Canvas Sizing

Sorry for coming up with another problem, but i’m really stuck here. I want to resize my Canvas without affect my image, something like just resize my view-port without the elements of my animation are affected. I looked at the documentation of Synfig about canvases and tried it myself without much luck, also tried with and without locks but stil the whole project resize and not just the viewport, i read what ‘Image Span’ is and tried also with ‘Image Area’ values (which i’m not sure what kind of units it use, not pixels for sure) and somethings seem changed but not as i expected, because the only thing that it does is ‘zooming’ the viewport, how can i just increase my vieport from 450x600 to 1200x 800 without the aspect radio being messed and the layers being resized too?

In my opinion from 450x600 to 1200x800 alters the aspect ratio whatever you do in any other parameter.
To keep the size of the objects in pixels you have to modify the span value:
450²+600²=a² ->a=750
1200²+800²=b² ->b=1442,22

Old span = 9,1788
New span = 9,1788*b/a=17,6504

Remember span=diagonal size

thanks, this will do the trick