I currently have, in full-frame, the span from 19mm to 210mm covered as follows...
From 19mm to 35mm, the Vivitar f/3.5 Series 1, which I believe is constant 3.5.
From 28mm to 90mm, the Pentax FA 28-90mm f3.5-5.6
At the tele end, I have managed to grossly overpopulate the 70/80-200/210mm bracket, but the important one here is a Sigma 70-210mm f/3.5-5.6, because of all of them it is the lightest, most compact, and (like its shorter focal length brethren) has A contacts.
Thus I have what amounts to full functionality all the way from 19mm to 210mm with three lenses with ALL my K-mount film bodies (all of which are manual focus). HOWEVER, the one glaring problem here is the dismal manual focus of the FA28-90, a thing which AFAIK is a feature of the lens rather than a bug of my copy. There is almost literally no damping at all, and I am seriously considering either swapping this back to the K-5 (on which its performance as a lightweight, outdoor fair-weather lens is more than adequate) or - shock-horror - parting with it. (Can you hear my dismal wailing beginning already?
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SO the gap I would like to fill is the immortal kit lens gap... from 35mm to 70mm, ideally in PK-A, mount or third-party compatible therewith, cheap and cheerful. I can make do without the A contacts if necessary, as the two most likely candidate cameras are the ME and the P30T, but my P3 would occasionally (e.g. flash) benefit from full auto, especially if I end up giving it to one of my kids at some stage.
I know there's some good, some bad and some extremely horrifically ugly K, M and A-era zooms out there in this range, and the lens reviews don't always tell the whole story, nor do they really allow a back-and-forth discussion. At this stage I'm mostly in the gathering-information phase; acquisition would most likely occur on a holiday, when I'm in a big city and can actually handle an example of one or more of the recommended lenses, put it on the K-5 for sample shots, etc, and possibly hand the 28-90 over in some sort of exchange for it (thus I try to mitigate my LBA).
At this stage my standard of focus damping could best be defined as "not worse than the 28mm, 50mm/1.4 or 135mm/2.8 FA primes", all of which are quite acceptable for me when put to that test. Slowing down to f/5.6 at the long end is a price I would be prepared to pay, but something faster (or constant aperture) would be a very definite advantage.
Your thoughts are welcome. For the record, yes, I have seriously considered making the 28-90 on a film camera a "single in" challenge contender to let it justify its presence, but you necessarily wouldn't be seeing the pictures without a significant delay, which seems to miss the whole point of "single in".