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on March 6, 2014
Users who don't know what they are doing or talking about is really getting on my wick. It could be a review on the latest electronic device or a set of spoons! But this explains the long amble to my final remarks on the Celestron 2x Omni Barlow in this review.

Observational astronomy has been my avocation for 33 years with hundreds of dusk to dawn sessions, and thousands of hours at the eyepiece.

I am afraid that most people who purchase a Barlow lens have performance expectations that are naive, or are trying to correct the mistake of having purchased a telescope whose f/ratio is so fast as to make any high magnification observations disappointing. An f/5 telescope, for instance, is fine for observing deep sky objects in a wide field of view. An f/15 refractor is best suited for planetary, lunar and binary star observations where high magnifications and high contrast images are required.

As we move through a range of eyepieces from low to high power what does the user notice most? It is the eye relief. The eye relief of a 32 mm is long enough even to use glasses. But as we drop down to 6 mm, 5 mm, and 4 mm the eye lens becomes very small. You must move in so close as to sometimes touch the eye lens with one's eye lashes. If you wear glasses, they must be removed to get close to the eyepiece. Now any malady your eyes suffer from are uncorrected. This may introduce your chromatic aberrations, serious astigmatism, &etc, to the telescopic image.

Of course there is the telescope itself. The best instruments under good atmospheric conditions can, at best, employ 50x to 60x (power) per inch of aperture. Further magnification is called "empty magnification". Why? Because you have already reached the theoretical resolution limit of the telescope. More magnification reveals no more detail. The images just get bigger, darker and fuzzier.

For instance, a 4" telescope will have an optical limit of 240x. An 8" telescope can theoretically achieve 480x. But there are so many variables to consider. Is the scope a Schmidt-Cassegrain, a Newtonian (is it a long or short f/ratio?), is it a refractor (long or short f/ratio)? What are the seeing conditions? An absolutely clear sky can have horrible "astronomical seeing" (unsteady air) which causes stars to twinkle, and any planetary or lunar image to go from sharp and crisp to a blob. You can throw those theoretical dictums right out the window!

The typical introductory or moderately priced scope will come with "run-of-the-mill" eyepieces of 25 mm and 10 mm that are not of high quality. Even a good quality Barlow will make flaws in poor quality optics stand out like a sore thumb. If it was not a good eyepiece at 10 mm what can you expect when it is a Barlowized 5 mm?

But we purchased a trusty, magical Barlow with the hopes of seeing Neil Armstrong's foot prints on the moon with our Barlowized 2 mm at 750x! Is it any surprise that novices are quickly jaded with the hobby altogether out of ignorance and unrealistic expectations, or perhaps lay the blame on their new, shiny, slick Barlow?

Barlows come in 2x, 2.5x, and 3x. Some are absurdities at 4x or 5x! Barlows are designed to extend an instrument's focal length. But in practice their primary function is to obtain higher magnifications with low power eyepieces while still retaining the low power eyepiece's long eye relief. This maintains comfortable viewing with high magnifications even while wearing glasses. Remember my earlier comments regarding eye relief and glasses wearers? Barlows are not intended to be used with the entire range of eyepieces in your kit.

A Barlow's performance excels with eyepieces from 32 mm down to 12 mm. That Barlowized 12 mm is now a 6 mm, but retains the eye relief of a 12 mm. 12 mm or 10 mm eyepieces are the absolute end-of-the-line for employing a Barlow and to expect any degree of visual integrity. Beyond that range and you are just playing with your "toys" and abusing them at that! A Barlow is a tool of convenience not a magic wand.

Yes, this is a review on the Celestron 2x Omni Barlow.

My neighbor just got his in the post today. He lent it to me to test. I compared it with a 60-year-old original Goodwin Barlow, an early Parks Barlow and a Unitron Achromatic Amplifier. I compared a full range of Unitron Orthoscopics, a set of König wide-field eyepieces, and a set of Vernonscope "limited edition" brass Brandons which use special glass that is hand selected. Brandons are the favorite eyepiece among professional astronomers.

The telescope was a 100 mm, f/15 Unitron refractor with an objective lens manufactured by Pentax for Unitron. These Pentax objective lenses are considered to be Unitron's "jewels-in-the-crown" objectives of perfect quality.

What did I conclude? That Celestron's Omni 2x Barlow was spot on, with no aberrations or errors even at the very edge of the field. What aberrations did become apparent were with high power eyepieces that shouldn't be attached to a Barlow. EVER! For the most part, it was the quality of the eyepieces that was being tested more so than the Omni Barlow. The eyepieces in question being pushed beyond their operational limits.

