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Model: WOswan-1Part Number: E-SWA09
William Optics Swan eyepieces are super-wide-angle designs with 72° apparent field of view. They use simple but sophisticated five-lens optical systems for generally higher contrast than the more complicated optical designs used in some other SWA eyepieces that use up to eight lenses.
All lenses are fully multicoated for high light transmission. Lens edges and internal field stops are blackened to reduce internal reflections and improve contrast. The rubber grip ring is useful for safer handling of the heavier 2” eyepieces in cold weather when wearing gloves. The eyepieces have soft roll down rubber eyecups for eyeglass use.They are remarkably good all-round eyepieces when used with telescopes with focal ratios up to f/6 and above.Technical specs:9mm Swan, 1.25" barrel5/4 lenses/groups72 degree FOV12mm eye reliefWeight - 70g15mm Swan, 1.25" barrel5/4 lenses/groups72 degree FOV14mm eye reliefWeight - 90g20mm Swan, 1.25" barrel5/4 lenses/groups72 degree FOV17mm eye reliefWeight - 100g25mm Swan, 2" barrel5/3 lenses/groups72 degree FOVEye relief 21mmWeight - 330g33mm Swan, 2" barrel5/4 lenses/groups72 degree FOV25mm eye reliefWeight - 410g40mm Swan, 2" barrel5/3 lenses/groups70 degree FOV28mm eye reliefWeight - 570g
Absolutely wonderful, like looking at a picture window of space! Beautifully made and finished item and a real joy to use giving such a large panoramic and clear view. I am not experienced enough to make. a judgement on optical quality but it seems superb to me.
I got the 15mm version to use with my Celestron C90 Maksutov, it gives 83x. Image quality is very good and distortion free (no barrel or pincushion that I notice). No chromatic aberration/astigmatism either, stars are sharp to the edge. The only complaint is that I don't believe the advertised 14mm eye relief; it's more like 10mm.I've no idea how it would perform in a faster scope.
I use these eyepieces with my mack 180 pro 9 and15 are very good moon and planets people say that skywatcher mac carnt do deep sky using 25 to 40mm eyepieces it can