On the other hand I admit I was trying to avoid some post production by using f 22. I understand it was a mistake because of the diffraction. I do use most of the techniques related above:
It is tempting. And gives inferior results. Been there. Done that.
1. the image above is focus stacked from 2 images - one focus on top, one focus on paper's surface.
Try focus stacking from 20 images. Youīll be surprised.
Generally speaking: The easiest way to get basically infinite resolution is to take a ton of detail pictures and stitch them together digitally.
2. I do use high pass to sharpen my images
Phew. It does not really sharpen. It enhances edges mostly. That would be the last step I think.
3. I am not using flat lighting. This light creates almost no shadow. I know the sidelight creates shadows and texture.
4. For some reasons, I thought pixel shift can not be used with flash, but flash is 100% my lighting source. I searched the manual - ... can not be used with X and B modes... Hm... I am always using M mode.
Frankly: Not much point in flash with macro for me. Not if it doesnīt move.
Other things to consider: Avoid vibration as good as possible. Stable tripod, stable table. Stable everything. Donīt even think about pushing the shutter release manually or trigger the shutter when the mirror is not switched up.
And donīt forget to switch off shake control. If you want to squeeze out the last bit of sharpness it wonīt help.
(Sorry if this is silly advice for beginners. Itīs just mistakes I made myself.)