How would i make this?

I need to make this camera out of cardboard, i've already made everything except for the things on the front, how should i make the lens? It needs to be detailed.

Much like image that is shown, you would cut out round sections and assemble,
place clear plastic layer where glass is or if only with cardboard, paint green / gray, and add painted reflection highlights,

if you can use bristol board as card board, you could measure and fold, or roll as lens extension, paint flat black or use black cardboard, draw details and numbers, and assemble,

http://www.pinhole.cz/en/pinholecameras/dirkon_01.html
http://www.amazon.com/...B000XY2IKS

http://www.labtechindia.net/pinhole-camera-kit-205.html
http://www.northlight-images.co.uk/article_pages/Canon_1ds_pinhole.html.