5 ms·

> When people talk about how a focal-length "compresses" or "exaggerates" an image, what they're really talking about is perspective. Each field of view carries

> When people talk about how a focal-length "compresses" or "exaggerates" an image, what they're really talking about is perspective. Each field of view carries with it its own perspective. This is kind of a misconception because what creates perspective distortion is not a given field of view, but the distance to the subject. That's why short (50-100 mm) macro lenses have a lot of perspective despite a clearly tele angle of view; you get very close to the subject. Someone using a 55 mm macro lens for photography of small products tends to be pretty obvious because of the strong perspective, things look distorted and "bulging". Of course subject size / angle of view => distance so it still kinda works.

Phrodo_00 5y ago
Yeah, I was going to point out that out when he talked about the portrait. It's not really about the focal length but about the distance you normally look at people (although your brain does a lot of compensation for wonky perspectives). Focal length doesn't change the perspective, but it just crops the image. Your feet changes the perspective.
IIAOPSW 5y ago
And, if you used an infinite zoom macro lens on a subject infinitely far away, it would not have perspective at all but instead appear as an isometric view. Where does one find an infinitely large lens? Don't worry, you can't afford it anyway. It costs infinite money. Jokes aside, the math on this really works out. Orthogonal projection is the limit as d tends to infinity of perspective projection.
- roywiggins 5y ago
  That's sort of what a telecentric lens does. https://www.lockhaven.edu/~dsimanek/3d/telecent.htm https://www.lockhaven.edu/~dsimanek/3d/telecent.htm https://www.youtube.com/watch?v=8xP4lr1ojTo https://www.youtube.com/watch?v=8xP4lr1ojTo And you can go further: the hypercentric lens. https://www.youtube.com/watch?v=iJ4yL6kaV1A https://www.youtube.com/watch?v=iJ4yL6kaV1A
- paulmd 5y ago
  > Where does one find an infinitely large lens? Don't worry, you can't afford it anyway. It costs infinite money. NRO: haha ok but anyway, where can we get one
pgreenwood 5y ago
Right, this is how I understand it too. Is it not true if you took two photos of the same subject, with say a 24mmm lens and 70mm lens, and the then cropped and enlarged the image from the 24mm lens shot, you'd end up with the same image with the same perspective?
- ISL 5y ago
  If the two images are made with the same distance between subject and camera, then yes.

Phrodo_00 5y ago

Yeah, I was going to point out that out when he talked about the portrait. It's not really about the focal length but about the distance you normally look at people (although your brain does a lot of compensation for wonky perspectives). Focal length doesn't change the perspective, but it just crops the image. Your feet changes the perspective.

IIAOPSW 5y ago

And, if you used an infinite zoom macro lens on a subject infinitely far away, it would not have perspective at all but instead appear as an isometric view. Where does one find an infinitely large lens? Don't worry, you can't afford it anyway. It costs infinite money. Jokes aside, the math on this really works out. Orthogonal projection is the limit as d tends to infinity of perspective projection.

roywiggins 5y ago
That's sort of what a telecentric lens does. https://www.lockhaven.edu/~dsimanek/3d/telecent.htm https://www.lockhaven.edu/~dsimanek/3d/telecent.htm https://www.youtube.com/watch?v=8xP4lr1ojTo https://www.youtube.com/watch?v=8xP4lr1ojTo And you can go further: the hypercentric lens. https://www.youtube.com/watch?v=iJ4yL6kaV1A https://www.youtube.com/watch?v=iJ4yL6kaV1A
paulmd 5y ago
> Where does one find an infinitely large lens? Don't worry, you can't afford it anyway. It costs infinite money. NRO: haha ok but anyway, where can we get one

pgreenwood 5y ago

Right, this is how I understand it too. Is it not true if you took two photos of the same subject, with say a 24mmm lens and 70mm lens, and the then cropped and enlarged the image from the 24mm lens shot, you'd end up with the same image with the same perspective?

ISL 5y ago
If the two images are made with the same distance between subject and camera, then yes.