FWIW @Angus ... whilst I don't particularly have a 'need' on my 1920x1080 15.6" ... I had a play with a Windows Magnifier (Docked Mode 200%- but you might like Full Screen) ... it worked very well (because the focus is always on your mouse pointer (customizable) - likely the part you wish to see the detail).
WinKey + '+' to activate.
... Or ... Leave it in Magnified Full Screen mode and use CTRL+ALT+SPACE to for quick refocus
CTRL+ALT+D to toggle to Docked
CTRL+ALT+F to toggle Full Screen
Familiarization with the Keyboard Shortcuts could actually make this a very effective tool.
(It even has some touchscreen zoom features).