More modern cameras tend to have brighter screens than older cameras, and DSLRs often have very bright screens that are not so easy to focus with, if you need manual focus, or at least that's true for Canon--I'm not sure about other brands. With the two Canon DSLRs I've owned, I've had focusing issues with the stock screen that were solved by installing an S screen. Another issue is that autofocus lenses aren't generally geared so well for precise manual focus, so it can often be easier to focus manually with a manual focus lens.