| Latest Review Posted | SMC Pentax-D FA 645 55mm F2.8 AL [IF] SDM AW
I just carefully examined the optical performance of three copies of the 55 D-FA lens on a 645Z body. By any traditional, fussy standard, all three copies were exceptionally fine lenses, in my tests being essentially perfect from corner to corner from f/5.6 on up.
But my hope for these lenses was to find one which would serve as a fine lens for super low light capture (stars), being actually capable of a strong performance in all four corners wide open at f/2.8. All three of the lenses had at least two sharp corners wide open. Two had, arguably, three sharp corners. All showed a fairly modest loss of contrast wide open, what one might call a smeary effect, but it wouldn’t, I think, prove to be problematic for stars. Dark wires against a blue sky turned blue from sky light spread around, but that effect went away by 5.6 when stopping down.
Wide open, specular highlights in the corners showed obvious coma, changing a small spot into a little triangular spaceship pointing toward the optical axis. With each successive stopping down, that improved, to the point where it was gone at 5.6. It may be the case that only brighter stars would show any coma, as some of the specular reflections showed less of it, but note that my 35A lens shows none of this wide open at f/3.5. My better of two copies of the 35A lens (which is much sharper in four corners on a 645Z than one 35 FA lens I tested recently) is much more smeary in the corners wide open than the 55 D-FA lenses are (... |
