Originally posted by derekkite If I remember correctly the design of the DA560 has relatively few elements. Each element reflects or absorbs a bit of light. The coatings and fewer elements would give you a lower Iso in the same conditions.
You're right, I just did not consciously expect such a noticeable difference to the Sigma/ Sigma + 1.4tc combo. I am still amazed at the low iso readings after a shoot, since with t-av mode I only beware not to overexpose, but hardly watch the resulting iso values. The practical benefit has greater value to me than I could suspect when switching from the Sigma to the DA560. I am slowly getting to know the DA560 in a great variety of circumstances, and although I wish it would pair better with the Pentax 1.4 tc (AF suffers in anything but good frontal light), it has some genuine strong points, and also a beautiful clarity and character. It also resolves highly, so with the 24mp K3 and the low iso values, it allows for quite some cropping provided you get the focus right. I don't use the 1.4 tc anymore. The weak point remains AF on small birds in flatter light, and low tolerance on over-exposure (leading to fringing).
Otherwise, this lens is a gem.
The DFA 150-450 most likely will also be a stellar lens in its own right. Pentax actually makes some fine lenses.
The AF motor in the new DFA lenses is new technology. Perhaps some day a 500mm/f4 prime with this new lens motor will come, now that the FF is coming and the zoom is here.
Chris