Depth of Field Control Using Two Nulls

reference materialDepth of Field Control Using Two Nulls

April 28th, 2004

Introduction;

This tutorial will show you how to easily set up and control depth of field for your LightWave scenes using parented null objects, the Depth-Of-Field custom object, and the Channel Follower modifier.

Depth of field is defined by two values: Focal Distance and Lens F-Stop. Focal Distance defines the distance away from the camera that will be in focus, and Lens F-Stop defines how far in front of and behind the Focal Distance the area of focus will extend. Larger Lens F-Stop values increase the depth of field, allowing many objects to be in focus. This is called "deep focus". Smaller Lens F-Stop values decrease the depth of field, thus restricing the area that will be in focus. This is called "shallow focus".

By default, the Focal Distance and Lens F-Stop settings are controlled through the Camera Properties panel or the Graph Editor in Layout; however, it is possible to control the depth of field settings using some of the many tools and modifiers that are included with LightWave 7.5

It is entirely possible to use depth of field without also using the technique described below, but the "parented nulls" technique allows the depth of field settings to be directly animated through the Timeline rather than forcing the user (you) to go through the Graph Editor.

Before you begin:

This technique uses null objects that are parented to the camera to control depth-of-field settings. The null objects must be properly aligned to the camera's coordinates, or else the display and control settings will not work. In order for the null's initial position and alignment to be set correctly when parented to the camera, Parent in Place must be turned off in the General Options panel ("o").

The Grid Size value in the Display Options panel ("d") needs to be adusted to properly fit the objects in your scene file. If your Grid Size is set too large, your cameras, lights, and nulls will appear to be much larger than your objects and it will be very hard to make small adjustments to object positions. If your Grid Size is too small, your camera, lights, and nulls will be very hard to see and you will have to move the mouse more to make small adjustments. Layout automatically sets the grid size when you load objects into a scene; if you add a very large object (such as a ground plane), Layout will set the Grid Size to a very high value, which will make it harder for you to select and manipulate the objects in your scene. The optimal Grid Size value depends on the scale of your objects; ideally, the camera and Nulls should be easily visible but not too large.

Enabling depth of field for a camera:

Before we can set up nulls to control our depth of field settings, first we need to enable depth of field. The Focal Distance and Lens F-Stop settings are not accessible until depth of field is enabled in the Camera Properties panel ("p").

Open the Camera Properties panel ("p") for the camera to which you would like to add depth of field.
Set Antialiasing to Medium or higher; depth of field is unavailable otherwise (and even if it was available at antialiasing levels lower than Medium, it would look very bad).
Under the tab labelled "Stereo and DOF", enable the Depth of Field checkbox. Depth of Field is now enabled and can be manipulated by changing the Focal Distance and Lens F-Stop values under the Stereo and DOF tab in the Camera Properties Panel.

In LightWave 7.5, it is possible to preview depth of field and motion blur in the OpenGL window in Layout. To use the OpenGL preview, first set one of your viewports to Camera View. Then, move the mouse cursor over the camera viewport, and press SHIFT + F9. Remember, in order to use the OpenGL preview for Depth of Field and/or Motion Blur, they must be enabled in the Camera Properties panel ("p").

Setting a null object to display depth of field settings in Layout:

One of the more useful tools in LightWave is the Depth-Of-Field custom object. The Depth-Of-Field custom object creates a wireframe object in the OpenGL viewports in Layout that roughly shows what will be in focus with the current depth of field settings. In order to apply it, all you have to do is parent a null object to the camera, and then add the Depth-Of-Field custom object to the null.

Add a null object to the scene (Items > Add > Objects > Add Null...).

Be sure to give the null a name that easily identifies it as the depth of field display object. For example, you could name the null DOF_Display (that's what I did).

DO NOT move, scale, or rotate the null! Otherwise it won't be lined up properly when you parent it to the camera! It is a good idea to disable all the movement, rotation, and scale axes (axes = plural of axis) in the lower right hand corner of Layout. Disabling the axes will prevent you from accidentally moving the null.

Open the Motion Properties panel ("m") for DOF_Display. and parent DOF_Display to the camera. (Make sure Parent In Place is off!). If you made sure that DOF_Display was centered at the origin (as per the previous step), DOF_Display should snap to the camera's position and alignment.

