Before anyone takes this too seriously (especially Norm or Ken, who as far as I know had nothing to do with coming up with the terminology...so apologies to them in advance), I started thinking about this after reading a bit in this thread...
Is there a high quality compact prime around 17-18mm for K1? - PentaxForums.com
I like to think most of us here generally wish success on our chosen favorite camera company, and there are threads about how to best have that happen. This is one of those... And like most, it's being started with no special insight or knowledge...
One of the points in the thread linked above is that there seems to be a divergence in the Pentax K-mount lens lineup between large, highly-corrected, fast, expensive lenses (Kenspo lenses, as exemplified by the recent 15-30 f2.8) and Pentax's former expertise in compact, slower lenses (Normhead lenses, as exemplified by the SMC-M 20mm f4.0, let's say).
The conundrum, as I see it, is that the market is in such a strange state right now, Ricoh is in a place where they really need to do both, but in a way that keeps them unique in the marketplace without bankrupting them. I think the way to do that is with four basic classes of lenses:
The Kenspo lenses... DFA*/DA*
Pentax needs these to be considered viable as a 'real' camera company. These are what I like to think of as industrial output lenses. Designed for production and high output, working pros. Highly corrected, rugged, and suited to high-volume workflows. The lenses need to be competitive with Pro offerings from Canikon, certainly, but also to alternatives like Fuji and micro 4/3. But Pentax can't keep up with the Canikon lineups in breadth, so I think they're following the right path here for their lineup, even if I never end up buying their new 50mm, for example. And it will say a lot about them if they keep a strong lineup in both K-mount formats.
The Limiteds (DFA and DA)
Part of what makes Pentax different from Canikon, and I think essential. Lenses with character, but optically excellent and fully compatible with all of the latest gear. The priority here is creativity, with a bias toward smaller size, perhaps at the expense of workflow. As an aside, I'd like to see aperture rings on future DFA limiteds, but I have a bias... and a K1000...
The 'Regular Lenses'
This includes the consumer zooms as well as the non-limited primes. The other classes of lenses will sell the brand, but this is where the money will be made. Parts of this lineup are pretty well represented (35-55mm, for example, and 18-85mm on APS...), others, not so much... FA wide prime anyone? Fixing this is its own thread or two already, I think...
The Normhead lenses... HD Takumar?
This is where I wandered off a bit, so apologies to Norm if I got him completely wrong.
The 20mm f4 is what got me started here. That's not really a lens that fits into any of the existing categories. It's slow, manual focus, and old.
The only things I've seen like that lately are the absurdly overpriced Kickstarters from companies that share names with folks who made lenses 50+ years ago.
But I'd buy one in a hot second if it were reasonably priced, especially if it talked to my camera.
And that's where the speculation comes in...
Pentax has an interesting back catalogue of lenses with some fantastic characteristics that I think are ripe for a revisit. Maybe things like...
18mm f11 pancake
20mm f4
24mm f3.5
28mm f3.5 (or heck, the Ricoh 28mm f3.5 pancake)
55mm f1.8 (or 2.2...)
120mm f2.8
The idea would be that each lens would be manual focus, with the mechanically-excellent feel of the original Takumars and robust construction to make them, if not completely WR, at least pretty tough. They wouldn't have to be all-metal, but they should feel substantial and solid (though I would prefer all metal...). They should also be relatively compact and less expensive than, say, a $1200 retro imitation Zeiss (that's not distortion, it's character!). And all the ones I listed are really small compared to most new lenses.
Optically, the lenses are relatively simple, though a few tweaks and some modern coatings should be able to tame the CA of the older lenses while maintaining the personality. But these would not need to be packed with the same level of Pixie Dust as the Limiteds...
They would come in what I'll call the Ka+ mount, which is basically FA without the autofocus. This would include a working aperture ring as well as the digital pin to send focus distance and lens correction data. I'm guessing that implies a mechanical aperture (see below). Some of these lenses are also probably pretty easily adapted to short-register mounts if Ricoh ever decides to do a mirrorless...
Crucially, the lenses should also be available in M42, not so much for use on Spotmatics, though that would be fun, but for users of other digital brands who would be allowed a sneak-peak into the Pentax ecosystem, though they would miss out on the extras, which provides a path to switch to Pentax...
Heck, if it made sense from a marketing perspective, Pentax could even float these things on Kickstarter...
And then who would buy them?
Hopefully, Norm...
A bunch of people across brands who like the look and feel of older equipment but who want modern, 'I bought it new, not at a junk shop' reliability.
Pentaxians who want to stretch a bit outside of what they can get from other brands.
So, if nothing else, I feel better for having written this down
-Eric