Originally posted by Arpe I have the Pentax 80-320, it's okay. It does hunt for focus a bit on my istDs as it has quite a large throw from nearest to farthest focus. It also hunts a bit and sometimes doesn't lock on if it goes the wrong way first.
I was visited my father a couple of weeks back, and put my 80-320 on his camera, a Pentax MZ-60. What a difference! The focus was much quicker! Every time. Put it back on mine - whirr whirr, put it back on his - zip!
This annoyed me. Why is my later model camera considerably slower and less positive to focus with this lens?
I currently have a ZX-L and a ist DL. I noticed the same thing. When I got the DL, I hadn't used the ZX-L in a year or two (was shooting digicams at that point) and I just thought my lenses are slowish. One day, I compared them because I was finding it a little weird that they were 'that' slow. The ZX-L does focus substantially faster, and quite differently actually. It's not as jerky as the DL - it feels like it has more authority over the lens and can control it better.
I also tried different batteries in the DL. Surprisingly, my rechargeable NiMH batteries are the worst, but actually, rechargeables offer the lowest voltages of any of the options. Lithiums were the best, but they aren't worth the cost for me. I actually got a split image viewfinder from hong kong, and when it frustrates me too much, I'll manual focus. You could try playing with the batteries, but none of the options were as good as the ZX-L.
I'm not sure why Pentax did this. It seems quite silly to me, but as a result, I've stopped using my long, big, slow lenses in favor of smaller ones that the AF motor can control more easily (or just use A lenses that are MF to begin with). Oh well, I knew that AF was one of the weakest points with the DL, and I'm not really too concerned about it for my needs at least.
FWIW, I got to play with the K10D the last couple of days. The AF motor in that body is far better than the ZX-L, and the AF system is quite good really. I don't have a recent body to compare it to in another brand, but I was impressed with how it handled some of my heavier lenses. I'm not sure what the K100D is like but I think pentax is heading in the right direction here. I am eager to try the SDM system once it's available.