The Celestron 2x Omni Barlow is a beautifully crafted Barlow, especially for the price. So if you have problems with this Barlow, it ain't the Barlow's fault.
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on April 5, 2010
I am new to astronomy so I went out on a limb and purchased this Barlow lens for my Celestron 80mm EQ Refractor. It works well. Keep in mind the lens seems to let in less light but I could see Mars, Saturn, the Orion Nebula and several star clusters with good clarity. I only have 10mm and 25mm eyepieces and this doubles my set. I live in an area with terrible conditions for backyard astronomy but this piece has brought out a few more objects. Next I'll try some Celstron Omni eyepieces.
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on March 9, 2014
Very nice 2x Barlow, very sharp and a definite improvement over the cheaper 3x Barlow that comes with the Celestron 127 EQ and 114 EQ telescopes. No noticeable chromatic aberration compared with the cheaper Barlows. On the Celestron Powerseeker 114EQ (no. 21045, fantastic optics btw, for the price) I use it combined with a Celestron 9mm Omni eyepice to give me a sharp 4.5mm equivalent magnification. With the $33 Celestron single axis RA motor drive installed and humming along I can see the two main bands on Jupiter very clearly, and two additional fainter bands. Five stars for the quality of the optics. Very much worth the $42 (on Amazon) investment.

Edit: To see how well it works, see the pictures I posted below (taken with a modified logitech c310 usb webcam) ...
review image review image review image
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on September 29, 2010
I picked up a Celestron 21024 3" tabletop reflector, hoping to get my feet wet in backyard astronomy. The scope actually turned out quite nice, but with its short focal length, the effective magnifications even with a 4mm eyepiece were pretty low. I tried some other barlow eyepieces, none of them would even focus.
The Celestron Omni barlow worked great on that telescope, and I was actually able to make out the bands on jupiter using the barlow, a 12.5mm plossl, and the celestron 21024. I was pretty surprised. If you have the celestron 21024, you'll want this barlow.
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on July 13, 2010
I just purchased an Orion 8 inch telescope--without the barlow Saturn's rings are nearly invisable when I use just the eyepiece that came with the scope. When the barlow is attached Saturn becomes amazing! I love this product and am considering purchasing a 4x to see what the difference is--I recommend this lens highly. If you are into astonomy-this is a must buy![[ASIN:B00008Y0TM Celestron Omni 2X Barlow Lens.
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on October 4, 2011
I've been an amateur astronomer for over 25 years. This is a great barlow and the first time I've used one. My wife and I used this in our 6" f5 Celestron Reflector (f/l 750mm). It provided great views with a 26mm lens inserted into the barrel of the Ring Nebula (M57), Andromeda Galaxy (M31), and several other deep sky objects. Even the moon looked great! With the 5mm lens, which was probably overkill, made us feel as if we were right on the moon itself. Of course, when jacking up the magnification this high the image quality isn't as great or as sharp (this is normal when using higher power). For the price, this is an awesome item! Can't wait to get the 3x version.
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on June 7, 2015
This Celestron Omni 2X Barlow Lens is amazing for the money! Crystal clear optics and instantly doubles the power of any telescope eyepiece.
20mm eyepiece becomes a 10mm eyepiece (i.e. if using a 1000mm aperture telescope, the 20mm eyepiece gives 50X power. Use the Celestron Omni 2X Barlow Lens, and it translates your eyepiece to a 10mm and also 100X power!).

The "hidden bonus" that I mentioned in the title? Look closely at the image of the Celestron Omni... See the bottom of it? That's where the main Barlow Lens is. You can unscrew it, remove it, and screw it into the bottom of ANY 1.25" telescope eyepiece! So, not only do you have a main 2X Barlow Lens, but you get the additional " hidden bonus" of a 1.5X booster lens as well!

Plain: 20mm eyepiece w/ 1000mm aperture scope: 50X power.
2X Barlow: 20mm (now 10mm) w/ 1000mm aperture scope: 100X power.
1.5X lens from Barlow: 20mm (now 13.3mm) w/ 1000mm aperture scope: 75.18X power.
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on March 23, 2013
Bought this because the 3x barlow that came with my powerseeker 70 was a piece of crap. This is a lot better quality and much more useable than the 3x was.
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on April 6, 2014
If you are the type to spend hundreds on your eyepieces, you may or may not like this Barlow, but for my beer budget use on a Celestron 90mm refractor, it makes a nice addition to my current 25mm and 10mm Celestron eyepieces. I really like the view through the Barlow and 25mm, but it is still quite usable even with the 10mm for 180x magnification of the 900mm focal length. I don't think more magnification would be useful with my current scope and eyepieces.

This obviously a fairly non-professional review, but casual stargazers are unlikely to be disappointed.
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on February 28, 2014
Bought this lens as an amplifier for my ETX-90 Meade telescope. It has worked well and i would recommend. Can't wait for the summer to get out and continue using it during my observations of the stellar sky!
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