Perspective – A most misunderstood Concept

Perspective – A most misunderstood Concept

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You are most certainly aware of perspective as you come across it every day. Despite that, it is a very less understood (or even a misunderstood) concept. Perspective defines the relative size of various foreground and background elements in an image and thus plays a very important role in photography.We look at images on a monitor or as a print, both of which are essentially flat (that is, two dimensional) without any depth. It is perspective that gives a feeling of depth by making foreground elements larger than the background elements. For example, you may see an image (or a print) where a person is looking taller than a high rise building. You will immediately conclude that the person is closer to the camera than the building thus creating a sense of depth.

This effect gets more pronounced as the foreground element get closer to your camera and as the distance between foreground and background elements increases. See Picture 1.

You will also see shortly, why what is often called a “distortion” is really not so but a manifestation of exaggerated perspective. Perspective is an optical property hence is not a defect whereas distortion as you have read previously in Viewfinder, is a lens defect.

1
The size of the foreground element will become relatively larger compared to the background element when distance D1 decreases and/or D2 increases.

 

Perspective, Focal Length and Subject distance: Here are a few concepts that you need to look into. Many think perspective is dependent on focal length of the lens you are using. This is not true. Perspective as you will see will only depend on the subject distance.

If you increase the subject distance by stepping back and but use a longer focal length lens to keep the foreground element of the same size, then you will find that the relative size of the background element also would have increased.

In other words, if you photograph two elements one behind the other with two lenses of different focal lengths, the relative size remains the same provided you did not change the camera position – that is distance is maintained same!

Conversely, with the same focal length you can make the relative size of the two elements change by changing the subject to camera distance.

Perspective therefore, is not dependent of focal length but on the subject distance. This concept is a little tricky to understand but plays a pivotal role in photography.

Still not convinced? Try this experiment.

Hold your thumb up. Keep one eye closed, keep your hand stretched and stick out your thumb. Now look at your thumb and a relatively distant object like a building together.  Now, move your thumb slowly closer to the eye while continuing to look. You will see that even though the focal length of your eye has not changed (God has not given us eyes that can zoom!), the size of your thumb will progressively become bigger and when it is very close to your eye, your thumb will be bigger than the building! It is that simple. So to reiterate, perspective is dependent only on the camera – subject distance and not focal length.

Practical applications: All this is fine, but how does this theory help me with my photography, you may ask.  To understand that let us look at three cases that you will come across frequently and where perspective plays a role.

Case 1 – Landscapes: Many landscape photographers exploit the concept of perspective to create apparent depth. They do this by placing the camera (usually with a wide-angle lens) very close to the foreground elements. This causes them look relatively large compared to background elements thus giving the feeling of depth (Picture 2). This is due to perspective. Now the question – if perspective is independent of focal length why do landscape photographers use wide-angle lenses? Here is the answer.

2
In this picture, the camera was placed close to the foreground elements (the steps). This has made them large relative to the fort in the background. This gives the impression of depth – that the fort is very far away. This is a classic example on use of perspective as a depth cue.

If they use lenses with a longer focal length from the same distance (other things permitting) the foreground element would have been just as large, relatively. However, long focal lengths usually don’t focus that close and due to their narrow angle of view cover only a small area.  This is the reason wide-angle lenses are used for such pictures. This also gives rise to the erroneous view (it is even written in some books) that wide angle lenses (especially super wide angle lenses) cause exaggerated perspective. This is not true. It is because of the way wide-angle lenses are used, close to the foreground elements!

Case 2: Surely you must have taken a photograph of a tall building from a close distance by standing near the base of the building. When you look at such a photograph you would have noticed that the building appears to “lean” backwards (Picture 3). It is once again due to perspective though often it is mistakenly called distortion. This is happening because you are very close to the base of building (foreground), making it look large. You are also far from the top of the building (background) making it look small. This makes the sides of building look as if they are converging at the top and hence gives the impression that the building is leaning. As explained before you will get the same effect regardless of the focal length of the lens used provided you are photographing from the same position.

3
The “leaning” of the building is due to perspective – you are close to the base and far from the top of the building. It is not because of focal length. It is not distortion, as you can see the sides of the building are straight (there is no curvature.

So how do you rectify such a situation? One solution is to move away from the building so that the relative difference in distance between (you and) the top and base of the building is very less. This reduces the difference in size (on the image) between the top and base of the building thus correcting this “leaning”. Another way is to get into a building in the front of the building you are photographing to take the picture. If both these are not possible then you need to use a tilt and shift lens or some post-processing techniques to make the slanted lines vertical.

Case 3: This concerns portraits. You might have heard many times that you should not take tight portraits using a wide angle lens. Here is the reason. If you try to fill the frame with a face with a wide angle lens, you will have to move very close to the subject. Once you do this, the nose will be very close to the camera and will look larger than what it is.  This gives a rather unflattering portrait and such a thing should not be attempted unless you want to pick up a fight with your subject!  The effect is due to perspective and this is not distortion. If you had used the same wide angle lens but had stepped back then the perspective will be more pleasing.

So you may ask why not use a wide angle lens, keep more distance to improve perspective and simply crop later? Well, there are some practical limitations. The face of the person will get progressively smaller as you move away and you need to crop heavily with all the disadvantages, – like greater enlargement required, loss of sharpness, more visibility of noise, etc. The remedy is to use a short telephoto lens (about 85mm to 105mm in 35mm format) for portraits. With a short telephoto, you can now move back for a nicer perspective and still get a picture with the face filling the frame. However, this erroneously gives rise to the impression that perspective has improved because of a longer focal length (short telephoto) lens. Not true. The perspective is now more pleasing since you stepped back. For the record a cropped image with a wide angle lens taken from the same position will be indistinguishable from the one you took with a longer focal length!

4
This portrait of a statue was taken with the camera less than a foot away from the statue. Note that the odd appearance of the statue is due to the exaggerated perspective caused by the very short camera to subject distance. The focal length has no bearing on this and also this is not distortion.
5
The same statue photographed with the same camera and lens combination. However, the subject distance was increased here. This resulted in a smaller subject size. Hence, it was cropped to give the same subject size as Picture 4. You can easily notice the much more pleasing and natural perspective. The important thing for you note is that, the perspective has improved due to increase in the subject distance though the same focal length was used. Perspective is thus independent of focal length.

 

Conclusion: You have now seen how perspective is important for landscapes, architectural photography, portraits, etc.  Here is the summary for you to remember easily:

  • Perspective essentially deals with relative size of foreground and background elements in an image.
  • It is independent of focal length but is dependent on the subject distance.
  • If you want to make the foreground elements larger compared to the background elements you need to move close to the foreground elements and to make them smaller you need to move away. Simply changing the focal length, either by zooming or by using a lens of different focal length, will not help. You must use your feet to change the perspective.
  • Even while keeping the foreground subject size the same, you can control the area of background being recorded in the image by using lenses of different focal length. A shorter focal length lens will give you a wider coverage of the background. On the other hand you can use a longer focal length to record a lesser background area. (Of course you need to increase the subject distance to keep the subject size the same when you use a longer focal length lens).

Often it is said that using fixed focal length (prime) lenses will improve one’s photography as it will force you to move rather than simply remain stationary and zoom. This statement in Author’s opinion is only partly true. What will really improve your photography is a thorough understanding of perspective. This will help you to get the right effect. If you want to keep the relative size of elements same but increase or decrease the overall image size then you must change focal length, either by zooming or by changing lenses. On the other hand, if you want to change the relative size of the elements, then you must change the subject distance. There is simply no other way!

All photographs, text and images © Ashok Kandimalla.
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