The beautifully applied, green-tinged multicoating on its three lens elements gives it an air of quality, and we particularly liked the ease of insertion into our star diagonal afforded by the barrel design.

However, if you are using eyepieces with a safety undercut you might well feel that this is a bonus, as this type of eyepiece can easily become stuck on some compression rings, which can be frustrating.

This design ensures that the original eye relief of the eyepiece remains unchanged, making it more suitable for longer focal length eyepieces and avoiding the risk of vignetting.

From a lunar and planetary imaging point of view, Powermates are the better choice as they can be stacked to produce high levels of magnification.

Typical Barlows have a magnification of 2x and are composed of two or sometimes three elements in a single group, forming a negative lens.

The lower lens housing is threaded to accept standard filters and the screw for holding the eyepiece doesn't unscrew the whole way, meaning it shouldn't fall out and get lost in the dark.

Its anti-marring brass compression ring is smooth and the internal micro-baffles, finished in a matt black, complete a well-thought-out design.

A Powermate is a telecentric design with four lenses in two doublet groups: a smaller negative lens and a larger positive lens arranged so that light exits the Powermate in parallel rays.

We also like the brass compression ring that holds the eyepiece firmly in place and, unlike a screw, won't cause damage to eyepiece barrels.

With our 26mm eyepiece in the Barlow we achieved a 1.25º field of view: with the Orion Nebula in the centre we could fit double star Struve 747 near the edge of the view.

Terahertz radiation penetrates many materials, such as dielectric coatings, paints, foams, plastics, packaging materials, and more without damaging them, Williams said.

The Tri-Mag 3x Barlow is a simple design neatly finished in a black silk with a plain, mainly chrome, 1.25-inch barrel measuring 139mm.

Views of Venus were excellent, and on the Moon plenty of sharp detail was visible. We very much enjoyed the view of the Orion Nebula’s Trapezium stars, which were very sharp and clear.

Linearly polarized light

Think of polarized sunglasses, which help people see more clearly in intense light. Polarizing works by filtering visible light waves to allow only waves that have their electric field pointing in one specific direction to pass through, which reduces brightness and glare.

A research team led by UCLA electrical engineers has developed a new technique to control the polarization state of a laser that could lead to a new class of powerful, high-quality lasers for use in medical imaging, chemical sensing and detection, or fundamental science research.

We turned to Orion's Sword and achieved splendid views with our our 26mm and 10mm eyepieces in the Barlow. We were able to observe the E and F stars in the Trapezium Cluster.

Named after English physicist and mathematician Peter Barlow, Barlow lenses add a second lot of magnification to each of your eyepieces while maintaining the existing eye relief.

P-polarized light

We also felt that of all the Barlows we've tried with a brass compression ring, this was the smoothest for inserting our 17mm undercut eyepiece, giving an almost airtight seal even before we tightened the locking bolt.

“So some applications include non-destructive evaluation in industrial settings, or revealing hidden features in the study of art and antiquities,” said Williams, who directs the Terahertz Devices and Intersubband Nanostructures Laboratory. “For example, our laser could be used for terahertz imaging, where the addition of polarization contrast may help to uncover additional information in artwork, such as improved edge detection for hidden defects or structures.”

Simply designed with a silk finish and plain chrome barrel, this is the only Barlow that incorporates a male T-thread so you can attach a camera.

Laser polarizationapp

This three-element multicoated design places the lower lens element at the very base of the barrel, meaning it does not include a filter thread.

Circularpolarization

The lead authors of the research are electrical engineering graduate student Luyao Xu and electrical engineering undergraduate student Daguan Chen. Other authors include electrical engineering graduate student Christopher Curwen; Mohammad Memarian, a postdoctoral scholar in UCLA’s microwave electronics lab; John Reno of Sandia National Laboratories; and UCLA electrical engineering professor Tatsuo Itoh, who holds the Northrop Grumman Chair in Engineering.

Our views of Venus were perhaps a little soft with this Barlow lens in comparison with others, but early morning lunar detail was enjoyable and clear.

