{"id":570890,"date":"2026-07-27T15:02:13","date_gmt":"2026-07-27T08:02:13","guid":{"rendered":"https:\/\/hoanghamobile.com\/tin-tuc\/?p=570890"},"modified":"2026-07-27T15:02:13","modified_gmt":"2026-07-27T08:02:13","slug":"thau-kinh-hoi-tu-la-gi","status":"publish","type":"post","link":"https:\/\/hoanghamobile.com\/tin-tuc\/thau-kinh-hoi-tu-la-gi\/","title":{"rendered":"Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 l\u00e0 g\u00ec? \u0110\u1eb7c \u0111i\u1ec3m \u1ea3nh, c\u00f4ng th\u1ee9c v\u00e0 \u1ee9ng d\u1ee5ng"},"content":{"rendered":"<p><strong>Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 l\u00e0 th\u1ea5u k\u00ednh c\u00f3 ph\u1ea7n r\u00eca m\u1ecfng h\u01a1n ph\u1ea7n gi\u1eefa, c\u00f3 kh\u1ea3 n\u0103ng l\u00e0m h\u1ed9i t\u1ee5 ch\u00f9m tia s\u00e1ng song song t\u1ea1i m\u1ed9t \u0111i\u1ec3m g\u1ecdi l\u00e0 ti\u00eau \u0111i\u1ec3m.<\/strong> Lo\u1ea1i th\u1ea5u k\u00ednh n\u00e0y c\u00f2n \u0111\u01b0\u1ee3c g\u1ecdi l\u00e0 th\u1ea5u k\u00ednh l\u1ed3i, c\u00f3 ti\u00eau c\u1ef1 mang gi\u00e1 tr\u1ecb d\u01b0\u01a1ng v\u00e0 xu\u1ea5t hi\u1ec7n trong r\u1ea5t nhi\u1ec1u thi\u1ebft b\u1ecb quen thu\u1ed9c nh\u01b0 k\u00ednh l\u00fap, m\u00e1y \u1ea3nh, k\u00ednh hi\u1ec3n vi hay m\u1eaft k\u00ednh cho ng\u01b0\u1eddi vi\u1ec5n th\u1ecb. \u0110\u00e2y l\u00e0 ph\u1ea7n ki\u1ebfn th\u1ee9c quan tr\u1ecdng trong ch\u01b0\u01a1ng tr\u00ecnh V\u1eadt l\u00fd l\u1edbp 9 v\u00e0 l\u1edbp 11. N\u1ed9i dung d\u01b0\u1edbi \u0111\u00e2y s\u1ebd gi\u00fap b\u1ea1n hi\u1ec3u r\u00f5 b\u1ea3n ch\u1ea5t, \u0111\u01b0\u1eddng truy\u1ec1n tia s\u00e1ng, \u0111\u1eb7c \u0111i\u1ec3m \u1ea3nh, c\u00f4ng th\u1ee9c t\u00ednh to\u00e1n c\u00f9ng b\u00e0i t\u1eadp c\u00f3 l\u1eddi gi\u1ea3i chi ti\u1ebft \u0111\u1ec3 n\u1eafm ch\u1eafc d\u1ea1ng b\u00e0i quang h\u00ecnh.<\/p>\n<h2>Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 l\u00e0 g\u00ec?<\/h2>\n<p>Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5, hay th\u1ea5u k\u00ednh r\u00eca m\u1ecfng, l\u00e0 kh\u1ed1i ch\u1ea5t trong su\u1ed1t (th\u01b0\u1eddng l\u00e0 th\u1ee7y tinh ho\u1eb7c nh\u1ef1a) c\u00f3 ph\u1ea7n gi\u1eefa d\u00e0y h\u01a1n ph\u1ea7n r\u00eca. Khi m\u1ed9t ch\u00f9m tia s\u00e1ng song song v\u1edbi tr\u1ee5c ch\u00ednh chi\u1ebfu t\u1edbi, th\u1ea5u k\u00ednh s\u1ebd b\u1ebb cong v\u00e0 l\u00e0m c\u00e1c tia l\u00f3 h\u1ed9i t\u1ee5 v\u1ec1 c\u00f9ng m\u1ed9t \u0111i\u1ec3m. \u0110\u00e2y l\u00e0 \u0111i\u1ec3m kh\u00e1c bi\u1ec7t c\u01a1 b\u1ea3n so v\u1edbi th\u1ea5u k\u00ednh ph\u00e2n k\u1ef3 (r\u00eca d\u00e0y h\u01a1n gi\u1eefa, l\u00e0m ch\u00f9m tia loe r\u1ed9ng ra). Ch\u00ednh kh\u1ea3 n\u0103ng &#8220;gom&#8221; \u00e1nh s\u00e1ng n\u00e0y khi\u1ebfn th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 tr\u1edf th\u00e0nh b\u1ed9 ph\u1eadn quang h\u1ecdc c\u1ed1t l\u00f5i trong h\u1ea7u h\u1ebft c\u00e1c d\u1ee5ng c\u1ee5 t\u1ea1o \u1ea3nh.