Using Tilt Shift lenses can be confusing, especially figuring out the complex interactions between the tilt setting and the focus adjustment. This page sets out to give a simple how-to, along with an important tilt shift calculator that will tell you just how much you need to tilt the lens in a given situation. The best resource on the web for a more complete explanation, including lens shifting – and great set of videos – is Keith Cooper’s set of tilt-shift resources. Keith also just published a book on the topic.
Why It’s Confusing
The crux of the confusion comes when tilt-shift beginners assume that – after having made a tilt adjustment – that the focus ring will behave the way it did before. It doesn’t. Once the tilt setting is activated, the focus control does not move the focus plane back and forth relative to the camera, like it used to. Rather, it will now swing the focal plane around a hinge point that was set by a combination of your tilt setting and the direction in which it was titled.
In order to put the tilt setting in just the right spot, you’ll do the following:
- Rotate the lens using the rotation control (closest to the camera) so that when you set it to a tilt, it will tilt toward your desired focal plane.
- Then, you’ll want to estimate the distance between the middle of your lens and the closest point your desired focal plane comes to it. That is the Distance measurement you’ll put in the calculator below.
- Then, you just need put into the calculator the focal length of your tilt-shift lens, and press the Calculate button. That’ll give you your tilt setting.
- Apply that tilt setting by making the articulating lens bend toward your target focal plane.
- Move the focus ring to swing the focal plane around to match your desired location. Remember, the focus is no longer going to move the focal plane back and forth relative to the camera, but rather swing the focal plane around a hinge line that was determined by your distance estimate and the angle at which you rotated the lens.
- Realize you haven’t gotten it quite exactly set the way you wish, so fiddle it until it looks right.
The Tilt-Shift Calculator
Notes on Calculator: The calculator above works for any focal length lens, and for any distance, but of course there are some physical realities that limit these ranges in the real world. There are only so many tilt-shift lenses (although tilt-shift adapters are changing this), and – most importantly – these lenses can only tilt but so far.
We give the tilt degrees to two decimal places not because anyone is going to be able to set a tilt lens with that accuracy with current hardware, but because there may be future products that allow for digitally setting tilt.
The formula used for the calculator was created by taking actual measurements of critical focus with three tilt-shift lenses available to Camnostic (a trio of older Canon TS lenses, including the 24mm, 45mm and 90mm) and comparing that to multiple tables on the web. All of these data were then averaged and a set of fitting curves generated. An exponential curve formula was found to that function, and the coefficient discovered (1/17.4755) baked into the algorithm above.
Testing of the formula against table sources on the web failed to reveal any discrepancies between the calculated results or any of the tables of more than 1/20th of a degree.
The explanation of how to measure distance is necessarily fudged a bit. People don’t initially know at what tilt they will be (that’s why they’re using this calculator, after all), so they can’t directly measure the hinge distance, as that hinge location is determined by tilt itself. So we’re asking people to think about the closest distance (tangent) between the middle of their lens and the desired focal plane. This will be approximately correct at normal distances.