Usually when you cannot get close enough to create a large enough image with a shorter lens, or wish to compress the depth of field.
A tele-conversion lens attaches to a digital camera to increase the lens magnification. It enhances the telephoto effect and adds focal length.
I think the root word is Tele
Photo meaning light.Tele meaning sound. Lens isn't a root word I'm just going to tell you that.
Yes, But they will have crop factor. For example a 28mm wide lens will become a 42mm lens (35mm equivalent). Or a 200mm tele will become a 300mm.
There are many different models in the Canon Power Shot line, each with its own lens. For example, the Power Shot G15 model includes a tele-converter lens while the SX230 model features a wide angle lens with a 14x zoom capability.
Some of the best telephoto lens options available for the iPhone 6 include the Moment Telephoto Lens, the Olloclip Telephoto Pro Lens, and the Ztylus Revolver Lens Kit. These lenses can enhance the zoom capabilities of your iPhone 6 camera and improve the quality of your telephoto shots.
most Basic SLR (Single Refraction Lens) Cameras use a single lens, however MOST advanced SLRS use multiple Lenses. it is best to use Multiple Lenses because a single lens can sometimes be bad for Wide-Angle shots, and when you take Macro (super close) images your restricted to a certain distance from the object, though the down fall on Multiple lenses is that it cam be more expensive then single lenses or if you meant only being able to use one lens at once, that isn't true, many Lenses can have add ons for example my Miranda FvT (yeah its old) can use multiple lenses, for Macro i use the Macro Tubes with a 2X Custom Tele-Converter Vivitar lens with the standard Soligor Wide-Auto lens, and so on
maybe
You would use a convex lens.
tele-conferencing,"A conference of people who are in different locations that is made possible by the use of such telecommunications equipment as closed-circuit television
television telescope teletex telephone
You could possible use " extra- " as in extraterrestrial. Probably better to use " tele -" as in telemetry, telepathy, television, telephone, and telegraph.