Tilt and Shift lenses are special lenses for landscape and architecture photography. I’m e.g. using Canon TS-E 17mm f/4 L and Canon TS-E 24mm f/3.5 L II lenses. The T/S lenses allow adjusting the plane of focus quite freely. The plane of focus does not need to aligned with the sensor plane, you can set it even perpendicular to the sensor plane. This can be used e.g. to align the plane of focus with the ground level. This is a good tutorial about T/S lenses.
All T/S lenses are manual focus lenses, and if you use the tilt feature, the focusing (e.g. aligning focus plane with ground) can be tricky. There are some pre-calculated tables (link to pdf table) that tell you the needed tilt based on camera height and focal length. You can also focus the T/S lenses without any aids, just by iteratively adjusting the lens tilt and focus. But that can be time consuming.
Guillaume Sébire, a friend of mine, has made Tilt Calculator application to iPhone (link to iTunes) to determine the needed tilt. You input the focal length, camera height to the ground (or to be precise the hinge line distance, see the last image), and camera body tilt to the application (I’m not using focus distance input). Based on this information the application calculates the needed tilt and focus distance. It has even automatic body tilt measurement: you just align your iPhone to your camera body (e.g. put the iPhone against the LCD display), and application measures the body tilt automatically (see image below).
With the automatic body tilt measurement, the photographer needs just to estimate or measure first the camera height, input it and focal length to the application, and then set correct lens tilt and focus to the distance calculated by the application. Easy! The the exact camera height is not so critical above one meter, but below 50 cm, even 5 cm error makes a noticeable difference. The most difficult part is to focus to certain distance. Most lenses do not have proper distance scale, and even if they have a good scale, it is not so detailed that you could could focus e.g. to 3, 4, 5, or 6 meter distance. So in practice the only possibility is to find some target that you estimate to be e.g. 6 meters away, and focus (use AF or manually) to that distance.
I have tested this application only briefly, and my initial impression is that it works nicely 🙂 If you have some error in camera height estimate or in focus distance, you may need to adjust slightly lens tilt or focus. But it is still much easier than to start the iterative process from scratch. After I have used this application more extensively I will write more about my experiences.