What is Auto Focus?
Auto focus is a system in which the lenses are adjusted automatically in order to sharpen the particular object or a part of it. Focusing the lens until the sharpest image is projected onto the film is the primary responsibility of auto focus mechanism. To make a clear image, the distance between the lens and the film has to be adjusted depending on the distance between the camera and the object. Simply, auto focus will increase the depth of field and thereby makes the image appear clearer and crispier than before. This feature is highly important in the modern DSLR and point-and-shoot camera besides being significant in the smartphones. There are two types of auto focus – active and passie and some cameras might have a combination of both these types. The type of auto focus used in a camera is purely dependent on the pricing of the device. Usually, the inexpensive point-and-shoot cameras incorporate active auto focus mechanism. On the other hand, the expensive SLR cameras with interchangeable lenses and high-end smartphone cameras use passive auto focus systems.
What is Fixed Focus?
Fixed focus is completely different than auto focus and in this mechanism the distance between the lenses are the same. In simpler words, the lenses are fixed and they cannot be adjusted. In a fixed focus system, the depth of field is minimal and hence, the region in front and behind the point of focus appears blurred. Also, both the foreground and the background cannot be focused at the same time. It has to be noted that the depth of field (D.O.F.) depends on many aspects such as the lens aperture and if this is large, the D.O.F will be small. The same strategy also applies to the zoom setting. Moreover, if the focused point is far-away, the D.O.F. will be high. Hence, the fixed focus cameras are usually made to focus to the infinity and it is made sure that the zoom settings and aperture are maintained small. This way, the cameras with fixed focus can be made to focus almost all the objects that lay on the field.
Difference between Auto Focus and Fixed Focus?
Talking about the difference between the two, auto focus needs mechanical movement to tweak the lenses in order to focus the particular object. But this is not the case with fixed focus systems as they the lenses do not move. While the fixed focus cameras are made to focus to the infinity, the auto focus cameras can be focused to varying distances that range from zero to infinity. The fixed focus cameras are used in basic mobile phones, whereas the auto focus (passive) cameras with contrast measurements are employed in high-end smartphones.
Which one is Better and Why?
As it is mentioned above, under similar good light conditions, the fixed focus cameras will deliver very crisp images only when the image is focused appropriately with a specific distance between the object and the lens. The fixed focus cameras have manual macro mode that allows users to capture objects that are pretty close to the lens and still deliver crisp images. On the other hand, the auto focus camera units will deliver crisp and focused images when the object is placed at any distance from the lens. But, in some cases, a bit of skill would be needed to obtain focused images.
Conclusion
Obviously, the auto focus cameras are preferred as the unit can deliver crisp and focused images in almost all situations. Also, there is no need for the user to adjust the distance between the lens and the subject in order to obtain high focus as all the tasks are carried out be the internal mechanism. But, there is a drawback in the auto focus cameras that are incorporated in the smartphones. The passive auto focus mechanism uses contrast to focus and hence, focusing a wall or during low light conditions becomes a trouble. However, the LED flash in the camera unit will assist in this case by lighting up the environment that will in turn provide better focus of the object.
