Quite some time ago, I explained how to focus adjust a K-5 camera using Live View. However, there are some confusions amongst Pentax users over time for the meanings and effects of the "Apply All" and "Apply One" settings. So, I opt to explain more this time. Well, the user manual tells nothing useful about these once again, just see page 126 of the K-5 user manual! >:-(
For a camera like the K-5 and K-30/50/500 which lacks a f/2.8 sensors, this "AF Fine Adjustment" is crucial so as to compensate the spherical aberration that exists on all lenses when stopped down against wide opened, which causes the camera to mis-focus depending on the amount of differences. It is because the AF system actually measures the more central part of the lenses optically for those f/5.6 AF sensors.
So, here we go, we have four scenarios:
1. Nothing is Set:
This is essentially the same as to set in the Custom Function that the "AF Fine Adjustment" is Turned Off / Disabled.
2. "Apply All" is Set but "Apply One" Not:
So, All lenses will use the "+5" setting as shown in the above example which is obvious. Do note that a +ve setting is meant to instruct the camera to focus fronter (to compensate back focusing) and vice versa for a "-ve" value to instruct the camera to focus backwards (to compensate front focusing).
3."Apply All" is Not Set and "Apply One" is Set (for Individual Lenses):
This is also obvious, the "Apply One" setting will take effect when individual lens is mounted of which the lens identity number is detected (for a Pentax F AF lens or later). So, I now know why the official user manual just tells you "Apply All" means apply all, "Apply One" means apply one or something like that but no more! ;-p
Choose this only if your camera does not contain any AF error primitively by itself, like my own K-5 unit which is a perfect copy already! :-D
4. Both "Apply All" and "Apply One" are Set:
Well, what does it mean under this case? Is it actually +2, +5 or +7?? What do you think? :-o For what I checked, it is actually +2, that means that the "Apply One" setting overrides the "Apply All". Whilst this does make sense somehow but however, the "Apply One" is not applied on top of the "Apply All" as many Pentax users wished!
Btw, if you have a copy of your Pentax camera which needs some slight adjustment by itself for *all* lenses, i.e. sample variations with some system errors, set both and remember to individually calibrate all your lenses unless the "Apply All" already works for all your lenses, i.e. scenario #2! Frankly, if you have more prime lenses like me, calibrating each lens is inevitably unavoidable!
Last but not least, some people would be puzzled for what to do with a cheap DAL or even "DA" lenses which does not have a focusing mark (namely, the DA35/2.4, DA50/1.8 and the DA40/2.8XS lens). Well, what you need to do is to put on a sticker and make the mark yourself before doing any further calibration! See the following example. :-)
Besides, some people would still wonder, do the K-5II/s need such "AF Fine Adjustment"? My answer is Yes, if you are using really Fast Prime like the DA*55/1.4 or just an old FA50/1.4 and etc., of which spherical aberration still occurs in between the widest aperture of f/1.4 down right to the f/2.8 aperture where the AF is detected and measured. So, the above techniques do still always apply! And also don't forget that not every copy of the K-5II/s is perfectly quality controlled when it was produced from the Pentax' (and now Ricoh's) factory.