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显微镜的构造及使用

作者:佚名  人气: 2390 次  时间:2004年10月09日  星级:

显微镜的构造及使用
(安徽省2004年中考新增考点)

人的眼睛只能识别大小为0.1 ㎜的物体。显微镜是精密的放大仪器,是生物学研究不可缺少的工具。我们用它可以观察肉眼看不见的微小生物的结构。中学最常用的是光学显微镜,为了正确操作、妥善保管和维护显微镜,使之延长使用年限,我们必须首先了解显微镜的结构和功能。 一台显微镜包括机械装置和光学系统两大部分,注意比较和识别。

(一)机械部分

1.镜筒 为显微镜上部圆形中空的长筒,筒口上端安装目镜,下端与物镜转换器相连。作用是保护成像的光路与亮度。

2.转换器 固着在镜筒下端,分两层,上层固着不动,下层可自由转动。转换器上有2~4个圆孔,用来安装不同倍数的低倍或高倍物镜。

3.粗准焦螺旋 位于镜臂的上方,可以转动,以使镜筒能上下移动,从而调节焦距。

4.细准焦螺旋 位于镜臂的下方,它的移动范围较粗准焦螺旋小,可以细调焦距。

5.镜座 是位于镜臂的下方,显微镜的底部,呈马蹄形的金属座。用以稳固和支持镜身。

6.镜柱 从镜座向上直立的短柱。上连镜臂,下连镜座,可以支持镜臂和载物台。

7.倾斜关节 镜柱和镜臂交界处有一个能活动的关节。它可以使显微镜在一定的范围内后倾(一般倾斜不得超过45°)便于观察。但是在使用临时封片观察时,禁止使用倾斜关节,尤其是装片内含酸性试剂时严禁使用,以免污损镜体。

8.载物台 从镜臂向前方伸出的金属平台。呈方形或圆形,是放置玻片标本的地方。其中央具有通光孔,在通光孔的左右有一个弹性的金属压片夹,用来压住载玻片。较高级的显微镜,在载物台上常具有推进器,它包括夹片夹和推进螺旋,除夹住切片外,还可使切片在载物台上移动。

(二)光学部分

1.目镜 它是安装在镜筒上端的镜头。是由一组透镜组成的,它可以使物镜成倍地分辨、放大物像,例如 5×、10×、15×、20×。

2.物镜 是决定显微镜质量的关键部件。安装在转换器的孔上,也是由一组透镜组成的,能够把物体清晰地放大。一般有三个放大倍数不同的物镜,即:低倍物镜(8×或10×)、高倍物镜(40×或45×)和油浸物镜(90×或100×),根据需要可选择一个使用。显微镜的放大倍数是目镜倍数乘以物镜的倍数。

3.反光镜 在聚光器的下面有一个一面平另一面凹的双面圆镜。可作各种方向的翻转,光线较强时使用平面镜,反之使用凹面镜。

4.聚光器 (学生用显微镜一般没有这个装置)是由凹透镜组成的,它可以集中反光镜投射来的光线。在镜柱前面有一个聚光器调节螺旋,它可以使聚光器升降,用以调节光线的强弱,下降时明亮度降低,上升时明亮度加强。

5.虹彩光圈 又称可变光阑,由多数金属片组成(学生用显微镜一般没有这个装置),在较高级的显微镜上具有此装置。使用时移动其把柄,可控制 聚光器 透镜的通光范围,用以调节光的强度。虹彩光圈下常附有金属圈,其上装有滤光片,可调节光源的色调。

6.遮光器 简单的显微镜无聚光器和虹彩光圈,而装有遮光器。遮光器呈圆盘状,上面有大小不等的圆孔(光圈)。光圈对准通光孔,可以调节光线的强弱。

显微镜的成像原理(放大原理)

光线→反光镜→遮光器→通光孔→标本(一定要透明)→物镜的透镜(第一次放大成倒立实像)→镜筒→目镜(再放大成虚像)→眼。

显微镜的使用

1. 取镜安放

取镜 右手握住镜臂,左手平托镜座,保持镜体直立。(特别要禁止单手提着显微镜走,防止目镜从镜筒中滑脱)。

安放 放置桌边时动作要轻。一般应在身体的前面,略偏左,镜筒向前,镜臂向后,距桌边7~10 ㎝处,以便观察和防止掉落。安放目镜和物镜。

2. 对光

转动转换器,使低倍物镜正对通光孔。左眼注视目镜内,右眼同时睁开,用手转动反光镜,面向光源。在目镜里看见一个圆形、明亮的视野(一定要用非直射光)。把一个较大的光圈对准通光孔。

3. 低倍镜的使用

观察任何标本都必须先用低倍镜。

(1)放置切片 升高镜筒,把玻片标本放在载物台中央,标本材料正对通光孔的中心,用压片夹压住载玻片的两端。

(2)调焦 两眼从侧面注视物镜,转动粗准焦螺旋,让镜筒徐徐下降,至物镜距玻片2~5 ㎜处。然后用左眼注视目镜,右眼同时睁开,(以便绘图),同时用手反方向(逆时针方向)转动粗准焦螺旋,使镜筒缓缓上升,直到看清物像为止。如果不够清楚,可用细准焦螺旋调节。(不可以在调焦时边观察边使镜筒下降,以免压碎装片和镜头。)

(3)低倍镜的观察 由所用的目镜放大倍数与物镜放大倍数相乘,即为原物被放大的倍数。如果物像不在视野中央,要慢慢移动到视野中央,适当再进行调节。

4. 高倍镜的使用

(1)选好目标 先用低倍物镜确定要观察的目标,将其移至视野中央。转动转换器,把低倍物镜轻轻移开,原位置小心换上高倍物镜。(用高倍物镜工作距离较短,操作要十分仔细,以防镜头碰击玻片)。

(2)调焦 在正常情况下,当高倍物镜转正之后,在视野中央即可见到模糊的物像,只要向反时针方向略微调动细准焦螺旋,既可获得清晰的物像。

在换上高倍物镜观察时,视野变小变暗,要重新调节视野亮度,可升高聚光器或利用凹面反光镜。

5. 油镜的使用(中学生一般不使用,在这里不做详述)

6. 使用后的整理

观察结束,应先将镜筒升高,聚光器下降,再取下切片,然后转动转换器,使物镜与

通光孔错开,做好清洁工作。清洁完毕,再下降镜筒,使两个物镜位于载物台上通光孔的两侧,呈“八”字形,将反光镜转至与载物台垂直,罩上防尘罩,仍用右手握住镜臂,左手平托镜座,按号放回镜箱中。

讨论

1.降低镜筒时,操作者最关键的姿势应该是什么?其重要性是什么?

2.当视野太明亮,光线刺眼时,这样的光线会使人眼的视网膜永久性损坏。其原因和解决的方法是什么?

3..在用显微镜观察切片时,由低倍镜换用高倍镜后,所观察到的物象与低倍镜相比是( )

A、视野亮,细胞数目多 B、视野暗,细胞数目多

C、视野亮,细胞数目少 D、视野暗,细胞数目少

提示

1.降低镜筒时,一定要从旁边注视物镜和玻片,防止它们接触和压碎盖玻片、磨损透镜。

2.原因是:(1)反光镜直对强光源或用反光镜捕捉直射的太阳光;(2)光线直射到物镜的透镜上。

3.D

解决方法:用平面镜、小光圈、加滤光片、转向暗处;移动显微镜的位置。


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