The Focus in Image quality requirements


Images can be “blurred” due to several reasons. It could be because the photographer’s hand was shaking while shooting with an exposure time of longer than 1/100 of a second. Blurred images could also be a result of imprecise focusing (manual or auto, when a camera focuses closer to or further from an object), as well as due to the use of certain lens types (such as telephoto lenses with longer focal distances).

In order to decrease the number of blurred images, which don’t get through moderation, keep in mind the following rules:
  • Take photos in a well-lit environment to be able to use faster shutter speeds;
  • Use more open aperture, although with caution since it decreases depth of field (DOF) – portion of scene that appears sharp in the image;
  • In case you can not follow described above advises, increase ISO number (film sensitivity). There is a risk of increasing grain/noise though. You should use a higher numbered ISO only in need of shooting an unique subject, which will be demanded by clients, and then using special software edit images to decrease noise;
  • Use a tripod in every possible case, and without one, `wedge` the camera against a solid object such as a pillar, signpost, table, wall etc. holding it very calmly while exposing the picture.

In spite of the fact that it is customary to reject a blurred image, there are methods of shooting, which allow obtaining a certain result and use slightly blurred image (or its parts) as an artistic technique. These are motion blur, soft focus and slow shutter speed techniques.

Motion blur:

You can use slower (1/15-1/30-1/60th) shutter speeds and “follow” the moving subject with the camera.

The subject turns out to be remarkably sharp in relationship to surroundings blurred by the camera’s movement. This technique requires some training & practice, but gives spectacular results when shooting moving subjects (cars, bicycles, horses and others), leaving a feeling of blazing motion (the shutter speed chosen should be relative to the speed of an object passing; faster speeds from a car can still blur effectively at 1/30th or 1/60th of a second, less (1/8th or 1/15th) for a bicycle rider, even less for someone walking (1/8th or 1/4 of a second can even be used in some cases).

Soft Focus:
Pictures done with a soft focus (defocus) are completely different from photos with poor focus due to, for example, shaky hands.

Images with soft focus can be obtained either by hardware methods (lenses with focus control (defocus) or soft-filters coupled with usual lenses) or by software editing (filters and plug-ins in programs for image-editing, such as Adobe Photoshop).

 A well designed image with “soft focus” is not blurred, but just slightly softened, keeping all details. Its bright parts acquire smooth and “magic” luminescence.

 Woman and kid portraits, done with soft focus, look wonderful due to unusual poetry and sense of gracefulness.

Slow shutter speed technique

This shooting technique is used when “freezing” an object looks unnatural and a photographer wants to obtain a more vivid image.

It is often used when shooting flowing water (fountain, waterfall) or during a night shoot (lights of moving cars turn into colorful lines) with sufficient exposure of city landscape (always use a tripod for best results, use of a Polarizer or neutral density filters help enhance this by slowing the shutter speed down even further for the correct exposure).

Summary: A photographer has to experiment with exposure (shutter speed and aperture size) in order to obtain spectacular “out of focus” photos. However, one should not over-use these techniques, keeping in mind that the standards for “stock” photos are good quality and well-focused images without the loss of details