Tilting at Focus

Last week I wrote a bit about the reasons tilt-shift lenses were becoming more  popular in the DSLR world. This week I’d like to provide a simple example of using tilt in an image to increase effective depth-of-field, and offer a basic overview of how that’s done.

To demonstrate what a difference this can make, I ran a quick example with and without tilt using the older ::amazon(“B00009XVCD”,”Canon TS-E 24mm f/3.5L”)::. (To make the effect a little more apparent on these small screen samples I focused the image without tilt near the “near” lens cap. Of course, in that image I could have chosen to focus farther into the image–which would have blurred the near image somewhat to reduce the blurring in the far image, but both would have still been out of focus. Both images were taken at f/3.5 with a ::amazon(“B000V5LX00″,”Canon 1Ds Mark III.”)::

The second image has more of the table top (including the two lens caps) in focus. You might almost believe that I’d just stopped the  lens down, yet both images were taken at f/3.5. You can tell that the increased apparent depth of field wasn’t a result of a smaller aperture by looking to the left of the table, at the base of the cat tree visible there. Note that the base of the tree there is out of focus, despite the fact that it’s not really much farther from the camera as the far lens cap, and that the upper visible parts of the cat tree are increasingly in focus the higher you go. It’s not that we’ve really increased the depth-of-field, we’ve just moved the plane that it’s measured from.

The two near lens caps are pretty similarly in-focus, but the far lens cap? What a difference! Remember again that this is at f/3.5!

While it can take a bit of effort to get a perfect result from a tilt-shift lens, if you’re working with a Canon or Nikon DSLR with LiveView, it’s much easier than it used to be, using the following process. (This assumes you’re trying to focus along a plane below the camera.)

1. Select two areas of your image, one near, one far, that you’d like to be 100% in focus.
2. Activate the Live View mode of your camera.
3. Set your lens to its widest aperture.
4. Zero out the tilt adjustment on your lens.
5. Get a “rough focus” by adjusting the focus somewhere between the two settings needed to bring the near and far areas you’ve selected into focus. (This is sort of like guessing where you’d focus even if you weren’t going to tilt the lens. In general, you’ll want to be closer to the near side. Both the near and far areas you’ve selected will appear out of focus.
6. Adjust the tilt to bring both points into greater focus. This will be slow, as you’ll need to zoom into both the near and far areas repetitively.
7. Repeat adjusting the focus and the tilt until both are in critical focus.
8. Stop down and shoot. You’ll probably need to experiment at first to build intuition about how much you’ll need to stop down for different situations but even on perfectly flat subjects, even with perfect placement of the focus plane, you’ll probably want to stop down at least a little.

While not a quick process, it’s relatively straightforward, and can allow you to capture shots that aren’t easily achievable in any other way. In the next few weeks I hope to show you another trick or two these lenses are good for, stay tuned!