# Real Life Cube - Seeing Perspective

I am currently learning how to draw and trying to understand perspective.

I have found a cube toy in my room that I want to draw in perspective. I then place the cube below my eye level. Also I close one of my eye and look at the cube trying to find the convergence of the parallel lines. But why I cannot see any convergence in real life?

But when I take my camera and take a picture of the cube I can see the convergence. How can I see this in real life though?

• Hi. Welcome to GDSE. You're probably not close enough to see the convergence of the lines of perspective. Just move it close to your eye. A phone camera has a wide angle lens which makes it more obvious. Also your brain will try to trick you because the brain uses perspective for depth perception, so much so, that it's hard to convince yourself that converging lines of real objects are not parallel. May 3, 2021 at 9:48

You'll see.

Take a square which has side length say =10 or 12 centimeters. Place it horizontally just below your eye level touching your cheek, Watch straight forward without turning your sight. The sides which point forward seem to converge. It's blurry if your eye doesn't get focusd near enough but the convergence towards a vanishing point is still visible.

+diopter eyeglasses will enable sharp focus at closer distance but poor lens quality often makes straight lines look curved and that hides the perspective effect.

The steepness of the perspective depends on what's the ratio of the distances to the near end and the far end of the objects and, of course, on how wide the object is when compared to watching distance. If your watching distance to the 10 x 10 cm square was 1 meter and the far end was 10 cm further no convergence would be apparent.

Have big enough target to be able to see it sharp but still with perspective. An example: Stand on a straight road and see how it looks less wide at the distant end.

If you really want to understand perspective you should know how in theory a perfect perspective drawing can be constructed with sight lines from the observing point to the vertices of the target and by marking where the sight lines meet the image plane, In descriptive geometry this is the idea of central projection. The next image shows the construction of a cube image:

The next is another view of the same construction setup:

This is the result seen straight on the face (omit the grid on the paper)

The perspective is strong because the distance differences are large. The image plane happens to be vertical like four edges of the cube. This generates only 2 vanishing points.

Albrecht Durer became famous as an artist and as a technician who designed practical tools to help making perspective drawings. Here's one direct application of the sight line idea built with technology of the 16th century:

The drawing is his own. Durer's machines became obsolete after invention how to make good enough lenses. Cameras based on lenses were handy even in case the artist had to draw manually the sketch over the image that the camera projected. Light sensitive films 2oo years later removed the problem. A camera without a lens (=camera obscura https://en.wikipedia.org/wiki/Camera_obscura) projected far too dim image to be handy. It could still be used in sunny conditions and well darkened imaging room.

The sight line idea can be used as well by constructing a perspective image from 2 engineering drawings where the target is seen as flat from top and from a side:

The magenta sight lines are drawn to all visible vertices in the top view and the side view. Try this in practice. The cube is drawn in the special position (=one side in parallel with the image plane) which generates only one vanishing point.

The images are collected for earlier perspective drawing problem discussions in GDSE. This is one of them. How to construct a cube in 3-point perspective

It's there its just that your brain counteracts this. A human does not normally see the world as it is. One sees what one expect the world to be like. So your brain knows it is a cube that has parallel lines. To counter this:

1. Make sure you only use one eye!
2. Observe what you see, it takes a bit of time to learn to see the world as it is rather than how you think it is.*
3. if you can place it behind a window then draw the points on the window this will make it easier for you to be objective about the results. The image is now flat its easier to appraise.
4. the ruler below the eye trick by user287001 is also good for verification but you should learn to see it nonetheless.

Its worth noting that the perceptive you now train to draw is based on e a perfect pinhole camera which your eye is not!

* So you see drawing is more about learning to see what is actually there, than making marks on paper. Similar illusion happen everywhere for example did you know that eyes are smack in the middle of the face horizontally, even through it seems that more of the face is dedicated to the nose and mouth. But no thats your brain making the illusion. To draw correctly it has to be illusion free or the illusion gets applied 2 times.