Upload & Sell: Off
| p.1 #2 · AF Fine Tuning... Torn on zoom. Help? |
Consider your subjects.
What you're finding is that your autofocus is off. That's different from what in your image is sharp.
For my uses, at 17mm, you have a greater depth of field and are more likely (typically) to be shooting a wide angle image, possibly at a smaller aperture or focusing further away. I haven't done a statistical analysis but I'm guessing that at focal lengths smaller than 20mm, my aperture is usually f/5.6 or f/8 and focused closer to infinity a lot more than at focal lengths longer than 35mm. Thus, for my purposes, it'd make more sense to adjust for that longer focal length.
Additionally, with the greater DOF at shorter focal lengths, your room for error is a lot bigger. This is where it's important to understand what you're adjusting: the error of the autofocus, NOT the sharpness of your image (per se). Using a DOF calculator, a subject 5 ft. away, at 17mm f/2.8, will have a DOF of around 3 ft. That same subject, at 35mm f/2.8, will have a DOF of 0.66 ft. So if your AF is a little off at 17mm, it's unlikely you'll notice. If the AF is off at 35mm, suddenly it might be a problem.
The upshot... I'd set my AF adjust to give me the best results at the longer focal lengths unless I had an extremely strong preference for the shorter focal length in my shooting.