To locate the maximum or native resolution for a projector, there are a few places this can be found. 

We highly recommend using the native resolution for LCD displays as this will provide the clearest possible image from the device.

Check the product page for your model on the Viewsonic website and you will see the native resolution displayed.

The user guide for will include and native resolution for your model as well as other resolution settings.

Display properties on Windows will display most settings that are available on the device as well as.