pin hole

I have a Nikon D90 new to all this Photography stuff dont get me wr- Ong, i am absolutely obing it. So basically what I am saying is i Need help to adjust the exposure So i can edit my pictures to be darker or lighter so please CAN someone help or guide me to takin tooknď

Is this possible? What I'm trying to do is create a pinhole camera that is portable and can produce a full-sized photograph, hopefully instantly all out in the field without going to a lab. I've researched ilfachrome, cibachrome, positive-positive photo enlargement paper. Are there any...