Not every picture is the same and each picture is made different by the type of picture it is, that is full length, portrait and so on. To be able to take good portrait pictures there is a certain type of lens that you have to use to get the image right. In the paragraphs that follow I will talk about some points to consider when shooting a portrait picture.
The type of lens that you choose will also depend on the environment at that particular time that is light conditions, wind etc. You need think about the focal length. Why this is a consideration is because it is dependant upon the film size. So you would find that in taking a portrait using a 35mm camera you would use a 105mm lens, a 80mm camera you would need a 160 mm lens. You can see then how the size of the film has an effect on the lens that you choose and the eventual picture that you take.
If you are unsure as to how to make these adjustments in focal length, size of lens and film you can always ask around from fellow photographers who understand the concept better . Sometimes having a practical experience provides a better explanation than theory.
The view of a picture is dependant on how near you are to the subject and not the size of the lens. What I am saying is the view of a picture will remain the same even if you change the size of the lens. What will be different is the number of things that will appear in each image that is the scope. Of course assuming everything else remains constant and only the focal length changes.
As I mentioned previously the one way you can grasp this concept of focal length and size of lens is if you experiment with taking various pictures and see the effect.Check out any of the following for good DSlR cameras and lenses that you can use: