Let’s suppose that we are outside on a beautiful summer day trying to take a picture of the family dog. We are using a film camera. We finally get the dog to lie still. You point the camera at him. What happens? Light goes into the camera lens and hits the shutter. In other words, nothing happens yet. Now let’s say that the dog looks really cute and you decide to snap a picture. What happens? When you press the button, the shutter opens for a very short period of time. A small amount of light passes through and hits the film at the back of the camera. This creates an upside-down and reversed (反向的)image on the film.

　　When you finish the roll of the film, you can take it to the photo shop to develop it and you will have a great picture of your dog!

　　Cameras come with different lens lengths. Why does it matter? Many small cameras have shorter focal lengths, which means that there is a small distance between the lens and the place where the light focuses at the back of the camera. This gives you a large view of the area you are taking a picture of. Lenses with a long focal length show a smaller area but allow you to focus on distant objects and make them bigger. They are often called telephoto lenses. A good example of a long focus lens is one that is used by sports photographers to get photos of football players as if they were standing right beside them.

　　Digital cameras

　　In digital cameras, the light falls not on film but onto a sensor (传感器) called a CCD (Charge Coupled Device). This digitally converts(转变) light and color into a digital information or pixels (象素). The CCD is the heart of any digital camera and usually the most expensive part ---- depending on how good it is.

【山西省2017高考英语二轮复习专题训练：阅读理解（61）】相关文章：

★ 湖南省汝城二中2014届高考英语一轮复习阅读训练 (72)

★ 山西省永济市涑北中学高三英语总复习：美文欣赏（2）（A Lunch with God）

★ 2014届高考英语一轮复习必修4参考答案（外研版）

★ 湖南省岳阳市2014高考英语一轮单项选择训练题（9）及答案

★ 【课堂新坐标】2017届高考英语（通用版）二轮复习短文改错专题训练：训练3 短文改错（Ⅲ）（含解析）

★ 重庆市2014高考英语阅读理解一轮（精品）训练题（18）附答案

★ 【优化方案】2017届高考英语二轮复习全国卷Ⅱ题型重组训练：第20组（含解析）

★ 2014高考英语（新人教版）一轮基础训练（11）A、B卷（附答案或解析）

★ 2017届高考英语二轮复习大题冲关秘籍完形填空之夹叙夹议文：创新押题（含解析）

★ 贵州省贵阳市2014高考英语（新人教版）一轮阅读训练（35）附答案