I would humbly suggest that the FA* 250-600/5.6 is or can be of prime sharpness. Of course YMMV with your technique, support setup(s), etc. Having shot with the Sigma 500/4.5 and the FA* 300/2.8, my FA* 250-600/5.6 loses a stop or two of light, but not sharpness.
Some are taken at F5.6 aperture. I tend not to shoot this lens wide open, given the narrow DOF and the subjects being so close.
F5.6:
Link to
EXIF
Camera PENTAX Corporation PENTAX K10D
Exposure Time 0.005s (1/200)
Aperture f/5.6
ISO 320
Focal Length 600mm (900mm in 35mm)
Photo Dimensions 2401 x 1606
F6.3:
Camera PENTAX Corporation PENTAX K10D
Exposure Time 0.002s (1/500)
Aperture f/6.3
ISO 400
Focal Length 600mm (900mm in 35mm)
Photo Dimensions 3113 x 2073
Crop:
F7.1:
Camera PENTAX Corporation PENTAX K10D
Exposure Time - 0.002s (1/500)
Aperture - f/7.1
ISO - 320
Focal Length - 600mm (900mm in 35mm)
Photo Dimensions - 2534 x 1691
Crop:
Last edited by Marc Langille; 09-03-2016 at 03:50 PM.