Lens Focusing Problems

craig1024 · 11-12-2008, 11:44 PM

I just recieved my new K20D today and placed my favorite lens, Tamron 17-50mm Di II, and it will not auto focus. I put it back on my K10 and it is perfect. I put my 50mm f/1.4 on both and it works perfect on both. What the heck can I do? I love my Tammy, but am I going to have to use it exclusively with the K10?

walter · 11-13-2008, 01:09 AM

Are you sure the lens was seated properly? The tamron should work on the K20D, using the same screw drive as with the FA50.

craig1024 · 11-13-2008, 01:28 AM

I am sure it was seated properly. I just did some informal tests with my tripod to make sure I wasn't imagining things.

The Tamron on my K10 is respectable. On the K20, it is respectable in the middle of the zoom range, but at 17 or 50mm it is horrible. Unusable, even. I will try to post some photos from my test, soon.

frank · 11-13-2008, 01:56 AM

Originally Posted by craig1024

I am sure it was seated properly. I just did some informal tests with my tripod to make sure I wasn't imagining things.

The Tamron on my K10 is respectable. On the K20, it is respectable in the middle of the zoom range, but at 17 or 50mm it is horrible. Unusable, even. I will try to post some photos from my test, soon.

So you mean the lens does AF but looks pretty out of focus at 17mm and 50mm end? Thought you meant the lens didn't AF at all ...

If it's just OOF problem, you can try to do an AF adjustment on your K20D and see how. Some users reported some copies of this lens have AF problem.

craig1024 · 11-13-2008, 02:16 AM

Yeah, I guess I was not real clear on that. It will auto focus, just not right. I just read in the manual how to set the focus for different lenses. I am a little worried, though since the middle (28-30mm) range looked usable. I will play with it today. It is too hard to set anything up at work.
Shhh...don't tell my boss I've been playing with my new K20 all night.

walter · 11-13-2008, 03:00 AM

oops, I misunderstood. I thought the AF was not turning. My Tamron 17-50 is pretty erratic too, which is a shame since it's really nice optically. I haven't had much luck with the AF adjustments settings since different adjustments are needed for different focal lengths and focus distances. If you do tweak the af adjust settings, I'd double check them at different distances. You might get it to focus perfectly at 6 ft, then find it can't focus on infinity.

One workaround is to autofocus at the zoom setting that works, then change it to the zoom setting you want. The focal plane seems pretty doesn't seem to change when zooming. Yeah, it's a pretty slow and crummy workaround, but I don't have any better ideas.

craig1024 · 11-13-2008, 10:36 PM

Thanks walter!

I did a little informal test tonight and found that the lens is much sharper and in focus at f/4.5 than at f/2.8. So maybe it isn't the focus, but the sharpness wide open that is the problem. But what is the point of having a 2.8 lens if you can't use it at 2.8?

*TourDeForce* · 11-13-2008, 11:03 PM

Originally Posted by craig1024

But what is the point of having a 2.8 lens if you can't use it at 2.8?

Marketing tool.

**Marc Sabatella** · 11-14-2008, 04:44 PM

Originally Posted by craig1024

I did a little informal test tonight and found that the lens is much sharper and in focus at f/4.5 than at f/2.8. So maybe it isn't the focus, but the sharpness wide open that is the problem. But what is the point of having a 2.8 lens if you can't use it at 2.8?

I guess I'd have to see samples to say. The images I've seen from this lens at f/2.8 have looked quite acceptable to me, if obviously not as good as they are at f/5.6.

walter · 11-14-2008, 05:05 PM

Originally Posted by craig1024

Thanks walter!

I did a little informal test tonight and found that the lens is much sharper and in focus at f/4.5 than at f/2.8. So maybe it isn't the focus, but the sharpness wide open that is the problem. But what is the point of having a 2.8 lens if you can't use it at 2.8?

If you take a picture of a angled surface (like the floor at 45 degrees), it's easier to find out if the camera is front/back focusing. Keep in mind that the center autofocus point is a lot larger than the small red square so some shift is normal.

I think the Tamron is pretty sharp at f/2.8, but I would expect it to be softer (when pixel peeping) on your K20D than on you K10D because of the additional megapixels.