Open the Object Properties panel ("p") for DOF_Display.
In the Geometry tab, add the Depth-Of-Field Display custom object through the Add Custom Object dropdown box (Geometry > Add Custom Object > Depth-Of-Field Display). When you add the Depth-Of-Field custom object, it will be added to the custom object list as "DOF Circle of confusion 3.125e-005 m" or something similar.
In almost all situations, the default settings for the Depth-Of-Field custom object will be acceptable. I have yet to encounter a situation where I needed to change the settings.

The Depth-Of-Field custom object creates a wireframe object in Layout that roughly shows what will be in focus. The wireframe will not render; it is only visible through the OpenGL viewports in Layout.
Combined with the OpenGL Depth of Field and Motion Blur preview capability, the Depth-Of-Field custom object makes setting up and animating depth of field much, much simpler by taking out the guesswork and manual measurement; with the Depth-Of-Field custom object and the OpenGL preview, you can just manipulate the Focal Distance and Lens F-Stop values in the Camera Properties panel until you get the results you want.

Setting a null object to control Focal Distance:

Now we have to set up a new null object to use as the control object. First we add the null, then we parent it to the object, and then we link the null's Z position to the camera's Focal Distance.

Add a null object to the scene (Items > Add > Objects > Add Null...)

Name the null something that clearly identifies it as the control object; for example, you could name it DOF_Control.

Make certain that you do not move, rotate, or scale DOF_Control at all! Any pre-exising coordinate values for DOF_Control will be carried over when you parent it to the camera, and that will effectively break this whole method of controlling depth of field with a null.
In order for you to effectively control both the Focal Distance and Lens F-Stop values using only DOF_Control, it needs to be constrained on all but two axes: Position Z and Scale Z. Disable Position X, Y; Rotation H,P,B, and Scale X, Y in the lower right-hand corner of Layout.

Open the Motion Properties panel ("m") for DOF_Control and parent it to the camera (Make sure Parent In Place is off!).

Open the Camera Properties panel ("p") for the camera that you're using.
Under the Stereo and DOF tab, set Focal Distance to be controlled by an envelope (click the button marked E next to Focal Distance). Setting Focal Distance to be controlled by an envelope places the channel in the Graph Editor, thereby allowing you to set keyframes for its value (i.e., animate Focal Distance). It also prevents you from changing the Focal Distance from the Camera Properties panel.

When you clicked the "E" button, the graph editor should pop up with Camera.FocalDistance as the only channel enabled (if the Graph Editor was already open, you will have to manually select the Camera.FocalDistance from the channel list).
Under the Curves tab in the Graph Editor, set the value for the first keyframe for Camera.FocalDistance to 0 m and delete all other keyframes for Camera.FocalDistance. Any keyframe values for Camera.FocalDistance will be added to the value set by DOF_Control, thus causing the Focal Distance value to be set improperly.

Under the Modifiers tab of the Graph Editor, add the Channel Follower modifier to Camera.FocalDistance.

The Channel Follower modifier uses a channel from another object (anything that can be animated in the Graph Editor) and adds it to the current channel. What we want to do is get the value for Camera.FocalDistance from DOF_Control.Position.Z.
Double click Channel Follower in the Modifier List to bring up the Channel Follower panel.
In the Channels list, select DOF_Control > Position.Z. Press OK.

Now the Z position of DOF_Control controls the Focal Distance of the the camera. That means that when you move DOF_Control along the Z axis, it essentially measures the distance between itself and the camera and uses that value for the Focal Distance.
By parenting it DOF_Control to the camera, and enabling only the Z position axis for DOF_Control, it now acts like a tape measure from the camera to the intended focal distance.
In order for the DOF Display box to be interactively affected by the position of DOF_Control, Auto Key must be turned on.

Setting a null object to control Lens F-Stop:

Now that our null is configured to act like a tape measure that controls the camera's Focal Distance, we want to set it to control the camera's Lens F-Stop. All we have to do is link the null's Z scale value to the camera's Lens F-Stop.

Open the Camera Properties panel ("p") for the camera that you're using.
Under the Stereo and DOF tab, set Lens F-Stop to be controlled by an envelope (click the button marked E next to Lens F-Stop). Setting Lens F-Stop to be controlled by an envelope places the channel in the Graph Editor, thereby allowing you to set keyframes for its value (i.e., animate Lens F-Stop). It also prevents you from changing the Lens F-Stop value from the Camera Properties panel.

