Every photographer welcomes the day a new lens arrives in the post. Just recently I had such a day. And do you know what, I was more excited than usual by this new lens. (I say new, it was second-hand but I’m more than happy to buy pre-used lenses from a reputable supplier. Let someone else pay full price is what I say.)
So, why was I excited? The lens is a wide-angle – 24mm to be precise – which is ideal for landscape photography. But then I’ve already got a 24mm lens so it wasn’t for that reason. The lens is manual focus only. That’s marginally exciting, but again it’s not why I ripped open the box as quickly as I could. No, the cause of my excitement was the fact that the lens is a tilt and shift lens. (PC-E in Nikon speak, or TS-E if Canon is your native language.)
A more, er….ordinary lens (after using a T/S lens other lenses do seem a bit ho-hum) has its focus plane – at the distance to which the lens is focused – parallel to the camera. Move the focus point, either using AF or manually, and this plane moves backwards and forwards relative to the camera. The focus plane determines what’s sharp in the photo, unfortunately for us photographers it’s razor thin. (An effect clearly seen when using a long lens with the aperture wide open. Trying to focus precisely on someone’s eye, for example, can be extremely tricky.) It’s only by stopping the aperture down – so increasing depth of field – that sharpness extends throughout the frame.)
The first party trick of a T/S lens – the tilt part – is the ability to change the angle of the front elements in the lens (tilting them in other words). This causes the focus plane to change angle too.
A T/S lens can be tilted one of two ways: up or down (or left or right if the tilt mechanism is set vertically). Tilt the lens up, the least useful/most fun direction, and focus plane tilts up too. This throws most of the scene out of focus, creating an effect often referred to as the ‘miniature model’ effect, when scenes look like model dioramas rather than full size. This is because macro shots often have minimal depth of field so we expect photos with this particular aesthetic to be close-ups. The only problem with using this particular effect is that it’s so easy replicate in software, or through a built-in camera effect, that it’s no longer novel.
Tilt the lens down, the most useful/least fun direction, and the focus plane tilts down. This is used to increase the apparent sharpness from the foreground through to the background, even when using a relatively large aperture. This means you can keep shutter speed reasonably high and, by not stopping down to the smallest of apertures, you can avoid problems like diffraction. However, there’s no such thing as a free lunch. Without taking care you can still find out-of-focus areas in your shot, it’s just that they’re generally in the middle-ground, not where you’d normally expect them.
Tilting the lens to maximise sharpness involves something known as the Scheimpflug Principle. According to Wikipedia the Scheimpflug Principle is ‘…the geometric rule that describes the orientation of the focus plane, the lens plane, and the image plane of an optical system (such as a camera) when the lens plane is not parallel to the image plane.’ Which isn’t that helpful practically speaking. You can use the Scheimpflug Principle to calculate the degree of tilt necessary to achieve the most useful focus plane – ie one that intersects the important elements in your shot. However, it’s far easier to do this by eye using the following sequence:
- Compose your shot, with the camera mounted on a tripod and with no tilt applied
- Set the required aperture (be daring and use a relatively small aperture such as f/5.6…)
- Decide which are the nearest and furthest elements in the shot
- Focus on the nearest element in the shot
- Tilt the lens down until the furthest element is sharp
- The nearest element will now be out of focus so refocus the lens until it’s sharp again
- Now the furthest element will be unsharp so tilt the lens up slightly until it’s sharp once more
- Repeat steps 4-7 until both the foreground and background elements are both sharp
Using tilt isn’t quick (at least when it’s done properly…) so it’s important to get to a location long before you need to make your photo. However, the end results will beat using a small aperture, or techniques like focus stacking, hands down. To speed up the process using focus peaking if your camera has this facility as it’s a very useful aid to see what’s sharp and what isn’t.
The second party trick is shift, in which you can move the front lens element up or down, or left or right. (T/S lenses generally have a lever that lets you change the orientation of shift to suit.) Shift is generally used when shooting architectural subjects. A T/S lens lets you keep the camera parallel to your subject, with the lens shifted (usually upwards) to keep the subject within the frame. Doing this avoids the odd visual effect of converging verticals, which is seen when a camera has been pointed upwards to fit the subject in. Converging verticals makes the vertical lines of a subject appear to converge as they are no longer parallel.
There are limitations to using shift. Shifting works because the image circle of a T/S lens is far larger than normal lenses. The shift mechanism lets you move the frame around this large image circle. However, at the extremes of shift you generally find image quality drops off, with vignetting becoming noticeable. Generally, you never use the last millimetre or so of shift unless you really, really have to.
Tilt/Shift lenses aren’t for everyone. They’re ideal for landscape and architectural photography, less so for subjects like portraits. However, if you think you need one and can afford it then go for it. You won’t regret it.
The featured image for this article (Tower Bridge, London) was captured by Jason Friend.