Originally Posted by amateur6 
Thanks again! Apologies, because I've expressed myself poorly in a few spots here...
Yes, point taken and understood. By "engineering" I didn't
necessarily mean "Make it better", I meant "If this is as well as it can be made, only use the good parts". In other words, don't try to say "this goes to 11" when all you've done is change the numbers. Personally, I'd rather have a lens that's really good through all its range, than one that goes oh-so-high and oh-so-low BUT is still only GOOD in the middle, if you see what I mean.
Take the LL example you provided -- as Mr. Reichmann says, f32 and 45 are "unusable" -- so WHY give the lens either aperture? If the diffraction is so great that it overwhelms the DoF gains, there's no point. The
effect may be a fact of life, but the decision to allow the lens to be stopped down that far and sold as "maximum aperture f45" is not.
To be fair, since I'm only working at one distance (also true of the LL examples), it's possible I'm not seeing the whole picture. But to me, it still smacks of mindless marketing-driven specs, which may sell more lenses and cameras to the unwary public BUT does nothing to build the long-term quality and reputation of the brand.
You are being somewhat assumptive about mindless marketing, although perfectly understandable in this age of kidology where marketing people believe that BS always baffles brains, to the extent that many believe that it's the case with everything!
Small apertures are neccessary for large DOF, unless you have a tilt and shift lens, but that brings about another whole bag of worms!
The fact is that a wide DOF is sometimes needed/preferred, rather than absolute sharpness. Not allowing people to have the choice would bring about another hue and cry from users. You just have to understand that if you start to stop down to achieve a greater DOF, then diffraction begins to take effect. YOU make the decision what to use for your particular need, not the manufacturer.
Lenses are designed to perform to different criteria for different purposes, you need to understand which lens suits a particular requirement best, and work within the parameters provided by that lens.
That's why there are zooms, primes, macros, etc., etc., that all exhibit different charictaristics, from very high central sharpness with soft edges, those that are deliberately soft at the wider apertures (for portrait use) and wide range zooms designed for convenience rather than outright optical performance and macro lenses with superb sharpness edge to edge and (hopefully) almost perfect flat field performance (i.e. no field curvature). It's impossible to manufacture a lens for all applications, the laws of physics rules, despite what some may believe!