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SmartAstronomy 2.5x and 5x Barlows

Posted by david elosser   09/26/2007 01:40AM

SmartAstronomy 2.5x and 5x Barlows
If you are looking for more power out of your eyepiece collection for a budget price, SmartAstronomy has two new Barlows that might fit your needs. They are 3-element fully multi-coated Barlows, one 2.5x and one 5x. You can purchase one by itself, or as I did, buy the pair for a discounted price. They are available from

Barlows, like eyepieces, are prolific in the marketplace; 2-element, 3-element, and even 4-element multiplier designs are available from many suppliers, with a number of magnifications from under 2x up to 5x. The latter promises to bring your low power eyepieces up to some serious star-splitting magnifications. But which would be better, using a 5x multiplier on your low power eyepieces, or simply buying eyepieces with comparable magnifications?

I own and use a lot of Barlows, multipliers, and high power eyepieces. I will say up front here, putting an inexpensive 25mm Plossl into a 5x Barlow does not a 5mm Nagler make. Having said that, I would also say that in many viewing applications I would not turn around for the difference. Although I would give the edge to any well made high power eyepiece, using Barlows in my experience produces excellent images, often for a fraction of the cost of another premium eyepiece. Also, the SmartAstronomy Barlow pair will in effect turn any well made eyepiece into three. A third advantage is viewing comfort. I love the images in my Orthoscopic eyepieces, but by the time you get to a focal length shorter than 9mm they become increasingly difficult for me to use due to their narrow field of view and short eye relief. Barlows increase the eye relief of the eyepiece it is paired with making moderate focal length Plossls and Orthos easier to use. But there are good arguments on the other side of the fence too. To begin with, a well made high power eyepiece is designed to have all of its elements work together to produce the best possible image that the designer intended. Barlows are not eyepiece specific in this regard, and can sometimes produce some unwanted consequences from your eyepiece. (I will go into this in detail later on.) There is also the assurance that, when purchasing eyepieces in the same product line, that you are getting an identical performance between the high and low power eyepieces. If you really like your 13mm Nagler, why not get the 7mm and the 5mm? You know the performance is going to be the same with each eyepiece.

Both of my Barlows arrived quickly after date of purchase, well packed, and in excellent condition. Both come with top and bottom caps, and have grooved barrels and brass compression rings. They appear to me to be well made with excellent fit and finish. I will start with the SmartAstronomy 3-element 2.5x Barlow. Keeping this Barlow capped is a good idea. There is an element right at the bottom of the chrome barrel that could easily get scratched if not protected during storage. Because of the placement of this element, the barrel is not threaded for filters. In use would say that this Barlow produces an excellent image. I have some eyepieces that are known for having poor edge performance, especially in short refractors, like my 25mm Erfle. The 2.5x Barlow produces a noticeably sharper edge of field, even in my 80mm/f6 achromat. There are no ghost images on bright objects and the overall image is well protected against unwanted flaring. Using my 102mm/F7.75 apochromat on a waxing gibbous moon for example, I saw little off-axis flaring and was able to easily see the moon occult a 7th magnitude star right at the southern tip of its dark side. When it reappeared minutes later, it could be easily seen very near the brightly lit edge of the lunar limb. Compared to using the 2.5x with my 12mm Konig, my 5mm Nagler produced a slightly sharper image, but the biggest differences were in the larger field of view with less flaring. However, I find that the overall image quality- the sharpness, contrast, and detail, make this Barlow a great choice for lunar viewing. The 2.5x Barlow produces excellent star images. A star test on a bright star produces well defined diffraction rings separated by black spaces. It also exhibits excellent contrast and light throughput, giving wonderful images on deep space objects, even dim ones like M1 in Taurus. The view of M42, the great Orion Nebula, is very pronounced using this Barlow, the increased magnification and contrast producing a beautiful view. Using a 16mm eyepiece, the E star in the Trapezium was easily seen through my 102mm refractor and the F star could be seen when seeing conditions allowed. Splitting tight doubles like Alnitak in Orion is easy when enough power from an eyepiece is used. The SmartAstronomy 2.5x Barlow easily stacks up well against the other 2 and 3-element Barlows I have in my collection. One of my favorite Barlows is the excellent Orion 3-element 2x Shorty-Plus, made in Japan. On the outside, the two Barlows look similar (see photo below.)

