The RF Rokkor 250 mm f/5.6 is one of the most sought after lenses in the Minolta SR system. Though it was produced in not-so-small quantities, used prices for this lens today are through the roof. This is often attributed to it’s astonishing compactness, which renders it the “perfect compact tele on a NEX”. But this aspect does not seem sufficient to single-handedly explain the hype.
Handling on a NEX-5T is a pleasure, with the only notable insight being that the lens is very light. Focusing presents a challenge with the RF, as the depth of field is extremely shallow and the 9.6x focus magnification on the NEX shakes wildly when used without a tripod.
For the RF Rokkor 250 mm f/5.6 I’ve created lens correction profiles, which are available for download. For further details on the lens like weight and dimensions, have a look at its entry in the Minolta SR mount lens database.
Condition of my copy
Optics: Very good. No visible scratches whatsoever. A handful of lonely dust particles and a slight shimmer on the inside of the front glass, probably from condensation.
Mechanics: Excellent. Smooth focus, filters (Skylight & ND 4x) in perfect condition.
Exterior: Excellent. Looks like new, except for minimal scratches on the mount.
Optical performance on NEX-5N / 5T
Since the RF Rokkor is a mirror lens, there is only one aperture of f/5.6 which is given by the front opening. Sharpness is not impressive, but good for a medium tele and very consistent across the frame. Contrast is equally good and chromatic aberrations are non-existent – even at 200% magnification. This is attributable to the fact that mirrors do not have a wavelength dependent refraction index and therefore do not produce CAs.
Vignetting is about 2/3 of a stop, distortion is low with 0.5% pincushion. The effective T-stop of the RF Rokkor is approximately T7.2 (-0.7 EV), which is not bad, considering that the center of the entrance pupil is obstucted by the secondary mirror.
Compared to the often praised MD Tele Rokkor 200 mm f/4 @ f/5.6, the RF Rokkor performs respectably. The RF looses by a notch in terms of contrast and sharpness, while it clearly outperforms the 200 mm in terms of CA.
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