The side access door will admit cameras as tall as the Canon 5D with lens attached. Most DSLRs with battery grips attached will not fit through the side door. Taller cameras such as the 1Dx will not fit in an upright position but fit well when laid flat without a lens.
Main Gear Compartment dimensions: 21″ x 12.5″ x 5.25″
Depending on how you pack the facing wall with the tablet compartment and mesh organizer pockets, you may be able to fit items that are taller than the 5.25” height of the sidewalls. Also, the wall between the clothing compartment and gear compartment has a bit of flex, so load the gear side first if you want to maximize the usable space on that side