| The Astro-Tech AT5XB is a very high magnification 5x apochromatic Barlow that will give a big magnification boost to any 1.25" eyepiece it is used with. It turns a 25mm eyepiece into a 5mm; a 20mm eyepiece into a 4mm; a 12mm into a 2.4mm. The Astro-Tech 5x Barlow is excellent for eyeglass wearers, as it will let them achieve high magnifications using low power long focal length/long eye relief eyepieces that are eyeglass friendly.
The Astro-Tech 5x apo Barlow is not for everyone or every telescope and its high power performance may push an eyepiece’s magnification past the usable limits allowed by the evening’s seeing conditions. Please be sure that you understand the limitations of this Barlow before buying. To get the most out of this 5x Barlow, you need to use it with a good telescope, a good eyepiece, and under good or better seeing conditions.
An often-quoted rule of thumb for observing is that the maximum usable magnification with any telescope is about 50x per inch of telescope aperture – under very good seeing conditions and with very good optics. Under average conditions, 30x per inch of telescope aperture is a more reasonable limit, and many seasoned observers routinely view at this magnification even when the seeing is good. Be careful that the 5x Barlow doesn’t push your magnification past these limits or you may find the images to be unsatisfactory, a fault of the seeing conditions and not the Barlow.
The 5x Astro-Tech Barlow uses a three-element air-spaced apo optical system with an ED glass element and fully multicoated optics. The housing is CNC-machined aluminum, hard anodized black for a long life. The lens edges and inner barrel are blackened for high maximum contrast. There is a safety undercut on the barrel and a non-marring brass compression ring to hold your eyepieces firmly in place.
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