Have you ever taken a picture with parallel lines in it? Silly question! But how often were they still parallel when you printed the pictures or viewed them on your screen? We have become so used to seeing buildings that lean away from us, or worse, that slope in towards the middle of the photo from either side that the photo that has been composed to prevent that is really striking! It’s not just buildings. Trees and telegraph poles that want to fall over, window frames and walls that should be square but look like a trapeze, lettering that appears to have been squeezed together at the top...
There was a time when all cameras came fitted with bellows and moveable backs to correct these aberrations, and perspective was considered as important as focus and exposure. Then “speed” cameras and other “portable” cameras without rise and fall elements in the lens took over reportage and candid photography; and with the advent of the miniature (i.e. 35mm) camera and the popularity of amateur photography, distorted photos became so familiar that many people hardly recognise the distortion. Photographers forgot about perspective control. Or most did.
In time, 35mm camera and lens makers began to offer "perspective correction" lenses to ensure that lines which are vertical in reality look vertical on the image. Such lenses make all parallel lines (such as four horizontal edges of a cubic room) cross in one point.
You can easily correct distorted images in PaintShopPro, Adobe Photoshop, or other similar photo editing software. Why then consider a special lens?
Software won’t correct one element in the picture without changing the entire picture; what is more, in correcting the perspective, it will crop away some of the image. A Perspective Control (PC) lenses doesn’t have those problems, and tilt-shift lenses add even more control. What’s the difference between them?
A PC Shift lets you move the lens up and down relative to the focal plane. That corrects vertical distortion and walls stop leaning in. Tilt adds the ability to change the lens focal plane relative to the sensor. Combine them in one lens and you can do very clever things.
Have you ever needed to include a highly reflective surface (say, a mirror) in the shot, but didn’t want the camera in the scene? You can't stand in front of the mirror, because you will be in the shot, but if you move to the side, your composition changes and anyway, the sqaure frame turns into a parallelogram. With a tilt-and-shift lens mounted, you just move the camera to the side, turn the lens and focal plane parallel to the mirror, then use shift to include the mirror without the camera!
Working in a small room with, say, a pillar in the way? Set up the camera to the side and shift horizontally to re-frame your shot – Who says you can’t see round corners?!
What else can tilt-and-shift do for you? How about infinite depth of field? Normally, your plane of focus is a set distance from, and perpendicular to the axis of your lens. When you use lens tilt you can alter that plane quite significantly. The plane of the back element of the lens, the film plane, and the focus plane will all intersect, resulting in those wildflowers at your feet and the distant mountains being equally sharp.
If you prefer, you can make everything out of focus except for the subject, even if they are in the same plane: say there is a row of soldiers squarely in front of you, but you just want young Johnny in focus. Twist the tilt control right over, focus on Johnny, and his equally distant neighbours to the left and right will just be blurs.
The main professional use of shift and tilt lenses is to control where the centre line of the lens axis is, relative to the centre line of the film/sensor. When you shift the lens elements up, the image moves exactly the same distance down on the sensor. This means the foreground is now below the line of the image and your vantage point offers a bigger image minus the distracting foreground.
How far from your target do you need to be to get the desired shot without twisting the perspective depends on the height of the target above your eye level, and the lens' focal length.
For instance, if the height of the subject image is 12mm above the centre line and you shift up twice that(23mm is about the limit for 35mm format shift lenses) you can can get twice as close to our target or shoot a target twice as tall without tilting the camera and converging the verticals!
So why aren’t we all using these marvels? Because there are a few limitations to Tilt and Shift.
First off, shift lenses have an unnaturally wide field of view, which results in light falloff in the corners (vignetting). That same width of field gives problems with filters: they intrude into the corners of the shot. Smaller apertures fix the vignetting, but accentuate the filter visibility. An auxiliary filter holder instead of screw-on filters can help, but is not foolproof.
Second problem: there are no auto-focus shift lenses, not even the Canon TS-E lenses which have an auto-focus mount. Some shift lenses are even more primitive, and you have to stop down manually before shooting. In fact, Tilt and Shift lenses generally do not communicate with the electronics of the camera. You can possibly use aperture priority metering, but it is not reliable.
Next issue: they cost around three times as much as non-shift lenses of the same focal length: actually, they all cost about the same, no matter what focal length you choose (about $US1500). That high price is partly for the optics that make a larger, shift-able image, and the hardware on the lens that let you move the glass; and the low volume of production. And the lens will probably have a smaller maximum aperture than you'd expect for the focal length.
There are a couple of options you could consider if you want to try Shift-and-Tilt photography and not break the bank: some camera hire companies have them on their books; bellows makers like Novoflex make bellows that give your standard lenses tilt and shift flexibility (and macro, incidentally). They aren’t cheap, either, but they make all your lenses potentially Tilt and Shift and retain full electronic control of exposure, which even the most expensive specialty lenses do not. However, as bellows, they will reduce the amount of light reaching the sensor.
And finally, for under $100 you can buy a Lens Baby, a fun lens whose basic functionality is based on the principles of Tilt and Shift.
