A perspective view of an object means that the object appears as it would in reality as we would see it using both eyes to give us a perception of depth. The closer we are to the object the larger the front parts appear compared to the size of the rear parts. If we are far away the difference in sizes between the front and the back is not so large. An orthogonal 3D view is a 3D view in Blender of an object which is NOT corrected for the perspective of the viewer. Theoretically, if you stood an infinite distance away from a cube with an infinitely powerful telescope the object would appear undistorted and there would be no sense of depth:
A more technical description would be a perspective view of a cube as you would see it through a standard 50mm camera lens. The apparent size is determined by the distance the camera is away from it.
Without changing the camera lens, if we move closer the image not only gets larger but it gets a more pronounced perspective distortion. The front parts are larger than the rear. Technically we call this a Perspective 3D Projection
If we switch off Perspective projection by toggling to tell Blender to show us an Orthogonal 3D Projection instead we get:
This looks terrible! It is an accurately displayed cube with no perspective correction applied. What you are seeing is an optical illusion where the back corner looks raised up.
If we stand back to the viewing location of the first image above we see:
Notice, the optical illusion is still there it still looks terrible – except this time somewhat smaller. Notice how the grid appears in the Perspective view vs the 3D orthogonal view. It’s little wonder that we seldom use 3D Orthogonal projection. It just looks wrong!
2D Orthogonal Projection
Despite what I said above, we do indeed use a tremendous amount of Orthogonal viewing!
But we use 2D orthogonal viewing instead of 3D orthogonal viewing. This is simply the viewing of the object along an axis running straight from the object to your eye so that you only see the dimensions of the other two Axes:
In this projection, we switch to “top view” which is actually looking at the object along the z-axis so that you only see the object’s X dimensions and the Y extents. Looking at the cube in the front view (along the Y-axis) or the side view (along the X-axis) would look identical because the object is a cube with identically sized faces. With 2D orthogonal views, you can control your construction properly. But this is a topic for Part 2.
To show another example of 3D projections, let’s look at a Cylinder:
Note how the top surface becomes more oval the closer we move in, but it still looks like a perfectly respectable cylinder
At the same close-up distance, it looks like a cone, but once again this is an optical illusion since the facet faces on the cylindrical body are actually vertical and not tapered at all – look closely.
Moving back to our original distance just makes it smaller but it still looks wrong:
A Longer Lens
So we can obviously see that the 3D perspective image is the way we want to go. But if we want a large image which does not display too much perspective distortion, then what do we do? Simple. Increase the focal length of the lens:
So, to get a “wide-angle” effect in perspective projection, use a short focal length lens for the viewport and move your eyepoint closer to the object (zoom). To get a good shape while still being in Perspective view, increase the focal length and move backward (zoom out). Just like in photography, if you put on a too powerful telephoto lens (very long focal length) in Blender, you will get a foreshortening effect.
What about Camera View?
These same perspective controls that we have been looking at in the Viewport View control work the same way for each camera.
Select a camera, physically move the camera back , and change the focal length:
We have looked at the 3D Perspective and 3D orthogonal views. Click here to go on to the discussion on 2D Orthogonal Views.