What is a telephoto lens?
A telephoto lens is a long‑focus lens whose physical length is shorter than its focal length, achieved by a special telephoto group that folds the light path.
It’s like a telescope that’s been folded up so it fits in a smaller tube but still lets you see far away objects.
How it works
A telephoto lens uses a front group of converging elements and a rear group of diverging elements called the telephoto group. This combination shortens the lens body while keeping the same focal length as a longer lens.
What it does and doesn’t do
It provides the same angle of view as a long‑focus lens of the same focal length, but it is physically more compact. It does not change the magnification; it only reduces size and weight.
What to check before buying
Look at the telephoto ratio (physical length ÷ focal length) – a value below 1 confirms a true telephoto design. Also consider optical quality, aperture, and whether the lens includes extra features like diffractive optics.
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▸ QUICK QUESTIONS
- Why is it called 'telephoto'?
- Because it lets you photograph distant subjects as if you had a longer lens, while the lens itself is shorter.
- Can any long lens be called telephoto?
- No. Only lenses that use a telephoto group to shorten the physical length qualify as true telephoto lenses.
- Do telephoto lenses work for video as well as photos?
- Yes, the optical design works the same for both still images and moving video.
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