19.2 THE LENS

The Lens is perhaps the single most important tool in the architectural photographer’s camera kit. This post will expand on some of the lessons that I can share for the benefit of architectural photography in the digital realm.

I always like to be reminded:

“Architectural Photography does require some specialized equipment but the art of photography primarily depends upon the artistic ability and skill of the photographer. Excellent tools are just that – they allow the artist to deliver even more excellent images. But make no mistake there is no substitute for the creative eye of the artist”.

While much of what can be gained from this post applies to the small format [35mm], time and space require that I sharpen my focus solely on lenses for medium format digital cameras. The subject of lens design is exhaustive so I will have to confine this post to what I consider to be key issues for architectural photography. We will have to leave the discussion of the full range of lenses including zooms and telephotos to another post in the future.

The digital realm demands higher resolution lenses than what we have been accustomed to during the film years. The change from film to digital altered the demands on modern lens design. The lenses designed for film were inadequate for use with high-resolution large sensors.  Lens design is dependent upon the size of sensor and this is another reason for the use of the integrated camera-lens as a closed system. Digital backs of 50-60 megapixels with 6-micron sensors require lenses of 60 – 80 lp/mm while medium format film would be happy with only 30 – 40 lp/mm. The additional glass to meet the resolution required for medium format sensors [particularly wide angle lenses] result in heavy and expensive lenses. One of the interesting benefits of the digital realm is that software adjustments are now integrated into the lens design process resulting in smaller, lighter and more economical lenses while maintaining the specification for higher resolving power combined with distortion-free optics.

The Hasselblad digital range of camera systems use the Digital Auto Correction of DAC system to correct chromatic aberrations and the next version, DAC III, promises to also correct vignetting [light fall-off]. Distortion can be in the form of barrel, pincushion or moustache but Hasselblad’s Phocus software makes automatic corrections for the specific lens being used. The connectivity between the sensor and the lens has an important part to play in the design of the digital camera as a ‘closed system’. Finally it is important to be able to assess the quality of lenses for digital photography and this is best achieved by reviewing the Modular Transfer Function Charts that measure the contrast [and sharpness] from the centre to the edge of the lens. So much for an introduction to modern lens design – a full explanation can be found in an article entitled ‘The Evolution of Lenses’ by Michael J. Hussmann.

Architectural photography relies heavily on the use of wide angle and super wide-angle lenses to capture buildings and spaces and yet this is where distortion can be at its greatest. In order to control distortion the architectural photographer must keep the image plane [camera sensor] absolutely vertical.  A solid tripod and tripod head along with bubble levels becomes a necessity in order to make the necessary micro adjustments. Furthermore, with one-point perspective, it is essential to keep the image plane [camera sensor] absolutely parallel to the plane of the image [the face of the building or wall]. Actually this is more difficult than it sounds but with practice there are certain visual clues that help us using trial and error fine adjustments in the camera position. Without control of both of these perspective planes, distortion is likely to result in an unsatisfactory image, even though it is possible, though not ideal, to correct perspective and distortion in Photoshop.

Quite often the photographer is standing at ground level and tends to want to tilt the camera upwards to get the whole building in the composition. This is where the laws of perspective create a problem for the photographer as tilting the camera upwards produces very strange distortions that changes all the proportions and makes building look as though it is falling backwards. The need to control perspective eventually led to the development of the tilt and shift lens. The tilt shift lens is a special lens designed with a wider than normal image circle that allows the lens to shift while keeping the sensor vertical and thus capture the image of the entire building without distortion. Hasselblad offers the HTS1.5 tilt and shift adapter that allows the control of perspective while using standard lenses. The HTS adapter, with its crop factor of 1.4, can also be very usefully used with other lenses to expand the range of lenses in your camera kit.

Serious architectural photographers prefer to have full control over perspective and opt for using a digital back on a technical camera to gain maximum benefit from greater lens cover, tilt and lens shift. In this case the luxury of an automatically corrected lens distortion integrated into a closed digital camera system is sacrificed in favor of greater perspective control. This then makes it necessary for the architectural photographer to manually measure the color cast of the lens at the specific lighting conditions, aperture and shift movement in order to adjust the image. This process is known as Lens Correction Calibration [LCC] and involves placing a white opaque translucent card over the lens and making an exposure that is corrected depending on the digital system being used to process the images. With Hasselblad’s Phocus software the use of the Scene Calibration feature applies the LCC to the image that corrects the colorcast. Although distortion is minimal with medium format digital lenses made by Sneider and Rodenstock it is possible in Photoshop to apply algorithms for specific lenses using the ALPA Lens Corrector.

My Hasselblad kit consists of a H4D/50 MP camera, a HCD ƒ4.8/24 mm, HCD ƒ4.0/28 mm, HC ƒ2.2/100 mm, HC ƒ4/210mm and HC ƒ3.5-4.5/50-110 mm lenses. With my HTS 1.5 Tilt and Shift Adapter the Hasselblad range of lenses can then be expanded because of the crop factor of 1.4 resulting in additional focal lengths of 36mm, 42mm and 140mm. My Sinar arTec camera kit that I use with the Hasselblad 50 MP back consists of Rodenstock Sinaron lenses HR ƒ5.6/23 mm, HR ƒ4/32 mm and HR ƒ4/40 mm lenses all rated at 60 – 80 lp/mm.

The combination of these two compatible systems offers me the highest quality tools and flexibility as an architectural photographer.