Re: Having trouble capturing my zoom...

What you were viewing in your viewfinder is called underscan.

It is what the image would look like on a CRT TV, where often about 10%+ of that image is lost from the edges on. The loss is less prevalent with moden screens, and especially with LCDs. Obviously when you capture it's all there. There is a switch to overscan on most viewfinders.

Now that this is out of the way, all you need to do is apply a garbage matte, in which case that extra stuff on the sides will disappear. It is not uncomon to actually shoot that way, especially if you need height but your screen isn't wide enough, it really is an easy fix in post.

Vince