[goatsNdonkey]

Paulo, thanks for the excellent and expansive account of your own lens and lens-expectation experience. While my lens collection is tiny compared to yours, I find myself looking more and more for lenses that have some kind of "character" of their own, even if that quality is made up partially by what others may list as defects of one kind or another. As mentioned in an earlier posting here, I do read the reviews, but try to give more weight to comments that point out those kind of particularities, or peculiarities. I find myself ignoring comments about "handling" since I usually don't mind the things others cite to downgrade lenses in that category, for example. I'd like to see a high sharpness score, but being able to control where the really significant sharpnesses go in the picture, strikes me as much more important than a bland sharpness all the time and everywhere whether there is a good reason for it or not. Somehow, I am often confused by the aberrations scores, except for things like purple fringing. So many of the other aberrations just seem to me like part of what the world looks like through a particular lens; when that isn't suitable for some picture you want to make, you just choose a different lens for that.

Reviews, especially those available on this site, have for sure an impact on the kind of expectations we have when we buy a new lens.
As a collector of large format historical objectives, and owner of more than 300 lenses readily usable on Pentax DSLR bodies, I'd say I have a minimum of knowledge about photographic optics, though I still depend, at least partially, on online reviews to shape up my personal expectations about the performance of a newly acquired lens.
How a certain lens matches the initial expectations is the key. If the lens is expensive and has a cult status, I'd be unhappy if the performance is just average. If I don't expect anything special and I find it's a decent performer, then I'm happy, even if it doesn't beat other more expensive lenses in the same focal range.
User reviews can be a valuable source of informations, especially those well done, but the averaged votes have little value. Better stick to a few selected reviews that evidence in a balanced way the pluses and minuses of a certain objective.
Some very low votes have a simple reason: the owner bought a lemon! If I think I have a bad sample, I'd never write a review... unless I have good reasons to think that it's a common problem, that is shared by many other examples of the same lens.
Sample variation is a reality, affecting even high_cost brand new optics. Of course the difference between apparently identical lenses could be quite dramatic, if we consider lenses that were built decades ago.
If one sample is damaged or in some way defective, it doesn't mean that other examples of the same lens will be as disappointing.
It is also true that the delta between a rather poor and a very good sample is not so wide. If on average a certain lens is barely decent, even the best of the crop will never be outstanding.
All optics are a compromise, you can't have at the same time cheap, sharp, fast and well built!
As others have already pointed out, knowledge is a good way to avoid frustration.
If we know what we can expect from a given lens, and what we can't, it's more likely that our new acquisitions will suit us better, and that we won't be disappointed (because we had unrealistic expectations in the first place).

In my personal experience I've been badly disappointed only a few times, and the reason was always an irrepairable damage. To be more precise, the real disappointments were lenses that were either missing rings/spacers, had badly bent focusing/zoom sleeves, had very bad "gravity accidents", or had been tampered with in some way. Even when possible, the repair was not economically viable.
As far as I remember I never returned them, cause it was either an "as is" purchase, or because the expense of a traceable shipment would have made it a loss anyway...
The biggest source of frustration doesn't come from irreparable lenses, it comes from expensive ones that are not in perfect conditions (as they were supposed to be), and that for some reason can't be returned. It happened twice to me, and in both cases the repair wasn't cheap! And both lenses showed absolutely no signs of damage. I found it rather infuriating...
Never happened with vintage lenses, AF or MF, M42 or PK, Pentax or 3rd party.
Considering I don't have many digital era lenses, but I have plenty of old ones, including a few pre-war micro objectives that are still very usable, well, I guess it makes sense to share my personal experience. I have old lenses that obviously fell to the ground multiple times (two have partially missing filter threads!), but almost all of them work more or less the way they are supposed to. Other contemporary lenses, looking perfectly mint, showed a number of important problems, namely: decentering, vignetting, hard to turn zoom ring, focus ring stuck to min focusing distance during AF operation.
From my personal experience, I tend to blindly trust the pictures of a vintage lens. Most of the times it will be more than ok, and if a repair is needed, it will likely be economical. I will never buy again a second hand contemporary zoom, without making sure it could be returned.

