Andrew Macpherson

Using a Tilt Shift Lens, let’s re-design for photographers not the convenience of lens makers

by on Oct.22, 2013, under Equipment, Off the wall

In the beginning cameras with lenses (vs pinholes) were built round a laboratory optical bench, where the various elements could be relatively easily adjusted. This led to the “Stand” and “Field” plate cameras where he lens and the plate (sensor) could be moved relative to each other.

This arrangement had lots of freedom, but the basic arrangements were relatively easily split into what we now call Shift or Perspective Control, and Tilt where we take control of the “plane” of focus. I put “plane” in quotation marks because in the general case, where very clever lens designers have not been at work, that plane is actually the round inside of a ball, and we rely on depth of field and the effective radius of that ball to compensate.

Perspective adjustment (shift) works by setting the back of the camera flat on to whatever we want to look straight, and then moving the lens up, down and sideways relative to the back of the camera until the image appears in then right place on the sensor. Shift lets you take photos of mirrors apparently in the centre of your frame without showing the reflection of the camera, of a tall building with its sides vertical without having to hire a helicopter to get to that position half way up and so on. The usual issue with these shots is the vignetting of the further parts of the image — in effect only half the image will suffer, and in digital post production one stage will be to add temporary blank pixels (or a layer with the 180°opposite shift for symmetry) to the “near” side of the image so that the vignetting circle is around the midpoint, allowing standard lens correction tools to be used to cancel it out in post. With a Canon TS lens on a tripod one can simply rotate the lens to get the perfect 180° reverse shift to make sure the generated composite is the correct size.

Tilt is much harder to use. What tilt lets you do is play with your plane of focus, either reducing it to a narrow line across your frame, or bringing a large receding plane into focus, from foreground right to the furthest distance. This is where the mechanical design of he lens can make all the difference to how easy the lens is to use for the photographer.

The ideal Tilt lens will have a tripod mount ring, and the tilt’s axis or point of rotation will be across the sensor of the camera. This lets the photographer compose their shot, and use the most sensitive central focal sensor on their camera to get a sharp focus, then switch to using a peripheral focal sensor and rotate the camera body (remember we’ve clamped the lens to the tripod, leaving the camera body mobile) until that point too is in focus. The central point will have remained in focus because that’s at the centre of rotation. The composition too will remain almost unaltered.

My Canon TS lenses completely fail on the usability front. They rotate about the front of the camera body rather than the sensor, with no regard to the photographer who will have to try to use it, each movement of the tilt mechanism changes the composition and the focus. This fault is also there in Lensbabys, Samyang and all sorts of other lenses with tilt capability. The “Why?” Is fairly obvious: by having a short radius the lens designer gives themselves twice the angle for a given movement, and reduces the consequential vignetting but at a massive cost in ease of use.

I’m still searching for a lens manufacturer with the guts to trade “spec” figures for usability

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