<\/p>\n<p><img fetchpriority=\"high\" decoding=\"async\" class=\"aligncenter size-full wp-image-570891\" src=\"https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/thau-kinh-hoi-tu-1.jpg\" alt=\"thau-kinh-hoi-tu-1\" width=\"800\" height=\"450\" srcset=\"https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/thau-kinh-hoi-tu-1.jpg 800w, https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/thau-kinh-hoi-tu-1-300x169.jpg 300w, https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/thau-kinh-hoi-tu-1-768x432.jpg 768w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/><\/p>\n<h2>C\u00e1c kh\u00e1i ni\u1ec7m c\u01a1 b\u1ea3n c\u1ea7n n\u1eafm<\/h2>\n<p>Tr\u01b0\u1edbc khi d\u1ef1ng \u1ea3nh hay \u00e1p d\u1ee5ng c\u00f4ng th\u1ee9c, b\u1ea1n c\u1ea7n thu\u1ed9c b\u1ed1n kh\u00e1i ni\u1ec7m n\u1ec1n t\u1ea3ng sau \u0111\u00e2y:<\/p>\n<ul>\n<li><strong>Tr\u1ee5c ch\u00ednh:<\/strong> \u0111\u01b0\u1eddng th\u1eb3ng \u0111i qua quang t\u00e2m v\u00e0 vu\u00f4ng g\u00f3c v\u1edbi m\u1eb7t th\u1ea5u k\u00ednh.<\/li>\n<li><strong>Quang t\u00e2m (O):<\/strong> \u0111i\u1ec3m gi\u1eefa th\u1ea5u k\u00ednh; m\u1ecdi tia s\u00e1ng \u0111i qua quang t\u00e2m \u0111\u1ec1u truy\u1ec1n th\u1eb3ng, kh\u00f4ng \u0111\u1ed5i h\u01b0\u1edbng.<\/li>\n<li><strong>Ti\u00eau \u0111i\u1ec3m (F):<\/strong> \u0111i\u1ec3m m\u00e0 ch\u00f9m tia song song v\u1edbi tr\u1ee5c ch\u00ednh h\u1ed9i t\u1ee5 t\u1edbi sau khi qua th\u1ea5u k\u00ednh. Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 c\u00f3 hai ti\u00eau \u0111i\u1ec3m \u0111\u1ed1i x\u1ee9ng qua quang t\u00e2m.<\/li>\n<li><strong>Ti\u00eau c\u1ef1 (f):<\/strong> kho\u1ea3ng c\u00e1ch t\u1eeb quang t\u00e2m \u0111\u1ebfn ti\u00eau \u0111i\u1ec3m; v\u1edbi th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5, f lu\u00f4n mang gi\u00e1 tr\u1ecb d\u01b0\u01a1ng (f &gt; 0).<\/li>\n<\/ul>\n<p>Ti\u00eau c\u1ef1 c\u00e0ng nh\u1ecf th\u00ec kh\u1ea3 n\u0103ng h\u1ed9i t\u1ee5 \u00e1nh s\u00e1ng c\u1ee7a th\u1ea5u k\u00ednh c\u00e0ng m\u1ea1nh. Ngo\u00e0i ra, kho\u1ea3ng c\u00e1ch g\u1ea5p \u0111\u00f4i ti\u00eau c\u1ef1 (2f) l\u00e0 m\u1ed1c quan tr\u1ecdng \u0111\u1ec3 x\u00e1c \u0111\u1ecbnh t\u00ednh ch\u1ea5t \u1ea3nh, b\u1ea1n s\u1ebd th\u1ea5y r\u00f5 \u1edf ph\u1ea7n b\u1ea3ng b\u00ean d\u01b0\u1edbi.<\/p>\n<p><img decoding=\"async\" class=\"aligncenter size-full wp-image-570892\" src=\"https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/thau-kinh-hoi-tu-2.jpg\" alt=\"thau-kinh-hoi-tu-2\" width=\"800\" height=\"450\" srcset=\"https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/thau-kinh-hoi-tu-2.jpg 800w, https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/thau-kinh-hoi-tu-2-300x169.jpg 300w, https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/thau-kinh-hoi-tu-2-768x432.jpg 