Quote Originally Posted by jfdupuis View Post
When you upscale from 4x5 to 8x10 for example, do you keep the same lens ? Are the covering of these lens are big enough to still allow movement amplitude. In fact, it goes back to a newbie question, is there different lens for each format ?
It is fairly easy to acquire a collection of lenses from 90mm and up that can be used on both 4x5 and 5x7. It is, almost, possible to do the same for 4x5 and 8x10 but shorter lenses than 200mm that cover 8x10 are usually expensive, somewhat rare and oftentimes quite heavy. But this is an extreme example.

You will find that several lenses of different focal length can be used on both 4x5 and 8x10, primarily when it comes to longer focal lengths.

I would follow the link Soeren provided above. After some reading you will be able to make a more informed decision on which lenses to get.