Making one filename variable populate two tag fields (Artist)

I would like Album Artist and Contributing Artists to be populated from %artist% when setting tags from filename.
How can this be done?

Try an action group with 2 actions of the type "Format value"
First action for field ARTIST
Format string: %_filename%
Second action for field ALBUMARTIST
Format string: %artist%

I see no such variable as _Filename available under Actions, but since I use filenme-to-tag, making the second item you mention completes the taggjng.

Thank you.

You would have to type in the name of the field _FILENAME.