Originally posted by joodiespost As I am a noob, I would like to know why the 55mm costs couple hundred more than the 50mm? Is it really the 5mm difference? They both seem to auto focus.
The FA 50mm has been on the market a number of years. The 55mm is relatively new and has a list of new features; SDM AF, it is water resistant, lens and coatings optimized for digital, has Quick-Shift, and a modern chip set that works with the newer bodies to correct CA and distortion in the lens. The DA 55mm also comes with a lens hood.
The DA 55mm is supposed to be better below f2.0 than the FA 50mm f1.4 in edge sharpness and in contrast. Build quality of the lens is also better. Manual focus of the DA 55mm is better both in the mechanics (longer throw for more accuracy) and ergonomics of use with a wide focus ring.
The elevated price of the DA 55mm over the FA 50mm plus the FA 50mm being one of the first lenses that people have bought in the past, have made uptake of the DA 55mm slow. The performance of the FA 50mm at smaller apertures is very close to the performance of the DA 55mm and most people are working with the lenses at the smaller apertures. The DA 55mm f1.4 as a portrait lens also has some stiff competition from the FA 77mm f1.8 to overcome.
All that said, it is good to remember that until the DFA 100mm f2.8 WR macro is released, the DA 55mm f1.4 is the only prime in the Pentax system with weather sealing.
Thank you
Russell