Nikon has announced a new PC convenience 19mm F4E ED tilt-shift lens (which the company calls ‘Perspective Control.’)
When I received the email notice from Nikon prior to it’s release, I knew this lens would be an indispensable tool for photographing architectural interiors and exteriors. I have been using Nikon’s 24 mm perspective control lens for about a year and prior to that I simply used my 17 – 35 mm wide angle zoom for architectural photography.

Nikon’s brand new 19mm Perspective Control lens for DSLR.
Most of my professional history has been as a studio photographer. Using 4×5 sheet film was the standard and the workhorse camera was a Sinar 4×5 large format view camera. When the digital revolution arrived in the late 1990’s, I was using that camera less and less. I didn’t realize how much I missed the features of a view camera until I purchased, and began using the 24 mm tilt shift lens for my Nikon D800 DSLR a year ago. With limitations, perspective control lenses for full frame DSLR cameras are the closest one can get to using a 4 x 5 view camera.
In my opinion, the greatest advantage in my perspective control lenses is being able to control what is in view. With a normal wide angle lens, zeroed out to level horizontal and vertical orientations, the frame usually does not contain a pleasing, or needed amount of subject matter in the upper portions of the frame.

Virtual horizon is level.

Camera is level, looking into the scene.
…and this view is captured.

Missing top of frame.
As you can see, all lines ( vertical and horizontal) are straight however we are missing the top of the roof!
One solution is to aim the camera up, negating our vertical and horizontal rules for perfect lines…

Breaking the perspective capture rules behind the camera.

Perspective is wacked out in order to get roof in the shot.
This is what I get:

Roof is now in but proper perspective lines are gone.
The perspective lines ( vertical ) can be digitally fixed in Photoshop however, as a professional, I try to get it right in camera and rely on Photoshop for as little as necessary. One note about fixing the perspective in Photoshop: a crop will be necessary in the final edit at the top so when shooting with a normal zoom, with the camera aimed up to get it all in, make sure to back off on the scene as not to loose the subject matter in that final crop if left or right must be in the final view.

Perspective fixed in Photoshop. (Notice the necessary cropping when done in post production)
Now, when shooting the same view with my 19 mm tilt shift lens, I do the same leveling (vertical and horizontal) in camera, looking directly into my subject.

Shot with 19 mm perspective control lens.
Nothing is cropped out from image. To get entire roof in shot, with camera leveled out vertically and horizontally, I simply shift the lens down with the shift knob on the lens. the lens will shift down, (just like that great Sinar 4 x 5 view camera) keeping all perspective lines straight.
Having a super wide angle perspective control lens available to me for architectural shooting, allows me to decide how much I want in the scene. With just a 24 mm PC lens, I was limited. Sometimes, the 19 mm, however, is too wide. I find that for exteriors, that is true more often than not.
A simple example of the tilt feature is illustrated in the next few images. The tilt can correct keystone-ing in camera.

Shot with normal 19 mm lens.

Shot with 19 mm using tilt feature to correct perspective.
As I mentioned before, perspective can be fixed in post production but with a cost, usually in cropping. I love using these PC lenses out in the field. For me, it brings me back to the basics of photography with the knowledge that when I upload my images to prepare them as finals, they will start out being the best they can be right out of the camera.
Theses PC lens have other capabilities, such as focus control while shooting at an open f stop or creative possibilities like capturing a scene that appears to be a miniature diorama, done by tilting the lens and controlling the focal plane. The hefty investment for these tools is justified by how much one would use it. It would not be a lens used to photograph your kids in action at the pool over the summer vacation. Have I mentioned that the all the PC lenses are manual focus? Enough said.