Televue Barlow

Posted by Scott Hill   08/29/2004 07:00AM

Televue Barlow
[ARTICLEIMGL="1"]When I was in college, I remember getting out my 60mm department store refractor for some stargazing. The rings of Saturn were barely distinguishable and looked more like ears than rings. So I decided to crank up the power for a closer look. I threw on my ultra-generic 2X barlow and 1.5X erector lenses, and topped it off with my SR-5mm eyepiece. With the eyepiece sagging from the weight of the lenses, I had to support it with my hand in order to see straight through. While Saturn did appear bigger, it also was very blurry. I soon stopped using the barlow and erector lenses altogether since the increase in magnification did not justify the decrease in image quality.

Fortunately, today you can buy premium barlows that do not detract from the image being viewed. After I bought a “real” telescope, I chose the Televue 3X barlow. For most people, 2X is sufficient, but I needed to triple the magnification of my telescope since I have a short focal length reflector.

Why I bought a barlow

Of course, the primary reason I bought the barlow lens was for increased magnification for lunar/planetary viewing. After I learned that stars hold their brightness as magnification is increased, the barlow was also helpful for filling the field of view with a globular star cluster or splitting a tight binary star. There are side benefits as well, such as increased eye relief since I can use larger eyepieces and still achieve high magnification, and improved contrast from a darker background sky resulting from using higher power. I even find the barlow useful for locating bright objects. The more out of focus an object is, the bigger it appears through the telescope. Rather than start out with a low power eyepiece to find a planet and then work my way up to the barlow, it is much easier for me to defocus the object and find it with the barlow at high power. Once I locate it, I just work to keep it in the field of view while I focus the object. Much easier and more convenient than repeatedly locking down the lever locks and switching eyepieces.

Why I chose Televue

I chose Televue largely because of their reputation for excellence. But the product description was also critical. Televue advertises that their 2X and 3X barlows are corrected for scopes down to F/4, and I can vouch for that as my reflector is an F/4. Also, it is a two element barlow as compared to an apochromatic barlow, which has three elements and therefore reflects a couple percent more light away. (Granted, apo’s have their advantages in other respects.) Being able to use my 32mm eyepiece with the Televue barlow was also a slight consideration since most barlows are designed to work with eyepieces 26mm and shorter. This gave me one more choice in magnifications to use than competing barlows. However, I have only done this once, and then only for the extra eye relief as the magnification is not that high.

Performance of the 3X Televue Barlow

I have been very pleased with the performance of my Televue barlow. When I first used it on Saturn, it was a little disappointing as my telescope was not collimated. The manufacturer’s statement about the telescope being perfectly collimated at the factory doesn’t mean anything if the factory is in China! All it takes is some rough seas, and you need to invest in a collimation tool.

Once I collimated the telescope, results were much better. I have not noticed any visual distortions when using the barlow, not even at the edge of the field of view. I was able to find the central star in M57 using the barlow to reach 200X. Also at 200X, M13 filled my field of view and I was able to distinguish between blue and white stars with my 8” reflector. The best view I have had of M13 was through a 13” reflector at 375X, and I could make out some red stars near the core of M13. But my telescope is smaller and was viewing M13 at lower magnification, so I cannot blame the weaker performance on my barlow. Overall, images were crisp, and I have not noticed any differences in image quality when viewing with just my Meade Series 4000 Super Plossls or when using my barlow in conjunction with these same eyepieces. I have noticed that it is difficult to achieve sharp focus higher than 200X, but that appears to be more of an issue with my standard rack and pinion focuser. I am looking into a focuser upgrade to correct this problem.

In addition, I am impressed with the sturdy construction of the Televue barlow. The strong metal tube has no problems supporting my 1-pound Vixen Superwide eyepiece. And the compression ring holds my eyepieces very firmly without leaving set screw marks.

The only concern one might have about purchasing a Televue Barlow is that it does require a bit of back travel with my telescope. This is no problem for my three inches of focus travel. However, I would recommend testing it out first at a star party before purchasing it for use with a 1” or 1.5” focus travel focuser.

Weakest link?

When considering which barlow to purchase, you want to consider the weakest link. For example, my Televue barlow would be almost worthless if I was still using my department store refractor. If the barlow you are looking at costs more than your telescope, you probably need a cheaper barlow, or a more expensive telescope! Since I have quality Meade telescope with quality Meade eyepieces, the Televue barlow does a great job of not limiting the performance of my telescope and eyepieces. However, if you have a premium refractor and the full set of Naglers, you may want to consider the Televue Powermates instead of the barlow. I hear the Powermates do perform a little better, but they are also considerably more expensive. So what it really comes down to is what kind of a budget you are on, and how discriminating you are!

Click here for more about the TeleVue barlows. -Ed.