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Convex and Concave Lenses Ground as a Pair

AntanO (Wikimedia Commons) · CC BY-SA 4.0

작성자

Penny

14. 10월 2026

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.

고급

Several days per pair

안내

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.

이 단계의 재료:

유리판1 개

송진 아교20 g

경목 오리목1 개

필요한 도구:

유리 칼

유리 집게

보안경

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.

이 단계의 재료:

탄화규소 연마입자50 g

물2 리터

필요한 도구:

자

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.

필요한 도구:

자

디지털 캘리퍼스 6인치

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.

이 단계의 재료:

탄화규소 연마입자30 g

산화주석(이산화주석)30 g

송진 아교100 g

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.

이 단계의 재료:

탄화규소 연마입자60 g

산화주석(이산화주석)20 g

필요한 도구:

디지털 캘리퍼스 6인치

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.

필요한 도구:

자

Focal length from the curve

Jupyter 노트북 불러오는 중…

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.