It multiplies the focal length, and the eye relief survives
A Barlow lens sits between the focuser and the eyepiece and multiplies the effective focal length of the telescope, so that every eyepiece in the case becomes two. Its quiet advantage over simply buying shorter eyepieces is that the eye relief is preserved: a comfortable long eyepiece behind a Barlow gives a high magnification with the eye still at a workable distance, where a very short eyepiece of simple design would press the eye against the glass. The amplification factor is the headline figure, and it is worth knowing that it is not fixed — moving the Barlow further from the eyepiece, as happens when one is used ahead of a diagonal or with an extension tube, increases the multiplication beyond what is printed on the barrel. Element count separates the shelf: a two-element Barlow is cheap and adds some false color at the edges, a three-element apochromatic design holds color and field better and costs accordingly. A Barlow is a piece of glass in the light path of every eyepiece used behind it, so a poor one degrades a good eyepiece. Read the camera thread, since many Barlows unscrew so that the lens cell alone can be fitted directly to a camera nosepiece — a quiet, useful feature that changes the amplification. Check the barrel size and whether the unit accepts filters. We compare amplification factor, element count, barrel size, camera thread, effect on eye relief, coatings, body and weight.
2x Barlow · 1.25 in (31.8 mm) · two-lens design · for observing and photography
Bresser's 2x Barlow in a 1.25-inch (31.8 mm) barrel, described on Amazon.com as a two-lens design for observing and photography, with a black lens cell and silver barrel.
Best for: An owner of Bresser eyepieces who wants a matching 2x and accepts a thin specification
≈ $98
2x Barlow · 2 in barrel · ED glass · multi-coated · 2 in filter thread · 1.25 in adapter included
A 2-inch 2x Barlow in ED glass with multi-coated surfaces, a 2-inch filter thread and a 2-to-1.25-inch adapter, so both eyepiece sizes can be doubled.
Best for: A 2-inch focuser and wide-field 2-inch eyepieces that no 1.25-inch Barlow can take
≈ $63
3x Barlow · 1.25 in · apochromatic glass · M42 × 0.75 male thread · 1.25 in filter thread
A short 1.25-inch 3x Barlow in CNC-machined aluminum with apochromatic glass, multi-coated optics, a 1.25-inch filter thread and an M42 × 0.75 thread that takes a camera T-ring.
Best for: A short-focus telescope that needs planetary magnification, or a camera that cannot otherwise reach focus
≈ $24
2x Barlow · 1.25 in · apochromatic glass · M42 × 0.75 male thread · 1.25 in filter thread
A short 1.25-inch 2x Barlow in CNC-machined aluminum with apochromatic glass, multi-coating, a filter thread and an M42 × 0.75 thread for a camera T-ring.
Best for: A first Barlow that will also carry a camera, on a telescope that struggles to reach focus
≈ $19
3x Barlow · three apochromatic elements · fully multi-coated · brass compression ring · 1.25 in filter thread
Celestron's X-Cel LX 3x: a three-element apochromatic, fully multi-coated 1.25-inch Barlow with a brass compression ring, a filter thread and a rubber grip, sold for fast short-focus telescopes.
Best for: A fast, short-focus telescope where a 2x does not reach planetary magnification
≈ $90
2x Barlow · three apochromatic elements · fully multi-coated · brass compression ring · 1.25 in filter thread
Celestron's X-Cel LX 2x: a three-element apochromatic, fully multi-coated 1.25-inch Barlow with a brass compression ring, a rubber grip and a filter thread.
Best for: An eyepiece collection worth protecting, where the compression ring and apochromatic glass are the reasons to pay
≈ $100
2x Barlow · 1.25 in · fully multi-coated with blackened edges · keeps eye relief · 2-year US warranty
Celestron's Omni 2x: a 1.25-inch Barlow with fully multi-coated optics and blackened lens edges, which doubles each eyepiece's power while keeping its eye relief.
Best for: A first Barlow for an existing 1.25-inch eyepiece set
≈ $35
Sold as 5x, measured 2.5x by its maker · 1.25 in · M42 thread · Moon filter included
A 1.25-inch Barlow sold as 5x whose own listing says it measures 2.5x, bundled with a Moon filter and fitted with an M42 thread for a camera T-ring.