When you clicked the "E" button, the graph editor should pop up with Camera.FStop the only channel enabled (if the Graph Editor was already open, you will have to manually select the Camera.FStop from the channel list).
Under the Curves tab in the Graph Editor, set the value for the first keyframe for Camera.FStop to 0 m and delete all other keyframes for Camera.FStop. Any keyframe values for Camera.FStop will be added to the value set by DOF_Control, thus causing the Lens F-Stop value to be set improperly.

Under the Modifiers tab of the Graph Editor, add the Channel Follower modifier to Camera.FStop.

The Channel Follower modifier uses a channel from another object (anything that can be animated in the Graph Editor) and adds it to the current channel. What we want to do is get the value for Camera.FStop from DOF_Control.Scale.Z.
Double click Channel Follower in the Modifier List to bring up the Channel Follower panel.
In the Channels list, select DOF_Control > Scale.Z. Press OK.

Now the Z scale value of DOF_Control controls the Lens F-Stop of the camera. That means that when you increase or decrease the Z scale of DOF_Control, the Lens F-Stop value increases or decreases (i.e. the focal depth gets deeper or more shallow) accordingly.
Now DOF_Control allows you to control both the Focal Distance and Lens F-Stop directly in the Timeline.
Just as with the Focal Distance, the Depth-Of-Field display object will not interactively show the changes made to either the Focal Distance or Lens F-Stop values unless Auto Key is turned on.

Summary and Conclusion:

In this tutorial, we learned how to:

Enable depth of field for a camera
Create a Depth-Of-Field custom object to preview depth of field in the OpenGL viewports in Layout
Preview depth of field in the OpenGL Camera View in Layout
Control a camera's Focal Distance with a null object's Z position with the Channel Follower modifier
Control a camera's Lens F-Stop with a null object's Z scale with the Channel Follower modifier

By using the technique described in this tutorial, now we can preview and animate the depth of field settings directly in the Timeline rather than using the Camera Properties and Graph Editor windows.

Back to Reference Materials

Last Modified Date: April 28th, 2004

Last Modified By: Joshua Albers

reference materialDepth of Field Control Using Two Nulls

by Joshua Albers
April 28th, 2004

Introduction;
This tutorial will show you how to easily set up and control depth of field for your LightWave scenes using parented null objects, the Depth-Of-Field custom object, and the Channel Follower modifier. Depth of field is defined by two values: Focal Distance and Lens F-Stop. Focal Distance defines the distance away from the camera that will be in focus, and Lens F-Stop defines how far in front of and behind the Focal Distance the area of focus will extend. Larger Lens F-Stop values increase the depth of field, allowing many objects to be in focus. This is called "deep focus". Smaller Lens F-Stop values decrease the depth of field, thus restricing the area that will be in focus. This is called "shallow focus". By default, the Focal Distance and Lens F-Stop settings are controlled through the Camera Properties panel or the Graph Editor in Layout; however, it is possible to control the depth of field settings using some of the many tools and modifiers that are included with LightWave 7.5 It is entirely possible to use depth of field without also using the technique described below, but the "parented nulls" technique allows the depth of field settings to be directly animated through the Timeline rather than forcing the user (you) to go through the Graph Editor.

Before you begin:

This technique uses null objects that are parented to the camera to control depth-of-field settings. The null objects must be properly aligned to the camera's coordinates, or else the display and control settings will not work. In order for the null's initial position and alignment to be set correctly when parented to the camera, Parent in Place must be turned off in the General Options panel ("o"). The Grid Size value in the Display Options panel ("d") needs to be adusted to properly fit the objects in your scene file. If your Grid Size is set too large, your cameras, lights, and nulls will appear to be much larger than your objects and it will be very hard to make small adjustments to object positions. If your Grid Size is too small, your camera, lights, and nulls will be very hard to see and you will have to move the mouse more to make small adjustments. Layout automatically sets the grid size when you load objects into a scene; if you add a very large object (such as a ground plane), Layout will set the Grid Size to a very high value, which will make it harder for you to select and manipulate the objects in your scene. The optimal Grid Size value depends on the scale of your objects; ideally, the camera and Nulls should be easily visible but not too large.