Btw, now my favorites are all vintage optics, the advent of the K-1 full frame has reinvigorated my appreciation for them. For example my choice for portraits is currently the Summicron M 2/90mm, and my go-to for bokeh is the Trioplan N 2.8/100mm. I guess it's already clear that absolute sharpness is not my main concern What leaves me cold is the lack of both sharpness AND those aberrations that give a peculiar rendition of the image. It can be either a pleasant bokeh, a smooth transition between focus planes, or a touch of field curvature that drives the attention to the center of the frame.
With vintage lenses, frustration almost always comes from irrational expectations.
I report a personal experience, which could be of some use.
I am the proud owner of an old "Pentax Distagon", the 2/28mm series K "Hollywood" with floating optics. It is a good lens, even today, but it's also a valuable collector's item, so years ago I decided to buy another fast 28mm for everyday use.
At first I found a Panagor (Kino made) 2.5/28mm in M42 mount. It didn't satisfy me, especially at large apertures. After reading a few positive reviews about the Kiron f/2, coming from the same factory but with a more modern optical layout, I decided to go for it. I bought both the 2/24mm and the 2/28mm, one marked Kiron and one Vivitar.
After trying them wide open, I realized that the improvement over the Panagor was quite marginal.
At f/5.6 or f/8 most 28mm perform quite well, including the Pentax-M f/3.5 and a late Komura in PK mount (which I suspect would be the best, if I ever decide to compare all of them).
The problem lies in my wrong expectations. Even if they proved their worth in the magazine tests published at that time, fast film lenses of that vintage were to be used wide open only in extreme circumstances, with very low illumination. The max aperture allowed for easy focusing, but pictures were mostly shot stopped down. If the performance wide open was deemed as "good", that judgement had a meaning if compared with other similar optics of the time. By today's standards, it's not "good" anymore... unless we are looking for a soft-ish look (which I often do).
At this point of my long learning curve (started buying PK lenses in the late seventies), I've come up to the conclusion that finding a fast vintage wide angle that fully satisfies me is a rather difficult task, while some very old super-fast teles have surprised me in the most positive way. My Helios 40 1.5/85mm, built in the Soviet Union on 1961, is still a great portrait lens, with a very nice optical signature.

Looking back, most of the lenses that I found rather disappointing were in fact just dull, bland. All of them, bar the defective ones, are perfectly capable to take decent pictures, if used at their sweet spot, and with a few caveats (use a lens hood, avoid sun/strong lights in the frame, a little PP to bump contrast and sharpen).
The best way to avoid frustration is knowledge, which sometimes involves reading a little between the lines. Some reviews are useful, some are misleading. Some reflect frustration from the acquisition of a bad sample, others show very little criticism (I bought it, it works, so it's a ten!... more a self-reassuring psychological mechanism than a real review).
I always try to have a "virgin" approach when I try a new optic, but I would never call my opinions as objective. There are lenses that for some strange reason you madly like, and others that are perfectly fine, but will never warm you up.
I have a couple of lenses that for some mysterious reason never took an ugly picture
One is the Revuenon (Tomioka) 1.2/55mm. Last journey I tried in its place the Pentax-K 1.2/50mm, but I didn't like it the same way. Now I have with me the Porst (Cosina) 1.2/55mm, but I haven't tried it enough to see how it fares compared to the others.
The format makes for an important difference. A 50/55mm is a proper portrait lens on APS-C, while on FF is usable for full figure or even group portraits.
While it's undoubtedly true that the cropped format hides the border miseries of some optics, I found that some old film lenses really shine only on full frame.

Sorry for the long, winded post. I hope it made some sense
I'm looking forward to other replies cause I'm always very curious about what people find frustrating in their lenses, and why it is so.

Cheers

Paolo

[cyberjunkie]

I find myself looking more and more for lenses that have some kind of "character" of their own, even if that quality is made up partially by what others may list as defects of one kind or another. As mentioned in an earlier posting here, I do read the reviews, but try to give more weight to comments that point out those kind of particularities, or peculiarities.
Somehow, I am often confused by the aberrations scores, except for things like purple fringing. So many of the other aberrations just seem to me like part of what the world looks like through a particular lens; when that isn't suitable for some picture you want to make, you just choose a different lens for that.

I fully agree.
Most of the times, supposed "defects" can be turned into precious assets, if we learn how to use them.
Others are a problem only on paper. For example the distortion of an extreme wide angle is important only if we use the lens in a certain way. I don't routinely do picture stitching (and when i did i used a moderate wide), nor i shoot architecture. If i had to document buildings with my Samyang 14mm, and i had straight lines close to the borders of the picture, i'd simply use a lens profile! Saying that the Samyang is a bad lens because it has some mustache distortion is a bit of a stretch, considering the kind of pictures that most photographers take with an extreme wide. If the images posted on this site are representative of the photographic habits of Pentax users, very few could claim to be really affected by such "defect". Some might even find it helpful, cause it would make the extreme perspective even more dramatic.
"Aberrations" and "optical character" are two opposite ways to call the same thing. Field curvature and undercorrected spherical aberration are the source of 3D "pop" and nice bokeh.
Sharpness can be just a totem. If you show a print, even rather large, to your friends, almost everybody (but a few tech savvy photographers/pixel peepers) would prefer the picture with a nice rendition of OOF areas, instead of the sharpest one.
Of course if we enlarge the photo to 100% on a 27" monitor the perspective would be quite different.
Now, let's ask ourselves: which are our aesthetic goals? What do we like in a photo, and what not?

cheers

Paolo