LIST
FEGURÐ OG VELLÍÐAN
HANDVERK
MENNING OG SAGA
SKEMMTUN
UMHVERFI
MATUR OG DRYKKUR
ÖFUGVERKFRÆÐI
VÍSINDI
ÍÞRÓTTIR
TÆKNI
KLÆÐANLEG TÆKNI
Varifocal Projection Objective
A lantern-slide projector threw one fixed picture size at a given distance; to fill a different screen, the lantern had to be carried closer or further. Clile C. Allen of Chicago put three lenses in one tube, fixed the first and last, and made the middle one slide on a spiral track as the tube was turned - changing the focal length, and so the picture size, from the same spot. A rack and pinion moved the whole tube to refocus.
**US 696,788**, "Optical objective", Allen, filed 25. February 1901, granted 1. April 1902: "three lens elements, the first and third of which are permanently fixed … while the second is movable and capable of being placed in any intermediate position". It is one of the earliest variable-focal-length objectives - the idea behind every zoom lens.
**You build it on a bench as a projector**, and measure picture size against the middle lens's position.
Miðlungs
2 hours
Leiðbeiningar
1
1
Draw a slide
Draw a slide
Draw a 24 mm square grid with a marker on transparency film. Tape it over the torch lens: this is the lantern.
Efni fyrir þetta skref:
Glæra fyrir bleksprautuprentara1 plata
Málningarlímband1 rúllaNauðsynleg verkfæri:
Merkipenni
LED-skoðunarljós
Stálreglustika2
2
Mount three lenses
Mount three lenses
Wall side: convex ~100 mm. Slide side: convex ~50 mm, 80 mm from the first. Between them: concave ~-50 mm on a holder that slides. Aim the bench at a wall 2 m away with the lit slide behind the 50 mm lens.
Efni fyrir þetta skref:
Safn safnlinsa1 sett
Íhvolf linsa1 stykkiNauðsynleg verkfæri:
Ljósfræðibekkur og braut
Linsuhaldarasett3
3
Slide, refocus, measure
Slide, refocus, measure
Set the middle lens 10 mm from the wall-side lens. Move the slide (or the whole lens group) until the grid is sharp on the wall; measure its width. Repeat at 30 and 60 mm.
Nauðsynleg verkfæri:
Málband4
4
Focal length vs position
Focal length vs position
Hleð Jupyter-vinnubók…
5
5
History & Context
History & Context
**What the patent specifies:** a three-element objective with fixed outer elements and a movable middle element carried by a spiral track, plus a rack and pinion to move the whole tube. **Modern build (derived):** stock lenses on an optical bench.
Allen's lens must be refocused after each change - a varifocal. A true zoom keeps focus while zooming by moving two groups together, which came later with cam-driven designs. Its limits: the picture dims as it grows, and aberrations change across the range.
Efni
4- Staðgengill
- 1 rúllaStaðgengill
- 1 settStaðgengill
- 1 stykkiStaðgengill
Nauðsynleg verkfæri
6- Staðgengill
- Staðgengill
- Staðgengill
- Ljósfræðibekkur og braut10% þóknunStaðgengill
- Linsuhaldarasett10% þóknunStaðgengill
- 1 vendor sell this, none ship to you yetStaðgengill
Tengd Blueprint
Þessi blueprint deila þekkingu — tækni, efni eða meginreglur
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