A few people reported back that they cannot/do not know how to zoom as they are used to use the mouse wheel. Zooming in MITK is done with the right mouse button, though, and it is fine as-is, comparing to other medical viewers. However, we should make sure that it is more clear how to navigate. For example, we could improve the Welcome page with hints on how to navigate.
A short but clear description of the interaction types is given in the MITK StdMultiWidget Editor help page (F1 on "StandardDisplay"):
Left click in any of the 2D windows centers the crosshair on that point. Pressing the right mouse button and moving the mouse zooms in and out. By scrolling with the mouse wheel you can navigate through the slices of the active window and pressing the mouse wheel while moving the mouse pans the image section.
In the 3D window you can rotate the object by pressing the left mouse button and moving the mouse, zoom either with the right mouse button as in 2D or with the mouse wheel, and pan the object by moving the mouse while the mouse wheel is pressed. Placing the cursor within the 3D window and holding the "F" key allows free flight into the 3D view.
The "Welcome Tutorial" on the Welcome page also has basic information on how to interact with the render windows.
Btw.: The "Welcome Tutorial" was created in 2015 and does not reflect the current status of MITK.