Welcome Manny
Those "radioactive lenses" don't pose the hazard some assign to them. Most all the radiation is stopped by common materials including the lens casing itself, and any distance between you and the lens does the rest. I wouldn't sleep on a pillow of them, but otherwise wouldn't give it much thought. Besides, after you get a collection of them, you'll be spending more for lead lined cases than for the lenses, not to mention all that extra weight you'd have to lug around.
DSLR viewfinders can be out of whack in terms of proper spacing of the focus screen from the lens mount or a misalignment thereof, and then they don't show the same thing as the sensor sees. If your camera has "liveview" or the like, you can easily check your viewfinder by using a fast lens at maximum aperture and comparing the "liveview" image to what you're seeing through the viewfinder (for a manual critically focused image or test chart). They should match, but in any case, you can trust the "liveview" to be correct since this is what the sensor is actually seeing. If you don't have a "liveview" function, you can do something similar by shooting some shots and manually adjusting the focus until you have a target perfectly focused in the result, and then compare that to what you see through the VF (same shot of course). The latter is more time consuming and tedious but it will let you know if your VF is not performing well.
Anyway, welcome aboard the Pentax forum - many happy returns.