Setting Camera Parameters

When a camera is first created, you can modify the camera parameters directly in the Create panel as long as the new camera is selected. After the camera object has been deselected, you can make modifications in the Modify panel's Parameters rollout for the camera.

Lens settings and field of view

The first parameter in the Parameters rollout sets the Lens value or, more simply, the camera's focal length in millimeters.

The second parameter, FOV (which stands for field of view), sets the width of the area that the camera displays. The value is specified in degrees and can be set to represent a Horizontal, Vertical, or Diagonal distance using the flyout button to its left, as shown in Table 26.2.

Table 26.2: Field of View Buttons
Open table as spreadsheet

Button	Description
	Horizontal distance
	Vertical distance
	Diagonal distance

The Orthographic Projection option displays the camera view in a manner similar to any of the orthographic viewports such as Top, Left, or Front. This eliminates any perspective distortion of objects farther back in the scene and displays true dimensions for all edges in the scene.

Professional photographers and film crews use standard stock lenses in the course of their work. These lenses can be simulated in Max by clicking one of the Stock Lens buttons. Preset stock lenses include 15, 20, 24, 28, 35, 50, 85, 135, and 200mm lengths. The Lens and FOV fields are automatically updated on stock lens selection.

Tip 

On cameras that use 35mm film, the typical default lens is 50mm.

Camera type and display options

The Type option enables you to change a Free camera to a Target camera and then change back at any time.

The Show Cone option enables you to display the camera's cone, showing the boundaries of the camera view when the camera isn't selected. (The camera cone is always visible when a camera is selected.) The Show Horizon option sets a horizon line within the camera view, which is a dark gray line where the horizon is located.

Environment ranges and clipping planes

You use the Near and Far Range values to specify the volume within which atmospheric effects like fog and volume lights are to be contained. The Show option causes these limits to be displayed as yellow rectangles within the camera's cone.

You use clipping planes to designate the closest and farthest object that the camera can see. In Max, they are displayed as red rectangles with crossing diagonals in the camera cone. If the Clip Manually option is disabled, then the clipping planes are set automatically with the Near Clip Plane set to 3 units. Figure 26.5 shows a camera with Clipping Planes specified. The front Clipping Plane intersects the car and chops off its front end. The far Clipping Plane is far behind the car.

Figure 26.5: A camera cone displaying Clipping Planes

Tip 

Clipping planes can be used to create a cutaway view of your model.

Camera Correction modifier

To understand the Camera Correction modifier, you first need to understand what two-point perspective is. Default cameras in Max use three-point perspective, which causes all lines to converge to a vanishing point off in the distance, but two-point perspective causes all vertical lines to remain vertical.

The visual effect of this modifier is that extra tall objects appear to bend toward the camera when corrected. For example, if you have a camera pointed at a skyscraper, then correcting the camera with the Camera Correction modifier makes the top of the building appear closer rather than having it recede away.

The Camera Correction modifier has an Amount value that lets you specify how much correction to apply and a Direction value that orients the angle of vertical lines in the scene. There is also a Guess button, which automatically sets the correction values for you based on the Z-axis vertical.

Note 

The Camera Correction modifier doesn't appear in the Modifier List in the Modifier Stack, but you can select it from the Modifiers menu.

Creating multi-pass camera effects

All cameras have the option to enable them to become multi-pass cameras. You can find these settings in the Parameters rollout when a camera object is selected. Multi-pass cameras are created by checking the Enable button and selecting the effect from the drop-down list. The current available effects include Depth of Field (mental ray), Depth of Field, and Motion Blur. For each, an associated rollout of parameters opens.

CROSS-REF 

The Depth of Field (mental ray) effect option is covered in Chapter 45, "Raytracing and mental ray."

The Multi-Pass Effect section of the Parameters rollout also includes a Preview button. This button makes the effect visible in the viewports for the current frame. This feature can save you a significant amount of time that normally would be spent test-rendering the scene. The Preview button is worth its weight in render speed. Using this button, you can preview the effect without having to render the entire sequence.

Caution 

The Preview button does not work unless the Camera view is the active viewport

The Render Effect Per Pass option causes any applied Render Effect to be applied at each pass. If disabled, then any applied Render Effect is applied after the passes are completed.

CROSS-REF 

You can also apply these multi-pass effects as Render Effects. See Chapter 44, "Using Atmospheric and Render Effects."

Using the Depth of Field effect

The Depth of Field Parameters rollout, shown in Figure 26.6, appears when the Depth of Field option is selected in the Multi-Pass Effect section of the Parameters rollout. It includes settings for controlling the Depth of Field multi-pass effect.

Figure 26.6: Use the Depth of Field Parameters rollout to set the number of passes.

You can select to use the Target Distance (which is the distance to the camera's target), or you can specify a separate Focal Depth distance. This location is the point where the camera is in focus. All scene objects closer and further from this location are blurred to an extent, depending in their distance from the focal point.

Note 

Even Free cameras have a Target Distance. This distance is displayed at the bottom of the Parameters rollout

Within the Depth of Field Parameters rollout, you also have the option to display each separate pass in the Rendered Frame Window with the Display Passes option and to use the camera's original location for the first rendering pass by enabling the Use Original Location option.

