Error when trying to "capture (only)" in SCCM 2012.

So I tried splitting up the build and capture task.
I had many problems to get my capture to work...

In the end, I tried to get only one task to work: the "capture operating system image" task in de task sequence. Error 0x80070490 was trown at me. I didn't find the solution immediately, but now I stumbled upon it:

Thanks Trevor:
http://trevorsullivan.net/2011/10/24/configmgr-you-receive-error-0x80070490-in-a-capture-task-sequence/

It seem defining one variable makes it work. Which makes me wonder I haven't found yet any good documentation about which variables are available, recommended and/or mandatory in each step of any common OSD task sequence.
Of course, at this point, I'm still learning a lot. Any help is appreciated.