现配发的投影器有一个缺点:教师在教学中连续使用几张投影片,换片时银幕上总免不了出现一片空白;如果投影片放置位置不当或颠倒,有时会引起学生哄堂大笑。如果采用关机的方法,既不方便又易损坏投影器。那怎样才能避免上述弊端,又便于操作呢?我校对投影器作了一点改进,即在放映镜头下方都安装了简易挡光板,教师用得得心应手。具体方 There is one drawback to the projector that is being dispensed. Teachers use several transparencies continuously in teaching. When changing trays, there is always a blank space on the screen. If the position of the transparencies is improperly or upside down, it can sometimes cause the students to laugh in laughter. If you use the shutdown method, it is neither convenient nor easy to damage the projector. How to avoid the above drawbacks, but also easy to operate it? My school made some improvements to the projector, that is, below the projection lens are installed simple light barrier, teachers should be handy. Specific side