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Wednesday, February 1, 2012

Depth of Field

The depth of field (DOF) is the range between the nearest and farthest objects in a scene that appears acceptably sharp in a picture. A large DOF makes the entire image sharp, while a small DOF makes subjects clear but blurred out the foreground and the background.

In assignment #1, you need to make a shallow depth of field. Luxrender provides the perspective camera that can control the DOF by configuring lens radius. Increasing the lens radius will make a shallow depth of field, since small aperture does not disperse the ray that is penetrating the lens like large aperture. In Blender, you can control the lens size with f-stop. Smaller f-stop is larger lens radius.

In order to focus an object in a scene, you may want to configure focal distance. Focal distance is the distance between the camera and the subject that you want to see clearly in an image.

In addition, decreasing the distance between the focused object and camera will help to get a shallow DOF. You can find out DOF formulas in the article of Jeff Conrad or Wikipedia. From this formula, you can see that the DOF is decided according to the focal length and f-number of the lens, and the camera-to-subject distance. In addition, the DOF is inversely proportional to the camera-to-subject distance. So, it will be useful to make it close-up.

When moving camera close to the subject, you would miss some objects in your image. In this case, you can  put every object you want to include in the image by increasing Field of View.

Scaling down the scene will be helpful see the shallow depth of field also. When the model shrinks, the camera-to-subject distance will decrease also.

http://www.luxrender.net/wiki/LuxRender_Cameras#Depth_of_Field:_lens_radius_and_focus_distance
http://en.wikipedia.org/wiki/Depth_of_field#Moderate-to-large_distances
http://www.largeformatphotography.info/articles/DoFinDepth.pdf

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