Split filter printing with a multigrade head such as the Arista vcl 4500 has the advantage of being able to go full blue and full green without touching the enlarger (no vibration) The control box is off to the side of the enlarger and allows you complete timer control of each exposure and the ability to burn or dodge on HC or LC! When changing filters on a single light source (Regular) enlarger you always risk vibration, this is also true with most color heads. Since you have to reset the filter on the head!