[Zubersoft]

If you haven't done so yet Harry777, I would recommend turning off high-quality zooming as mentioned earlier in this post. As far as the lag getting worse while zooming in, that seems to be related to the Win2D performance when drawing such a large image (as it's rendering the entire zoomed image, and not just the section shown on the screen). The more powerful the device (and if you've switched the battery mode to performance), the less lag you will see while zoomed in. I would recommend only zooming in about 80% of the maximum allowed to get better performance, as you'll definitely see more lag if you zoom in the max amount. I'm trying to look into ways to improve the performance while zoomed in (i.e. only drawing the section of the image that is zoomed in), but so far, none of the approaches I've tried have really provided much of a performance benefit, and they caused other bugs that would take a fair amount of effort to address. I'm considering clamping the maximum allowed zooming amount to something smaller, such as 250% instead of 300%, as users will still get the benefit of zooming, but will experience less lag. I'm not certain how many people really need 300% zoom, or if they are just zooming in the maximum amount and then annotating. 

Mike