Other: Making Zoom Lenses Parfocal with Metabones Speedbooster...

[Bern Caughey]

Metabones claims their adapter is made to exacting standards and you shouldnt worry about back focusing. If that were the case, then why is there a back focus adjustment.?

There's also the issue of how precise is the flange distance of your FS7? ARRI's, RED's, & Sony's F, cameras have provisions for adjusting the backfocus, so I wouldn't be surprised if a SpeedBooster needed some calibration.