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REVERSE ENGINEERING
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ÀWỌN OHUN WÍWỌ̀
Convex and Concave Lenses Ground as a Pair
Rub one glass disc over another with wet grit and both change shape: the one on top goes hollow, the one beneath goes domed, and they stay a perfect fit. Grind both faces of a pair this way and the bottom disc becomes a double-convex lens, the top one a double-concave lens of the same curve. Longer work gives deeper curves and shorter focal lengths.
The picture: a double-convex lens held at arm's length shows the scene small and upside down.
Ilọsíwájú
Several days per pair
Ìlànà
1
1
Cut two discs
Cut two discs
Score two equal circles on the glass sheet, snap them out and nibble the edges round with grozing pliers. Fix a short wooden handle to the back of each with warm pitch.
Àwọn ohun èlò fún ìgbésẹ̀ yìí:
Àwo dígí1 ẹyọ
Lẹ́ẹ̀ Oda Páínì20 g
Tẹ́ẹ́rẹ́ igi líle1 ẹyọÀwọn irinṣẹ́ tí a nílò:
Ohun ìgé dígí
Ẹmú ìjẹ gíláàsì
Gíláàsì ààbò2
2
Rough grind the first faces
Rough grind the first faces
Lay one disc face up on a firm table, wet it and sprinkle coarse grit. Push the other disc over it, face down, in short strokes, turning both a little all the time. The top one becomes concave, the bottom convex. Rinse and recharge as the grit wears.
Àwọn ohun èlò fún ìgbésẹ̀ yìí:
Omi2 lítàÀwọn irinṣẹ́ tí a nílò:
Ìdíwọ̀n
Ọkà kaboidi silikoni3
3
Check the curve
Check the curve
Lay a ruler across the hollow disc and measure the depth at the centre with the caliper. Keep the top disc on top to deepen the curve; swap them to flatten it.
Àwọn irinṣẹ́ tí a nílò:
Ìdíwọ̀n
Òṣùwọ̀n Kálípà Díjítà Ìnṣì 64
4
Fine grind and polish
Fine grind and polish
Go through finer grits, washing everything clean between grits. Polish each face on a pitch lap pressed to the other disc's curve, with tin oxide (putty powder) and water, until clear.
Àwọn ohun èlò fún ìgbésẹ̀ yìí:
Oxide tìnì (oxide stannic)30 gLẹ́ẹ̀ Oda Páínì100 gÀwọn irinṣẹ́ tí a nílò:
Ọkà kaboidi silikoni5
5
Turn them over, do the second faces
Turn them over, do the second faces
Move the handles to the finished faces and grind the other sides the same way, the same disc on top, to the same depth. The bottom disc is now a double-convex lens, the top one double-concave.
Àwọn ohun èlò fún ìgbésẹ̀ yìí:
Oxide tìnì (oxide stannic)20 gÀwọn irinṣẹ́ tí a nílò:
Òṣùwọ̀n Kálípà Díjítà Ìnṣì 6Ọkà kaboidi silikoni6
6
Find the focal length
Find the focal length
Hold the convex lens in sunlight over paper and move it until the spot is smallest; that distance is its focal length. Grind more pairs to different depths for a set of focal lengths.
Àwọn irinṣẹ́ tí a nílò:
Ìdíwọ̀n7
7
Focal length from the curve
Focal length from the curve
Ń ṣí ìwé Jupyter…
8
8
Limits
Limits
Which disc goes hollow is the mirror makers' rule (Sky & Telescope, Stellafane); the lens formula is from Wikipedia. Window glass is not optical glass: expect some colour fringes and bubbles.
Àwọn ohun-èlò
5- 1 ẹyọÀyè
- 120 gÀyè
- 1 ẹyọÀyè
- 2 lítàÀyè
- Àyè
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