download photos from tablet to mini iMac

Is this "tablet" an iPad? Then the best choice is to synchronize Photos with iCloud.

Set up iCloud Photos on all your devices - Apple Support

Otherwise, you would need to tell us more about exactly what you are trying to do and with what devices and OSs.

Two things to look at:

Sync photos between your Mac and iPhone, iPad, or iPod touch - Apple Support

Sync content between your Mac and iPhone, iPad, or iPod touch over Wi-Fi - Apple Support

Pay special attention to "Remove automatically synced photos from your device" This seems to get lots of people into trouble.

In fact, you're way better off using iCloud to sync Photos Libraries. We get lots of questions here about losing pictures and stuff like that from people messing up with manual syncing.