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I was watching a tutorial on the 3D Extrude & Bevel Options and I did not understand how Perspective work. I know it's viewing something at an angle, but I don't see from where it references it from.

I placed the object in front and left position, and at these basic positions, the perspective option only becomes more mysterious to me.

What exactly is going on?

Thank you.

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up vote 1 down vote accepted

To provide the Idiot's Guide version of Scott's answer ;)

Think of the perspective as your vanishing point from basic drawing. Bigger numbers create a more dramatic vanishing point angle. They'll give you a closer more epic impression. Lower numbers will more accurately represent the geometry of your original object.

Remember to expand the lighting options and play around with the light angle to better control the effect. Regardless of what vanishing point you use, you can make big improvements with the light.

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Ah, now that makes more sense. Thank you! – Matt Jan 12 '13 at 9:00

I'm not an expert on 3D rendering or optics, but most-likely that setting represents the angle of view being simulated. The larger the angle of view, the greater the perspective distortion. This is similar to using longer or shorter focal lengths at a fixed distance.

So using a high "perspective" angle causes the image to look distorted similar to using an ultra wide-angle or fisheye lens.

More info here: Perspective distortion (photography).

A similar setting in Flash's 3D rendering is discussed here.

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I believe, and this is merely my interpretation, the objects front plane minus extrude value is used.

The greater the perspective value the lower the z value for the back plane and the more reduction in scale. So ...

perspective + 1 = ((front plane - extrusion value) + (z - 1)) + ((width - 1) + (height - 1))

Thus moving the back plane further away from the viewer while reducing its size. It is not true 3D, merely a representation which looks accurate.

Since each object is wholly independent, all numbers are based of of the actual object as opposed to any scene or camera setting.

Illustrator's 3D effect has always been "best guess" and has never really been anywhere close to real 3D. Real 3d bases extrusion and perspective on the camera or view angle. Illustrator bases extrusion and perspective on the object and the center of its front plane.

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Wow, I'm not sure if I understood that completely, but thanks. I didn't expect a very technical approach to it, but I will certainly keep your reply in mind. – Matt Jan 11 '13 at 1:55

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