P.C. – Perspective Control

In this modern age with ‘people pictures’, ‘selfies’ & ‘social media etc. you may well imagine that the more traditional forms of photography such as objects or architectural images are now taking a back seat. Visit any exhibition however, and you will soon discover that this is far from the case, and although arguably less in number, both modern and historic buildings, castles, churches etc are still an ever popular subject to photographers. In normal picture taking, providing the camera is held level and steady, modern equipment can virtually guarantee an acceptable image time after time. However when photographing a subject such as a building, the situation is not always that straightforward.

Look at any tall building through a camera, and invariably you will need to point the camera upwards to get the whole building in the frame. Switching to a wider angle lens or moving further away from you subject would allow you greater scope in the composition, pointing the camera upwards would probably still be required. The first thing you notice in the resulting photograph are the converging verticals, with the building looking much narrower at the top than the bottom, the taller the structure the greater the amount of convergence. You don’t ‘see’ this when simply looking at the building as the human brain accommodates for this, it knows that the building isn’t leaning in, so what you ‘perceive’ is a normal upright building. This phenomenon was recognised from the earliest days of photography, when static objects such as buildings were often the subjects of choice, due primarily to the long exposure times due to the relatively low sensitivity of photographic emulsions at the time. Exposures could stretch to minutes, taking pictures of moving subjects was hence impossible.

It was soon discovered that by keeping the camera level but raising the lens upwards, but parallel to the camera body would correct for this distortion. Hence the introduction of what became known as a ‘rising or sliding front’, which became so popular a feature that all but the simplest cameras had this feature incorporated in their construction from the 1880’s. This remained the case up until the 1950’s, when with faster emulsions moving subjects could be captured and the architectural requirements were considered less important and rigid bodied fixed lens cameras became the standard model. Architectural photography do not go away, rather becoming the preserve of ‘large format’ cameras which featured not only rising front but also cross front, tilt and swing to both the lens and film planes, with the most sophisticated cameras having a vast array of movements to help undertake a broad range of photographic subjects.

By the early 1960’s and the popularity of 35mm SLR cameras, manufacturers soon realised that there was still a requirement for perspective control lenses with this smaller format. Hence the introduction in 1961 by Nikon of a P.C. shift lens. Canon went one better in 1973 by also incorporating tilt with the shift movements, and over the subsequent years other companies such as Olympus, Minolta, Pentax, Schneider etc. have all offered shift lenses – some also with a tilt feature. Up until the advent of digital cameras Perspective Control was the only way to photograph a tall structure on film without any distortion.

Perspective Control lenses for the 35mm format were produced in a range of focal lengths; they tended to be primarily in the 24mm to 35mm range, although focal lengths of up to 135mm are now being offered.

In this digital age, software such as Photoshop, Lightroom, DXO Viewpoint etc are available to help correct perspective errors, you may hence well wonder why would you spend money on P.C. lenses, when it can all be done in the computer? As with all things in photography, life is not that simple, and although software can and does do a reasonable job of correcting for perspective distortion, it does introduce its own optical anomalies, thus is still no match for a properly used P.C. lens that has been accurately set up.

Having used both methods of perspective control successfully I can certainly see positive and negative points for each choice, so let’s start with P.C. lenses. If optimal image quality is your ultimate goal then a P.C. lens is the way to go, with one or two reservations. Not least is the actual cost of such lenses, as due to both the high optical and construction quality coupled with limited sales of such specialist tools, the cost is quite high. Also, these lenses do take a little practice to get the very best out of them; accurate setting up is essential prior to taking the shot. The fact that they are all manual focus is almost irrelevant as they are not designed for quick point and shoot. One big advantage is the fact that these lenses can be used on your existing SLR system without any problems. Also worthy of note is that these lenses are capable of far more than simply correcting for converging verticals, rather offering the photographer a wide range of unique photographic possibilities.

As for the software route, if cost is a significant factor then the software route is a far more cost effective option, again with reservations. Depending on the amount of convergence in your image, the software has to stretch the images top corners outwards until the sides of your main subject are parallel, then re-cropped back to a rectangle, this stretching has the effect of redistributing the pixels hence the image’s resolution and quality will suffer. Once parallel, depending on what software is being used, the building itself may look foreshortened so will need to be stretched upwards to have a more natural look, again redistributing the pixels with subsequent image quality loss.

Traditionally, perspective correction could be done in Photoshop using first perspective adjustment followed by transform, however the lens correction features in Photoshop, Lightroom and DXO Viewpoint 3 now make this process a lot more straightforward. This correction of the converging verticals as well as compensating for the foreshortening effect  is to a large extent an automatic process, so manual adjustment is offered in all cases to help you achieve the exact desired effect. Irrespective of which software is used however, it is important to remember that pixels are still being redistributed with subsequent image loss, governed to a great extent on how extreme a correction was required.

It is also worth remembering that the converging of a building should not be classed as true distortion but more of an optical illusion, as your eyes and brain will know the expected correct position and shape of the converging building and will accommodate for this in a 3D environment, but less so on a 2D computer screen or print.  Once the convergence and foreshortening has been corrected for, some stretching upwards of the building may still be required, and one quick way to ascertain the amount of stretching is to look at the uncorrected image, selecting something like a window and remembering its height to width ratio. When stretching the building upwards try and get the same window to roughly the same ratio, after all in most cases providing the final result is visually pleasing, your work is done.

All taken on a Canon 5DsR and TS-E 17mm lens, f8, ISO 100, RAW. All the interior shots were taken from exactly the same spot.

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(above) De-Montfort University – Leicester. 9mm upwards shift on lens.

De-Montfort University

(above) De-Montfort University – Leicester. 9mm upwards shift on lens. This is made up of 2 vertically taken shots, then stitched together in Lightroom.

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(above) St Mary de Castro Church – Leicester. 10mm upwards shift on lens.

St Mary de Castro

(above) St Mary de Castro Church – Leicester. 8mm upwards shift on lens.

St Mary de Castro Window1

(above) Camera pointing parallel to the wall and ‘0’ shift on lens.

St Mary de Castro Window2

(above) Camera pointing parallel to the wall with lens shifted upwards 9mm to frame the whole window.

St Mary de Castro Window3

(above) Camera pointing upwards to frame window and ‘0’ shift on lens.

St Mary de Castro Window4

(above) Image corrected in DXO Viewpoint 3 prior to cropping. The extra cropping at the top and bottom is required due to the camera being slightly off square when the upwards shot was taken, but easily corrected with the L/R perspective shift slider.

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(above) An early folding pocket camera from the 1930’s showing the lens in both the standard and raised positions.

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Setting up outside St Mary de Castro church. Canon 5DsR and TS-E 17mm lens, set on ‘0’ shift.

 

 

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