according to some people, it is because they are using a particular brand and are limited by their equipment.
there could be many reasons though:
1) handshake, this could be due to too slow shutter speed for focal length, or improper handholding technique.
2) poor lens quality, most consumer grade lens will be ok at reasonably stopped down apertures though, but that will limit you in light. a bright day out in the sun will not be a problem in any case though.
3) over-high ISO used causing IQ degradation and loss of details
the list goes on.... as you can see, it could very well be non-exhaustive.
improperly calibrated lens will only be one factor in the whole equation. more often than not it is usually user fault though. :bsmilie:
My moda of operandi always is to ask myself first what did I do wrong. It is the easier way to check if you already know beyond your basis photography. If you are not even that, hardware is the least of your reason for blaming. Look at your photo. Look at the data that is contain in it.. see what happen by looking at what shutter speed was use? What aperture was used? Did you snatch the shutter trigger? Was your subject moving too fast? Too slow? Were you on manual mode? did you compensate an exposure shot and forgot to reset it? alot of this details you can find in your camera preview or with one of those photo view S/Ws. I can think of many things that could have contributed to me to making a bad shot before I even start to blame the equipment.
Sorry... you must be wonder why I jump to this conclusion? It is because you are actually asking bro. Most with enough photographic experience would be looking at themselves and handling technique first and only after which equipment will considered and they will not be phrasing their question this way. heh.
Upload your shot and let's analyze it? Help you sharpen your skills.
increase shutter speed
reduce ISO if too high
increase ISO if too low
use monopod / tripod
use mirror lock-up
use remote release / cable release
use smaller aperture from wide open
buy better lens
check for fungus
1) Eliminate user error
2) Eliminate incorrect settings
3) Identify the cause of the problem
4) Identify exactly which bodies/lenses are in error
4) Eliminate any possible alternative causes, or note them
5) Take the necessary steps to rectify the issue(s), if any.