GSO 1.25" 5x Apochromatic Barlow Lens # BL501

Our Price: $60.00
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Our Product ID: OBAR-GS-BL501
Manufacturer SKU: BL501
Item Can Ship: Worldwide
GSO 1.25" 5x Apochromatic Barlow Lens # BL501

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Product Details

If you need more power than your eyepieces alone can provide, we offer a new apochromatic 5x Barlow lens from GSO (Guan Sheng Optical) to give a big magnification boost to any 1.25" eyepiece it's used with.

Nothing has been compromised in GSO's latest and finest offering. This Barlow features an air-spaced, three-element, apo design with fully multicoated optics. The housing is precision machined from aluminum stock and black anodized to a hard finish. The lens edges and inner barrel are blackened to provide maximum contrast. The Barlow body includes a safety undercut on the lower barrel and a brass compression ring so that your eyepiece barrels are not marred by the captive set screw. The 5x model has a clear aperture of 13mm, but it is not threaded to accept 1.25" filters.

For those blessed with great optics and dark skies, the 5x could be an exciting new addition to your arsenal for visual and photographic use. If you've never used such a powerful barlow before, please be aware that to get the best out of this barlow, you need to use it with a good telescope, a good eyepiece and under good seeing conditions. See more on this topic below.


  • Barrel size = 1.25" (31.7mm)
  • Magnification factor = 5x
  • Weight = 3.8oz (108gm)
  • Total height = 3.46" (88mm)
  • End caps = 2
  • 1.25" filter threads on bottom of barlow: No
  • Made in Taiwan

Please note: This is a very high magnification barlow. It is not for everyone or for common viewing conditions. Before buying, please make sure that you are using realistic magnifications with your telescope. A good rule of thumb is that under very good conditions and with a very good telescope, the maximum power you will be able to use is about 50x of magnification per inch of telescope aperture. With average telescopes and/or average conditions, you should be able to use 30x of magnification per inch of telescope aperture. So for example, if you have a 6" telescope, under typical conditions you will be limited to 6x30 = 180x of magnification, and 6x50 = 300x of magnification at best.

Boosting the magnification beyond this recommended maximum for your telescope aperture is not realistic. This is bound to result in image break-down, causing fuzzy images, focusing difficulties, increased color around objects (caused by other optical elements in the telescope which are magnified by the barlow) and general disappointment, but this is not a fault of the barlow.

Manufacturer GSO
Size Format 1.25 inch
Magnification Factor 5x
Number of Lens Elements
Lens Coatings Fully multicoated
Total Length 3.46 inches / 88 mm
Length of Nosepiece 1.22 inches / 31 mm
Outside Length of Upper Body 2.31 inches / 58.7 mm
Insertion Depth 2.13 inches / 54 mm
Max Diameter Excluding Thumbscrew 1.92 inches / 48.7 mm
Clear Aperture 0.39 inches / 10 mm
Weight 3.8 oz / 108 g
Barlow Lens Cell Removable No
Filter Threads at Bottom of Barlow Cell No
Filter Threads Between Barlow Cell and Tube N/A
Barrel Type With safety undercut
Compatible Agena Bolt Case (with Screw Removed) 42x80
Compatible Bolt Case (with Screw Attached) 52x80
Number of Thumbscews 1
Thumbscrew Thread Specification M4x0.7
End Caps (Subject to change without notice) 2
Compression Band/Ring in Eyepiece Holder Yes
Country of Manufacture Taiwan