Originally posted by stevebrot It seems you have had your share of problems with focus and sharpness. (Did Pentax figure out what was wrong with your D FA 24-70?) A lens that falls out of range for AF fine adjust is pretty rare and when it happens, it is usually a good indication that there is a serious optical problem with the lens that makes it difficult for the PDAF system to attain accurate focus (decentered or defective element). A few questions:
[*]Are you using a slant-ruler device? If so, is the target portion parallel to the sensor or is it at an angle?
For the tests I'm using a Spyderlenscal tool. The target portion is parallel to the sensor
Datacolor SpyderLENSCAL
[*]What distance are you using for your tests?
About 3 metres
[*]Are you using other than the center AF point for your focus adjustments?
No
[*]Are you able to attain acceptable center focus using full manual technique (manual focus using magnified live view)? You said there is fringing full open. Is the fringing bad enough to make manual focus difficult?
Yes
[*]Is the camera able to attain CDAF focus under live view without excessive hunting or inaccuracy?
Yes
I call particular attention to the fringing wide open. The FA 31/1.8 should be free of both LoCA and LaCA at center at all apertures. CA at its core is degraded focus and the PDAF sensor has a difficult time with it in much the same way as you or I do. Given your difficulties with the 24-70, I hate to suggest that your FA 31 has problems, but it very well might. If it is on warranty, now might be the time to have it checked out.
Steve
(I answered some of your questions in the quote)
I have an email that my 24-70 is ready to be picked up from the dealer.... which I will do later this week (currently on holiday). It's been away for about 4.5 weeks, but I don't know if that means anything.
I will redo the tests on the 31mm when I have time - next 5 days or so, and share some of the photos here. Warranty is still good for another 2-3 months.
---------- Post added 07-10-18 at 12:22 PM ----------
Originally posted by pasorro Dont do the test at 1.8. repeat the test at 2.8. Your camera AF central point is designed to work at 2.8 as Max Aperture.
Sorry bad english
What does that mean in practice? E.g. for the new 1.4 lens...
---------- Post added 07-10-18 at 12:25 PM ----------
Originally posted by leekil I assume you have ruled out that the camera is not significantly out of AF calibration, if you have adjustment problems with several lenses?
My DFA 70-200 and DFA 28-105 are sharp and don't need adjustment. (28-105 is less sharp).
How do I 'rule out' that the camera is not significantly out of AF calibration, just if all my lenses need strong AF adjustment?