I am glad people appreciate my contribution, but I would fall short of calling myself an "expert" on such things. For one, there is an absence of hard data on the many variations -- their optical formulas for example. (I did once make contact with a Vivitar engineer but nothing came of it.) Second there are simply too many different variants for me to be cognisant of all the differences. Even though I have six or seven of them, that is nothing compared to the complete list (37 and counting!).
Another issue when looking at a particular sample is that these lenses are old enough for problems like oily blades (as Mike said) to raise their heads. And yes, the only reports I have heard of this happening are from Kiron lenses. Does this mean one should avoid Kiron? No! For one, they tend to have top-notch image quality. For another, there may simply be more reports of Kiron blades getting stuck because people are more aware of Kiron as a manufacturer in the first place. (For example there is a dedicated Kiron
Yahoo group.)
Add to this the issue of sample variation even between lenses made identically and we have a very large morass to wade through. My starting point is always the
Vivitar Bestiary, which at least lets us know which lens we are talking about.
OK, now to your two lenses. The
first, "Vivitar 24MM 1:2.8 MC WIDE ANGLE 52MM" is not a 28mm and in fact does not appear in a similar variant in our chart. Neither do you indicate manufacturer. If the serial starts with "28" it would be made by Komine, and hence might be a wider version of the A04. If it is truly like the picture in the review section -- and has the A setting -- it might well be useful to you, due to its automated use and wider field of view. "MC" is a good sign, though most of these lenses are coated... we simply do not know how well.
The second lens appears to conform to the M14: "Vivitar / WIDE-ANGLE / 28mm 1:2.5 / No. 22xxxxxx / AUTO" [62mm], except that the serial is truncated in the sample shown in the
review. If it is that lens note that it is an M42 mount mount. The reviewers refer to the similar K-mount lens with a 67mm filter ring, but I have documented none with exactly the same markings. perhaps they are referring to the similar K14, which is marked "Vivitar / 28MM 1:2.5 / AUTO WIDE-ANGLE / NO. 22xxxxxx / Ø67MM"?
I would have no way of telling which would be a better lens, but ask yourself if you would prefer 24mm to 28mm. They are different enough, comparable to the difference between 35mm and normal on full-frame.
In terms of IQ, I think people rating these as 8 and 9 are being too generous. Any contemporary Pentax lens is likely to be as good or better, even the zooms. However Pentax does not make a 24mm or 28mm prime, and when they did they were relatively poor (except the FA*24). So if you really prefer a prime (for street shooting say) they are worth checking out.
Please note that I always stop down once and prefer to stop down twice for optimum quality. These lenses are soft wide open. Thus the difference between f/2.5 and f/2.8 may be greater than it appears. By which I mean that at f/4 the faster lens might be proportionally sharper. Or it might now. Don't get your hopes up!
Value for money is what we are talking about here, with nice manual focusing and solid build. But do not expect supreme quality. However for many the quality will be good enough. If you've got the cash, try one and see!
Last edited by rparmar; 07-18-2010 at 08:16 AM.