Perspective Control – What’s It All About Then?
Perspective is determined by the position of the camera in relation to the subject and isn’t directly related to the focal length of the lens (although this does, of course, dictate the angle-of-view). However, when shooting a large subject – such as a building, for example – often a wide-angle lens is used to get it all in the frame and, inevitably, the camera is angled up (or, if it’s a long building, angled to the right or left). This means that the focal plane (i.e. the plane at which the imaging sensor or film is located) is no longer parallel to the subject plane and so, due to the variation in subject distance, the subject’s shape is distorted. This is where the shift adjustment comes in. It allows for the optical centre of the lens – and, obviously, its whole imaging circle – to be moved in relation to the centre of the sensor (or film frame) which alters which part of the scene or subject will be recorded. In the example of the tall building, shifting the lens upwards allows for more of it to be included in the frame without having to angle the camera backwards.
With the light rays from the subject all travelling exactly the same distance to the focal plane from the lens, there’s no distortion.
Additionally, all of the subject will be in focus even when using a comparatively large aperture setting. What’s at work here is something called the Scheimpflug Rule and it requires that the subject plane, lens plane and focal plane must all intersect at a common point in order to ensure the greatest possible subject sharpness.
How does this work when all three of these planes are absolutely parallel as in the above example? Simple. This common point then occurs at infinity.
However, the Scheimpflug Rule can also be met when the subject plane isn’t parallel to the focal plane… which is what happens when the lens is tilted or swung. Then the plane of focus – and its associated depth-of-field – will become more closely aligned with an angled subject plane, thereby enabling sharp focus to be obtained front-to-back, even with a large aperture. If you think of the plane of sharpness as a piece of paper that, when held vertically, represents next-to-no depth-of-field (i.e. just the thickness of the sheet), but when it’s laid down over the subject – which is the effect of the tilt adjustment – then everything covered by it, from front to rear, will now be sharply rendered… which, in visual terms, represents great depth-of-field even at, say, f4.0 or even f2.8.
Importantly, a tilt/swing adjustment doesn’t change the shape of the subject as there’s no displacement of the optical axis involved. The big advantage, of course, is that an extended depthof-field can be obtained when still using large apertures which has real benefits in terms of shooting in lower light levels. If you apply a tilt or swing away from the subject plane, the effect will be to greatly reduce the zone of sharp focus with a rapid fall-off on either side so the visual appearance is similar to that of the ‘Miniature’ digital special effect (and different from a shallow depth-of-field). or swings horizontally, and either lateral shifts (i.e. left or right) or horizontal shifts (i.e. up or down which, in view camera terms, was called the rise or fall). And, as just noted, these can be done independently… so, for example, you can correct for vertical convergence and maximise depth-of-field at the same time.
Super smooth microdrives perform the tilt/swing and shift adjustments; the former through a range of +/-7.5 degrees and the latter over +/-12 mm. These may look like pretty small adjustments, but in lens movement terms they actually represent a considerable amount of correction. There’s a switch to lock the tilt/swing mechanism at its zero position and locking knob to hold it at any other setting. A pair of levers facilitate the rotations – either the tilt/ swing mechanism separately or the whole lot, moving around the lens mount. The former rotates though 90 degrees to the left with a click-stop at 45 degrees while the latter rotates though 90 degrees either left or right with click stops at 30-degree intervals. Being able to rotate the lens around its mount also allows the vertically-orientated adjustments to be applied when the camera is still held horizontally or, naturally, vice versa.
In The Field
For technical reasons, it’s not possible to have autofocusing with a tilt/shift lens and, for a long time, only stop-down metering was possible for manual exposure control. However, Nikon’s electromagnetically controlled diaphragm allows for full open-aperture metering – so the viewfinder image is always at its brightest – and auto aperture control means that any
“There’s a fairly steep learning curve associated with using the PC Nikkor 19mm, but it really doesn’t take too long to get the hang of it.”
exposure mode can be used, including program.
As aperture setting (and control) is from the camera body, there’s a long list of older Nikon SLRs (both digital and film) which can’t support this lens. In fact, full and unrestricted compatibility extends to the D3, D4 and D5 pro-level full-35mm D-SLRs; the D810, the Df and the D500. To quote Nikon, “With other cameras, some combinations of shift and rotation may not be available due to the lens contacting the camera body”.
The adjustment gear housings add some bulk and weight, plus the various controls sprouting from the barrel can look at bit daunting at first, but the most alarming visual aspect of the PC 19mm is the huge exposed dome of the front element. The bespoke bayonet-fit lens cap is shaped like a dessert dish – and is just as big – so there’s a lot of very valuable polished glass on show when it comes off.
