Double the magnification of your telescope's eyepieces (TeleVue 2x Barlow Lens)

Member Name: markos9

Product:	TeleVue 2x Barlow Lens
Date:	07/10/09 (137 review reads)
Rating:

Advantages: Superb quality at a reasonable price.

Disadvantages: None.

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.

Summary: An essential addition to the amateur astronomer's kit.