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RE: As beautiful to look at as through.
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.