camera tips

This series of tips is geared toward showing how the Maya camera is similar to a real world camera. It mimics real world settings to lallow you to match images captured by real cameras (illustrations come from the Maya documentation).

Camera Basics

  • To create a new camera in a scene go to Create > Camera. There are different choices (of course!) and the 3 node camera is the one that most professionals use. To play with the orientation of the camera choose View > Camera Tools.
  • To step back and forth between camera views use the ] and [ keys. There is no undo for camera moves. If you want your camera views to be included in the undo queue go to Camera Attribute Editor > Display Options > Journal Command (although I wouldn’t recommend it). The View > Bookmarks > Edit Bookmarks is useful to store and compare shots.
  • Selection and Frame Selection: try View > Look at Selection (to have the selected object centered in the window) and View > Frame Selection (to have the object centered in the window and close up to the camera). These commands also establish a new point of interest. Nice hotkeys are F (frame object) and A (frame all) .
  • Dolly vs Zoom: the difference is that when you dolly you move the camera while zooming changes the focal length of the camera. When you dolly the perspective changes. When zooming the perspective doesn’t change. Perspective could be thought of as the rate that objects change in size in the frame as their distance from the camera changes. And how about both at the same time? When watching the Hitchock movie Vertigo you can find some shots that use that eeerie camera effect.

Advanced Camera Attributes

  • Resolution gate – Overscan
  • Film Gates and Film Backs: the following illustration shows what the terms mean.

  • The film back corresponds to the size of the film negatives and is measured in millimeters (35mm for instance). Only the region of negative inside the film gate ends up being exposed by light. It is this region that is rendered in Maya. It sis expressed as the Camera Aperture attribute. Another attribute describing the region inside the Film Gate is the Film Aspect Ratio.

  • But what is this all about you ask? It’s all going to affect your picture eventually in terms of Focal Length and Angle of View (which in turn affect the flavor of what you are saying with your shot). If you change different Film Gate presets you will notice that the angle of view changes but that the Focal Length doesn’t right? Now if you adjust the Focal Length you will notice that the angle of view changes. The focal length of a lens is defined as the distance from the lens to the film plane. Lenses are identified by their focal lengths.

  • Normal length: different film backs have different normal lenses. A normal lens is the lens that most closely approximates normal vision for a given film back. For instance it woud be 50mm on 35mm film back but a 50mm lens on 16mm back would look like a telephoto lens.
  • How does the FIlm Gate relate to the Resolution Gate? Turn on Resolution Gate and Film Gate to ON in the Camera Attribute editor. The two gates don’t match because they are two rectangles of different shape at that point. Change the Film Fit and notice how the Film Gate is drawn differently relatively to the Resolution Gate. The Film Fit can allow you to create a Letterbox look. When maya renders the entire Resoultion Gate is rendered. To create the black bars make sure the Ignore Film Gate in the Maya Software Render Globals is turned OFF .
  • Clipping planes: they are used to determine what objects will be rendered in the scene. As shown below. Clipping planes play an important role when working with z-depth . The z-depth value will be between -1 and 0 depending on how far the geometry is from the near and far clipping planes. If the clipping planes have a large distance between them z-depth precision will be lost. For example if your clipping planes are set far apart and you have a cluster of objects their realtive z-depth numbers will be rounded off and too close to one another. Auto Render Clip Plane must be turned off is you are using z-depth (auto render clip plane can move the clipping planes from one frame to another). More about z-depth later.

  • Camera Output Settings: selecting what will be rendered. In order to be rendered a camera needs to be renderable. For the Depth Further Visible Depth needs to be on for proper handling of depth with Paint Effects, however it can interfere with proper Depth of Field rendering.

