The top of the window consists of 3 buttons with which you can change the current directory. The first button displays the current directory name. Clicking on the button brings up a popup menu showing the entire directory hierarchy with the current directory at the bottom. Select one of the other directories to jump to that position in the hierarchy.
The next button, showing a folder icon with an arrow, will move you up one directory level.
The final button, initially reading "FTP...", will allow you to connect to an FTP server and browse its files. You will be prompted to enter a host name, user name, and password. If no user name is entered, fv will open an anonymous ftp connection. When connected, the button text will change to "Local...". Clicking it will return you to your local computer.
The file listing shows the names of all files which have the form specified in "File of type" field, their file sizes, and last modification dates. When the "List Fits files only" is selected, only FITS files are shown as well as all the compressed files. Double click a file name to open that file. Directories are listed with "/" (":" on MacOS). Double click a directory name to move to that directory.
In the "File Name" field, the currently selected file name is shown. One can type a partial filename and press TAB to invoke automatic filename completion. One can also type a directory path to move quickly to another location without having to navigate all the intervening directories.
The file list will be filtered using the wildcard string contained in this entry field.
To open the current file as read-only, enable the check button. If a file is opened as read-only, you will not be able to save any changes you make to the file. You will still be able to edit the file and save the modifications to a new file, though.
Click this button to open the currently selected FITS file and bring up a overview of the FITS file. This button will instead read "Save" after selecting the "Save As" command.