I origianly posted this 3 years ago, but recently was brought up again when a challenge to prove that sensor size will affect perspective. Here is the original posting I did.
Perspective is used to define the relationship of subject size in relation to the background. Though many use the term incorrectly, suggesting that a wide angle lens has a different perspective as a telephoto lens. Saying such is not completely true nor is it completely false. Usually when we use a wide angle lens and shoot subjects at very close distance, the subject appears larger than the background thus giving us an exagerated perspective, while when using a telephoto and shooting subjects at a distance, we get a subject that appears similar sized as our background or we can say we have a compressed perspective. Though the example shows that a wide angle and telephoto has different perspective, but the key here is not the focal length use but the distance of the camera and subject. Perspective is solely a function of disitance of camera and subject, meaning no matter what lens is used for as long as camera and subject remain in the same position, perspective will be the same. Focal length affects distortion (barrel or pin cushion) and field of view.
Here is a little test I did:
I did a series of photos of a static subject and the camera on a tripod. I used the following lenses:
Nikon 16mm F2.8 Fisheye
Nikon 28mm F2.8
Nikon 50mm F1.8
Nikon 60mm F2.8 Macro
Nikon 85mm F1.8
Sigma 15-30mm @ 15mm
All shot at F5.6, I converted it to black and white to avoid confusion with color rendition. I also cropped everything to make the subject all relatively same size. Can you easily tell which was shot with which focal length? This clearly shows that perspective is similar no matter what lens is used, for as long as subject to camera distance is the same.
Now here is a more recent test that I did:
Persepective or the compression effect or exagerated effect has nothing to do with the sensor, if you shot a subject at the same distance (ex. 5 ft away using 50mm on a crop body and a 75mm on a FF) their perspective is going to be the same, the difference is depth of field which is around 1 stop. Remember perspective is a function of distance not focal length nor sensor size.
2 photos shot with a D90 @ 135mm and D700 @ 200mm, using the same zoom lens (to keep quality constant) and distance. Only had to adjust aperture (D90 @f/4 and D700 @f/5.6) to equalize the DOF. You be the judge if there is any difference in perspective.
You can bring out your ruler then measure the size of the cow and the martian at the back then see how similar the ratio is, which simply means perspective was neither compressed nor exagerated by changing camera and focal length since the key here is distance to subject, which in both photos are similar.
If you want to do a practical excercise, try this:
Part 1 – Keeping perspective similar
1. Make sure you a way to keep the camera at the same place for the first half of this activity. A tripod is reccomended.
2. Use multiple focal length lenses or a zoom lens.
3. Line up 2 still objects, preferably 1 is double the size of the other. Put the larger object behind the smaller one.
4. Shoot with a small aperture to make DOF wide enough for us to see the subject and background.
5. Shoot at different focal length while still keeping the focus on the smaller object at all time.
As you do this you will notice the subject (or the object in focus) will keep changing magnification, but the amount of magnification will be proportional to the rear object. This proportional gain is what perspective is all about, keeping the ratio of the subject to the background similar means perspective is the same. To see the similarity, you can gather all your photos in an editing software and crop the images to keep the subject appearing the same size. You can even measure the front object (subject) from the rear object (background) and see how the ratio of their size will remain the same all throughout the test.
Part 2 – Keeping magnification similar
1. Once again I reccomend using a zoom lens.
2. Zoom in to the subject and note size of the subject relative to the whole photo.
3. Now after each shot, change the focal length to a wider one (zoom out) but to keep the subject to appear the same size as the previous shot, so you have to keep stepping forward. Do this until you have max out the wideness of your lens.
As you do this you will notice that though the size of the subject will remain the same, the object at the rear will appear to get smaller and smaller. This is what you call an exagerated perspective.
These test will prove that perspective can only be altered if distance to subject is changed, no other things can affect perspective.
