As many if you know, I recently just got the new Nikon D810 full frame camera for my 21st birthday. This is all very exciting for me, and this camera is just amazing. I went from a Nikon 3100, to the 810. This camera's quality is such a BIG difference as you might expect. Here are some of the comparisons to show you how much better this camera is! The link below is going to show you more charts in case you are interested in this camera as well!
General
Model Number: 3100 D810
Camera Format: SLR Pro SLR
Currently Manufactured: No Yes
Retail Price : $699.95 $3299.95
Effective Megapixels: 14.2 36.3
Video Capture yes yes
Movie Resolution: 1920x1080 (24) 640x424 (24)1920x1080 (60p/50p/30p/25p/24p)
1280x720 (60p/50p)
Here is the link below to look into this camera a lot more if you are interested. Getting this camera was the best decision i have made in a really long time:)
http://cameradecision.com/compare/Nikon-D3100-vs-Nikon-D810