The best thing you could do, and get a lens of quality to go with a camera like the K-5, is save up and get the DA 18-135mm WR DC. Its autofocus (AF) performance is unbeatable, and great on the K-5. The K-5 is a great camera, but its AF is no longer up to current standards, especially with some lenses. But with this lens, performance is so good it would be hard to differentiate its AF from the latest! Quiet, fast, and accurate. Even in dimmer light! I know because although I usually shoot these days with my KP, or sometimes my K-S2 or K-5 IIs, I still have my original K-5, and I've had the DA 18-135mm WR DC for years. it is capable of producing superb images, is built like a tank but compact, and it has a very versatile zoom range. It handles very nicely. I have some of the most expensive zoom lenses and prime lenses, but the DA 18-135mm is one lens I would not want to be without. Its price is considered mid-point, so for what it can do it is a bargain. Even a well cared-for used one would be better than not having it.
It is a good thing to shoot with your old lenses and develop your eye for manual focus. In the meantime, save up and go for the DA 18-135mm WR DC! It will also open up many features of your K-5 now not available to you, so you will be able to explore and take full advantage of what you have.
3rd party lenses are not available having WR. With Nikon or Canon brand cameras, WR lenses start in the $1,000 range. Believe me, you have a real bargain that is within reach.
Last edited by mikesbike; 08-28-2018 at 12:16 PM.