Our highly rated D21 Eyepieces are matched to 1/100th focal length. Typically 21.6mm, they have a 65 degree AFOV, of course are fully multi-coated. Order WITH your Binotron 27 and we build your Bino USING your D21s for a perfectly matched optical system. They exhibit NO pin cushion distortion and produce amazing contrast whether used for nigh-time observations of planets, lunar and deepsky or daytime views in white light and H-a. They are amazing for H-a observations. We and many end users feel that the D21s are UNSURPASSED for contrast and sharpness on Ha!
Photo shows our D21 Eyepieces in a Binotron 27 Super System with Filter Switch (not included with D21 Eyepieces)
 
Specifications:
Available Focal Lengths: 21mm & 14mm
1.25" Eyepiece Barrel format
65 degree AFOV
Fully Multi-Coated on all air to glass optical surfaces for
ultra-high-efficiency transmission
High Index Japanese Glass utilized
20mm Eye-relief
Black anodized aluminum housings and barrels with rubber
knurled grip
Laser engraved logo
Rotating batwing Eye-Guards
Weight: D21s: 8 oz each  D14s: 9 oz each
Full one-year warranty