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Magnifying Glass from a Hand-Ground Lens
A magnifying glass is a convex lens in a frame with a handle. A typical one has a focal length of 25 cm, an optical power of 4 dioptres, and is sold as "2×": its magnifying power is 0.25 m × 4 + 1 = 2 for an eye whose near point is 25 cm. Here the lens is ground plano-convex from crown glass (refractive index about 1.52). For a plano-convex lens the focal length is R / (n − 1), so a 25 cm focal length needs a curve of radius about 13 cm. The lens is then set in a turned wooden ring with a handle; those sizes are ours.
高级
2–3 days
说明
1
1
Grind the lens
Grind the lens
Following the lens-grinding blueprint, grind one face of a glass disc to a spherical curve of about 13 cm radius, working down through the grits, then polish it clear with cerium oxide on a pitch lap. Leave the other face flat.
此步骤所需材料：
玻璃板1 个
碳化硅磨料200 克
氧化铈抛光粉50 克
松脂胶100 克所需工具：
直尺2
2
Check the focus
Check the focus
Hold the lens in sunlight and move a card behind it until the spot is smallest; the distance from lens to card is the focal length and should be close to 25 cm. Do not look at the Sun through it.
所需工具：
直尺3
3
Turn the frame
Turn the frame
Turn a ring from a hardwood blank with a groove on the inside just wider than the lens edge, and part it off.
此步骤所需材料：
枫木碗坯1 个所需工具：
木工车床
圆凿
车床切断刀4
4
Turn the handle
Turn the handle
Turn a handle from a hardwood dowel and fix it into a hole drilled in the ring.
此步骤所需材料：
硬木销钉1 个
双组分环氧胶5 毫升所需工具：
木工车床5
5
Set the lens
Set the lens
Saw the ring through at the handle, spring the lens into the groove, glue the cut closed and wax the wood.
此步骤所需材料：
蜂蜡10 克材料
8- 1 个占位符
- 200 克占位符
- 50 克占位符
- 100 克占位符
- 1 个占位符
- 1 个占位符
- 5 毫升占位符
- 10 克占位符
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