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Message: <blockquote data-quote="Nixterdemus" data-source="post: 3615607" data-attributes="member: 96265">The Pentax 20mm SMC XW FS-24mm tfov-2.546* arrived yesterday. As other eyepieces this fit is taut somewhat tapered. If you push it all the way down then release, w/o tightening, it moves up a bit. It has to be all the way down to focus at infinity.I read where another gent w/M2 100 had problem w/20mm ES 68* in that the view at the bottom of eyepiece was clipped a bit. Conventional wisdom says the prisms in TS & M2 65/80/100 would be the same size. Maybe more of potluck.No vignetting whatsoevah in mine. Thanks to the M2 design I see some field curvature. I looked at a birdfeeder 25-30' away noting a copper emblem would become a mite soft at the edges. Cloudy today, but when clear I'll aim at a star. I read where 27-27.5MM is the maximum field stop for 1.25 eyepiece. As previously mentioned at 6.7 oz is the 6 element X-Cel LX 25mm 60* 21.7X 2.779*. Though one FS was measured by a gent at only 25mm for a tfov 2.652*. Still, this economical offering by Celestron would be me pick to check out the integrity of the prism. Even at a measured 25mm it's still a slightly greater tfov of the Pentax.Wider eyepieces in this range are few & far between. Here's a calculator that'll give you a close tfov of various eyepieces. I load the moon image and save the wider eyepieces starting w/Celestron 15mm 82* that has been pointed out to be somewhere around the mid 70*. Looks las a bullseye and the differing eyepiece rings are their own colour depending on order of saving I suppose.<a href="https://astronomy.tools/calculators/field_of_view/" target="_blank">https://astronomy.tools/calculators/field_of_view/</a>For more accurate calculations stick w/ tfov[FS/FL(of scope)X57.286] Pentax 20mm SMC XW-----24/540X57.296=2.546*</blockquote>

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