The PhotoScope helper reads your image library (it never modifies it itself) to send the information to PhotoScope on your iOS device. It sends: the lists of albums and projects; thumbnail images; suitably scaled images for the current magnification as you zoom into an image.
In principle this should allow you to view even very large images, limited only by the speed and memory of your computer, and not by the iOS device itself. PhotoScope has been tested with 70 and 80 megapixel images in this way, so you can view your medium format photos on your iPad in full detail!
When dealing with RAW images in Aperture or iPhoto PhotoScope relies on the preview JPG images which these programs generate. Aperture can be configured to generate preview images of unlimited size OR it can limit their size. If you want to be able to zoom in to full magnification and if you want to see all meta data you must configure Aperture not to limit Photo Preview size (in preferences).