Working in 3D space gives you the ability to animate cameras, add lights, and even mimic the depth of field of real cameras. Along with all this power comes complexity and some gotchas. In this article we will look at 13 tips that will let you work smarter and not harder. Let's get started.

Tip 1 - Changing the Camera Preset to a lower or higher number changes the Angle of View

Create a new camera (Layer > New > Camera).

Doing this opens up a dialogue box. 50mm is the default camera. Changing the Camera Preset to a lower or higher number changes the Angle of View.

A smaller number a wider angle of view, a higher number a more narrow angle of view (these are often referred to as wide angle and telephoto lenses). If you originally select the 50mm and then change the preset later, the distance between your camera and the layers will change.

Here is a good reference on different focal lengths in traditional photography.

http://en.wikipedia.org/wiki/Focal_length#In_photography

Tip 2  - Enable 3D: When to enable, and when not to

When you click in the Enable 3D box, you add a Z position for the layer. A negative number will bring the layer closer to the camera, a positive number further away.  

A 2D layer will not interact with camera and lights. This technique is often used with background layers that you don't want to be effected by the camera/lights.

Tip 3 - In Active Camera View, the Unified Camera Tool actually changes your camera position

Click on the Unified Camera icon in the Tools panel. There are three other options for this tool. (Type C repeatedly to cycle through, or by using a three button mouse.)

You can read more on this here. 

When you  make a change in the Active Camera View (ex. you move the camera closer to the layers with the Track Z Camera Tool), you are actually changing the position of the camera.

Tip 4 - In Custom View, the Unified Camera Tool changes your view

Select the Custom View 1 from the 3D View Popup in the Composition Panel.

Using the Unified Camera Tool in this tool just changes your view, not the camera. This is useful for moving around your scene and looking at it from different angles.

Tip 5 - Using Auto-orient to have layers look at cameras or follow paths

Select the Layer in the Timeline Panel (Layer > Transform > Orient). The default is off, but you have the options of orient to path or camera.

Orient to camera keeps the layers turned toward the camera, so you don't see that they are actually flat layers. You also have similar options available for Cameras and Lights.

Tip 6 - Animate Nulls for complex camera moves and not the camera (CS 5.5 and later)

Creating complex camera moves can get messy if you do all the animation with the camera. It is common to create a Null and then animate the Null, with the camera following along. In CS 5.5 and on, creating a Null has been simplified.

Select the Camera in the Timeline panel and from the Menu (Layer > Camera > Create Orbit Null). This automatically creates a Null that becomes the Parent of the camera.

If you move or rotate the Null, the Camera follows, as it acts as a child of the Null.

Tip 7 - keep your camera/spot lights wireframe from disappearing when not selected

By Default Cameras & Spot Lights disappear when they aren't selected in the Timeline panel. In the Composition click the Tab pulldown at the top right and select View Options. Then choose ON from the Camera or Spotlight Wireframes pulldown menus.

Tip 8 - Use Draft 3D to improve performance

Selecting the Draft 3D switch in the Timeline turns off Lights, Shadows, and Depth of Field. This can speed up RAM previews, and is helpful when you just need to see the Animation. Remember to turn this back on to see Lights, Shadows, and Depth of Field.

Tip 9 - Quick way to make a camera look at a specific layer (CS 5.5 and later)

Select the Camera. Select the Camera Tool. Shift-Command-F will frame all the layers. (use the Camera Tool to finesse the framing).

Set a position and point of interest keyframe. Move your playhead then select the Camera and a layer you want to look at. F will move the camera to look at that specific layer.

Tip 10 - Enabling Depth of Field (DOF) for the Camera

When you create a Camera, you can enable 3D by selecting the Enable Depth of Field box.  To turn on DOF for an existing camera, select the Camera in the Timeline and the shortcut AA (tapping A twice) will reveal the Camera Options. Click on OFF in Depth of Field to turn it on.

Tip 11 - Quick way to have Depth of Field follow a layer (CS 5.5 and later)

You have an animation where the camera moves and you want a particular layer to always be in focus. Turn on DOF for the camera, then select the Camera and the Layer.

Layer > Camera > Link Focus Distance to Layer. After Effects creates an expression that does the math for you and keeps the layer in focus when you move the Camera or the Layer.

Tip 12 - Why are layers not casting shadows?

When you create a New Light (all except Ambient), you have the Option of Casting a Shadow in the New Light Dialogue box.

This alone will not cast a shadow though. Select the Layer AA (tapping A twice) will reveal the Material Options. Click on OFF in Casts Shadows to turn on shadows.

 Tip 13 - Adding Falloff to Lights (CS 5.5 and later)

By default Lights don't have Falloff. That means 3D layers are all evenly lit by the Light. If you want a more natural look with light falling off with distance, you have two choices.

Create a new Light: Layer > New > Light.

In the Light Settings under Falloff choose Smooth or Inverse Square Clamped. Smooth gives you the most flexibility with control over Radius & Falloff Distance. Inverse Square Clamped mimics real light falloff, in that if you double the distance the falloffs to 1/4 of the original power.

Hopefully these tips get you up and running quickly with 3D space in After Effects.