I used to have a third party MD 135mn f/2.8 lens, sold it since I didn't use it much. But when I did have it, for some reason I could never focus to infinity. Even if the lens said that it was at the infinity mark, it would still look like it was focused close to around 5m. Is that a common occurance with the LT/SB's? I'm looking to purchase something along the lines of a 200mm zoom lens. Anyone who has used the adapter have any problems with the focusing distances?