Pentax D FA 28-105mm on Pentax K-5, it is OK?

[Adam]

Of course it is, and the image quality will be really good, too. The only problem is that 28mm isn't very wide on APS-C, but that's personal preference.

[TER-OR]

If I had the budget, I'd get one. I have an old Promaster 28-105 and find the FL range very versatile.
If I had one, it might live on my old K5...

[surfar]

Seems quite nice, mine arrived a few days ago...Put it on the K-5(0) first,then the K-1.

All good...tried the crop mode on K-1 too.

[CarlJF]

It's OK in the sense that it'll work with excellent IQ. However, as Adam mentioned, 28-105 isn't the most practical range on an APS-C camera, although it always depend on what you're doing. Something like the 16-85 is way more useful and versatile than 28-105. Unless planning to buy a K-1, I would rather go for the 16-85... Because 28mm isn't very wide on an APS-C camera and going wider is often needed.