A focus free lens is a lens whose focal point is fixed at its hyperfocal distance. Rather than having a method of determining the correct focusing distance and setting the lens to that focal point, a focus free lens relies on depth of field to produce acceptably sharp images. Most cameras with focus free lenses also have a relatively small aperture which increases the depth of field. Cameras with these lenses generally use a viewfinder for composition.
Focus free lenses are used in the lowest-end and cheapest cameras; disposable cameras and low-end point and shoot cameras. They are usually wide angle with fixed aperture.
Pros and cons[]
Pro:
- Can be produced very inexpensively
- No need to worry about focus
- More predictable than automatic systems
Con:
- Less sharp than a lens that has been set to the best focal point for a given scene
- Unable to produce sharp images of objects close to the camera (within 8-12 feet)
- Unsuitable for portraits, as they cannot fill the frame of an image with a person's face and render it sharp at the same time
Links[]
- This article contains information originally taken from the Wikipedia article "Focus_free_lens". You can see the authorship and revision history of that article here.