Celestron Ultima Series 2x Barlow
By Chuck Hawks
This Celestron 1.25" - 2x Ultima Barlow (#93506) does what Barlow's do, and does it well. Specifically, it halves the effective focal length of your ocular, thus doubling the magnification. To do so, any 2x Barlow lens reduces the amount of light reaching your eye by 75%, so only 25% remains. Although seldom mentioned in ads promoting Barlow lenses, this light loss equation is a mathematical fact and there is no way around it.
Celestron's 1.25" (31.75mm) Ultima Barlow is a good one. It is an apochromatic design made from top quality optical glass and it is fully multi-coated. It uses an air-spaced, 3-element design and features a 27mm clear aperture. The 2x Ultima Barlow is compact (2.75" long) and weighs only 5 ounces, so it should not be an excessive burden for any decent focuser. Like Celestron's Ultima oculars, this Barlow is well made and nicely finished.
I tested the Ultima Barlow on my Celestron Omni XLT 102ED (4") refractor (900mm focal length) telescope with a number of oculars, including a 32mm Celestron Plossl, 26mm Meade Super Plossl, 25mm Celestron X-Cel, 17mm Celestron Plossl, 14mm TeleVue Radian, 12mm Celestron Ortho and 9mm Burgess Planetary. I am pleased to report that it worked satisfactorily with all of these, despite their diverse designs. I thought it was at its best with the Orthoscopic and the Plossl oculars, the types with which it is most likely to be used.
It slightly degraded the image quality, as all Barlow lenses do (despite advertising claims to the contrary), but the loss of resolution was never dramatic. One advantage to a good Barlow lens is that you are getting the effective magnification of an ocular of only half the focal length, while viewing with a longer focal length ocular that is easier to look through. It is, for example, easier to look through a 12mm Plossl and a Barlow than a 6mm Plossl, even though the view is slightly degraded. To me, that is the primary benefit of a good Barlow lens, as I am not a fan of peering into very short focal length oculars.
If you need a 2x Barlow lens, the Ultima is an excellent choice. The 2009 MSRP is a reasonable $110.99 and the Celestron 1.25" - 2x Ultima Barlow can be purchased online for only $69.90 from Optics Planet (www.opticsplanet.com).
Copyright 2009 by Chuck Hawks. All rights reserved.