The SMC Pentax [K] 1:1.8/55 (1975) lens has its roots in the Takumar lenses.
(K 55/1.8 optical design: 6 elements in 5 groups)
It's gone in the M and A series, replaced by the SMC Pentax-M (1977) and Pentax-A (1984) 1:1.7 50 lenses.
(M/A 50/1.7 optical design : 6 elements in 5 groups)
The Pentax K 55/1.8 is sometimes considered to have a more interesting character than the Pentax M/A 50/1.7.
I have both (K 55/1.8 and A 50/1.7) lenses:
And I did some comparisons at f/1.8-f/1.7. The paired shots were taken with the Sony a7c (FF, 24MP) from the same point, but the scenes may differ slightly due to the wind.
1.
(K 55/1.8)
(A 50/1.7)
2.
(K 55/1.8)
(A 50/1.7)
3.
(K 55/1.8)
(A 50/1.7)
4.
(K 55/1.8)
(A 50/1.7)
5.
(K 55/1.8)
(A 50/1.7)
The Pentax A 50/1.7 obviously gives a wider angle of view. The Pentax K 55/1.8 gives a more contrasty image (I think it's the effect of this concrete copy of the Pentax A 50/1.7). The circles of confusion are larger with the K 55/1.8, which is to be expected due to the longer focal length. But I do not see a big difference in the character of the images.
Since I shoot with an adapter, I chose the K 55/1.8 because I like the K-series itself better than the A-series. But when shooting with a Pentax digital camera, the A-series is much more convenient, I would prefer the A 50/1.7 (that I used to shoot with Pentax DSLRs).
See also related notes:
- Pentax K 55/1.8: Samples [2] - FF - f/1.8 (2024-12-10)
- Pentax K 55/1.8: Samples [1] - FF (2024-03-18)
- Pentax K-m vs Sony a7c: Size comparison (2024-03-04)
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