SMC Pentax K 85mm f/1.8

SMC Pentax K 85mm f/1.8

A compact telephoto with a large aperture is an extremely useful lens when combined with a nice compact body like the Pentax K-5, K-7, or even the old MX. How does the K 85mm f/1.8 work with a modern DSLR body?

Pentax has had 3 series of manual focus primes with a K mount. These are the K, M, and A series lenses. The K are lenses not otherwise marked M or A. The M series was the replacement to the K series, mainly making them smaller and cheaper to construct, and the A series added electrical contacts for the program cameras.

The SMC Pentax 85/1.8 is a very solidly constructed lens. It is compact for the aperture, and even at close focus remains fairly small The front element extends when you focus, but doesn’t rotate so filters maintain their orientation.

The lens is 6 groups with 6 elements. There is an 8 straight bladed diaphragm, and minimum focus is a very reasonable 0.85 m (2.75 ft) which is typical of lenses in this class. It has 52mm filter threads, and is fairly light at 331g given.

So how does this 85mm f/1.8 perform given that it is about 35 years old?

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  1. Zhou Yu says:

    Great work!

    The result is consistent with my experience with both lenses. The Samyang certainly provides higher resolution at the maximum aperture even though the largest aperture of the Samyang is at f1.4. However, I enjoy the K85 for portrait which gives soft glows at f1.8. Perhaps K85 is more sensitive to light source. Certainly, K85 is better built in almost all regards.

  2. martyn says:

    Good job,

    Very useful review although bit incosistent with my own experience. I used to own 2 copies of
    FA 77/1.8 Limited, DA 70/2.4 Limited and K85/1.8. Recently I tested all lenses on K-5 and to my surprise K85/1.8 managed to resolve slightly more details than FA77 and DA70 in the centre and also in the corners. I should add that all lenses were used with the sun hoods, so that may impact their performance. There’s another field where K85/1.8 has advantage over FA77/1.8. K85 controls chromatic aberations better and doesn’t show any purple fringing at all.