Best for: A first telescope that needs a Moon filter anyway, bought knowing the factor is 2.5x
≈ $22
2x Barlow · two elements in one group · green multi-coating · 1.25 in · M42 × 0.75 thread
SVBONY's metal 2x Barlow: a cemented two-element, one-group design with broadband green multi-coating, a blackened housing and an M42 × 0.75 thread that takes a camera T-ring.
Best for: The cheapest way to double an existing 1.25-inch eyepiece set, with a camera thread included
≈ $18
The amplification factor is what a Barlow brings: it multiplies the magnification of every eyepiece already owned.
Published element count explains the correction obtained. A simple Barlow degrades more than a multi-element formula.
It lengthens the instrument’s effective focal length, which multiplies the magnification of any eyepiece placed behind it.
The coefficient by which the magnification is multiplied. It is published and is most often two or three.
It adds optical surfaces. Published element count and coatings say how the maker deals with that.
Yes, and the effect on eye relief is published for that reason. It is often favorable.
The published camera thread spells it out. This site describes no photographic setup.
The published barrel size has to match the focuser and the eyepieces used.
Makers publish their own guidance. This site describes no such assembly.
The construction of the barrel, published by the maker. It explains part of the weight and of the hold when tightened.
A Barlow doubles the eyepiece range for the price of one accessory. The published factor says what it allows; the element count says what it costs the image.
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 | Amplification factor | Barrel size | Body |
|---|---|---|---|---|
| SVBONY 2x metal | $18 | 2x, stated | 1.25 in | Aluminum, black anodized |
| Astromania 2x with T-thread | $19 | 2x, stated | 1.25 in, for 1.25 in eyepieces from most brands | All-metal, CNC-machined aluminum, black anodized · two large locking thumbscrews · 1.25 in filter thread |
| Starboosa SB-0215a 5x with Moon filter | $22 | 5x in the title · 2.5x "in the actual measurement", stated in the maker's own bullet | 1.25 in, stated to work with Celestron, Sky-Watcher, Meade, Orion and most brands | CNC-machined frames for the Barlow and the Moon filter, with an anti-rust surface treatment |
| Astromania 3x with T-thread | $24 | 3x, stated (one bullet says it doubles the eyepiece's power, a copy error from the 2x version) | 1.25 in, for 1.25 in eyepieces from most brands | All-metal, CNC-machined aluminum, black anodized · two large locking thumbscrews · 1.25 in filter thread |
| Celestron Omni 2x | $35 | 2x, doubles the magnification of each eyepiece, stated | 1.25 in, slides into 1.25 in focusers and diagonals and accepts 1.25 in eyepieces · threaded barrel | Threaded 1.25 in barrel |
| Astromania 2 in ED 2x | $63 | 2x, stated | 2 in · a 2-to-1.25-inch adapter is included so 1.25 in eyepieces can be used as well | Textured high-grip exterior stated usable with gloves · 2 in filter thread on the lower barrel and on the adapter |
| Celestron X-Cel LX 3x | $90 | 3x, triples the magnification of any 1.25 in eyepiece, stated | 1.25 in | Black anodized with orange highlights matching the X-Cel LX eyepieces · brass compression ring instead of setscrews · central rubber grip · threaded for 1.25 in filters |
| Bresser 2x Barlow (4950110) | $98 | 2x, doubling the focal length, stated | 1.25 in (31.8 mm) | Black Barlow element cell, silver barrel |
| Celestron X-Cel LX 2x | $100 | 2x, doubles the magnification of any 1.25 in eyepiece, stated | 1.25 in | Black anodized with orange highlights · brass compression ring · central rubber grip · threaded for 1.25 in filters |
$18 – $22
3 models
SVBONY 2x metal, Astromania 2x with T-thread, Starboosa SB-0215a 5x with Moon filter
$90 – $100
3 models
Celestron X-Cel LX 3x, Bresser 2x Barlow (4950110), Celestron X-Cel LX 2x
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.
