Following on from the release and discussion of Michael Tapes new MFA tool here on Lula
, plus having recently had a few less than optimally focused shots myself, I decided to have a fresh look at FoCal and see if things have progressed since this thread was started.
The first observation is that FoCal is now a very well documented, easy to use and reliable program. It also works well on hardware below their recommendations, so I've been able to work outdoors with a little 1.4ghz netbook to calibrate longer lenses without being tied to a desktop system.
The target validation routines seem to work well and are simple to use which should ensure good reliable results.
FoCal Pro automatically shoots and evaluates dozens of shots without any intervention. I would expect the greater number of samples should lead to more accurate results.
The analysis information being presented in real time as testing progresses instils a good degree of confidence in the procedures used. The reports generated and saved at the end of analysis add to that confidence by including the sample images for user review.
As the process is so simple once the target has been set up, it's easy to carry out extensive testing of how MFA changes with f stop and how consistent the AF system is. Trying to do this sort of testing manually would take a very long time and might be prone to errors unless it was carried out with meticulous attention to detail recording results.
As previously noted in this thread, one curiosity of the whole MFA testing procedure is that it reveals the differences in AF performance on lenses depending on the selected f stop and shooting distance and, in the case of zoom lenses, focal length too. This is information that people may be unaware of if they just do very basic testing with only a few variables.
Once you do have a full picture of how AF performance is varying with different settings it's possible to consider the optimum value for one's own shooting style and preferences. For some this might be easy, e.g. always using a 85mm f1.2 wide open for portraits at 15ft. For others it might need more consideration e.g. when FoCal shows a wide ranges of values for a zoom that will be used at many different settings.
I'm tending towards using the setting recommended for the most critical conditions, wide open at the longer focal length, so far that's working well for me.
My own initial testing is suggesting that previous chart based manual evaluations had given poorer results than I realised, or that values have shifted over the last two years, possibly a bit of both. It will be interesting to see if these values actually change over time or with different environmental conditions.
The next question is "Does AFMA make a difference in real world shooting ?"
There's no easy answer to that. Although unlikely, you may have a set of lenses that are so close to perfect AFMA isn't necessary or your technique may be so poor that you wouldn't see any difference anyway.
More probable, is that one or more of your lenses will benefit from applying an AFMA correction that will deliver sharper results. Anyone doubting this can try the simple test of doing some shots with large changes in AFMA settings and studying the results. It does make a difference.
With the back garden tests I've done so far, I can see significant improvements after getting the correct AFMA and now AF performs better than I can achieve manually through the OVF.
I've also done some compassions using different ISO values. FoCal recommend using the base ISO for best performance, but I doubt there's much difference in the resolution of JPGs out of my 5Dii up to 400iso. So in the UK winter gloom with long lenses I can see improvements in consistency of results by using a higher ISO to use faster shutter speeds.
Given that getting AFMA correct is worthwhile, FoCal is a worthwhile investment as it seems to deliver the results you need to make an informed decision about settings without needing the large amounts of effort needed to check settings manually.