768w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/><\/p>\n<h2>\u0110\u01b0\u1eddng \u0111i c\u1ee7a ba tia s\u00e1ng \u0111\u1eb7c bi\u1ec7t<\/h2>\n<p>\u0110\u1ec3 d\u1ef1ng \u1ea3nh c\u1ee7a m\u1ed9t v\u1eadt qua th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5, ta d\u1ef1a v\u00e0o ba tia s\u00e1ng \u0111\u1eb7c bi\u1ec7t c\u00f3 \u0111\u01b0\u1eddng truy\u1ec1n \u0111\u00e3 bi\u1ebft tr\u01b0\u1edbc:<\/p>\n<ul>\n<li>Tia t\u1edbi <strong>song song v\u1edbi tr\u1ee5c ch\u00ednh<\/strong> cho tia l\u00f3 \u0111i qua ti\u00eau \u0111i\u1ec3m F \u1edf ph\u00eda b\u00ean kia th\u1ea5u k\u00ednh.<\/li>\n<li>Tia t\u1edbi <strong>\u0111i qua quang t\u00e2m O<\/strong> cho tia l\u00f3 ti\u1ebfp t\u1ee5c truy\u1ec1n th\u1eb3ng, kh\u00f4ng \u0111\u1ed5i ph\u01b0\u01a1ng.<\/li>\n<li>Tia t\u1edbi <strong>\u0111i qua ti\u00eau \u0111i\u1ec3m F<\/strong> cho tia l\u00f3 song song v\u1edbi tr\u1ee5c ch\u00ednh.<\/li>\n<\/ul>\n<p>Trong th\u1ef1c h\u00e0nh, b\u1ea1n ch\u1ec9 c\u1ea7n v\u1ebd hai trong ba tia l\u00e0 \u0111\u00e3 x\u00e1c \u0111\u1ecbnh \u0111\u01b0\u1ee3c v\u1ecb tr\u00ed \u1ea3nh: giao \u0111i\u1ec3m c\u1ee7a hai tia l\u00f3 ch\u00ednh l\u00e0 \u1ea3nh th\u1eadt, c\u00f2n n\u1ebfu hai tia l\u00f3 ph\u00e2n k\u1ef3 th\u00ec giao \u0111i\u1ec3m c\u1ee7a ph\u1ea7n k\u00e9o d\u00e0i cho ta \u1ea3nh \u1ea3o.<\/p>\n<h2>\u0110\u1eb7c \u0111i\u1ec3m \u1ea3nh t\u1ea1o b\u1edfi th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5<\/h2>\n<p>T\u00ednh ch\u1ea5t c\u1ee7a \u1ea3nh (th\u1eadt hay \u1ea3o, c\u00f9ng chi\u1ec1u hay ng\u01b0\u1ee3c chi\u1ec1u, l\u1edbn h\u01a1n hay nh\u1ecf h\u01a1n v\u1eadt) ph\u1ee5 thu\u1ed9c tr\u1ef1c ti\u1ebfp v\u00e0o kho\u1ea3ng c\u00e1ch d t\u1eeb v\u1eadt \u0111\u1ebfn th\u1ea5u k\u00ednh so v\u1edbi ti\u00eau c\u1ef1 f. B\u1ea3ng d\u01b0\u1edbi t\u1ed5ng h\u1ee3p \u0111\u1ea7y \u0111\u1ee7 c\u00e1c tr\u01b0\u1eddng h\u1ee3p:<\/p>\n<table>\n<thead>\n<tr>\n<th>V\u1ecb tr\u00ed v\u1eadt (d l\u00e0 kho\u1ea3ng c\u00e1ch v\u1eadt \u0111\u1ebfn th\u1ea5u k\u00ednh)<\/th>\n<th>\u0110\u1eb7c \u0111i\u1ec3m \u1ea3nh<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>d &gt; 2f<\/td>\n<td>\u1ea2nh th\u1eadt, ng\u01b0\u1ee3c chi\u1ec1u, nh\u1ecf h\u01a1n v\u1eadt<\/td>\n<\/tr>\n<tr>\n<td>d = 2f<\/td>\n<td>\u1ea2nh th\u1eadt, ng\u01b0\u1ee3c chi\u1ec1u, b\u1eb1ng v\u1eadt<\/td>\n<\/tr>\n<tr>\n<td>f &lt; d &lt; 2f<\/td>\n<td>\u1ea2nh th\u1eadt, ng\u01b0\u1ee3c chi\u1ec1u, l\u1edbn h\u01a1n v\u1eadt<\/td>\n<\/tr>\n<tr>\n<td>d = f<\/td>\n<td>\u1ea2nh \u1edf v\u00f4 c\u1ef1c (kh\u00f4ng h\u1ee9ng \u0111\u01b0\u1ee3c \u1ea3nh r\u00f5 n\u00e9t)<\/td>\n<\/tr>\n<tr>\n<td>d &lt; f<\/td>\n<td>\u1ea2nh \u1ea3o, c\u00f9ng chi\u1ec1u, l\u1edbn h\u01a1n v\u1eadt<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>C\u00f3 th\u1ec3 th\u1ea5y quy lu\u1eadt chung: khi v\u1eadt \u1edf ngo\u00e0i ti\u00eau c\u1ef1 (d &gt; f) th\u00ec \u1ea3nh lu\u00f4n l\u00e0 \u1ea3nh th\u1eadt v\u00e0 ng\u01b0\u1ee3c chi\u1ec1u; ch\u1ec9 khi v\u1eadt l\u1ecdt v\u00e0o trong kho\u1ea3ng ti\u00eau c\u1ef1 (d &lt; f) m\u1edbi cho \u1ea3nh \u1ea3o c\u00f9ng chi\u1ec1u v\u00e0 ph\u00f3ng to, \u0111\u00e2y ch\u00ednh l\u00e0 nguy\u00ean l\u00fd ho\u1ea1t \u0111\u1ed9ng c\u1ee7a k\u00ednh l\u00fap.