The term fisheye originates from a camera lens, having more detail in the center of the image and less detail on the edges. In a fisheye user interface, the item in focus grows and the non-focus items remain unchanged.
Fisheye view can be used in any of the cases where the intent is to display more information to the user for the selected/focused item or portion of the display screen.
This kind of implementation makes sense in applications such as where you have list of items like contacts/buddies etc, or even map/camera kind of applications. For details on map implementation image check  Usability First Glossary].
A true fisheye list interface would have one item in the middle of the screen, with 2-3 lines of data, a two-line item listing above and below, and all other item having a single line. This thus allows the user to be able to get more content for the item in focus which otherwise might have been missed out with normal view.
Before implementation of fish eye
The image below shows how the list box looks without the fish eye implementation, where the content is not displayed in a user friendly way so to speak.
After implementation of fish eye
The image below shows how the list box looks after the fish eye implementation, where the content is displayed in a user friendly way, in multi lines and the details are more clearly visible and also the highlight with different colored background for the selected text gives the window a distinct visibility as compared to the earlier image.
Fish eye can be used when the intention is to show more information for the selected item or the area of the device under focus. The resultant fish eye view/window can be used to show a snapshot of the complete information for the selected item. For example showing the cricket score in 2-3 lines, where you can show the batsmen at the crease, balls faced etc. User can select the list item to explore further, on which if there is still information which would not fit into the fish eye window, you can think about opening a detailed view where the information can be displayed.
- In the case of implementation of fish eye view on a list view, as the list is scrolled, the selected item will reveal additional information in the ensuing fish eye window. This information should be chosen smartly as it will be altering the normal flow of actions if the items were displayed without a fish eye window. Since this information would be used by the user to determine the value/state of the item, you don’t possibly want to show not relevant information.
- Different screen-size and screen-orientation should be taken into account, especially when designing in the case of list view implementation where most likely you would have to do custom drawing to get the fish eye.
- In case of fisheye list, general list-layout guidelines should apply, i.e. if items have been searched using the search box, the fisheye view for the selected item should show the details for items matching the search pattern only and not otherwise.
- Denote the fish eye window with either different colored backgrounds/boundaries etc in case of usage with a list view, so that it stands out from the remaining content.
- Since the fisheye implementation alters the general viewing pattern for the user, it makes sense to allow the user the choice if they want to have fisheye enabled or not. It’s also a nice idea to let them decide what content they possibly want to see in the fish eye view.
- It might also be a good idea to give user more choices pertaining to the selected item through the fish eye window like in the case of a messenger the choice to do calls/send sms etc as options.
--- Edited by Mayank on 25/06/2009 ---