Motion Blur

  • With the Maya renderer there are two types of motion blur: 2D and 3D.
  • Understanding the shutter angle attribute: the shutter angle value that you specify for motion blur will determine the amount of blur that results according to the following: take the Shutter angle value and divide it by 360 degrees. for instance 144/360=0.4
    which represents the interval in time between the shutter open and shutter close samples. For example, for motion blur at frame 1, shutter open would be at frame 0.8 and shutter closed at frame 1.2
  • A shutter angle of 360 would give samples that are one frame apart. At 360 the motion blur increases because the longer the shutter is open the further apart the samples are taken.
  • To set the shutter angle of a camera open the Special Effects tab in the attribute editor for the camera.
  • 2D vs 3D motion blur: the decision to use 2d or 3d is a mater of determning which one is more appropriate for a given scene and the time avaiilable to render the sequence. 3D motion is slower but there are times when it is necessary to use 3D motion blur due to limitations of 2D motion blur.
  • You can turn motion blur off selectively for some objects in the Render Stats tab in the attribute editor (the object’s attribute editor).
  • Limitations of 2D motion blur: 2D motion blur doesn’t work well in the following situations: moving transparent objects with a background, detailed background behind moving objects, rotating objects, objects entering from outside the image or leaving the image.

Other Camera Techniques

  • Depth of field effect. There is a tutorial here. I would like to add the following notes: Transparent surfaces can cause problems with depth of field because the transparent surface is at a certain depth from the camera. Maya only stores one depth perpiel and it chooses to store the nearest point to the eye. For transparent surfaces the depth of the trasnparent surface will determine the blur, so the background will show through, un-blurred or at the same level of blur than the transparent surface. Always better to render in layers and passes to blur elements in your compositing application. The other limitation is that Environment Fog cannot be used with depth of field.
  • Attaching a camera to a path for dollying and panning: create a curve object. Select your camera and shift select the curve. Make sure you are in the animate section and choose Animate > Motion Paths > Attach to Motion Path. A new Motion Path tab will appear in the Attribute editor for the camera and there you can edit camera orientation attributes such as Up Axis or Front Vector. The information drives where the camera is looking from the path. Please note that if you had a camera with an aim that remains static you can have the camera move on the path while always looking at the aim (or look at) point. Also note that you can select the frame number that appears in the view panel and if you press the letter T on your keyboard it will activate the Show Manipulator Tool. If you move the number around on the curve you will notice that you can have the camera be place at that point on the curve faster. You can also do this with the starting point and in the attribute editor you can active the positionMarkerShape tab to edit the time of that marker.
  • Setting Up Image Planes: in the camera attribute editor look for the Environment tab.Click on Image Plane and the image plane attribute editor is going to open. You can select a picture from a folder such as a sky background (get one here). A big yellow X should appear in your view panel. Activate the Resolution Gate view . In the camera attribute editor a new imagePlane1 has been created. Activate it. In Image Plane Attributes you should be able to choose an Image Name. Choose the sky picture for instance. Place a couple of objects in your scene and see how the image plane actually appears in front of them. You need to move the image far away in depth. in the Placement tab increase the Depth number (1500 maybe). If the image plane disappears altogether you need to adjust your clipping planes of course! You can also use an image sequence (let’s say you are rotoscoping some live action footage)
  • Perceptual Perspective Correction using Film Offset (removing the top perspective vanishing point). Adjust Film Offset in the Camera Attribute Editor. Not of much use on animated cameras but this can make a still plate look nicer.
  • Using the z-channel in compositing: you can use compositing tools such as After Effects or Shake to read the depth channel in an image rendered from Maya. To read more about it here is a AE tutorial There are only a couple of steps that are important:

    > (For AE) Make sure you render your scene to the RLA format and that the Z Depth attribute in the render globals is set to on. After Effects will not read the Z off an IFF file (Shake will).

    > in AE apply create a comp with your RLA sequence and apply the Effect > 3D Channel > 3D Channel Extract. Choose Z-Depth. You are going to have to change the extravagant values on the black and white point until you see the zchannel appear in the comp window. See below

    > Now create another comp with your footage on the top layer and the comp where you extracted the z depth at the bottom (and turn off its visibility). Apply a Effect > Blur > Compound Blur to the top layer:

    > You will see how the background objects are blured and the foreground objects are not. This is an approximation of a depth of field effect. For more exact effects it is recommended to use Shake’s ZDefocus node or AE plug ins such as Lenscare.

    > Download the After Effect Project and related files here .

  • Creating natural camera motion: scene examples . All camera motion has been keyed by hand. Key randomizers scripts or a noise function can also be used.


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