<\/p>\n<h2>C\u00f4ng th\u1ee9c th\u1ea5u k\u00ednh v\u00e0 \u0111\u1ed9 ph\u00f3ng \u0111\u1ea1i<\/h2>\n<p>M\u1ed1i li\u00ean h\u1ec7 gi\u1eefa ti\u00eau c\u1ef1 f, kho\u1ea3ng c\u00e1ch t\u1eeb v\u1eadt \u0111\u1ebfn th\u1ea5u k\u00ednh d v\u00e0 kho\u1ea3ng c\u00e1ch t\u1eeb \u1ea3nh \u0111\u1ebfn th\u1ea5u k\u00ednh d&#8217; \u0111\u01b0\u1ee3c cho b\u1edfi c\u00f4ng th\u1ee9c:<\/p>\n<p><strong>1\/f = 1\/d + 1\/d&#8217;<\/strong><\/p>\n<p>\u0110\u1ed9 ph\u00f3ng \u0111\u1ea1i \u1ea3nh \u0111\u01b0\u1ee3c t\u00ednh b\u1eb1ng: <strong>k = \u2212d&#8217;\/d<\/strong>. D\u1ea5u v\u00e0 \u0111\u1ed9 l\u1edbn c\u1ee7a k cho bi\u1ebft b\u1ea3n ch\u1ea5t \u1ea3nh: n\u1ebfu k &lt; 0 th\u00ec \u1ea3nh ng\u01b0\u1ee3c chi\u1ec1u (\u1ea3nh th\u1eadt); n\u1ebfu k &gt; 0 th\u00ec \u1ea3nh c\u00f9ng chi\u1ec1u (\u1ea3nh \u1ea3o); c\u00f2n tr\u1ecb tuy\u1ec7t \u0111\u1ed1i |k| cho bi\u1ebft \u1ea3nh l\u1edbn g\u1ea5p m\u1ea5y l\u1ea7n v\u1eadt. Khi \u00e1p d\u1ee5ng, c\u1ea7n th\u1ed1ng nh\u1ea5t quy \u01b0\u1edbc d\u1ea5u: v\u1edbi th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 f &gt; 0, \u1ea3nh th\u1eadt c\u00f3 d&#8217; &gt; 0, \u1ea3nh \u1ea3o c\u00f3 d&#8217; &lt; 0.<\/p>\n<p><img decoding=\"async\" class=\"aligncenter size-full wp-image-570893\" src=\"https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/thau-kinh-hoi-tu-3.jpg\" alt=\"thau-kinh-hoi-tu-3\" width=\"800\" height=\"450\" srcset=\"https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/thau-kinh-hoi-tu-3.jpg 800w, https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/thau-kinh-hoi-tu-3-300x169.jpg 300w, https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/thau-kinh-hoi-tu-3-768x432.jpg 768w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/><\/p>\n<h2>\u1ee8ng d\u1ee5ng c\u1ee7a th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 trong \u0111\u1eddi s\u1ed1ng<\/h2>\n<p>Nh\u1edd kh\u1ea3 n\u0103ng t\u1ea1o \u1ea3nh linh ho\u1ea1t, th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 c\u00f3 m\u1eb7t trong h\u00e0ng lo\u1ea1t thi\u1ebft b\u1ecb:<\/p>\n<ul>\n<li><strong>K\u00ednh l\u00fap:<\/strong> \u0111\u1eb7t v\u1eadt trong kho\u1ea3ng ti\u00eau c\u1ef1 \u0111\u1ec3 t\u1ea1o \u1ea3nh \u1ea3o l\u1edbn h\u01a1n, gi\u00fap quan s\u00e1t chi ti\u1ebft nh\u1ecf.<\/li>\n<li><strong>V\u1eadt k\u00ednh m\u00e1y \u1ea3nh v\u00e0 camera \u0111i\u1ec7n tho\u1ea1i:<\/strong> t\u1ea1o \u1ea3nh th\u1eadt, thu nh\u1ecf tr\u00ean c\u1ea3m bi\u1ebfn \u0111\u1ec3 ghi h\u00ecnh.