Studio quality describes a lighting setup, not a place

The most used phrase in this category and the least examined. Splitting it in two makes it useful.

The reproducible half

Controlled light and a controlled background. Nothing mysterious: a main source at eye level rather than from the ceiling, a surface behind the subject that separates from their hair colour, and distance between the two so the background goes slightly soft.

That is geometry rather than equipment, and geometry travels.

The half that is not

A person looking at you who says your chin is slightly too high, or that your shoulders look tense. That feedback loop is the actual product of a session.

Which half you need

For one important headshot, the second — frequently worth the whole fee.

For forty portraits of people hired in different months, the first, because the problem there is a calendar rather than a critique.