EXPOSURE - PART 2

Exposure Part 2

Correct Exposure in Photography, of course, depends on shutter speed, aperture value and ISO.

Most of the technical terms in Digital photography have been adopted from Film photography. The emulsion coated on the film has got some of the characteristics which present day sensors have, for recording images. However, there is no big difference in optics of Film Photography and Digital Photography. The glaring difference must be understood about light sensitivity. There is different film for different sensitivity which measured in ISO units. In Digital photography the same sensor will change its sensitivity using digital technology and circuitry.  The size of one frame of 35 mm film is 36mm x 24mm for all cameras of 35 mm format cameras. Where as the size of the sensor is different for various digital camera models.

Though the optics is generally same, as said above, there are of course, some difference because of the size of the sensors. Due of this, in digital cameras, there are numerous sizes of Digital cameras

The correct exposure can be achieved with correct combination of shutter speed and aperture for a particular lighting of the subject. It is interesting to study this subject with examples normally highlighted during Film Photography era.

The correct exposure can be achieved with the following combination with constant ISO value.[ Shutter Speed – Aperture Relationship].

Shutter speed in seconds------------Aperture[f/stop]

1/ 1000--------------------------------------f/2.8

1/500-----------------------------------------f/4

1/250-----------------------------------------f 5.6

1/125-----------------------------------------f/8

1/60------------------------------------------f/11

1/30------------------------------------------f/16

It should be understood that same amount of light will strike the sensor in all the above COMBINATIONS.

The above combinations give an idea of choosing higher shutter speed, say 1/1000 at

 f/ 2.8 to freeze an image of a fast moving object. For normal stationary subject, a shutter speed of 1/ 125 at f/8 is recommended.

In the present digital technology, cameras are having much finer controls than the illustration shown above.

It will be a nice idea to study the EXIF details after transferring the image to the computer.

EXPOSURE

EXPOSURE

To understand this concept, one is expected to understand the function of our eyes. What happens when we have to see things in a very bright lighting condition or in a very dim lighting condition?  At such situations ,the iris in our eyes contracts to allow only bearable light inside the eye and opens wide  allowing sufficient light inside the eye for better identification of objects.

The same concept may be kept in mind to understand EXPOSURE in photography.

The following equation will help understand Exposure in a simple manner

Exposure = Illumination x time.

 Where, illumination means the brightness of light entering the camera and time means duration of time the light is allowed to enter the camera.

Therefore, Exposure can be varied by either changing the brightness of light or controlling the time the light allowed inside the camera, or changing both.

The question is why the exposure to be changed!

The reason being that the quality of the final image to be pleasing and nice.

Studying the  following pictures will help understand the effect of exposure on the final image.

On examining the above picture, one can select an acceptable one..

 There are three parameters with which each Photograph has been made and can be understood by closely going through the Exposure details, written on the Photos.

These Photographs were made in manual mode for the purpose of this tutorial.

The Auto mode in the camera will set all the required parameters to get a good final image.

ISO is a mere number indicating the degree of sensitivity of the sensor while capturing an image. Higher the number, more the sensitivity to light. That means, one can get good image in poor lighting condition by suitably adjusting the ISO number. Some model of the present day digital camera will adjust ISO also automatically.

It is photographers experience, that some times, despite setting the camera in Auto mode, that images are either under exposed or over exposed . In such cases it is better go for Manual mode and take several shots with different settings and select the best one.

Before shooting in manual mode it is advisable to understand various controls of the camera.