Perceiving Depth

[Noakram]

This is a useful thread on perception of depth. It is in Chinese.

http://www.mobile01.com/topicdetail.php?f=257&t=417877&last=3875056

 

[cantaresg]

Interesting. For the benefit of those who cannot understand Chinese, or have difficulties, let me try to translate the document.

(below image 3)
Controlling the perspective of an image is simply controlling the size of the foreground and background in the picture.

Comparing image 1 and 2,
using packet drinks of similar size, "I" have taken the picture such that the packet on the right appears bigger.
Using packet drinks of similar size, "I" have taken the picture such that the packet at the centre appears smaller.

In this case, when there is an increase and decrease in the size of the object at the same time, there is a change in perspective.
This can only be achieved by a change in the distance between the object and you, and a change in the field of view.

(Image 4-6)

4. -> 5. The position in which the picture is taken is not changed, while the field of view is changed.
All three packet drinks increased in size at the same time, this means that the perspective is not changed.

(Image 7-8)

Now here's the main point.
From image 4, I had added another two packets.
Though in theory, image 7 and image 5 has the same perspective,
people tend to compare the sizes of different objects.

Thus, even though image 4 and 7 has the same perceptive, the [perspective feeling] is totally different.

*Correct me if I had translated anything wrongly.

 

[Noakram]

Interesting. For the benefit of those who cannot understand Chinese, or have difficulties, let me try to translate the document.

(below image 3)
Controlling the perspective of an image is simply controlling the size of the foreground and background in the picture.

Comparing image 1 and 2,
using packet drinks of similar size, "I" have taken the picture such that the packet on the right appears bigger.
Using packet drinks of similar size, "I" have taken the picture such that the packet at the centre appears smaller.

In this case, when there is an increase and decrease in the size of the object at the same time, there is a change in perspective.
This can only be achieved by a change in the distance between the object and you, and a change in the field of view.

(Image 4-6)

4. -> 5. The position in which the picture is taken is not changed, while the field of view is changed.
All three packet drinks increased in size at the same time, this means that the perspective is not changed.

(Image 7-8)

Now here's the main point.
From image 4, I had added another two packets.
Though in theory, image 7 and image 5 has the same perspective,
people tend to compare the sizes of different objects.

Thus, even though image 4 and 7 has the same perceptive, the [perspective feeling] is totally different.

*Correct me if I had translated anything wrongly.

Thanks for the translation.

 

[Clockunder]

Thanks.

It really put across some very important photograhy information which is often not so apparent to many photogaphers.

Perspective doesn't change with focal length and only changes with shooting distance.

In this regard, perspective refers to the relative sizes of things in the picture. This means that although the field of view (what is included and seen in the picture) changes with a change in focal length, the perspective remains.

This can be explained from a technical point of view :

De-Magnification factor is f/D where f is the actual focal length and D is the distance.

For e.g. A 3.6m x 2.4m sign board shot with a full frame camera standing from 20m with a 200mm lens will have a de-magnification factor of

200mm/20m = 200/20,000 = 1/100 times.

So the sign board will become 3.6m/100 x 2.4m/100 = 36mm x 24mm image which fits just nicely on the 36mmx24mm image sensor of the full frame.

If there are 2 objects A and B at shooting distances D1 and D2 away where D1 is nearer than D2, then their de-magnification factors would be :

f/D1 and f/D2.

So the relative size of A over B in the picture will always be D2/D1.

1) As long as the shooting distance remains the same (i.e. D1 and D2 is fixed), their de-magnification ratio remains the same D2/D1 regardless of what focal length f you use.

2) If you move nearer by Y cm, then their distances would be D1-Y and D2-Y

So their ratio will become (D2-Y)/(D1-Y) which becomes mathematically a bigger ratio than D2/D1.

So if you move closer, the difference of their de-magnification become more pronounced.

3) If you move further away by Z cm, then the ratio becomes :

(D2+Z)/(D1+Z) which is a mathematically a smaller ratio than D2/D1.

Thus, the difference in their image sizes becomes less pronounced if you move further away.

=====
From a photography point of view, interesting pictures are often made with an interesting/refreshing perspective.

Don't be too lazy to just use your zoom. Zooming will only give the same perpective which may make only a boring picture.

Instead, use your legs to move nearer to or further away from the subjects to give the picture the perspective you want to show.