￼Many Canon 90D owners have been complaining that their images are not quite as sharp using the optical viewfinder as they are in Live View. ￼ The cereal box and ruler method allows photographers to quickly visualize where their lenses are focusing and to verify if they are out of alignment. This video demonstrates the philosophies of MFA (micro focus adjustment) and some of the principles to become familiar with if you decide to try this on your own. ￼I think learning how to do this manually is a good exercise because sometimes you may need to make an adjustment and not have access to certain tools.
I did decide to keep my micro focused adjustment at -15 simply because I was getting better peak sharpness at that point.
It may appear that the Live View focus is off. A couple notes: MFA doesn't change Live View focusing, Im wayyyyy zoomed in, and finally it is normal for cameras to focus towards the front of the DOF.
If you haven't seen it already, please check out the 5 focusing tips before trying MFA: https://youtu.be/6Kq3ESNQbgY
If you like my teaching style, check out my training videos on specific cameras:
Michael’s Training Videos
Michael’s Maven Straps