>>3394543>but the range of focus in the image is narrower then i'd like.
Let me first state that I am in no way an expert on this subject. To get more stuff in focus, you have to use higher F-number (like F8 or F11) BUT, the sharpness in your images could become softer. This can be negated by resizing your images to really tiny resolutions like 2000x1333 pixels and then applying some sharpening.
However, if you need 100% crop full resolution, maybe try getting your hands on a prime lens (fixed focal lenght, not zoomable in any way) since those are generally sharper because the lens engineers only have the fixed focal length to work at.
My canon midrange DSRL kit lens is sharp at F5,6 but not much is in focus. if I increase to F11 more is in focus but the image is noticable softer.
I also have a cheap canon 50mm lens and even at F11 it is much much sharper (however, 50mm won't be likely to capture museum objects if they are in narrow quarters).
are you using a tripod? There can also be some motion shakeblur especially at the edges if you are shooting handheld and at lower shutting speedo
also some zoom lenses are more sharper at different focal lengthes because it apparently is hard for lens engineers to make every focal lenght sharp for zoomer lens
additional notes: i am not professional.