Enabling depth of field for a camera:

Before we can set up nulls to control our depth of field settings, first we need to enable depth of field. The Focal Distance and Lens F-Stop settings are not accessible until depth of field is enabled in the Camera Properties panel ("p").

Open the Camera Properties panel ("p") for the camera to which you would like to add depth of field. Set Antialiasing to Medium or higher; depth of field is unavailable otherwise (and even if it was available at antialiasing levels lower than Medium, it would look very bad). Under the tab labelled "Stereo and DOF", enable the Depth of Field checkbox. Depth of Field is now enabled and can be manipulated by changing the Focal Distance and Lens F-Stop values under the Stereo and DOF tab in the Camera Properties Panel.

In LightWave 7.5, it is possible to preview depth of field and motion blur in the OpenGL window in Layout. To use the OpenGL preview, first set one of your viewports to Camera View. Then, move the mouse cursor over the camera viewport, and press SHIFT + F9. Remember, in order to use the OpenGL preview for Depth of Field and/or Motion Blur, they must be enabled in the Camera Properties panel ("p").

Setting a null object to display depth of field settings in Layout:

One of the more useful tools in LightWave is the Depth-Of-Field custom object. The Depth-Of-Field custom object creates a wireframe object in the OpenGL viewports in Layout that roughly shows what will be in focus with the current depth of field settings. In order to apply it, all you have to do is parent a null object to the camera, and then add the Depth-Of-Field custom object to the null.

Add a null object to the scene (Items > Add > Objects > Add Null...).
Be sure to give the null a name that easily identifies it as the depth of field display object. For example, you could name the null DOF_Display (that's what I did).

DO NOT move, scale, or rotate the null! Otherwise it won't be lined up properly when you parent it to the camera! It is a good idea to disable all the movement, rotation, and scale axes (axes = plural of axis) in the lower right hand corner of Layout. Disabling the axes will prevent you from accidentally moving the null.

Open the Motion Properties panel ("m") for DOF_Display. and parent DOF_Display to the camera. (Make sure Parent In Place is off!). If you made sure that DOF_Display was centered at the origin (as per the previous step), DOF_Display should snap to the camera's position and alignment.

Open the Object Properties panel ("p") for DOF_Display. In the Geometry tab, add the Depth-Of-Field Display custom object through the Add Custom Object dropdown box (Geometry > Add Custom Object > Depth-Of-Field Display). When you add the Depth-Of-Field custom object, it will be added to the custom object list as "DOF Circle of confusion 3.125e-005 m" or something similar. In almost all situations, the default settings for the Depth-Of-Field custom object will be acceptable. I have yet to encounter a situation where I needed to change the settings.

The Depth-Of-Field custom object creates a wireframe object in Layout that roughly shows what will be in focus. The wireframe will not render; it is only visible through the OpenGL viewports in Layout. Combined with the OpenGL Depth of Field and Motion Blur preview capability, the Depth-Of-Field custom object makes setting up and animating depth of field much, much simpler by taking out the guesswork and manual measurement; with the Depth-Of-Field custom object and the OpenGL preview, you can just manipulate the Focal Distance and Lens F-Stop values in the Camera Properties panel until you get the results you want.

Setting a null object to control Focal Distance:

Now we have to set up a new null object to use as the control object. First we add the null, then we parent it to the object, and then we link the null's Z position to the camera's Focal Distance.

Add a null object to the scene (Items > Add > Objects > Add Null...)

Name the null something that clearly identifies it as the control object; for example, you could name it DOF_Control.

Make certain that you do not move, rotate, or scale DOF_Control at all! Any pre-exising coordinate values for DOF_Control will be carried over when you parent it to the camera, and that will effectively break this whole method of controlling depth of field with a null. In order for you to effectively control both the Focal Distance and Lens F-Stop values using only DOF_Control, it needs to be constrained on all but two axes: Position Z and Scale Z. Disable Position X, Y; Rotation H,P,B, and Scale X, Y in the lower right-hand corner of Layout.

Open the Motion Properties panel ("m") for DOF_Control and parent it to the camera (Make sure Parent In Place is off!).

Open the Camera Properties panel ("p") for the camera that you're using. Under the Stereo and DOF tab, set Focal Distance to be controlled by an envelope (click the button marked E next to Focal Distance). Setting Focal Distance to be controlled by an envelope places the channel in the Graph Editor, thereby allowing you to set keyframes for its value (i.e., animate Focal Distance). It also prevents you from changing the Focal Distance from the Camera Properties panel.

