Sometimes it's hard to visualize composition without looking through a specific lens. But this new iPhone app shows you how hundreds of lenses will see your subject.

The app is called Mark II Artist's Viewfinder, and what it does is simulate frame lines in your iPhone's camera display by accessing a database of hundreds of camera and lens combinations. It's a pretty cool function, and it could come in handy if you're the type of photographer who likes to plan carefully ahead.

The app can record GPS coordinates and metadata about the frame lines you choose, so you can consult each perspective you see later on. But the biggest limitation is that since the iPhone's camera has around 30mm focal length depending on the model, it can't show you frame lines for lenses any wider than that unless you buy the wide-angle adapter the company sells separately.

That, and the price. It's $25, and that's a LOT for an app.