Separate 3D Window Aspect Ratio?

[snmavronis]

Is there a way to make the Separate 3D Window preview have a specific aspect ratio like 4:3 and 16:9, etc. for composing the rendering angle and view area? Right now I have to put a plastic ruler up to my display to approximate what I want. No biggie but it would be nice to have that option in the 3D view window.

[Keet]

Technically it should be possible but very few users will use it.

But there's an easier way than using the plastic ruler:
Place the separate 3D window over your 2D grid and use that grid to resize your 3D window. You can zoom to change the scale of the grid. Then move the 3D window to where you want it.
You'll probably get a closer approximation than with your ruler.

[Puybaret]

You could also display the photo creation tool and compare the image sizes when you change the ratio proposed in the Apply proportions drop-down list.

[snmavronis]

I mean in the lower 3D window when you show it in a separate window, to preview the exact shot edges before I render. I already am using 4:3 aspect ratio when I render my view.