Boris, Pentax has a long history with lenses back into the '50's. Designs have been changed over time, often gradually. Some of the evolution can be seen in the old screwmounts. They had manual diaphrams, cocking diaphrams, semi-auto, and full auto. The underlying optical designs changed as well, often more compact in size.
When Pentax introduced the K-mount bayonette, it had a full line (30+) of SMC Takumar screwmount lenses. They were/are great quality optics, but none fit on the bayonette... So they took many of the lenses and just put a bayonette on the same optics. I think the 85mm/1.8 and 135mm/2.5 are two lenses where they did just that. On other lenses in the new K-bayonette, they made minor adjustments, think of them as running changes in a manufacturing process. They didn't try to surpass the optical qualities of the SMC Takumars, they were just matching them in a form factor designed for the new KX, K2, and KM cameras. The breakthru was the ME camera. The ME and MX are 3/4th size compared to the KX, K2, and KM. They needed to be partnered with a smaller set of lenses. The original K designs were/are that much bigger. The ME was an extreemly successful camera. Micro electronics did the same thing for cameras as it did for watches. Now a quality 35mm SLR was available at a much lower price. Pentax sold millions of them and had the marketing savy to sell a whole new line of lenses with them. Because of the size changes, not many of the optics are identical from the first K's to the M's... maybe only the 50mm's. With the A's, the size stayed generally the same as the M's and optics was often identical. The A's also introduced/re-introduced some of the more exotic stuff like the star (*) lenses. The designs in the F and FA lenses also change to make autofocus practical. Looking at it from the other side, I'd speculate that more has changed optically from series to series than has stayed the same. Only the 50mm's seem to retain a direct heritage to the original screwmount Takumars. Regards, Bob S. Boris writes: > On the time line first we M42 lenses, then K lenses, then M lenses, > then A lenses, then F lenses, then FA lenses. So far so good <g>... > > There is something that confuses me. Let us take for example 50/1.7 > lens. As far as I understand the optical formula is precisely the same > through M, A, F, FA range. I am not certain about K, but probably K is > also the same as others. What changed with time was coating and mount > (electronics and such). > > Now, I'd like to know how many of modern Pentax lenses are original! > optical design? It would seem that some lenses are carry over from > previous generations. > > I have another question. One which is related to M vs K discussion and > such. > > Some of the K and some of M lenses were very good optically. I mean in > terms of resolution, MTF charts, whatever spec minded people have in > their mind. > > Why would Pentax then want to produce same lens (I mean focal length > and aperture) with different optical formula? > > Also, I would like to know about computer involvement in > lens design. > When it started? How it changed the world, so to say?