Be very, very careful when shooting and get into the habit of replacing the cap immediately you’re finished, otherwise it could all end in tears. The fluorine anti-grime coating needs to work overtime here.
The PC 19mm’s optical construction comprises 17 elements in 13 groups, including two aspherical types for correcting distortion and three made from extra-low dispersion (ED) glass for minimising chromatic aberrations. Nikon’s advanced ‘Nano Crystal Coat’ anti-reflection multi-coatings is applied to help reduce ghosting and flare. The minimum focusing distance is 25 cm and the diaphragm has nine blades to give smoother out-of-focus effects.
At 885 grams it’s a comparatively heavy lens for a prime wide-angle and, although the shape looks awkward, in practice the PC 19mm handles surprisingly comfortably and feels very well balanced, especially on Nikon’s bigger full-35mm D-SLRs. It’s also not nearly as difficult to use as you might first expect either, especially when you see through the viewfinder exactly what each adjustment is actually doing visually. The extra control – especially over sharpness – quickly becomes addictive. Now that depth-of-field isn’t harnessed to the aperture setting, there’s much more freedom as far as exposure control is concerned so, for example, you can use larger apertures in situations where the only option otherwise would have been to use a higher ISO setting, thereby increasing noise with its attendant implications for image quality. Or you can maintain a faster shutter speed, maintaining hand-held shooting in a situation which would otherwise have required using a tripod. Additionally, being able to use larger apertures without reducing depth-of-field avoids the diffraction issues associated with apertures smaller than f11 which actually reduce sharpness.
Of course, the 19mm focal length has inherently loads of depth-of-field, but you can really exploit it with a tilt adjustment when you want everything in the shot – from just in front of the camera out to infinity – to be pinsharp… as might be the case with a vertically-orientated landscape shot where there’s a much going on in the foreground as in the far distance. Then there is the creative potential if you choose to deliberately reduce the depthof-field if you apply a tilt or swing away from the subject plane, so the divergence with the plane of focus is increased. The sharpness
fall-off becomes quite pronounced and you end up with a visual appearance similar to that created by the ‘Miniature’ digital special effect that’s available on many D-SLRs or mirrorless cameras.
Performance
A critical requirement for a perspective control lens is that it has a big enough image circle to ensure optical performance is maintained across the frame even with the largest shifts. This is actually very evident with the PC Nikkor 19mm as there’s absolutely no brightness fall-off even with the maximum displacement applied at f4.0. However, as with any widerangle PC lens, there is a limit to some combinations of a tilt or swing along with a shift before some slight shading appears in one or other corner. For example, an extreme right swing combined with an extreme left shift… although, in practice, this isn’t something you’re likely to do anyway. As many of the applications for this lens are highly technical, the demands on the optical performance are considerable, but the PC 19mm delivers. Thanks to the larger image circle, the centre-to-corner uniformity of sharpness is very good even at f4.0 when the lens is centred, but truly excellent at f5.6 and beyond. As it happens, there’s minimal loss of sharpness due to diffraction at f11 or f16, but it becomes more evident at f22 and f32. There’s a very slight loss of sharpness in the corners at the extremes of the shifts, but it’s minimised in the aperture range of f5.6 to f11. Small tilts or shifts don’t affect either the overall sharpness or brightness. The PC 19mm is exceptionally well corrected for distortion with just a hint of barrel-type bending at the frame’s edge when the lens is centred. Ghosting and flare are reasonably well suppressed, but given that huge expanse of curved front element, they’re unavoidable at times. Chromatic aberrations are well controlled even when the lens is shifted. The typically ‘punchy’ Nikkor contrast characteristics enhance definition, complementing the 19mm’s exceptional resolving power which results in crisply rendered fine details and textures. Nikkor 19mm, but it really doesn’t take too long to get the hang of it and then it just becomes a case of experimenting with exactly how much tilt/swing and/or shift is needed to optimise sharpness and correct for convergence. You’ll generally find a little goes a long way.
Obviously too, this is a lens primarily designed for professional applications, but it’s also a huge amount of fun to use and its usefulness for landscape photography, in particular, is undeniable. From an amateur’s perspective (no pun intended), the PC 19mm is an expensive lens, but for anybody in the pursuit of technical excellence – achieved in-camera – it’s arguably a justifiable investment. Minimising the need for any post-camera corrections is a definite time-saver and also preserves the integrity of an image file.
Additionally, the 19mm focal length is extremely versatile – and not just for landscapes – and the optical performance is supreme in all departments… so any costbenefit analysis would have a positive outcome.