But on the inside they are somehow quite different as they are not parfocal with each other (that is, they do not focus at the same spot using the same eyepiece), and the SmartAstronomy Barlow has a slightly wider true field of view. I haven’t figured out why the SA Barlow produces a wider field. The Orion Shorty has less magnification and sports a full clear aperture of 27mm. In my opinion the SA Barlow performs equally well with the Orion Shorty-Plus 2x Barlow as far as image quality goes.

I was really anxious to see how the SmartAstronomy 3-element 5x Barlow stacked up against my Meade 5x TeleXtender. The physical differences between the two are rather obvious (see photo below).

The SA 5x is smaller, lighter weight, and has one less element than the Meade. Although I would say the fit and finish of the SA 5x is excellent, the Meade clearly has a more robust construction. Consequently, the Meade is quite a bit pricier. Both come with top and bottom caps, and both have brass compression rings. As with the SA 2.5x, the SA 5x has an element right at the bottom of the barrel, so keeping this one capped too during storage is advised. Because the Meade has a recessed bottom element, it comes threaded for filters while the SA does not. It was when I put these two to the test behind the telescope that the superiority of the Meade’s fourth element and more expensive optical design showed up. On most targets there is little or no difference. Both produced excellent star images, tack sharp right up to the field stop. It didn’t matter what design eyepiece I used, even simple designs with poor edge performance sharpened up well in both brands. On a star test with my 102 apo, both produced a well defined “bull’s eye pattern” of diffraction rings separated by black zones, right down to the center spot. I got the impression that the Meade has a slightly sharper and better defined star test pattern, but I had to look hard to see it. Neither unit produced any ghost images or reflection on bright point sources. When I pointed my telescope at the waxing gibbous Moon though, I got quite a different story. Whereas the Meade produced a very clean lunar image with very little flaring, the SA showed a whopping amount of off-axis flaring. So much so, I found that what would otherwise have been an excellent, sharp, and contrasty image was nearly ruined by the glare. This was not dependent on the eyepiece used. Every eyepiece brand and design I used produced this glare, although some less than others. No eyepiece produced a satisfactory lunar image along the terminator due to the glare in the SA 5x in my opinion, although the glare was much less pronounced when I moved away from the terminator to the brightly lit portion of the lunar disc. In contrast, my 5mm Nagler produces a much cleaner image almost devoid of flaring and glaring. So, if you are looking for something to give you higher power views of the Moon, I feel that the SmartAstronomy 2.5x Barlow is a much better choice. The SA 5x however, does work very well on all other targets I viewed: planets and double stars certainly (there is no glare viewing Jupiter or Mars), but even deep space objects like globulars and nebulae look good if you have enough aperture to overcome the diminished light from the high 5x magnification. The Orion nebula shows excellent contrast and detail even through my 3” achromat. In fact, other than lunar use, I can recommend this 5x Barlow for any small, short tube refractor, 80mm being the smallest aperture I tested it on.

Now, I would like to mention one other characteristic of these Barlows, and all 2 and 3-element Barlows in particular. They tend to noticeably increase the eye relief. This is a good thing, or a bad thing, depending on the eyepiece you are using. Eyepieces with short eye relief, like Plossls and Orthos, can benefit from this characteristic. But eyepieces with eye relief in the 17-20 millimeter range might be difficult to use. I recommend choosing such an eyepiece that has a flip-up or twist-up eyecup, so you can position your eye at the proper distance. An adjustable eyecup is not entirely necessary, but getting in too close to the eyepiece can cause immediate blackouts if you have one with a long eye relief. In contrast, a 4-element multiplier like the Televue Powermate will have little effect on the eye relief of the eyepiece used. They are also more parfocal with the eyepiece, that is, you will have to do little refocusing with a 4-element multiplier compared to a simper designed Barlow.

My conclusions: I think both of these Barlows from SmartAstronomy perform very well. In both Barlows I noticed no significant loss in image sharpness and contrast, other than what you would expect to get from such a higher power in the first place. Other than the problems and cautions I mentioned above, I believe these two Barlows would make a good addition any anyone’s eyepiece collection.

David Elosser
Kernersville NC