> >First, a great many M lenses were identical optically to either the
> >preceding K lens, or to the following A lens, so I don't think that in
> >those (many) cases anybody can credibly claim that the Ks or As were better.
They CAN'T be identically optically to the K lenses in most cases because they are enough smaller that you cannot fit the same elements in the smaller container and have them work right.
....
Note also that two lenses with the same specs (elements, groups, minimum focus distance) may in fact be different optical designs.
I don't have any first hand info on the lens design, but I took a look at the charts on Bojidar Dimitrov's K mount site:
http://www.bdimitrov.de/kmp/
If you click on the lens there is the optical formula there, which is typically x elements in y groups. Click on that you get a chart showing the actual layout of the elements. I looked at which ones had the identical chart, not just elements / groups specs. For example, if you look at the detail regarding the M 28 f2.8 versions 1 and 2, you'll see that while they share the same specs (7 elements in 7 groups), the charts that details the optical construction are different.
> I agree. If you look at the optical formulae on Boz's site, it's apparent
> that the majority of M lenses have the same optics as either the preceeding
> K lenses or the succeeding A lenses.
> After you factor out the lenses that
> were truly unique - like the 40 f2.8 and 150 f2.8
Huh? That would be unique.
Sorry, mistyped - that should of been 150 f4.
But my essential point remains. Specifically, once you factor out the M lenses that are totally different than preceding and succeeding lenses (and there cannot reasonably be compared to them) and factor out lenses that are optically identical to the comparable K and A lenses, you wind up with a relatively small number of M lenses with distinct designs.
I have looked only at the primes - the M zooms may be more unique.
> - there are only a > handful of M lenses that have distinct optical designs and that can be > compared to the K's or A's,
There is very little overlap between the K line and the M line lens designs as far as I can tell, and this is the bone of contention. A lot of K lenses were replaced with new M designs that seem to be held to be not quite as good.
There is less overlap between the K and M lines than the M and A lines. But I was responding to the comments that the M line was a low point in Pentax lens engineering. If your argument is that K lenses were generally superior and things have gone downhill since then, that argument is probably more sustainable on its face.
A lot of M lenses do appear to have been continued in the A line unchanged optically and basically unchanged physically except for cosmetics. Where M lenses are identical optically to the A lenses I have seen a lot of comments suggesting that the A version is better. This could be from factors of manufacturing (glass, coating, grinding technique, precision of manufacturing, quality control) or some other way that "experience" has improved the lens without changing the optical formulation.
Some folks have noted that SMC coating improved over time and A's are better than M's in regards to that. That's a believable argument, and just looking at M and A lenses you can see differences in the color tint of the coatings that suggest they are different.
Personally, I see a lot of variability in lens evaluations among lenses that are optically identical - like the F 50's (1.7 and 1.4) seem to rated higher than the A and FA counterparts. Similarly, the 100 f2.8 macro seems to be consistently regarded as slightly better than the FA 100 f2.8 in tests, though these lenses should be identical in all ways except internal electronics and cosmetics. I have no idea what could account for the differences, though the factors you mention may play a roll.
- MCC
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Mark Cassino Photography
Kalamazoo, MI
http://www.markcassino.com
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