<\/li>\n<li><strong>K\u00ednh vi\u1ec5n th\u1ecb:<\/strong> h\u1ed7 tr\u1ee3 ng\u01b0\u1eddi b\u1ecb vi\u1ec5n th\u1ecb (m\u1eaft kh\u00f3 nh\u00ecn g\u1ea7n) nh\u00ecn r\u00f5 v\u1eadt \u1edf kho\u1ea3ng c\u00e1ch g\u1ea7n.<\/li>\n<li><strong>K\u00ednh hi\u1ec3n vi v\u00e0 k\u00ednh thi\u00ean v\u0103n:<\/strong> k\u1ebft h\u1ee3p nhi\u1ec1u th\u1ea5u k\u00ednh \u0111\u1ec3 ph\u00f3ng \u0111\u1ea1i v\u1eadt r\u1ea5t nh\u1ecf ho\u1eb7c v\u1eadt \u1edf r\u1ea5t xa.<\/li>\n<li><strong>M\u00e1y chi\u1ebfu:<\/strong> t\u1ea1o \u1ea3nh th\u1eadt, ph\u00f3ng to n\u1ed9i dung l\u00ean m\u00e0n h\u00ecnh.<\/li>\n<\/ul>\n<p>N\u1ebfu b\u1ea1n mu\u1ed1n t\u00ecm hi\u1ec3u th\u00eam v\u1ec1 c\u00e1c hi\u1ec7n t\u01b0\u1ee3ng quang h\u1ecdc li\u00ean quan, c\u00f3 th\u1ec3 tham kh\u1ea3o b\u00e0i <a href=\"https:\/\/hoanghamobile.com\/tin-tuc\/quang-pho-la-gi\/\">quang ph\u1ed5 l\u00e0 g\u00ec<\/a> v\u00e0 b\u00e0i <a href=\"https:\/\/hoanghamobile.com\/tin-tuc\/guong-cau-loi-la-gi\/\">g\u01b0\u01a1ng c\u1ea7u l\u1ed3i l\u00e0 g\u00ec<\/a> \u0111\u1ec3 so s\u00e1nh c\u00e1ch t\u1ea1o \u1ea3nh gi\u1eefa th\u1ea5u k\u00ednh v\u00e0 g\u01b0\u01a1ng.<\/p>\n<h2>B\u00e0i t\u1eadp v\u1eadn d\u1ee5ng c\u00f3 l\u1eddi gi\u1ea3i<\/h2>\n<ul>\n<li><strong>B\u00e0i 1:<\/strong> V\u1eadt \u0111\u1eb7t c\u00e1ch th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 30 cm, ti\u00eau c\u1ef1 10 cm. \u1ea2nh c\u00f3 \u0111\u1eb7c \u0111i\u1ec3m g\u00ec? <em>L\u1eddi gi\u1ea3i:<\/em> v\u00ec d = 30 &gt; 2f = 20 n\u00ean \u1ea3nh th\u1eadt, ng\u01b0\u1ee3c chi\u1ec1u v\u00e0 nh\u1ecf h\u01a1n v\u1eadt.<\/li>\n<li><strong>B\u00e0i 2:<\/strong> Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 f = 12 cm, v\u1eadt c\u00e1ch th\u1ea5u k\u00ednh 6 cm. \u1ea2nh ra sao? <em>L\u1eddi gi\u1ea3i:<\/em> d = 6 &lt; f = 12 n\u00ean \u1ea3nh \u1ea3o, c\u00f9ng chi\u1ec1u, l\u1edbn h\u01a1n v\u1eadt (\u0111\u00e2y l\u00e0 nguy\u00ean l\u00fd k\u00ednh l\u00fap).<\/li>\n<li><strong>B\u00e0i 3:<\/strong> V\u1eadt c\u00e1ch th\u1ea5u k\u00ednh 20 cm, ti\u00eau c\u1ef1 10 cm. T\u00ednh kho\u1ea3ng c\u00e1ch \u1ea3nh v\u00e0 \u0111\u1ed9 ph\u00f3ng \u0111\u1ea1i. <em>L\u1eddi gi\u1ea3i:<\/em> 1\/d&#8217; = 1\/f \u2212 1\/d = 1\/10 \u2212 1\/20 = 1\/20, n\u00ean d&#8217; = 20 cm; \u0111\u1ed9 ph\u00f3ng \u0111\u1ea1i k = \u2212d&#8217;\/d = \u221220\/20 = \u22121, t\u1ee9c \u1ea3nh th\u1eadt, ng\u01b0\u1ee3c chi\u1ec1u v\u00e0 b\u1eb1ng v\u1eadt.<\/li>\n<li><strong>B\u00e0i 4 (tr\u1eafc nghi\u1ec7m):<\/strong> Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 c\u00f3 \u0111\u1eb7c \u0111i\u1ec3m n\u00e0o? A. R\u00eca d\u00e0y h\u01a1n gi\u1eefa; B. R\u00eca m\u1ecfng h\u01a1n gi\u1eefa; C. Hai m\u1eb7t ph\u1eb3ng; D. Ti\u00eau c\u1ef1 \u00e2m. <em>\u0110\u00e1p \u00e1n:<\/em> B.