NexStar Evolution 8 Eyepiece Calculator
The NexStar Evolution 8 uses the same 203mm f/10 optics as the 8SE (2032mm), but ships with two eyepieces: a 40mm (51x) and a 13mm (156x). This page loads that pair so you can see where the gaps are and what to add first.
- Telescope
- Celestron NexStar Evolution 8: 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 |
|---|---|---|---|---|---|---|
| 40mm (43°) | 51x | 4mm | 0.76° | 1.5 | Deep sky, Moon | – |
| 13mm (50°) | 156x | 1.3mm | 0.32° | 0.6 | Moon, Planets | – |
Gaps in your set
- Gap between 51x and 156x: an eyepiece around 23mm (~89x) would fill it.
The Evolution 8 numbers
| Aperture | 203mm |
|---|---|
| Focal length | 2032mm (f/10) |
| Eyepiece(s) in the box | 40mm (51x), 13mm (156x) |
| 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 Evolution 8
- You already own the widest 1.25" view. The stock 40mm Plössl reaches the 27mm field-stop limit, about 0.76°. A longer 1.25" eyepiece won’t show more sky.
- The big gap is between 51x and 156x. Something around 22–24mm (about 85–90x) fills it, which is the power most galaxies and globular clusters look best at.
- A 2-inch upgrade adds less than on an 8SE. The C8’s ~37mm rear baffle caps a 2" diagonal at about 1.04°, only ~0.28° more than the stock 40mm. Spend on the mid-power gap and a planetary eyepiece first.
- Planets: Barlow the 13mm, or add a 9mm. A 2x Barlow on the 13mm gives about 313x, which is more than most nights allow. A 9mm (226x) or 7mm (290x) is the more usable planetary step.
Common eyepieces on the Evolution 8
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 |
|---|---|---|---|---|---|---|
| 40mm (43°) | 51x | 4mm | 0.76° | 1.5 | Deep sky, Moon | – |
| 32mm (50°) | 64x | 3.2mm | 0.76° | 1.5 | Deep sky, Moon | – |
| 24mm (68°) | 85x | 2.4mm | 0.76° | 1.5 | Deep sky, Moon | – |
| 18mm (60°) | 113x | 1.8mm | 0.53° | 1.1 | Moon, Planets | – |
| 13mm (50°) | 156x | 1.3mm | 0.32° | 0.6 | 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. |
The stock pair with a 2x Barlow
A 2x Barlow doubles the focal length (2032mm → 4064mm). With only two eyepieces, check which Barlowed combinations are actually usable.
| Eyepiece | Magnification | Exit pupil | True field | Moon widths | Best for | Notes |
|---|---|---|---|---|---|---|
| 40mm (43°) + 2x Barlow ≈ 20mm | 102x | 2mm | 0.38° | 0.8 | Moon, Planets | – |
| 13mm (50°) + 2x Barlow ≈ 6.5mm | 313x | 0.6mm | 0.16° | 0.3 | Planets, Double stars | Most nights the atmosphere limits useful power to about 200–250x. Save this for very steady nights. |
Gaps in your set
- Gap between 102x and 313x: an eyepiece around 11mm (~178x) would fill it.
FAQ
What eyepieces come with the NexStar Evolution 8?
A 40mm (51x) and a 13mm (156x), both 1.25-inch, with a 1.25-inch star diagonal.
What eyepiece should I buy first for an Evolution 8?
A mid-power eyepiece around 22–24mm (about 85–90x) to fill the gap between the two stock eyepieces, then a 9mm for planets.
Are the Evolution 8 and 8SE the same for eyepieces?
The optics are the same (203mm, 2032mm, f/10), so the numbers are identical. The difference is the stock eyepieces: the Evolution includes a 40mm and 13mm, the 8SE a single 25mm.
Next steps
- Main eyepiece calculator: any telescope, custom aperture and focal length
- 6SE eyepiece calculator
- 8SE eyepiece calculator