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Filed under: 3D •Motion Graphics •Post Production •Visual Effects •

Camera Control, Part 2: Graph Editor & Dolly Rigs

In the previous column, we discussed a handful of tricks and techniques which can be used in different situations to make it easier to animate the 3D camera in After Effects, including one node cameras, two node cameras, auto-orientation, and building a special orbiting camera rig using parenting and null objects. In this column we’ll show how to build a “dolly” rig for the camera in older versions of After Effects as well as the new version 7.0, plus give a quick introduction to the new Graph Editor also introduced in After Effects 7.0.

Dolly Rig

One of the complaints that professional users have had about cameras in After Effects through 6.5 is that you have to keyframe the X, Y, and Z Position values all at the same time. This makes it harder to craft some common camera moves, such as traveling forward with a constant speed in the Z dimension while performing more acrobatic moves up and down in the Y dimension (imagine a camera being pushed forward on a track, as a crane raises and lowers it): You wish you could have linear keyframe interpolation on the Z value, while easing into and out of Y value keyframes.

To more easily achieve this, you need to break up the position values of the camera into parameters you can animate independently. There are two ways to do this. One is to create a series of Null Objects - each dedicated to one dimension - and set up a parenting chain where they are all connected together with the camera at the end of the chain. Another is to attach the camera to a single Null Object, and control each parameter of the null’s Position using Expression Controls. We’ll demonstrate the latter, as ultimately it is easier to control due to having fewer layers to manage. A .zip archive of our AE 6.5 (and later) project is available by clicking here.

In a composition inside After Effects, create a Layer > New > Null Object, and enable its 3D Layer switch. Note its Position; it will default to the middle of the composition, such as 360,243,0 for an NTSC D1 comp. Then create a Layer > New > Camera, and set its Layer > Transform > Auto-Orient to Off to make it a one node camera. Set its Position to the same value as the null object. Then reveal the Parent column in the Timeline window, and set the parent of the camera to be the null object.

Select the null, and apply Effect > Expression Controls > Slider Control. The Effect Controls window will open; in it, select the effect’s name Slider Control, hit return, rename it something that makes more sense (such as X Pos), and hit return again (this process is shown at the right). Duplicate this Slider Control, and give the duplicate the name Y Pos. Duplicate it one more time, and give this third slider the name Z Pos.

Back in the Timeline window, with the null object still selected, type P to reveal its Position. Option+click on Mac (Alt+click on Windows) on the stopwatch icon next to the word Position in the Timeline window to enable expressions; the expression will default to the word position (meaning the null’s Position is expressed to equal itself). With the expression text selected, type [ (left square bracket) and drag the pick whip tool (the curled-up icon) to the Slider value for X Pos. Then type a comma, and drag the pick whip to the Slider value for Y Pos. Type another comma, drag the pick whip to the Slider value for Y Pos (see the figure below).

Express the null’s Position property to follow your three sliders by using the pick whip tool. Start and end the expression with square brackets; type comma between pick whipping to the three slider values.

Finally, type a ] and click elsewhere in the window. Your expression text should now look like:

[effect(“X Pos”)(“Slider”), effect(“Y Pos”)(“Slider”), effect(“Z Pos”)(“Slider”)]

As Slider Controls default to a value of zero, the camera will now be in the center of the comp. Scrub (click and drag) the Slider values for each dimension to move the camera; keyframe them to animate the camera. To rotate the camera, you can use the Orientation and Rotation parameters of either the null or the camera itself. Note you can still open the Auto-Orientation dialog for the Null Object and set it to Orient Along Path, causing the null/camera combination to automatically rotate so that it is always aimed at a tangent to the path.

To see the null’s path in the Comp window, click on the Show Post-Expression Graph icon (the one to the left of the pick whip) for the null’s Position property. The drawback to this technique is that you will no longer have Bezier handles in the Comp window to tweak the camera’s path; you will need to do all of this with keyframe interpolations. To access those, in After Effects 6.5 or earlier, twirl down the arrow in the Timeline next to Slider for each of the null’s controllers to gain access to the Value and Velocity graphs.

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