| Key Specifications | |
|---|---|
| Focal Length | 18mm |
| Apparent Field of View | 60° |
| True Field of View | Varies by scope (7.5° in f/5 scope) |
| Eye Relief | 25mm |
| Lens Elements | 4 (multi-element ED design) |
| Barrel Size | 1.25" |
| Weight | ~160g |
| Coatings | Fully multi-coated (ED glass) |
| Waterproof | No |
| Available From | First Light Optics, Amazon UK |
The BST StarGuider 18mm is the eyepiece for observers who want to see the full context of what they're looking at. Where the 8mm burrows deep into planets and lunar craters, the 18mm pulls back and shows you entire nebulae, open clusters spanning multiple eyepiece widths, and the Milky Way in all its sprawling glory.
The 18mm is lower power than the 8mm, designed for finding objects and seeing their full extent:
f/5, 650mm focal length
36×Perfect for finding faint objects. The Pleiades fit in the field with room to spare. Large nebulae show their full structure.
f/5, 750mm focal length
42×Wider view with more aperture. The Orion Nebula shows extended structure. Galaxies look less like tiny dots.
f/6, 1200mm focal length
67×A larger scope at medium power. Open clusters show dozens of stars. The Andromeda galaxy sprawls across the view.
f/10, 900mm focal length
50×A refractor at lower power means beautiful contrast and crisp stars. Perfect for star clusters and large nebulae.
The 18mm is the "I just want to see pretty things" eyepiece. You'll spend most of your observing time here, especially on first nights with a new scope.
The 8mm and 18mm pair is legendary. On Stargazers Lounge and Reddit's r/astronomy, when someone asks "what two eyepieces should I buy?", the answer is always "the BST 8mm and 18mm". Observers own these for years.
"The workhorse eyepiece." Forum regulars describe the 18mm as the eyepiece you use 70% of the time. Low power, wide field, comfortable eye relief. It's the one that gets grabbed on every clear night.
Excellent for discovering your observing style. The 18mm at low power is forgiving. You can scan the sky, locate objects without star-hopping effort, and find the targets you actually enjoy observing. Once you know what interests you, the 8mm lets you push magnification on those specific targets.
Same quality as the 8mm. The ED glass and multi-element design deliver sharpness that rivals eyepieces costing 2–3 times as much. At £45, it's objectively one of the best eyepiece bargains on the UK market.
The essential pairing. Low and high power from one matched pair. Most observers own no other eyepieces for months.
~£45Eventually, you'll want a wider-field alternative to the 18mm. The 68° field is immersive for deep-sky objects. Requires a 2" focuser (Skyliner 200P+).
~£120Use it with the 18mm to get a medium-power eyepiece (9mm equivalent). Adds versatility without buying a third eyepiece.
~£27A premium alternative to the 8mm, if you decide you want better planetary performance. Or keep the 8mm and step up only after confirming you love the hobby.
~£80The 8mm and 18mm together are the foundation. Many observers stay with this pair for their entire first year. It's not a stepping stone — it's a complete observing system.
The next step is specialisation. After a year observing, you'll know whether you love planets (in which case upgrade to a Celestron X-Cel LX or premium eyepiece for the 8mm range) or deep-sky objects (in which case explore wider-field options like the Explore Scientific 68°). The 18mm is happy either way.
Buy the 18mm. Use it for a year. Let it tell you what you love observing. Then upgrade appropriately.