Compression is Real

Started 11 months ago | Discussions thread
dsjtecserv Veteran Member • Posts: 3,754

Brian_Flex wrote:

Mike CH wrote:

Brian_Flex wrote:

Incorrect. The focal length changes perspective.

As you can easily see in the illustration you provided, the view point was changed between the two shots. The black dot is much closer to the foreground cowboy in the left example. This, and not the focal length, changes the perspective.


And the explanation in first paragraph of the illustration is wrong. A wideangle lens and a tele cannot have the same field of view.

Regards, Mike

Firstly, the documentation is correct. Secondly, I responded to the poster who wrote:

"Changing the focal length of a lens doesn't affect the perspective of the picture. But, subject distance does."

The point of having different focal lengths is to change perspective, otherwise we'd shoot an entire movie on a 25mm lens, and I'd be out of a job.

In response to your statement, "a wide-angle lens and a tele cannot have the same field of view". You are correct, they don't have the same FOV, but it clearly illustrates keeping the subject the same size.

The change in distance is the cause; the change in focal length is the effect, When you change your shooting position relative to the subjects, you have change the perspective, period. You then have a choice as to how to frame the scene. You can leave the focal length the same and frame the scene wider than before, or you can adjust the focal length so that the field of view is narrower than before, and keep one or the other of your subjects the same size as before.

So while you may choose to change the focal length as a consequence of your change of position, there is no sense in which the change in focal length causes the change in perspective. That was already done when you moved.

Even if you choose a focal length first, and then move back in order to recreate the framing you had, the change in perspective does not happen until you change your position. If you change to a longer focal length but don't move, the framing becomes tighter, but the perspective (the size relationships among the objects in the scene) does not change.


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