<\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-570894\" src=\"https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/thau-kinh-hoi-tu-4.jpg\" alt=\"thau-kinh-hoi-tu-4\" width=\"800\" height=\"450\" srcset=\"https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/thau-kinh-hoi-tu-4.jpg 800w, https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/thau-kinh-hoi-tu-4-300x169.jpg 300w, https:\/\/hoanghamobile.com\/tin-tuc\/wp-content\/uploads\/2026\/07\/thau-kinh-hoi-tu-4-768x432.jpg 768w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/><\/p>\n<h2>C\u00e2u h\u1ecfi th\u01b0\u1eddng g\u1eb7p<\/h2>\n<h3>Ti\u00eau c\u1ef1 c\u1ee7a th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 c\u00f3 d\u1ea5u g\u00ec?<\/h3>\n<p>Ti\u00eau c\u1ef1 c\u1ee7a th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 lu\u00f4n mang gi\u00e1 tr\u1ecb d\u01b0\u01a1ng (f &gt; 0), th\u1ec3 hi\u1ec7n kh\u1ea3 n\u0103ng l\u00e0m h\u1ed9i t\u1ee5 ch\u00f9m tia s\u00e1ng.<\/p>\n<h3>Khi n\u00e0o th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 cho \u1ea3nh \u1ea3o?<\/h3>\n<p>Khi v\u1eadt \u0111\u1eb7t trong kho\u1ea3ng ti\u00eau c\u1ef1 (d &lt; f), th\u1ea5u k\u00ednh cho \u1ea3nh \u1ea3o, c\u00f9ng chi\u1ec1u v\u00e0 l\u1edbn h\u01a1n v\u1eadt; \u0111\u00e2y l\u00e0 c\u00e1ch ho\u1ea1t \u0111\u1ed9ng c\u1ee7a k\u00ednh l\u00fap.<\/p>\n<h3>C\u00f4ng th\u1ee9c th\u1ea5u k\u00ednh l\u00e0 g\u00ec?<\/h3>\n<p>C\u00f4ng th\u1ee9c l\u00e0 1\/f = 1\/d + 1\/d&#8217;, trong \u0111\u00f3 d l\u00e0 kho\u1ea3ng c\u00e1ch t\u1eeb v\u1eadt v\u00e0 d&#8217; l\u00e0 kho\u1ea3ng c\u00e1ch t\u1eeb \u1ea3nh \u0111\u1ebfn th\u1ea5u k\u00ednh; \u0111\u1ed9 ph\u00f3ng \u0111\u1ea1i k = \u2212d&#8217;\/d.<\/p>\n<h3>Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 kh\u00e1c th\u1ea5u k\u00ednh ph\u00e2n k\u1ef3 \u1edf \u0111i\u1ec3m n\u00e0o?<\/h3>\n<p>Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 c\u00f3 r\u00eca m\u1ecfng h\u01a1n gi\u1eefa v\u00e0 l\u00e0m ch\u00f9m tia s\u00e1ng h\u1ed9i t\u1ee5, c\u00f2n th\u1ea5u k\u00ednh ph\u00e2n k\u1ef3 c\u00f3 r\u00eca d\u00e0y h\u01a1n gi\u1eefa v\u00e0 l\u00e0m ch\u00f9m tia loe r\u1ed9ng ra, ti\u00eau c\u1ef1 \u00e2m.<\/p>\n<h3>Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 d\u00f9ng l\u00e0m g\u00ec?<\/h3>\n<p>Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 d\u00f9ng l\u00e0m k\u00ednh l\u00fap, v\u1eadt k\u00ednh m\u00e1y \u1ea3nh, k\u00ednh vi\u1ec5n th\u1ecb, k\u00ednh hi\u1ec3n vi, k\u00ednh thi\u00ean v\u0103n v\u00e0 m\u00e1y chi\u1ebfu.<\/p>\n<h3>V\u00ec sao m\u1eaft vi\u1ec5n th\u1ecb ph\u1ea3i \u0111eo th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5?<\/h3>\n<p>V\u00ec m\u1eaft vi\u1ec5n th\u1ecb h\u1ed9i t\u1ee5 \u1ea3nh ra sau v\u00f5ng m\u1ea1c; th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 gi\u00fap gom tia s\u00e1ng s\u1edbm h\u01a1n, k\u00e9o \u1ea3nh v\u1ec1 \u0111\u00fang v\u00f5ng m\u1ea1c n\u00ean nh\u00ecn g\u1ea7n r\u00f5 h\u01a1n.