Saturday, April 9, 2011

Tilt/Shift Lenses

Canon 24mm t/s - f3.5 - 1/1250 - 400 ISO
      A long time ago, before digital…even before roll film, all cameras tilted and shifted and correcting perspective was as important as focussing or selecting aperture and shutter speed.

     Then along came the newfangled "box" cameras (as opposed to bellows cameras) and with the rise of their popularity, the accessibilty to tilt and shift declined.

     Many of the optical tricks these lenses permit would be difficult and more time consuming to recreate digitally, as well as requiring a sacrifice in resolution and quality—making tilt/shift lenses indispensable for certain landscape, architectural and product photography.
     By shifting a lens we can influence the convergence of parallel lines…straightening their apparent perspective.
Original  -  Canon 24mm t/s - f3.5 - 1/500 - 400 ISO  -  Shifted
     Another classic example is landscapes. You have flowers at your feet and mountain at infinity. f/22 won't give you the depth of field you need (at least without sacrificing sharpness). There's not much light (sunset/sunrise/overcast), and wind moving the flowers so a long exposure won't work. Fast shutter speeds dictate a larger aperture, which means shallow depth-of-field... normally.
     However, by tilting the lens, we tilt the focus plane. Tilting the lens towards the inclined subject, it starts to come further into focus, all without touching the aperture. This makes it possible to shoot images with an effective increase in depth of field, even with the lens set wide open. As the shutter speeds are higher at wider apertures, it becomes possible to shoot hand held
     Eventually the flowers, are as perfectly focused as the distant mountains.
     Tilt can also be used to reduce apparent depth of field, This can be particularly useful for portraits when a wide aperture is insufficient to create the desired effect, or when one wishes to focus on only part of a vertical object. By tilting the lens away from the subject plane, the top and bottom of the image are pushed selectively out of focus no matter where the lens is pointed, even if focussed at infinity.

     The more tilt that you give the lens, the more the extreme the effect becomes. At infinity, this can create a miniaturizing effect on the world, especially when images are taken from above or at a distance. People turn into models, cars and trucks become toys and the city starts to look like a train set.

Canon 24mm t/s - f3.5 - 1/100 - 400 ISO
     The key is to optimally place not only the focus plane, but also its wedge-shaped depth of field.
     For macrophotography, the ability to selectively focus at wider apertures gives us better control of the subject and background. If two flowers are at different heights, the lens can be tilt/shifted to bring everything into focus at wider apertures. With a conventional macro lens the only option would be to stop the lens down as far as possible. This means slower shutter speeds, lens diffraction and the risk of movement blur. With a tilt/shift lens distracting elements will remain out of focus at wider apertures, unlike the conventional macro approach which will reveal far too much background detail with smaller apertures. Many close-up photographers use this approach to photograph jewellery or small products, as sharpness can be placed where it is needed.

f27 - 1/3 - 200 ISO -  Nikon 85mm t/s  - f3.5 - 1/18 - 200 ISO
     Tilt/shift lenses are used in multi-shot panoramas. This technique has the advantage of not moving the optical center of the camera lens, negating having to use a panoramic head to prevent parallax error. The stitching process is straightforward, as each photograph does not have to be corrected for perspective and lens distortion, and lens vignetting will not be uneven between images. There will be some overlap to help you assemble the final image, but the overlap can be minimized by using a tele-converter.

Canon 24mm t/s - f3.5 - 1/1250 - 400 ISO
     A tele-converter on a tilt/shift lens will increase the amount of shift (for example on the Canon 24mm tilt/shift a 1.4x tele will extend the shift from 11mm to 15.4...a 2x to 22mm).
     Normally, when photographing a mirror head on, you will be in the shot, and by moving to the side, the mirror turns into a parallelogram. With a shift lens we can move the camera to the side and play with the movements until we get the original composition back - minus our reflection.
     Even when unshifted, T/S lenses will typically have better image quality at the edges of the frame—similar to using full frame 35 mm lenses on cameras with a crop potentially less softness, vignetting, and distortion.


Kurt Knock Photography said...

Great tips! Thanks for posting!

Kurt Knock Photography said...
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