From my testing it seems that rendercam.zoom(x) continuously zooms on each update pass into infinity, the value passed in.
Not like “zoom up until x and stay there even if called again with that same value”. So a zoom(1) for example, in update, would zoom out forever. It then becomes trickier to interpolate and do math stuff to get a nice easing.
Or I could do an animation with go.PLAYBACK_ONCE_PINGPONG from 0 to -1 to 0 to zoom in a bit, but then it’d be a lot of trial and error to figure out the exact second length for that animation to end up at my desired zoom level.
I wish the zoom worked more like a “zoom to this value” than a continuous zoom.
Or a new function, zoomTo 
Edit: aaaaand that’s what I have set_ortho_scale for, which I was already using in my player explosion. Once again, I have scientifically proven that working late lowers perceptiveness 