Televue have been a company synonymous with quality for a number of years, they are arguably one of the finest producers of astronomical equipment on the market today. There's a good reason for this, the owner of Televue, Al Nagler is an enthusiastic astronomer himself and pours his efforts into making a superior product.
A barlow, for those who don't know, is a lens that an eyepiece is slotted into then attached to the telescope. The barlow magnifies any eyepiece inserted into it by a certain factor. This can be useful for a number of reasons. First and foremost it can effectively double your eyepiece collection at a relatively low cost. Secondly it allows you to keep a decent eye relief while observing under higher magnification (eye relief being the maximum distance you can hold your head from the eyepiece lens). A long eye relief means you don't have to keep your eye pressed against the glass of the lens to see the entire field. Thirdly and by no means least importantly, the barlow is an indispensible tool for the astrophotographer providing much needed magnification which is especially useful on the moon and planets where a good image scale is required.
Aesthetically Televue's Barlow is quite stylish, it's done out in the traditional Televue black and green. Eyepieces are attached via a single silver thumb screw. The Barlow is 5 inches long and quite light, it doesn't cause any balancing issues when I add/remove it from use.
What makes Televue's barlow better than a lot of the competition is that it only uses two lens elements in it's design as opposed to the more common three lens setup. When you consider that the addition of a barlow is adding extra glass between you and the object you're observing (which can only stand to degrade image quality) the fact that there's one less element than you'd expect is very welcome indeed. This makes the Televue a little sharper than some other barlows I've looked through and there is a significant reduction in light scatter.
At £80 it's not the lowest priced Barlow available but with so many dodgy cheap Barlows out there which degrade image quality to an unusable extent it is well worth splashing out that bit extra to ensure you're getting a decent lens.
A definite recommendation for it's optical quality as well as it's light but robust build.
Autumn and winter are great seasons for amateur astronomy. The early nights and dark skies allow the astronomer to view the stunning constellations at their best. There are so many sights to see in the sky; star clusters, galaxies, and nebulae all clamour for the viewer's attention and hours (even though they can be very cold) just fly by.
As astronomical telescopes owners will know, in order to view different sized objects at differing detail levels, it's necessary to use interchangeable eyepieces to give a range of magnifications.
There is one problem with this, however; the expense. An excellent eyepiece will cost £100 to £400, so having an extended range of them is only for the dedicated (or rich) amateur.
Fortunately, there is a way to double the range of magnifications available from your eyepieces in one go; use a Barlow lens.
The Barlow lens is not an eyepiece; it fits into the telescope focuser and the eyepiece is then inserted into the Barlow. The 2x Barlow lens has the effect of halving the focal length of the eyepiece. Magnification for a telescope/eyepiece combination is calculated by:
Focal length of telescope / focal length of eyepiece = magnification
This has the effect of doubling the magnification of the eyepiece (there are Barlow lenses available that have a different effect including 3x and 5x magnification).
If a user has (say) 10mm and 26mm eyepieces giving magnifications of 100x and 38x on his or her telescope, adding a Barlow lens will add magnifications of 200x and 76x. A useful range of magnifications with only two eyepieces!
There is a problem, however. Any lens placed between the telescope and eyepiece will have an effect on the final image. Any distortions in the Barlow will be transmitted to the user's eye and many Barlow lenses on the market today are of very poor quality.
If an astronomer has invested what can be a large sum of money in telescope and eyepieces, it seems silly to ruin their view of the night sky by fitting an inferior quality Barlow lens. That's where TeleVue can help.
TeleVue make some of the highest quality (and expensive) eyepieces in the world. They have also in their range this 2x Barlow lens. It is expensive compared to other Barlow lenses (I bought mine from Telescope House for £80) but cheap compared with a top quality eyepiece.
The lens is simple in design; a straight tube with a two element lens at the bottom of the tube and the fitting for the eyepiece at the other. The lens has a screw fitting to secure the eyepiece to the telescope.
At 95mm long, it is longer than other Barlow's I've used, but the light weight of 134g means that it's unlikely to affect the balance of the telescope. The only effect is to move the eyepiece around two inches further away from the scope.
In use, the quality is impressive; so impressive that the user cannot tell the lens is in place. In testing it with my Meade 5000 series 14mm eyepiece, I could detect no degradation in image quality, despite looking for all of the common problems.
Putting the eyepiece in and then fitting the TeleVue simply increased the magnification; there was no sign of any darkening, chromatic aberration, or distortion of the image at all.
When swapping from eyepiece to Barlow lens and eyepiece, refocusing is required. This is not a problem with the TeleVue, merely a physical property of the lens and is a minor irritation only.
Testing this on Jupiter and the 14mm was a revelation. Even though seeing conditions were not perfect, the 142x magnification was enough to clearly see the swirling bands of clouds that encircle the planet.
The great red spot was not currently visible, but I feel would be easily detected on the right night. The squashed nature of the planet (yes, Jupiter is flattened rather than circular due to its speed of rotation!) was easily evident.
Several of Jupiter's moons were visible and these showed as tiny discs rather than points of light, with no sign of any distortions at all.
Clearly, the TeleVue 2x Barlow lens is a superior piece of kit. Unless you have the money to buy a set of high quality eyepieces, this is the best way to increase the range of magnifications available. For £80 this is a bargain.