<\/p>\n<h2>K\u1ebft lu\u1eadn<\/h2>\n<p>T\u00f3m l\u1ea1i, <strong>th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 c\u00f3 r\u00eca m\u1ecfng h\u01a1n gi\u1eefa, ti\u00eau c\u1ef1 d\u01b0\u01a1ng, cho \u1ea3nh th\u1eadt ho\u1eb7c \u1ea3nh \u1ea3o t\u00f9y v\u1ecb tr\u00ed v\u1eadt, v\u1edbi c\u00f4ng th\u1ee9c c\u01a1 b\u1ea3n 1\/f = 1\/d + 1\/d&#8217;<\/strong>. N\u1eafm v\u1eefng b\u1ea3ng \u0111\u1eb7c \u0111i\u1ec3m \u1ea3nh v\u00e0 c\u00e1ch x\u00e1c \u0111\u1ecbnh \u0111\u1ed9 ph\u00f3ng \u0111\u1ea1i s\u1ebd gi\u00fap b\u1ea1n gi\u1ea3i nhanh m\u1ecdi d\u1ea1ng b\u00e0i quang h\u00ecnh. \u0110\u1ec3 m\u1edf r\u1ed9ng ki\u1ebfn th\u1ee9c V\u1eadt l\u00fd quang h\u1ecdc, m\u1eddi b\u1ea1n tham kh\u1ea3o th\u00eam b\u00e0i <a href=\"https:\/\/hoanghamobile.com\/tin-tuc\/tia-tu-ngoai-la-gi\/\">tia t\u1eed ngo\u1ea1i l\u00e0 g\u00ec<\/a> tr\u00ean chuy\u00ean m\u1ee5c tin t\u1ee9c c\u1ee7a Ho\u00e0ng H\u00e0 Mobile.<br \/>\n<script type=\"application\/ld+json\">\n{\n  \"@context\": \"https:\/\/schema.org\",\n  \"@type\": \"FAQPage\",\n  \"mainEntity\": [\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Ti\u00eau c\u1ef1 c\u1ee7a th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 c\u00f3 d\u1ea5u g\u00ec?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Ti\u00eau c\u1ef1 c\u1ee7a th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 lu\u00f4n mang gi\u00e1 tr\u1ecb d\u01b0\u01a1ng (f > 0), th\u1ec3 hi\u1ec7n kh\u1ea3 n\u0103ng l\u00e0m h\u1ed9i t\u1ee5 ch\u00f9m tia s\u00e1ng.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Khi n\u00e0o th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 cho \u1ea3nh \u1ea3o?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Khi v\u1eadt \u0111\u1eb7t trong kho\u1ea3ng ti\u00eau c\u1ef1 (d < f), th\u1ea5u k\u00ednh cho \u1ea3nh \u1ea3o, c\u00f9ng chi\u1ec1u v\u00e0 l\u1edbn h\u01a1n v\u1eadt; \u0111\u00e2y l\u00e0 c\u00e1ch ho\u1ea1t \u0111\u1ed9ng c\u1ee7a k\u00ednh l\u00fap.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"C\u00f4ng th\u1ee9c th\u1ea5u k\u00ednh l\u00e0 g\u00ec?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"C\u00f4ng th\u1ee9c l\u00e0 1\/f = 1\/d + 1\/d', trong \u0111\u00f3 d l\u00e0 kho\u1ea3ng c\u00e1ch t\u1eeb v\u1eadt v\u00e0 d' l\u00e0 kho\u1ea3ng c\u00e1ch t\u1eeb \u1ea3nh \u0111\u1ebfn th\u1ea5u k\u00ednh; \u0111\u1ed9 ph\u00f3ng \u0111\u1ea1i k = -d'\/d.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 kh\u00e1c th\u1ea5u k\u00ednh ph\u00e2n k\u1ef3 \u1edf \u0111i\u1ec3m n\u00e0o?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 c\u00f3 r\u00eca m\u1ecfng h\u01a1n gi\u1eefa v\u00e0 l\u00e0m ch\u00f9m tia s\u00e1ng h\u1ed9i t\u1ee5, c\u00f2n th\u1ea5u k\u00ednh ph\u00e2n k\u1ef3 c\u00f3 r\u00eca d\u00e0y h\u01a1n gi\u1eefa v\u00e0 l\u00e0m ch\u00f9m tia loe r\u1ed9ng ra, ti\u00eau c\u1ef1 \u00e2m.