When you clicked the "E" button, the graph editor should pop up with Camera.FocalDistance as the only channel enabled (if the Graph Editor was already open, you will have to manually select the Camera.FocalDistance from the channel list). Under the Curves tab in the Graph Editor, set the value for the first keyframe for Camera.FocalDistance to 0 m and delete all other keyframes for Camera.FocalDistance. Any keyframe values for Camera.FocalDistance will be added to the value set by DOF_Control, thus causing the Focal Distance value to be set improperly.

Under the Modifiers tab of the Graph Editor, add the Channel Follower modifier to Camera.FocalDistance.

The Channel Follower modifier uses a channel from another object (anything that can be animated in the Graph Editor) and adds it to the current channel. What we want to do is get the value for Camera.FocalDistance from DOF_Control.Position.Z. Double click Channel Follower in the Modifier List to bring up the Channel Follower panel. In the Channels list, select DOF_Control > Position.Z. Press OK.

Now the Z position of DOF_Control controls the Focal Distance of the the camera. That means that when you move DOF_Control along the Z axis, it essentially measures the distance between itself and the camera and uses that value for the Focal Distance. By parenting it DOF_Control to the camera, and enabling only the Z position axis for DOF_Control, it now acts like a tape measure from the camera to the intended focal distance. In order for the DOF Display box to be interactively affected by the position of DOF_Control, Auto Key must be turned on.

Setting a null object to control Lens F-Stop:

Now that our null is configured to act like a tape measure that controls the camera's Focal Distance, we want to set it to control the camera's Lens F-Stop. All we have to do is link the null's Z scale value to the camera's Lens F-Stop.

Open the Camera Properties panel ("p") for the camera that you're using. Under the Stereo and DOF tab, set Lens F-Stop to be controlled by an envelope (click the button marked E next to Lens F-Stop). Setting Lens F-Stop to be controlled by an envelope places the channel in the Graph Editor, thereby allowing you to set keyframes for its value (i.e., animate Lens F-Stop). It also prevents you from changing the Lens F-Stop value from the Camera Properties panel.

When you clicked the "E" button, the graph editor should pop up with Camera.FStop the only channel enabled (if the Graph Editor was already open, you will have to manually select the Camera.FStop from the channel list). Under the Curves tab in the Graph Editor, set the value for the first keyframe for Camera.FStop to 0 m and delete all other keyframes for Camera.FStop. Any keyframe values for Camera.FStop will be added to the value set by DOF_Control, thus causing the Lens F-Stop value to be set improperly.

Under the Modifiers tab of the Graph Editor, add the Channel Follower modifier to Camera.FStop.

The Channel Follower modifier uses a channel from another object (anything that can be animated in the Graph Editor) and adds it to the current channel. What we want to do is get the value for Camera.FStop from DOF_Control.Scale.Z. Double click Channel Follower in the Modifier List to bring up the Channel Follower panel. In the Channels list, select DOF_Control > Scale.Z. Press OK.

Now the Z scale value of DOF_Control controls the Lens F-Stop of the camera. That means that when you increase or decrease the Z scale of DOF_Control, the Lens F-Stop value increases or decreases (i.e. the focal depth gets deeper or more shallow) accordingly. Now DOF_Control allows you to control both the Focal Distance and Lens F-Stop directly in the Timeline. Just as with the Focal Distance, the Depth-Of-Field display object will not interactively show the changes made to either the Focal Distance or Lens F-Stop values unless Auto Key is turned on.

Summary and Conclusion:

In this tutorial, we learned how to: Enable depth of field for a camera Create a Depth-Of-Field custom object to preview depth of field in the OpenGL viewports in Layout Preview depth of field in the OpenGL Camera View in Layout Control a camera's Focal Distance with a null object's Z position with the Channel Follower modifier Control a camera's Lens F-Stop with a null object's Z scale with the Channel Follower modifier By using the technique described in this tutorial, now we can preview and animate the depth of field settings directly in the Timeline rather than using the Camera Properties and Graph Editor windows.


Back to Reference Materials

Last Modified Date: April 28th, 2004
Last Modified By: Joshua Albers