How to Zoom on Reference Photo in Develop Module

[Rachael5C3D]

This may be a simple answer, but I can't figure out how to zoom correctly on a reference photo. When editing in the develop module with a reference photo, I can zoom on the photo I'm editing, anywhere and however close up I need to, but when I click on the reference photo, it zooms in to a random amount and I can't change it. How would I get it to zoom in how far I need it to on the reference photo?

[Rob_Cullen]

I believe the Reference photo zoom is set to 100% and nothing changes that (not that I can see!).

When editing for detail and sharpening 100% is always the favoured zoom level.