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 d\u00f9ng l\u00e0m g\u00ec?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 d\u00f9ng l\u00e0m k\u00ednh l\u00fap, v\u1eadt k\u00ednh m\u00e1y \u1ea3nh, k\u00ednh vi\u1ec5n th\u1ecb, k\u00ednh hi\u1ec3n vi, k\u00ednh thi\u00ean v\u0103n v\u00e0 m\u00e1y chi\u1ebfu.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"V\u00ec sao m\u1eaft vi\u1ec5n th\u1ecb ph\u1ea3i \u0111eo th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"V\u00ec m\u1eaft vi\u1ec5n th\u1ecb h\u1ed9i t\u1ee5 \u1ea3nh ra sau v\u00f5ng m\u1ea1c; th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 gi\u00fap gom tia s\u00e1ng s\u1edbm h\u01a1n, k\u00e9o \u1ea3nh v\u1ec1 \u0111\u00fang v\u00f5ng m\u1ea1c n\u00ean nh\u00ecn g\u1ea7n r\u00f5 h\u01a1n.\"\n      }\n    }\n  ]\n}\n<\/script><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 l\u00e0 th\u1ea5u k\u00ednh c\u00f3 ph\u1ea7n r\u00eca m\u1ecfng h\u01a1n ph\u1ea7n gi\u1eefa, c\u00f3 kh\u1ea3 n\u0103ng l\u00e0m h\u1ed9i t\u1ee5 ch\u00f9m tia s\u00e1ng song song t\u1ea1i m\u1ed9t \u0111i\u1ec3m g\u1ecdi l\u00e0 ti\u00eau \u0111i\u1ec3m. Lo\u1ea1i th\u1ea5u k\u00ednh n\u00e0y c\u00f2n \u0111\u01b0\u1ee3c g\u1ecdi l\u00e0 th\u1ea5u k\u00ednh l\u1ed3i, c\u00f3 ti\u00eau c\u1ef1 mang gi\u00e1 tr\u1ecb d\u01b0\u01a1ng v\u00e0 xu\u1ea5t hi\u1ec7n trong r\u1ea5t [&hellip;]<\/p>\n","protected":false},"author":102,"featured_media":570895,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_yoast_wpseo_focuskw":"th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 l\u00e0 g\u00ec","_yoast_wpseo_title":"Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 l\u00e0 g\u00ec? \u0110\u1eb7c \u0111i\u1ec3m \u1ea3nh, c\u00f4ng th\u1ee9c v\u00e0 \u1ee9ng d\u1ee5ng","_yoast_wpseo_metadesc":"Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 l\u00e0 g\u00ec? T\u00ecm hi\u1ec3u \u0111\u1eb7c \u0111i\u1ec3m \u1ea3nh theo v\u1ecb tr\u00ed v\u1eadt, c\u00f4ng th\u1ee9c 1\/f=1\/d+1\/d', \u0111\u1ed9 ph\u00f3ng \u0111\u1ea1i v\u00e0 \u1ee9ng d\u1ee5ng trong k\u00ednh l\u00fap, m\u00e1y \u1ea3nh.","footnotes":""},"categories":[3910,30453],"tags":[],"class_list":["post-570890","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-kham-pha","category-kien-thuc"],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v27.3 (Yoast SEO v27.4) - https:\/\/yoast.com\/product\/yoast-seo-premium-wordpress\/ -->\n<title>Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 l\u00e0 g\u00ec? \u0110\u1eb7c \u0111i\u1ec3m \u1ea3nh, c\u00f4ng th\u1ee9c v\u00e0 \u1ee9ng d\u1ee5ng<\/title>\n<meta name=\"description\" content=\"Th\u1ea5u k\u00ednh h\u1ed9i t\u1ee5 l\u00e0 g\u00ec? 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