This is something that cropped up before over a year ago and I am not sure we ever got to the bottom of the question. I have a Televue 41mm and that has a 68 degree FOV, now TV being who they are have always pushed the limit of the envelope. Myself I find it hard to accept that a company albeit a very good one can out Tele-vue Tele-vue, with 1 more millimeter and 4 more degrees, without vignette issues. The 41mm in fact show a mild vignette when used in my LX 12 inch scope with a diagonal, the one it was bought for. The limit of what can be seen as you probably know is governed by the size of the field stop of the eyepiece, this must be within a very tiny amount identical on both eyepieces in order to fit the telescopes. If the Vixen is 72 degrees and 42mm I struggle to understand how they do it. I am not saying this is not the case but personally I do not believe it. I have even considered buying one to see for myself. If there are like eyepieces (65) from your supplier and you ordered 72 degrees based on a picture then I for one would not be happy with what you have received, my advice is send it back and make sure they pay for the postage, it's their mistake. Alan