IṢẸ́ ỌNÀ
ẸWÀ ÀTI ÌLERA
IṢẸ́ ỌWỌ́
ÀṢÀ ÀTI ÌTÀN
ÌṢERÉ
ÀYÍKÁ
OÚNJẸ ÀTI OHUN MÍMU
REVERSE ENGINEERING
SÁYẸ́ǸSÌ
ERÉ ÌDÁRAYÁ
ÌMỌ̀-Ẹ̀RỌ
ÀWỌN OHUN WÍWỌ̀
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.
Àárín
2 hours
Ìlànà
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.
Àwọn ohun èlò fún ìgbésẹ̀ yìí:
Fíìmù tí ó tàn fún inkjet1 ewé
Tépù ìbòmọ́lẹ̀1 ìyípoÀwọn irinṣẹ́ tí a nílò:
Ààmì Tí Kò Ní Parẹ́
Tọ́ọ̀ṣì LED fún àyẹ̀wò
Ìwọ̀n Irin2
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.
Àwọn ohun èlò fún ìgbésẹ̀ yìí:
Àkójọ ẹ̀rọ ìgbéhìn tí ó gbò1 ìtò
Lẹ́ǹsì tí ó gbẹ̀gbẹ́1 ẹyọÀwọn irinṣẹ́ tí a nílò:
Tábìlì ìmọ̀ ìmọ́lẹ̀ àti ojú irin
Ìṣètò ìdìmú lẹ́ńsì3
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.
Àwọn irinṣẹ́ tí a nílò:
Okùn Ìdíwọ̀n4
4
Focal length vs position
Focal length vs position
Ń ṣí ìwé Jupyter…
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.
Àwọn ohun-èlò
4- Àyè
- 1 ìyípoÀyè
- Àyè
- 1 ẹyọÀyè
Àwọn irinṣẹ́ tó nílò
6- Àyè
- Àyè
- Ìṣètò ìdìmú lẹ́ńsììdá 10%Àyè
- 1 vendor sell this, none ship to you yetÀyè
Blueprint tó jọra
Àwọn blueprint wọ̀nyí pín ìmọ̀ — ọ̀nà, ohun-èlò tàbí ìlànà
CC0 Àgbègbè Gbogbogbò
Blueprint yìí ti jáde lábẹ́ CC0. O lè ṣe àdàkọ, yí padà, pín, àti lò láìsí ìyọ̀ǹda.
Ṣàtìlẹ́yìn Olùṣẹ́dá nípa rírà àwọn ọjà nipasẹ̀ Blueprint wọn Ẹ̀san Olùṣẹ́dá tí àwọn Olùtajà gbé kalẹ̀, tàbí ṣẹ̀dá àtúnṣe tuntun ti Blueprint yìí kí o sì fi sínú Blueprint rẹ gẹ́gẹ́ bí ìsopọ̀ láti pín owó-wíwọlé.