Explore Scientific 2x Focal Extender 2″ Barlow Lens
The Explore Scientific 2x Focal Extender is a premium Barlow lens built around a telecentric optical design - an approach that sets it apart from conventional Barlow lenses and makes it particularly well suited for both visual observation and astrophotography. The four-element optical system with fully multi-coated (FMC) surfaces delivers sharp, high-contrast views while cleanly doubling the effective focal length of any telescope it is used with.
Telecentric Design - What It Means in Practice
A standard Barlow lens diverges the light cone leaving the objective, effectively increasing the focal length of the telescope. A telecentric design goes further: it produces a parallel output beam rather than a diverging one. This has several important practical consequences.
For visual observation, the telecentric design means that the magnification factor remains constant regardless of how deep the eyepiece is inserted into the barrel. With a conventional Barlow, the amplification factor changes slightly depending on the distance between the Barlow and the eyepiece field lens - an effect that can make the stated 2x factor only approximate in practice. The Explore Scientific Focal Extender eliminates this variability entirely.
For astrophotography and eyepiece projection, the parallel output beam is particularly valuable. The telecentric design preserves the parfocal characteristics of eyepieces and ensures consistent, predictable results when the extender is used with cameras or other imaging accessories. It is also better suited for use with filters and other optical accessories placed in the light path.
Optical Construction
The four optical elements are all fully multi-coated to minimize reflection losses and maximize contrast. Each lens element has blackened edges to absorb any stray light that might otherwise cause internal scatter and reduce image contrast - a detail that is especially important at higher magnifications, where even small amounts of stray light can visibly degrade the view on bright objects such as the Moon or planets.
The result is an image that is bright, sharp, and high in contrast - qualities you would expect from a premium accessory in the Explore Scientific lineup, which is well regarded among serious amateur astronomers for the optical quality of its products.
Build Quality and Connections
The housing is solid metal construction with a 2″ barrel that fits any standard 2″ focuser. A metal compression ring clamp holds the inserted eyepiece securely without the risk of marring its barrel - the same type of clamp found on high-quality focusers. A standard filter thread on the barrel allows 2″ filters to be attached directly to the extender, which is convenient when using nebula or light pollution filters together with higher magnifications.
At 665 grams and 123 mm in length with a maximum diameter of 70 mm, the Focal Extender is a substantial piece of equipment - its weight reflects the quality of materials and the four-element optical system inside. When selecting a focuser or mounting accessories, this weight should be taken into account to ensure stable balance.
Practical Use
The 2x amplification factor makes this extender an excellent tool for planetary observation and lunar detail work. Paired with a quality wide-field eyepiece, it effectively doubles your magnification range without any degradation in image quality. For example, an eyepiece delivering 100x becomes a 200x eyepiece - with full eye relief preserved, since the telecentric design does not affect the working distance between the eyepiece and the observer's eye.
The extender is also compatible with all standard 1.25″ eyepieces via a 2″ to 1.25″ adapter (not included), giving full flexibility across your entire eyepiece collection.
Technical Specifications
- Magnification factor: 2x
- Optical design: telecentric, 4 elements
- Coatings: fully multi-coated (FMC) on all surfaces
- Barrel diameter: 2″
- Eyepiece clamp: metal compression ring
- Filter thread: yes (2″ standard)
- Length: 123 mm
- Maximum diameter: 70 mm
- Weight: 665 g
