Today everyone is having a mobile camera and able to take a picture with single click. The memorable event that is captured in digital form most often are dull, blurred, overexposed or low in contrast. There is a wide gap between what was seen and what is available as image [1].
To master the art of photography one should understand the elements of science of photography. One needs lot of practice and patience to master an art. Digital technology merely makes picture acquisition, storage and transmission processes much simpler and economical than earlier film technology. Knowledge on technology will help to work with modern camera with ease. Access to modern digital camera with its all fancy features does not guarantee a good photograph. Taking snap of beautiful females (in photography they are called subjects) does not guarantee a beautiful picture either.
The simple fact is “Light falls on the subject and it is captured by the camera”. With this “each photograph is expected to convey an emotion”. In this post let us know three important settings of digital camera that will help to acquire a picture properly. They are aperture, shutter speed and ISO. These three form a golden triangle. By adjusting these controls one can produce beautiful pictures.
Aperture
Aperture controls the light that falls on the lens. Aperture is circular in shape. Aperture adjustments are expressed in F-stops [2]. They are f/2, f/2.8,f/4, f/5.6, f/8, f/11, f/16, f/22 and f/32. The above list gives the various aperture ratios that are possible. The numerator ‘f’ stands focal length of lens and it is divided by a number.
Let lens focal length be 50 mm.
(i) f/2 => 50 mm / 2 => 25 mm (aperture diameter)
(ii) f/16=> 50 mm / 16=> 3.125 mm (aperture diameter)
(iii) f/32=> 50 mm / 32=> 1.563 mm (aperture diameter)
Moral of the example is bigger the denominator lesser the aperture diameter and in turn less light falls on into the lens. The denominator series do possess regularity. Aperture area of f/16 is 7.6 sq. mm, f/22 is 4.15 sq. mm and for f/32 is 1.9 sq. mm. As F-stop denominator increases by one step (say 16 to 22) aperture area doubles. Likewise, as F-stop denominator decreases by one step (say 32 to 22) aperture area halves.
In digital camera, if the aperture is set then automatically other things are adjusted in tandem to the aperture value. The aperture settings used in cameras are calibrated in f/stops [1].
Shutter
It is a device that allows the light to fall on the lens for finite duration of time. Mostly time will be in seconds. Unlike aperture, it has only two states Open and Close. It has following speeds 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, 1/2000. Above speeds are called stops. Here also increase in stop means shutter speed is doubled and decrease in stop means shutter speed in halved. The basic question arises in every mind is what is need for variable shutter speed? This will be answered in following ISO section.
ISO
Appropriate title for this section will be film sensitivity. In digital camera it should be sensor sensitivity. Typically it is represented as ISO 100 or ISO 200. In this sensitivity is represented in number format and prefix ISO and ASA denote the standard setting organization (like ISO, ASA and EI). These organizations specify film sensitivity in numbers. The ISO range is, as follows 25, 50, 100, 200, 400, and 800 up to 3200. Higher the ISO number means more it is sensitive to light. It indicates that less light is sufficient take a photograph. If a fruit bowl is photographed keeping shutter speed as 1/8”, F-stop as f/5.6 and ISO having 100 and 1600 values will result in darker fruit bowl image and brighter fruit bowl image. Refer [1] shows series of photographs to illustrate this concept very clearly.
A photograph is taken when sufficient light is not available to record details in the darker regions then it is called underexposed. A photograph is taken when too much is light wash out details in brighter regions then it is called overexposed. Aperture size and shutter speed also can be adjusted to handle this situation. Various ISO numbered films are available to freeze the picture with available light .
The shutter speed and aperture size determines the amount of light sent into the lens. The ISO number indicates the amount of light required to freeze a picture properly. If the ISO number is fixed then either shutter speed or aperture size can be varied to get a correct exposure.
This will be explained with an example. Let
Aperture: f/11
Shutter Speed: 1/250”
ISO: 100
If the aperture is reduced by a stop (f/8) then correspondingly shutter speed has to be increased by an F-stop (1/500”). Likewise if the aperture is increased by a stop (f/16) then shutter speed should be reduced by an F-stop (1/125”). Please refer [2] to find a exercise on this matter.
(f/11, 1/250”, 100) = (f/8, 1/500”, 100) = (f/16, 1/125”, 100)
Depth of field
It is difficult to convey in words. Figure 1 shows billiards table and a railway over bridge. In the billiards ball image one infer that white ball is near and black ball, lamp shade and green screen are far away from the camera. Having a closer look reveals that only white ball is crisp while rest of the image that is very near to camera (say stick) as well as far away (say green screen) are very blurry. This type of images are called shallow depth of field. In the railway over bridge image railway track that is near to the camera and last girder of the bridge that is far away from camera are equally crisp irrespective of the distance. This type of images are called deeper depth of field. Changing the size of the aperture has a bearing on depth of field. Larger aperture area creates a shallow depth of field and narrow depth of field creates deeper depth of field.
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| Image Courtesy : Reference 2 |
Creation of Motion
The shutter speed is made slower than the motion of the subject and photograph is taken. These kinds of pictures create an illusion of motion. In figure 2 two darts are in board and another one is just arriving the board. This is very useful when taking photographs of athletes in action.
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| Image Courtesy: Reference 2 |
Note
I came across the Science Reporter magazine in a railway station. As it was only Rs. 20 (40 cents) I bought it. It is a wonderful magazine and worth the prize. It is published by Council of Scientific & Industrial Research (CSIR), Research Labs of govt. of India. (http://www.niscair.res.in/sciencecommunication/Popularization%20of%20Science/scirep0.asp). In that I studied Ref. [1] and it was nice. Later I studied few books on photography in the library. Armed with knowledge I searched in Google and I found out Ref. [2]. It is a 40 page document and it worth studying the document fully. The document contains very nice illustrations, less theory, exercise and top of all answers to exercise questions.
References
- Somya Maitra, “Playing with Photons – Clicking the ‘Right’ Photograph”, Science Reporter, Vol. 50, No. 3, March 2013, pp. 8–13, ISSN 0036-8512.
- John M. Setzler Jr., “Expoure”. http://www.shutterfreaks.com/Tips/Exposure/exposure111.pdf (PDF, 1375 KB)
