than this scope's ~37mm rear baffle passes cleanly (~1.04°): expect darker edges (vignetting). |
| 24mm (68°) | 85x | 2.4mm | 0.76° | 1.5 | Deep sky, Moon | – |
FAQ
What is the widest view I can get with an 8SE?
About 0.76° with 1.25-inch eyepieces, roughly 1.0–1.1° with a 2-inch diagonal and a 35–40mm 2-inch eyepiece, or about 1.2° with 1.25-inch eyepieces and the f/6.3 reducer (with some edge darkening).
How much magnification can an 8SE really use?
Celestron lists 480x, but most nights the atmosphere limits it to around 200–250x. Steady nights may allow 300x on the Moon and planets.
Is the stock 25mm eyepiece enough to find objects?
It works, but at 81x with a 0.6° field it’s tight. A 32mm (63x) or a 2-inch low-power eyepiece makes finding and framing easier.
Next steps
- 8SE guide: every accessory guide for this scope
- Main eyepiece calculator: any telescope, custom aperture and focal length
- 6SE eyepiece calculator
- Evolution 8 eyepiece calculator