The Total Passes is the number of times the scene is rendered to produce the effect, and the Sample Radius is the potential distance that the scene can move during the passes. By moving the scene about the radius value and re-rendering a pass, the object becomes blurred more away from the focal distance. If you have a fairly tight scene, the default Radius value does not produce very visible results. Try increasing the Sample Radius value and re-rendering. Figure 26.7 shows a scene with Sample Radius values of 1 and 5.

Figure 26.7: Changing the Sample Radius value changes the amount of blur added to the scene.

Note 

The Depth of Field effect is applied only to rendered scene objects. It is not applied to any background images.

The Sample Bias value moves the blurring closer to the focal point (for higher values) or away from the focal point (for lower values). If you want to highlight the focal point and radically blur the other objects in the scene, set the Sample Bias to 1.0. A Sample Bias setting of 0 results in a more even blurring.

The Normalize Weights option allows you to control how the various passes are blended. When enabled, you can avoid streaking along the object edges. The Dither Strength value controls the amount of dither taking place. Higher Dither Strength values make the image grainier. The Tile Size value also controls dither by specifying the dither pattern size.

With lots of passes specified, the render time can be fairly steep. To lower the overall rendering time, you can disable the Anti-alias and filtering computations. These speed up the rendering time at the cost of image quality.

Tutorial: Applying a Depth of Field effect to a row of windmills

In the dry plains of Southwest America, the wind blows fiercely. Rows of windmills are lined up in an effort to harness this energy. For this example, we use the Depth of Field effect to display the windmills.

To apply a Depth of Field effect to a row of windmills, follow these steps:

1. Open the  Depth of field windmills.max file from the Chap 26 directory on the DVD.

   This file includes a windmill object (created by Viewpoint Datalabs) duplicated multiple times and positioned in a row.

2. Select Create Cameras Target Camera, and drag in the Top viewport from the lower-left corner to the center of the windmills. In the Left vewpoint, select the camera and move it upward, and then select the Camera Target and also move it upward, so the entire row of windmills can be seen. If the windmills don't fill the camera view, adjust the Field of View (FOV) setting.

   Tip 

   You can select both the camera and its target by clicking on the line that connects them.

3. Select the Perspective viewport, right-click on the viewport title, and select Views Camera01 (or just press the C key) to make this viewport the Camera view.

4. With the Camera selected, open the Modify panel, enable the Multi-Pass Effect option, and then select Depth of Field in the drop-down list.

5. In the Depth of Field Parameters rollout, enable the Use Target Distance option and set the Total Passes to 15, the Sample Radius to 3.0, and the Sample Bias to 1.0.

6. Select the Camera viewport, and click the Preview button in the Parameters rollout. This shows the Depth of Field effect in the viewport.

Figure 26.8 shows the resulting Depth of Field effect in the viewport for the row of windmills.

Figure 26.8: Multi-Pass camera effects can be viewed in the viewport using the Preview button.

Using the Motion Blur effect

Motion Blur is an effect that shows motion by blurring objects that are moving. If a stationary object is surrounded by several moving objects, the Motion Blur effect blurs the moving objects and the stationary object remains in clear view, regardless of their positions in the scene. The faster an object moves, the more blurry it becomes.

This blurring is accomplished in several ways, but with a multi-pass camera, the camera renders subsequent frames of an animation and then blurs the images together.

The Motion Blur Parameters rollout, shown in Figure 26.9, appears when the Motion Blur option is selected in the Multi-Pass Effect section of the Parameters rollout. Many of its parameters work the same as the Depth of Field effect.

Figure 26.9: For the Motion Blur effect, you can set the number of frames to include.

The Display Passes option displays the different frames as they are being rendered, and Total Passes is the number of frames that are included in the averaging. You can also select the Duration, which is the number of frames to include in the effect. The Bias option weights the averaging toward the current frame. Higher Bias values weight the average more toward the latter frames, and lower values lean toward the earlier frames.

The remaining options all work the same as for the Depth of Field effect.

Tutorial: Using a Motion Blur multi-pass camera effect

The Motion Blur effect works only on objects that are moving. Applying this effect to a stationary 2D shape does not produce any noticeable results. For this tutorial, you apply this effect to a speeding car model created by Viewpoint Datalabs.

To apply a Motion Blur multi-pass effect to the camera looking at a car mesh, follow these steps:

1. Open the Car at a stop sign.max file from the Chap 26 directory on the DVD.

   This file includes a car mesh (created by Viewpoint Datalabs), a camera, and a simple stop sign made of primitives. The car is animated.

2. Click the Select by Name button on the main toolbar to open the Select by Name dialog box (or press the H key). Double-click the Camera01 object to select it.

3. With the camera object selected, open the Modify panel. In the Multi-Pass Effect section of the Parameters rollout, click the Enable check box and select the Motion Blur effect from the dropdown list.

4. In the Motion Blur Parameters rollout, set the Total Passes to 10, the Duration to 1.0, and the Bias to 0.9.

5. Drag the Time Slider to frame 57. This is the location where the car just passes the stop sign.

6. With the Camera viewport active, click the Preview button in the Parameters rollout.

Figure 26.10 shows the results of the Motion Blur effect. This effect has been exaggerated to show its result. Notice that the stop sign isn't blurred. The only problem with this example is that, with the Motion Blur effect enabled, you can't make out the license plate number, so you can't send this speeder a ticket.

Figure 26.10: Using the Motion Blur multi-pass effect for a camera, you can blur objects moving in the scene.