Very often I hear Pentaxers comparing the FA 77/1.8 Limited to the FA* 85/1.4. In some ways, the comparison is valid - they're Pentax's two autofocus portrait lenses, but many of the comparisons do point out the many differences between the two lenses, too - they're really very different lenses by design.
I think that the comparison that should be made is of the 77/1.8 to the A* 85/1.4. Forget for a moment that the 77/1.8 is an autofocus lens, and, instead, think of it as the A* 85/1.4's baby brother - i.e., think of the A* 85/1.4 and the FA 77/1.8 Limited as being optical siblings: Both the A* 85/1.4 and the 77/1.8 share the same basic optical "ingredients" - 7 elements in 6 groups. (In contrast, the FA* 85/1.4 uses 8 elements in 7 groups.) In addition, the 7 elements in 6 groups are arranged in virtually the same way in the two optical siblings: Here's the optical diagram for the A* 85/1.4 - http://www.cetussoft.com/pentax/lensdiags/PentaxA^85f14Diagram.jpg And here's the optical diagram for the FA 77/1.8 - http://www.cetussoft.com/pentax/lensdiags/PentaxFA77f18Diagram.jpg Note the similarity between the arrangement of the "ingredients" - the two lenses do not have their 7 elements in 6 groups arranged in any ol' way, but in exactly the same way (which the two lenses happen to share with just the "fast 50's", i.e., the 50/1.2 and 50/1.4 lenses, but not with the other, slower 50mm or 55mm lenses). [Note that the same basic "ingredients" can be arranged in other ways, of course, too - the FA 43/1.9 Limited also happens to have 7 elements in 6 groups, too but they are arranged totally differently.] In contrast, here's the optical diagram for the FA* 85/1.4 - http://www.cetussoft.com/pentax/lensdiags/PentaxFA^85f14Diagram.jpg Note that the newer, autofocus 85/1.4 is quite different, both in its "ingredients" and in how they are arranged, as compared to the older, manual focus 85/1.4, and its baby brother, the 77/1.8. Furthermore, the FA* 85/1.4 focuses entirely differently, too. It's an autofocus lens, of course, but so isn't the 77/1.8, yet the 77/1.8 focuses exactly as does the A* 85/1.4. The FA* lens is an internal focusing lens, and the length of the lens does not change as the lens is focused. In contrast, both the A* lens and the 77/1.8 become longer as they are focused to closer distances (and without the objective end of the lens rotating, too.) In addition, for focusing, both the A* 85/1.4 and the 77/1.8 happen to be FREE focusing lenses (FREE is Pentax-ese for the "Fixed Rear Element Extension" focusing system). Not counting several macro lenses, the only Pentax FREE lenses that I am aware of are the FA 77/1.8, the A* 85/1.4, the A* 135/1.8, and the A 400/5.6. [Boz's K-mount site does not mention the 77/1.8 as being a FREE lens, but the Pentax USA site does state that the 77 Limited "features PENTAX's exclusive FREE (Fixed Rear Element Extension) focusing system to ensure sharp, crisp image reproduction over the entire focusing range".] Finally, it is generally (although not universally) agreed to by users that the FA* 85/1.4 appears to have been specially designed with portrait use for its main target (being a bit soft wide open, with better imaging at closer focusing distances, perhaps exhibiting a bit of back focus, and with excellent bokeh), while the 77/1.8 and the A* 85/1.4 are more "all around" lenses, focusing "right on", and being sharp at all apertures and at all focusing distances (but still having excellent bokeh). So, I prefer to think of the A* 85/1.4 and the FA 77/1.8 Limited as being sibling lenses, two peas out of the same pod, just one of which (the baby brother) happens to also have autofocus capability. That is to say that the 77/1.8 is not the replacement for the FA* 85/1.4, but was likely designed to be the replacement for the A* 85/1.4. Comments? Fred
