How to connect nikon d800 camera to iMac via hdmi lead

Hi,

Thanks for looking.

I have two iMacs, 2010 & 2012 (slim version).

I would like to connect my Nikon D800 camera which as a HDMI out into my iMac. I want to do this so I can view live video (makes focus easier than using the camera's in-built small screen).

It is possible to link to a TV with HDMI input: https://m.youtube.com/watch?v=8gmwRBJSERM

Any ideas which adaptor I need, can I use the Thunderbolt?

If anyone knows how to link to a iPad (2) to view live video that would also be helpful.

Thanks !

Kevin