For a lens that appears small, the #126 2x Barlow packs a punch. It can be used with other instruments but works best on short focus refractors and reflectors.

Their new metasurface covers an area of 2 square millimeters and has a distinct zigzag pattern of wire antennas running across its surface. An electric current runs through the wires, selectively energizing particular segments of the laser material, which allows a user to change and customize the polarization state as needed.

Displaying a green tinge, the multicoated lens surfaces are blemish free, and the long body possesses micro-baffles with a good matt black finish throughout its length.

“While there are a few ways to quickly switch polarization in the visible spectrum, in the terahertz range there is currently a lack of good options,” said Benjamin Williams, associate professor of electrical engineering and the principal investigator of the research. “In our approach, the polarization control is built right into the laser itself. This allows a more compact and integrated setup, as well as the possibility for very fast electronic switching of the polarization. Also, our laser efficiently generates the light into the desired polarization state — no laser power is wasted generating light in the wrong polarization.”

Celestron’s X-CEL LX 3x Barlow is designed to be the perfect companion to the company’s range of X-Cel LX eyepieces, with a matching rubber grip pattern, copper-coloured banding and an all black silk finish.

The work is based on the group’s recent development of the world’s first vertical-external-cavity surface-emitting laser, or VECSEL, that operates in the terahertz range.

Laserdiodepolarization

There is no anti-marring compression ring, although, depending on your eyepiece barrel type, this may be considered as an advantage.

Linearpolarization

This lens produces a diverging ray of light which, as well as magnifying the view, moves the eyepiece’s exit pupil farther outwards, thereby increasing the eye relief.

Altair’s Lightwave Premium 3x Barlow has a four-element lens design. It has a middling weight of the lenses reviewed at 165g, and the body is elegantly designed, with a silver undercut lens barrel and chunky rubber grip.

This effect is not too noticeable with short to medium focal length eyepieces, but it is more significant in longer focal length eyepieces as it can lead to vignetting if the eyepiece lenses aren’t wide enough to let the full width of the altered light cone through.

Views through the lens were excellent. Star Procyon was sharp across the whole view with our 26mm eyepiece, although we did notice the slightest of distortions at the edge.

Unpolarizedlaser

For example, this means a 17mm eyepiece will behave like a 5.6mm eyepiece. As a bonus, the increase in the scope’s focal ratio can improve image sharpness, but only under ideal conditions.

This excellent lens delivered great views of the Trapezium stars at the heart of the Orion Nebula with our 17mm eyepiece.

Inserting a Barlow lens into the light path of any type of telescope increases the effective focal length, usually by doubling it, although some designs have an even greater effect.

Like brightness and color, polarization is a fundamental property of light that emerges from a laser. The traditional way to control the polarization of a laser was to use a separate component like a polarizer or a waveplate. To change its polarization, the polarizer or waveplate must be physically rotated, a slow process that results in a physically larger laser system.

S-polarization vs p-polarization

Lunar observations in the early morning, when the seeing was at its best, gave most enjoyable views of the lunar surface, with sharp detail on the terminator.

The fully multicoated, three-element design is the second lightest in this group at 142g, and the lens is the second smallest in terms of length, but it has a solid, well constructed feel to it that gives plenty of confidence in use.

The team from the UCLA Henry Samueli School of Engineering and Applied Science developed a specialized artificial material, a type of “metasurface,” that can tune the laser’s polarization state purely electronically, without any moving parts. The research was published in Optica. The breakthrough advance was applied to a class of lasers in the terahertz range of frequencies on the electromagnetic spectrum, which lies between microwaves and infrared waves.

The soft rubberised material of the dust caps for both barrel and eyepiece holder made for a pleasant change from plastic inserts.

It is elegantly designed with a conical top and a tapered lens barrel for secure attachment, and its centre is neatly wrapped with a simple patterned rubber grip to make it safe to handle even when wearing gloves.

Both Barlow lenses and Powermates act as image amplifiers by increasing the effective focal length of your telescope, thereby increasing the magnification achieved with any eyepiece.