I have an old Heinz Kilfitt mounted on my Nikon D300. It's a great lens as long as I stop it down, but it seems that I can't focus to infinity. When I took the photo below, I had the lens focus mark on infinity. The "High Voltage" sign is in focus (~100m away) while the bus stop / kids are out of focus (~200m away). Is there anything wrong with my lens or am I doing something wrong? I don't use manual focus very often.