get autofocus capability for your manual lenses! - Page 4

Adnan EROL · 05-03-2009, 02:39 PM

Originally Posted by F16

It just depends on the camera and lighting conditions, and when using a TC some will have a more negative impact on AF than others. Take a lens rated at 5.6 and try to AF in a dim interior room and chances are decent that AF will struggle. Take the same lens out on a sunny day and it will behave much differently. You can get a lens with the equivalent of F8 or even F11 to AF under ideal conditions. The rough conventional number is somewhere between F5.6 and F8, the reality is that there is no hard number, it will just depend on the circumstances.

Which camera body has advantage in the same circumstances?

*F16* · 05-03-2009, 04:27 PM

Originally Posted by Adnan EROL

Which camera body has advantage in the same circumstances?

In the Pentax family of cameras, I couldn't answer that - I don't know what camera you're using and I don't know, for example, if low light AF performance is worse on a K100D vs. a KM/K1000 or K20D. My comment was more of a general comment that some AF SLRs perform much better under low lighting conditions than others. But I'm not that familiar with head to head low light AF performance between the Pentax DSLRs. The new KM is supposed to have the fastest AF performance overall, but that doesn't mean it's the best performer in low light.

*Canada_Rockies* · 05-03-2009, 04:35 PM

Originally Posted by Lowell Goudge

... <snip> ...
one additional point I discovered with the AF TC, and it is only because I now have my first KA mount lens, is that the TC corrects for apature when mounted to the KA lens. An F1.4 lens shows as F2.8 in the viewfinder.

Yes, I have noticed this with my 50-135 when I tried it. This may end up as my only converter after a while. It's only 1/2 stop slower than the 1.4X - S, and seems to give a bit better quality with the 400.

*jensm* · 05-15-2009, 12:22 PM

I just go myself an AFA 1.7, and I'm finding that while focus is spot on with one lens, it front focuses quite a bit with another.

I've got a K10D and have been looking forward to a K7 upgrade (skipped the K20D) with lens specific AF adjustment - but I don't suppose it will recognize that the AFA has different lenses mounted to it.

Any ideas if this can be solved, or if I'm stuck in a "just doesn't work with this particular lens" situation?

Thanks,

Jens