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Telephoto Lens
To photograph a distant subject large, you need a long focal length - and a long lens means a long camera. In 1891 Thomas Rudolphus Dallmeyer in London, and Adolf Miethe in Germany, independently put a negative lens behind a positive one. The pair acts like a single lens of much longer focal length, yet it is physically shorter than that focal length. That is what 'telephoto' means, and nearly every long camera lens since uses it.
**No patent number is cited here**: Dallmeyer patented it in Britain, and no US patent for his design was verified, so none is claimed.
**You build one on an optical bench**, measure its focal length from the size of a distant image, and let a ray-trace notebook redesign it.
Mwanzo
90 minutes
Maagizo
1
1
Know your lenses
Know your lenses
Focus a distant window onto paper with each convex lens; the lens-to-paper distance is its focal length. Pick one about 100 mm. Take a concave lens about half that (its label gives it; it will not focus alone).
Vifaa kwa hatua hii:
Seti ya lenzi mbonyeo1 seti
Lenzi bonyeo1 kipandeZana zinazohitajika:
Rula ya chuma2
2
Set up the bench
Set up the bench
Mount the convex lens in a holder at one end of the bench, pointing out of a window at something far away. Tape tracing paper to a holder as the screen.
Vifaa kwa hatua hii:
Roli ya karatasi ya kufuatilia mifano1 karatasi
Utepe wa kufunika1 roliiZana zinazohitajika:
Meza ya macho na reli
Seti ya vishikio vya lenzi3
3
Image with one lens
Image with one lens
Slide the screen until the far scene is sharp. Measure the height of one chosen feature on the screen - a window, a chimney.
Zana zinazohitajika:
Rula ya chuma4
4
Add the negative lens
Add the negative lens
Put the concave lens 60 mm behind the convex one. The image is now far behind; move the screen back until it is sharp again and measure the same feature. Try 55 and 65 mm spacing too.
Zana zinazohitajika:
Tepi ya kupimia5
5
Design it on paper
Design it on paper
Inapakia daftari la Jupyter…
6
6
History & Context
History & Context
**What the 1891 designs did:** a positive front group and a negative rear group, spaced so the system focal length exceeds its length. **Modern build (derived):** two stock lenses on a bench.
Early telephoto attachments screwed behind ordinary lenses; modern long lenses build the idea in. Its limits: spacing is critical, the negative group adds distortion (pincushion), and the image is dimmer at the same aperture diameter because the focal length grew.
Vifaa
4- 1 setiKishikilia Nafasi
- 1 kipandeKishikilia Nafasi
- 1 karatasiKishikilia Nafasi
- 1 roliiKishikilia Nafasi
Zana Zinazohitajika
4- Kishikilia Nafasi
- Meza ya macho na reliKamisheni 10%Kishikilia Nafasi
- Seti ya vishikio vya lenziKamisheni 10%Kishikilia Nafasi
- 1 vendor sell this, none ship to you yetKishikilia Nafasi
Blueprint zinazohusiana
Blueprint hizi zinashiriki maarifa — mbinu, vifaa au kanuni
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