[snake]

What was the designed failure mode in those lenses?

I don't know. Have any insights?

[lytrytyr]

people are complaining, who use some brands, that these plastic parts are not replaceable.

Hopefully soon we'll be able to reproduce them with 3D printers.

[Racer X 69]

The electronic contacts aren't made of plastic and the gears and the shafts of the AF is also off metal most likely

Carbon fiber is electrically conductive, and could be used for electrical contacts.

Do these lenses have any bearings in them?

I'd expect a lot of the gears in a small lens to be made of plastic, though.

I would think the shafts the gears run on would need to be metal, perhaps steel or an alloy of some kind, maybe even titanium.

Optical grade plastic and related coatings have reached a point where in certain applications they seem to be superior optically to glass. I used to be dead set against against viewing my world through plastic lenses. Today, I can't imagine going back to glass.

I only need "cheater" reading glasses. I get frustrated when I find a decent pair, only to see them become scratched so badly over time that they become useless. The light passes through the scratches causing annoying glare, and making it very difficult to read or look at small details of things close up.

I always take care to clean them properly, using compressed air to blow the grit and dust of, then flood the remainder with commercially available lens cleaning solution, and wipe with a micro fiber lens cloth.

I even went so far as to see an ophthalmologist, and have a set of glasses made with the very best polydoublethrowdownplasticcoatedwithscratchresistantunobtanium stuff at a cost equal to what some folks earn for a day's wages.

Wasted my money.

*sigh*

If I could just get some made with real glass, like my fine Pentax lenses.

[vonBaloney]

If I could just get some made with real glass, like my fine Pentax lenses.

You can get them from Germany.

[Alizarine]

I don't mind the plastic, really, it helps keep the weight down.

I like this part, especially for the "rugged workhorse lenses" like the DA*s. A friend of mine has the Tokina 80-200, and while it's a superb lens, he gets shoulder aches every time we do whole-day events. I'm good with the K-5 and 50-135 on the default strap around my neck, somehow my neck vertebrae don't feel like falling apart after 6 hours of shooting with the pair. It would be a nice looker and feeler if the 50-135 was all-metal like the Tokina, but it's going to be less friendly to wield, and even more costly to produce.

I can't imagine the price of the 50-135 going even higher

But in terms of build... the Limiteds are where it's at. They just feel awesome to the hand and shoot mighty fine too. But well, they're not that fast compared to offerings from competition, and no WR seals too.

[Racer X 69]

You can get them from Germany.

Do tell!

I'm all eyes.

[Tom S.]

Absolutly not true
The electronic contacts aren't made of plastic and the gears and the shafts of the AF is also off metal most likely

Sorry to be so late here, but I'd be willing to make a substantial wager you are wrong about the gears, at least. I raced slot cars in the 60's, and even then, they had nylon gears. Take apart any vhs player or dvd player and you'll find plastic gears. Many cars even use them in their engine for camshaft timing. I wouldn't even doubt the contacts being made of metallic coated plastic.

[lytrytyr]

Sorry to be so late here, but I'd be willing to make a substantial wager you are wrong about the gears, at least.

Check out my earlier post (#17) in this thread:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/211793-plastic...ml#post2239438