Magnification is a division, not a number on a box
An eyepiece does not have a magnification. Magnification is what happens when one is put in a particular telescope, and it is found by dividing the focal length of the telescope by the focal length of the eyepiece — which is why the same eyepiece gives one figure in a short refractor and three times that in a folded catadioptric. Everything else about choosing follows from understanding that division. Dividing the eyepiece focal length by the focal ratio of the telescope gives the exit pupil, the width of the light cone reaching the eye: too wide and light is wasted outside the pupil, too narrow and the image dims and shows floaters. The apparent field of view, printed in degrees, is how wide the view looks; multiply nothing, but understand that a wide apparent field at high magnification is what makes an object feel like it is floating rather than peered at down a tube. Eye relief — the distance the eye can sit behind the glass — is the specification that decides comfort and whether spectacles can be worn, and short-focal-length eyepieces of simple design have notoriously little of it. Read the barrel size, since the 1.25 inch and 2 inch fittings are not interchangeable without an adapter and the larger barrel exists to pass a wider field. Weight matters more than it seems: a heavy eyepiece can unbalance a small mount. We compare focal length, apparent field, eye relief, barrel size, optical design, coatings, weight and supplied accessories.
8 mm (0.31 in) Plössl · 50° apparent field · four elements · fully multi-coated · 1.25 in
Astromania's 8 mm Plössl: a four-element, fully multi-coated 1.25-inch eyepiece with a 50-degree field, an aluminum body, a filter thread and a fold-down rubber eyeguard.
Best for: A step up from a supplied short eyepiece, for planets and the Moon
≈ $17
10 mm (0.39 in) Plössl · four lenses in two groups · fully multi-coated · 65 g (2.3 oz) · 37 × 37 × 45 mm
Bresser's 10 mm Plössl: four lenses in two groups, fully multi-coated, in a metal 1.25-inch housing with a filter thread, reversible eyecup and storage case, published at 65 g.
Best for: A dependable medium-power eyepiece for a case being built properly
≈ $98
4 mm (0.16 in) Plössl · 50° apparent field · four elements · fully multi-coated · 1.25 in
Astromania's 4 mm Plössl: a four-element, fully multi-coated 1.25-inch eyepiece with a 50-degree field, an aluminum body, a filter thread and a fold-down rubber eyeguard.
Best for: High-power lunar and planetary work on a long-focus telescope, by an observer without glasses
≈ $16
6 mm (0.24 in) Plössl · 50° apparent field · four elements · blackened lens edges · anodized aluminum
Celestron's Omni 6 mm: a four-element Plössl with a 50-degree field, multi-layer coatings, blackened lens edges, an anodized aluminum barrel with a filter thread and a fold-down rubber eyecup.
Best for: Planetary detail on a medium-focal-length telescope, from a maker with a US warranty
≈ $32
20 mm (0.79 in) · 66° apparent field · 16 mm (0.63 in) eye relief · fully multi-coated · edge-blackened
SVBONY's 20 mm 66-degree eyepiece: a multi-group, fully multi-coated wide-angle with edge-blackened optics and 16 mm of eye relief that lets eyeglass wearers see the whole field.
Best for: The low-power eyepiece that stays in the focuser: wide, long-relief, usable with glasses
≈ $37
12 mm (0.47 in) · 60° apparent field · six elements · 16 mm eye relief · fully multi-coated
Celestron's X-Cel LX 12 mm: a six-element, fully multi-coated eyepiece with a 60-degree field, 16 mm of eye relief, blackened lens edges, a twist-up eyecup and a treaded rubber grip.
Best for: The eyepiece that stays on the planets, used with glasses or gloves on a cold night
≈ $93
The eyepiece’s focal length, divided into the instrument’s, gives the magnification. The eyepiece sets it, not the telescope.
Apparent field decides between the impression of an open window and looking down a tube. Nothing distinguishes two eyepieces more.
Eye relief decides whether the whole field stays visible with corrective lenses. Below a threshold it does not.
By dividing the instrument’s focal length by the eyepiece’s. Both values are published, each on its own side.
The angle the eye perceives through the eyepiece, in degrees. It is published and decides the sense of immersion.
The one the instrument’s focuser accepts. The published diameter is the first compatibility filter.
Mostly for spectacle wearers. The published value says whether the whole field stays reachable with lenses.
The formula used, published by the maker. It explains the field, the correction and part of the price.
It changes neither the telescope’s diameter nor its focal length. This site publishes characteristics and promises no gain.
Supplied accessories are published: caps, eyecup, occasional filter. They vary from model to model.
This site publishes each one’s characteristics. The eyepiece sets section handles the question of focal length spread.
It is the eyepiece that sets the magnification, not the telescope. Apparent field decides the impression, and eye relief decides whether the spectacles stay on.
The column is shown only when four instruments in five publish the figure. Below that, it would be comparing the absence of numbers.
| Model | Price | Barrel size | Coatings | Focal length | Apparent field |
|---|---|---|---|---|---|
| Astromania Plössl 4 mm (PT14) | $16 | 1.25 in, with a female filter thread | Fully multi-coated, stated | 4 mm (0.16 in) | 50°, stated |
| Astromania Plössl 8 mm (PT18) | $17 | 1.25 in, with a female filter thread | Fully multi-coated, stated | 8 mm (0.31 in) | 50°, stated |
| Celestron Omni 6 mm (93317) | $32 | 1.25 in, threaded for filters | Multiple layers of high-transmission coatings · blackened lens edges | 6 mm (0.24 in) | 50°, stated |
| SVBONY 20 mm 66° ultra-wide | $37 | 1.25 in | Fully multi-coated broadband green optics · edge-blackened, internally blackened | 20 mm (0.79 in) | 66°, stated |
| Celestron X-Cel LX 12 mm (93424) | $93 | 1.25 in, threaded for filters | Fully multi-coated · blackened lens edges | 12 mm (0.47 in) | 60°, stated |
| Bresser Plössl 10 mm (4920210) | $98 | 1.25 in (31.7 mm), with a filter thread | Multi-coating on all lens surfaces, stated | 10 mm (0.39 in) | Not published by the maker. |
Specifications: manufacturer sheets for telescopes and observing optics and the matching Amazon product pages. Prices and availability: Keepa. Every figure in this table names its source.
Most recent revision in this category: November 7, 2026.
Any figure written into the body of this page was true on the day it was written. The amount shown next to each instrument is requested from the retailer as the page loads, and it is that amount, not the text, that stands.
