Why does my screen saver "zoom" in on photos from my iPhoto? Can I stop it from doing this?

Some screen savers have settings options, but others are pretty static in their behaviors. You can see these options by going to the Desktop & Screen Saver system preferences, and then clicking the Screen Saver tab. In here, you will see a number of alternative picture-based screen savers you can try, some of which will not have zooming behaviors. If your current one does have some alternative settings, then you may see a button to adjust these underneath the preview to the right.

The only fix here is to find a third-party screen saver that supports the behavior you want. Apple has adjusted its screen saver options over the years, and the latest ones are what you see in the system preferences.

The only way to change these behaviors is to hack the screen savers. The effects descriptions and some of the behaviors have settings in this folder:

/System/Library/PrivateFrameworks/Slideshows.framework/Versions/A/Resources/Cont ent

There may be a way to modify one of those settings to prevent the zooming for the given set of screen savers (or at least one of them), but I would not recommend modifying these files arbitrarily as you might break something (or at least make sure you have a full and restorable backup you can access before doing so). There are a couple of known modifications to them that can adjust some behaviors, but image zooming isnt one I know of.

You've probably added the entire Pictures folder as source. Change to merely the iPhoto Library.

However, for many users, it seems as the latter is greyed out and doesn't allow itself to be added.

That, in turn, might be fixed by rebuildning the iPhoto database, etc. Hold down cmnd + opt when launching iPhoto.

Might add: I reverted from Mavericks to Snow Leopard and never succeeded in making the iPhoto Library visible as a choice. But as I also have an old version of Aperture, I simply imported the iPhoto library to that and selected that folder in the screen saver preference pane.

Why Apple won't people use the iPhoto Library, I haven't a clue.....