A focus free lens is a photographic 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. Cameras with these lenses generally use a viewfinder for composition.
The advantage of this design is that it can be produced very inexpensively, more so than automatic or manual systems. The system is also effectively automatic; the photographer need not worry about focusing. It can also be more predicable than automatic systems.
The disadvantages are the fact that lenses of this type produces images that are less sharp than a lens that has been set to the best focal point for a given scene, and they are unable to produce sharp images of objects close to the camera, usually within 8-12 feet. The later limitation makes them unsuitable for portraits, as they cannot fill the frame of an image with a persons face and render it sharp at the same time. This limitation is likely to confuse inexperienced photographers.
A focusfreelens is a photographic 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 focusfreelens relies on depth of field to produce acceptably sharp images.
Focusfree lenses are used in the lowest end and cheapest cameras; disposable and low-end point and shoot.
An eyepiece is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes.
They vary in their internal lens configuration, and different designs are sometimes more appropriate both for different types of viewing, and for different types of telescope.
Magnification is calculated by dividing the focal length of the telescope objective (the main lens or mirror) by the focal length of the eyepiece.