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Reference: Tutorials: Conversion 101 - Converting LDR Files to POV Files for Rendering

Conversion 101 - Converting LDR Files to POV Files for Rendering
By: Jeroen de Haan and Jake McKee
Posted: March 26, 2002
Version: v1 rev.1 110202

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Chapter 6: Camera and lenses (part 2)
The radius (distance) of the camera from the model is calculated by L3P automatically for you. The camera radius depends on two things: the size of the model and the camera angle (or actually camera lens angle).

Camera angle, you ask? The lens of a camera has a certain angle, which determine what is visible and what is not. Basically how far to either side the camera can see. Human eyes have a viewing angle of 45 degrees, while the default camera angle in L3P is 67 degrees. Look at the picture below.

Lenses have their own characteristics:
The normal lens (45°) will give a normal view.
The telelens (<45°) will even the perspective: when using an extreme telelens you won't have perspective at all and all objects will have the same size; objects in the front and in the back of the picture.
The wide lens (>45°) will distort the perspective: objects in the front look extremely big while objects in the back are very small, even in short distances.

Let's say the camera in the pictures above has a fixed distance towards a, b and c. The first camera has a standard lens. Not all the objects are visible (from this distance). The second lens is a tele-lens; only a small part of the picture is visible. Sports and wildlife photographers use this kind of lenses because you can get very "close" to an object from a distance (zoom in). The last lens is a wide- or fisheye lens; all the objects are visible. This is used in landscape and interior photography because you can get a lot on a picture without taking too much distance.

L3P uses the size of the model and the camera angle to calculate the radius. Lets say the two outer c's are the outer most part of a model. If you want to use a 45 degrees lens (as in the first camera), you have to move from the object. When using a 15 degrees lens you also have to move but a bit more extreme. In the last picture, you have to move to the model a bit.

Confused? Well let's try how it looks.

Open the CAR.DAT in L3PAO, add a floor and background and make 3 POV-files using Camera Globe Positions:

30,45,0 and Camera Angle 10 for CARCA010.POV
30,45,0 and Camera Angle 45 for CARCA045.POV
30,45,0 and Camera Angle 100 for CARCA100.POV

Open POV-Ray and render the pictures one by one.

The three pictures look like this:

This is the image rendered at a 10 degrees camera angle. You notice that the perspective lines are almost parallel. This is great when you want to render building steps of a model. The camera radius is roughly 1453 LDraw units (a 1 x 1 Brick is 24 LDraw units high).

This is the image rendered at 45 degrees camera angle. It has a much more life-like perspective. The camera radius is now just 334 LDraw units.

And last: the image rendered at a 100 degrees camera angle. You will notice that the picture is quite different: you can see the horizon now because the camera is closer and lower to the floor, which causes the car to look a bit odd. You can see how distorted the perspective is: the two red studs on right side of the bonnet are almost twice as large as the two studs on the left side. The camera is now only 194 LDraw units away.

If you look at the shadows on the floor, you will notice that these are different too. This is because, by default, L3P places 3 lights on fixed globe locations and at the same radius as the camera. Therefore, in the CARca045 image the lights are very far away and lit a large part of the floor while in the CARca100 image the camera, thus the lights are very close to the model, and a much smaller part of the floor is lit. Hence, the floor looks darker on the horizon.

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