Originally posted by Rondec Even with the 6 megapixel digital cameras that Pentax released in the beginning, softness wasn't as readily apparent. When you get up to 12 or 14 megapixels, it is a lot harder to get sharp phots and even small focus problems show up.
AF issues or other blur-introducing factors can easily be seen on a 6MP image. A 14MP camera has 53% more resolution, that doesn't make it
a lot harder to get sharp photos. It does make it harder but that doesn't mean you cannot readily see softness in a 6MP image.
Originally posted by cbaytan That sounds impossible, if it was so same batch of same lenses all would be need to same correction, but all individual lens might need different adjustment.
Every single lens copy differs from another in slight ways even if they are from the same batch. The lens elements aren't perfect, sometimes rotating them can improve lens performance and there are tolerances in how the elements are fit into the barrel. Decentering is a known phenomenon with lenses and it isn't either present or not, it occurs in many forms of severity.
Originally posted by cbaytan So that tells us, in the focusing gear physically there are/is incorrect parts, or aging/worn parts needs to be adjusted IMO.
No, I'm very sure this is not the reason. Note that lenses may have FF/BF when they are brand new. And again, unless the AF gear is in very bad shape (no tight transmission), the camera would keep adjusting until it has obtained focus.
Originally posted by Cannikin If I can get a DOF that's less than 1 cm wide to appear in the dead center of the frame at ~100% magnification on every object I test on, and infinity is right on as well, I'd say that's plenty precise enough for me
.
Your focus is dead centre in the frame but where has the AF system focused on? You have no way of knowing whether it picked up the structure to focus on before, at, or beyond the centre of the frame. Remember we are talking about AF
areas and the AF system is happy if it can find focus within that area.
Originally posted by Cannikin I do not use a ruler or test chart because I know that it would hunt for the numbers and lines on the target rather than the actual texture at the center.
Rulers are a bad idea (as a focusing target) because again one has no way of knowing where the camera focused on exactly.
A good test chart has a very small focusing target (i.e., a black and white transition, not a small bar) which one can centre in the frame. Then it is clear where the focus was obtained and then it makes sense to check whether a ruler structure next to the target is sharp in the centre of the frame.