Digital Photography Technique: Image Stability in Digital Photography

When taking a picture we almost always have the possibility of choosing between many speed/aperture combinations with the same exposure value. In 2.1 we say the diaphragm aperture properties with regard to the depth of field. The advantage of being affecting the depth of field makes the choice of an aperture and important influence on the image and it's constant use.

In 2.3.2 we saw the relationship between shutter speed and the movement of the camera and other objects. The presence of objects in movement in the frame recommends the use of fast speeds. Slow speeds recommend a steady support to avoid complete blurriness.

In between the combinations available in an exposure value, the choice has to be made based on the possibilities and limitations we have just seen. If we want to control the depth of field, meaning we need a determined aperture, or have to resolve a movement problem, the choice of a variable implies settling the other within the correct exposure value.

If we have to face two problems at a time, or one in extreme light conditions, it can be impossible to use the combination we need because of the film's sensitivity; in these cases, we can always use higher or lower exposure values by increasing or decreasing the sensitivity (4.1.3, 11.3).

Fortunately, the great majority of pictures don't have special depth of field or speed problems. If we exclude shutter speeds below 60 when holding the camera in hand and large apertures, which aren't the best choice unless specifically necessary (they have less depth and sharpness), we can affirm that the choice is indifferent. A very frequent practice is maintaining the shutter speed at 60 or 125 and regulating the exposure with the diaphragm (who's ring is comfortably found next to the focus ring).

Note:

•  99 out of 100 pictures that are taken in available light conditions (exteriors or sufficiently lit interiors) and most problems that arise when taking a picture, can be correctly resolved applying the concepts seen until now. The necessary technique for a good photograph consists in focusing carefully taking in account the possibilities of depth of field, measuring the light of the zone we consider the most important to avoid erroneous photometer readings, choosing a speed and an aperture that don't involve movement in the image and shooting.

When framing, first we will try to identify the main zone, which will give us a brightness to measure and a distance to focus to. Before shooting we will go over the three requirements that have to be fulfilled in each and every one of our photos:

• Is the focus right?
• Is the exposure value right?
• Am I sure it's not going to move?

If the answer to any of these questions is negative, or not sure, it's best to find out and solve it before shooting , because afterwards will be too late. Not missing any of these points requires attention and some patience at first; with experience we will end up doing it without realizing.

We have seen how a picture is made, supposing we have access to the focus, aperture and speed controls, meaning we are using a manual focus and exposure camera. The automatic systems follow the same criteria and limitations we have seen. In theory it should accomplish in a fraction of a second of what we do manually adjusting controls. Although in practice these systems work without discriminating characteristics of each particular scene. An automatic exposure and/or focus camera without the possibility of manual control can be a limitation in some situations (3.4.2.2).