The eyecup on my Canon T90 decided to jump off the camera and run away while I was out shooting, and I have the impression that I cannot now see the screen quite as clearly as I'd like to. The T90 manual says the camera has built-in -1 diopter, implying that there's a diopter glass built into the rubber eyecup. As I've lost mine, I can't verify that, so I'd appreciate it if some kind soul having a T90 would have a look and let us all know the answer -- is there a glass element in the eyecup.
If the original T90 eyecup is just an eyecup without a diopter lens built-in, I've read that a Canon EF eyecup fits well and may actually stay on the camera better, and it's actually available on the market. But if the T90 eyecup has a diopter lens, my life just got a bit more difficult -- I'll have to post a WTB add here on APUG to see if anyone has a spare one they'd like to sell.
Thanks for taking a look at your T90 and posting back re: the diopter issue.