2.35 screen questions

[cinemaphile]

So I'm getting my projector and doing a DIY screen. I'm just trying to figure out dimensions.

Ideally I would like to go for a 2.35:1 screen, to get the most out of my wider "scope" movies. But then, since I'm not adding an anamorphic lens to my projector, that means to fill the screen with the movie it'll be projecting black space above and below the screen, right? Is it possible to rig something up to put in front of the projector when I'm watching 2.35 to mask that part from projecting to the wall?

Also, when switching between projecting 1.85 or 2.35 content, is it as simple as adjusting the zoom on the projector, or would that compromise quality and so instead it would involve physcally moving the projector forward or backward? (maybe sliding track mount if this is necessary?)

I could always just do a standard 16:9 screen, but then my 2.35 movies will be much smaller.

Advice?