Just created this post for another thread, but added it to this sticky to expand upon the principles discussed in this sticky.
Perspective -- the relationship of a subject to objects around it -- can distort our perception of its relative size.
Perspective distortion, a simple principle to illustrate for yourself, no need for any texts...
Put one hand very close to the lens (1') note how 'big' it appears to be, relative to the size of the other hand (farther from the lens). For this exercise, your front hand is 'the subject' and the rear hand is one of the 'objects surrounding the subject'.
Now without moving your two hands' position relative to one another,
- initial position 1' away from the lens, observe the relative size of the hands.
- back away from the lens by about 2' and observe the relative size of the hands.
- back away from the lens by about 4' and observe the relative size of the hands.
Now let's look at constant framing (relative to size of closest hand)...I did this via postprocessing crop, but you could have done it at time of shooting with framing change by selection of FL, at the same three shooting distances to subject as used for the previous series!
Obviously your two hands have not changed in size, only the relative distances of lens vs. each hand.
Another example of relative size, hold our hand out in front of you, as jumbo jet passes by in the sky. We know the jumbo jet truly dwarfs our hand, yet in the sky it is so small it is easily concealed from view by a hand.
And the relative size of the two hands -- at one set distance from the camera -- does NOT change simply due to the use of a different FL lens to shoot the shot. FL changes framing only, not perspective.
Camera position matters, FL of the lens is NOT what changes perspective!