Phil if you check out on of strikers old eyepiece postings there is a link that lets you work out the amount of vignetting from different 2" eyepieces. From memory up to 35 or 36 mm there should be no problem but more than that then vignetting starts to affect FOv. That's with all of the meade SCT OTA's (LX models) You can get around it by changing the visual backing to one with a larger opening. I'll have a dig around and see if I can find the link
Here it is. The crossed out eyepieces are the ones that are most affected by vignetting.
http://www.petersonengineering.com/s...8_inch_SCT.htm
Check out the "Eyeopener" page for more info
http://www.petersonengineering.com/SkyDiv/EO.htm