Originally posted by Kryscendo If you frame a portrait with someone square in the middle and a telephone in the background with an 85mm, the pole will look a lot closer than if you used an 18mm, stepped up closer, and had the exact framing on the person.
Yes, because you moved forward after you put the 18mm on, which reframes and changes perspective with regard to object distances.
However, if you took the shot with the 18mm and the 85mm from the exact same position, then cropped the 18mm shot to the same FOV as the 85mm, it will have the exact same 'compression' effect. It's the distance to subject that compresses, not something innate to the telephoto lens.
You would probably never crop an 18mm that much, you'd just use a longer lens. This is why people mistakingly think that it's some property of the telephoto lens that compresses the space, and it's not, it's the distance to subject.
Knowing this really only has applications in figuring out how to frame a shot, keeping the subject the same size without radically changing the relationship to background when you have to move around for whatever reason. In practice a telephoto can be used to 'compress' things more effectively than a wide-angle lens because you don't have to crop the telephoto image at all
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