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BST 1.25" 58-deg UWA Planetary Eyepiece - 20mm

5.0 (1 Reviews) Read Reviews Write Review
Brand BST
Part Number E-BS-UWAP20
Availability available

Product Info

Manufacturer Description

Outstanding Planetary and Lunar Eyepieces

These BST 1.25" fully multicoated (FMC) eyepieces give maximum detail and definition across the entire 58 degree field of view (FOV). A great value, these eyepieces are exceptional at nearly eliminating lateral color aberration and light scatter often associated with more expensive eyepieces that are better suited for deep space objects. Though primarily made for planetary observation, these eyepieces still excel when viewing deep sky objects.

More expensive eyepieces that have similar wide fields of view need many exotic glass elements to achieve that wide view - as many as 9 lenses or more. More lenses mean more cost and more glass, which attenuates the amount of light you see. That also means there are more air-to-glass surfaces that can scatter light - reducing contrast and sometimes causing multiple reflections (ghosting) when viewing very bright objects such as the Moon and planets. Extra lenses can also mean compromises in the overall design that can often lead to other issues.One such issue of all that glass is lateral color aberration that appears as a cloud of false color around bright objects. Another issue is light scatter seen as a distracting halo or glow around bright objects. This can also reduce contrast.

Each BST UWA Planetary eyepiece has 5 lens elements in 3 or 4 groups. These eyepieces provide high contrast, no scattered light, and the highest possible definition.

Comfortable Eye Relief

The eyepiece eye relief averages around 16mm for the entire series. The 25mm eyepiece features 20mm of eye relief. Even the 2.5mm eyepiece has almost 17mm of eye relief! Experienced observers will truly appreciate such generous eye relief at significant magnifications.

Excellent Fit and Finish

These eyepieces are fully internally baffled and all internal spacers have antireflection microbaffles on their edges with flat black anodizing to reduce reflections. Every air to glass surface is broadband multicoated for peak light transmission and outstanding contrast on subtle lunar and planetary detail. The lens edges are blackened to eliminate internal reflections.

Each eyepiece has a flexible rubber fold-down eyeguard. Dust covers are provided for both ends of each eyepiece. A groove is machined into the nose piece barrel to ensure the eyepiece is less likely to fall out of the diagonal or focuser.

Please Note: While these eyepieces look similar to the TMB / TMB II ED eyepieces (and are also sold by some other sellers incorrectly under the TMB label), they are not the same as or copies of the 6-element TMB eyepieces. The factory making these eyepieces just uses the same external housing for the eyepieces.


5.0 (Based on 1 Reviews) 100% of reviewers recommended this product.
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      User Notes:
      Review by Carol
      Dec 26, 2018

      5.0 BST 20mm eyepiece is fantastic!




      I just received the BST 20mm eyepiece from Agena Astro, and the fit and finish on this eyepiece is beautiful. The eyecup rotation is smooth and the view is crisp and clean snaps to focus terrestrially. I was so happy with it, I ordered another focal length to round out my collection of this eyepiece design. I’ll hopefully get to try it astronomically soon. Thanks Agena Astro!

      Bottom Line: Would you recommend this item? Yes
      Was this review helpful? Yes / No

      This review was provided courtesy of AgenaAstro.com

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      Apparent Field of View 58°
      Barrel Size 1.25" (31.7mm)
      Bolt Case Included Yes - Free Agena Eyepiece Container
      Bolt Case Size Agena 52x80mm
      Coatings Fully Multi-Coated
      End Caps 2
      Eye Relief by Design 18mm
      Filter Threads Standard 1.25" Filter Thread (M28.5 x 0.6)
      Focal Length 20mm
      Lens Elements 5
      Lens Groups 4
      Rubber Eye Guard Yes
      Blackened Lens Edges Yes
      Manufacturer BST
      Eyepiece Focal Length 15.1mm - 20mm
      Eyepiece Field of View 51 - 60 degrees
      Eyepiece Series BST UWA Planetary
      Barrel Type Tapered barrel
      Eyepiece Weight 5oz (141.75g)