Originally posted by jpzk Sounds right to me: I am still always struggling to focus this lens at f1.4.
Part of the reason could be that DSLRs have a relatively small viewfinder, because it is expected that AF will be used and viewfinder is only for general composition. Secondly, the DSLRs have a focusing screen made mostly for zoom lenses. Often these screens are not accurate for lenses faster than f2.8. A lot of Pentaxians replace the stock screen with KatzEye, Focusing screens com or JinFinance focusing screen if they are planning on using fast manual lenses. While these screens might not be perfect for slow lenses, they are better for fast lenses.