I fill the 24mm and 28mm slots with decent Vivitar primes. I don't care that they are manual focus, but I imagine much of the market would. Maybe I should be keeping my eye out for an FA 135/2.8.

Hi John, this is a good discussion to have. Nice to get your potted history of focal lengths! One day I have to get a "swinging sixties" fisheye. Never wanted one before now, but that phrase has done it!

The lenses I suggested are not necessarily because I would want them (though I might) but because they are gaps in the existing line-up. I try not to be too self-centred on matters like this... just enough to be interesting! To that end, here's a list of the prime focal lengths Pentax makes available:

14mm
15mm
21mm
31mm
35mm
35mm macro
40mm
43mm
50mm
50mm macro
55mm
70mm
77mm
100mm macro
200mm
300mm

Where are the gaps? Taking into account that field of view is not linear with focal length, between 21mm and 31mm and between 100mm and 200mm are ill-served. Plus longer focal lengths than 300mm, though Pentax tried offering one of those and no-one wanted it.

Er, actually it does upset quite a few people. But others seem to pay the extortionate price and just get on with taking pictures.

And what was the standard ISO in 1957? 100? 200? 400? I realise that higher ISO and SR are no substitute for thinner DOF, but this isn't exactly a portrait lens we're talking about here. Overall we are much further ahead in terms of what we can do with f/2.4. Not to mention the lenses are better now: sharper, with more micro-contrast, greater resolving power, more flare resistance etc.

The new Leica X1 has a standard lens of f/2.8 and that doesn't seem to upset too many people.

I think you need to re-read the focal lengths you just determined. I think you missed a thing or two.

35mm is the perfect walk-around lens. How many 35mm lenses were there in film days? How about "lots"! As I am sure you are aware, many famous photographers used only this focal length. So, yes, we need 24mm in APS-C.

43mm is the perfect normal lens on full-frame, so we need a fast 28mm on APS-C. How many normal lenses were there in film days? Well, several billion, although only Pentax got the focal length right. The rest just copied an arbitrary focal length from cinema work that was only more-or-less correct.

200mm equivalent field of view in a fast lens would be perfect for stage work, theatre, runway and just about any time you want a flattering portrait but cannot get close enough for 115mm field of view (which is what the FA77 gives you). How many 200mm lenses were there in film days? I'd say it was not exactly unorthodox.

Without unreasonable expectations of speed where Pentax shows no sign of delivering, the obvious holes are:

DA 24mm f/2 Limited
DA 28mm f/2 Limited
DA 135mm f/1.4 Limited

Plus a tilt/shift adapter that permits use of Pentax 645 lenses on KA mount.

If the DA L 35/2.4 comes bundled with the K-r as a kit in the UK (as it does in Japan) then no doubt it will work out cheaper than list price, especially as prices become more competitive some months down the line. In that eventuality, this will be the cheapest Pentax prime ever.

The new 35mm comes as kit lens in Japan. How it will be done elsewhere is still guesswork, but as this is the coolest aspect of the lens release I do hope it is also the case in other markets.

Short version: it's cheaper, lighter, smaller, comes in multiple colours and is optimised for digital rendering (coatings etc.). It may very well turn out to have better IQ than its predecessor.

Longer version: this blog article.

Small changes to the glass formulas and coatings could have resulted in a small light loss. Pentax tends to be very honest in reporting their apertures, so rather than fudge it as an f/2 they have called it f/2.4.

I anticipate the first tests, since it is the IQ that matters more than half a stop of light.