Spherical correction stage for 24 inch mirror completed

自製天文望遠鏡 牛頓望遠鏡 杜蘇式 卡式 設計和磨鏡方法<br>
佛科試鏡法 佛科刀片儀 光柵試鏡法 光柵片
文章: 3837
註冊時間: 週四 09 10月, 2003 21:06

Spherical correction stage for 24 inch mirror completed

文章 Chanlunlun » 週一 16 2月, 2004 10:12

Dear ATMs,

After the finishing of rough grinding we proceed to surface correction stage. We place the mirror on bottom and tool on top hoping that it would bring the curve back to f/3.5.

It was after a continuous of SIX and A HALF HOURS of grinding with #40 crab did we see the two surfaces start to match each other. The time required to bring the surface down to a true sphere was unexpectedly long. The final focal length of the mirror is 82 inches or f/3.4. The remaining discrepancy will be further corrected during the coming #80 fine grinding stage. Our aim is to keep the edge thickness of the mirror as thick as possible to avoid astigmatism of mirror during mounting on the mirror cell.

Sometimes thing could happen in an unexpected way.

Best regards
Chan Yuk Lun
What a big hole !
The hole represented unmatched surface between mirror and tool. The red line was drawn through the center of the mirror as shown. When the red line vanished, it meant that a true spherical surface was achieved. To our surprise the thin
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