Originally posted by Conqueror
I've got the 16mm Samyang f2... but desperately need to get round to calibrating the infinity
Make sure that lens doesn't have any focus shift toward greater distances as you stop down. For instance, on the 8mm lens infinity comes at 2 meters when the lens is at f/3.5, but at f/16 infinity is at infinity. No one would want to use that lens at f/3.5, and the ideal sharpness is reached at around f/8 where infinity is around 3-4 meters. A lot of folks who have recalibrated mistakenly at wide open end up complaining that the lens has lost some sharpness(!).
The 14mm is off a bit too, but I don't see any focus shift in that lens. No idea about the 16mm... all you really lose is a bit of close focus real estate if you don't re-calibrate. If you don't, just make a mental note of where infinity mark should be when focusing by judging distance. If you do choose to re-calibrate an UWA lens, you'll be most accurate by taking an intermediate distance such 2 meters, measure from the object to the focal plane mark at the back of the camera (not the lens mount and not the front of the lens), use LV magnified and focus peaking to nail focus, and make sure you don't see any shift upon stopping down. I'd still allow for just a little play beyond the infinity mark. Lenses are generally calibrated to focus just beyond infinity, allowing for filters and various environmental variables (or just plain slop).