Originally posted by psoo my images seem quite satisfactory for my type of photography.
This is the key. If you don't see a problem, most likely there isn't one. And unless done carefully, meticulously, and precisely with everything lined up perfectly during your test, you can easily make the focus worse than it was. Unless you are quite careful and use a good focusing target your margin of error in the testing can be larger than the actual error in focusing.
That said:
- I check all of the lenses I purchase, either new or used.
- I use a careful, tedious method that takes 20 to 30 minutes per lens after setup time, which can take another 10 minutes or so to align the camera to target precisely
- Most of my lenses have needed a small adjustment, one that most likely is not really noticeable in the real world
- For slow lenses such as consumer zooms, the depth of focus is usually large enough to mask any small error
- For very fast lenses such as an f/1.4 50mm, fine tuning is almost certainly needed (or at least should be checked) due to the tiny depth of focus you can achieve at that aperture
So bottom line: If your results are good, you don't likely need to mess with it. And if you do want to check, do so very carefully, keeping in mind that precise testing is needed.