Commercial magnifiers offer many features that you won't find in a free option, like the ability to magnify the screen before logging on. The free options are aimed at people who need only a relatively low level of magnification and mainly use the mouse.
The free applications often have no installation process or they have an installation process that does not require administrator privileges. This means they can be easily installed on a public computer, or even run from a pen drive plugged into a computer. Even so, you should always check with the owner of the computer before installing a screen magnifier or plugging in your pen drive.
Windows Magnifier
Windows contains a magnification utility called Magnifier. Since Windows 7 it can be started by pressing Windows + Plus and it gives full screen magnification, with Lens and Docked modes available. On Windows 7 it doesn't work with the High Contrast themes, but it does have an inverse colour option. There is no font smoothing so as text is made larger, it becomes more difficult to read.
Windows Magnifier can zoom from 125 per cent to 1600 per cent (x16). By default it starts at x2 magnification. Also by default it only tracks the mouse, although it is possible to turn on keyboard and text insertion tracking.
Lightning Express
Lightning Express works with 32-bit versions of Windows XP, Vista and 7. It also works with desktop apps in Windows 8. No installation is required and it works with all colour schemes. It defaults to x3 full screen magnification with an inverted-colour mouse pointer, and tracks the mouse pointer, keyboard focus and insertion point. Magnification goes up to x6 with basic font smoothing, and there is an inverse colour option and a lens mode. It replaces the Windows mouse pointer options with a larger pointer for which you can choose between four colours.
A significant limitation of Lightning Express is that it has to be downloaded or run from the Internet each day - if you download it today, it will only work until midnight, and then has to be downloaded again tomorrow. Its big plus is that it offers free full screen magnification to Windows XP and Vista, or Windows 7 users who use a High Contrast theme.
Desktop Zoom
Desktop Zoom works with Windows XP, 2000, Vista and 7. It doesn't require installation and turns off Aero when it's started. It starts with x3 magnification and a yellow mouse, tracking the mouse only and with text smoothing turned on.
It has lots of options such as keyboard control for zooming in and out and for turning some features on and off, mouse pointer size and shape enhancements, and speech output using the Windows TTS voice. Multiple configurations can be saved. An overview of the original screen with the magnified area superimposed appears at a bottom corner of the screen (this is called a "thumbnail").
As well as the default whole screen mode there are two others called "around mouse" and "fixed window". In these alternatives most of the other options - colour, tracking, speech - aren't available. Desktop Zoom has some unusual features, such as the ability to turn magnification off simply by moving the mouse pointer to the bottom right corner of the screen.
Desktop Zoom isn't as reliable as Magnifier or Lightning Express. Keyboard tracking and text smoothing don't work smoothly and zoom level settings are difficult to set. At high levels of magnification, smoothing and general movement deteriorate.
Around the mouse magnifiers
There are a number of free magnifiers that only magnify an area around the mouse pointer. They are usually aimed at people who need to do detailed graphics work and do not track the keyboard.
Virtual Magnifying Glass
Virtual Magnifying Glass has versions for Windows, Mac OS X, Linux and FreeBSD. It claims to support multiple-display systems on Windows. It can display in Classic or Dynamic mode at seven levels of magnification up to 16x with no font smoothing.
In Classic mode no mouse pointer is visible, and no interaction is allowed in the magnified window. Clicking the mouse causes the magnified window to close, and the arrow keys change the size of the lens.
Dynamic mode is a beta feature. The magnified area is static, but can be moved and resized with the keyboard. Within the magnified area you can use the mouse and keyboard as usual, and so might be useful to a user with sight loss. Dynamic mode does not work on Windows 8.
The mode and other settings can be changed through a notification area icon, but only when the application is not active. There is an option to invert colours.
Zoom Lens
Zoom Lens is a tiny download that requires no installation. On Windows Vista and 7, it is unusable with an Aero theme active, so you have to manually change to a non-Aero theme before starting it. By default the magnified lens fades out when the mouse moves more than a small amount. This is described as a feature so that areas under the mouse can be made visible, but it needs to be switched off for a user with sight loss to find it practical.
Although the size of the lens can be increased, movement of the mouse becomes increasingly jerky as the size increases. Magnification goes up to x10 with no smoothing. It has few other options.
Desktop Magnify
Desktop Magnify works on Windows NT, 2000, XP, Vista, 7 and 8 (desktop apps only), and it supports all colour schemes themes. It creates a separate window showing a magnified area of the mouse when it is moved outside the window. It tracks only the mouse and allows magnification of x1, x2, x4 and x8 with no smoothing. The menus within the window are not magnified, but all the controls have keystrokes. There is no mouse pointer visible in the magnified window.
Desktop Magnify was created by eyeClaxton software but is available from shareware sites e.g. Softpedia,
Magnifying Glass
Magnifying Glass supports Windows versions from 95 up to 7. It has options to magnify up to x32 and - unusually - down to x0.7. A non-Aero theme must be chosen before starting Magnifying Glass.
When the programme is started, it creates a Notification Area icon; you can then use a keystroke to toggle the magnifier on and off, or use the icon to change options. Annoyingly, magnification toggles off whenever the options screen is opened.
By default it has x2 magnification and shows as a semi-transparent window - this transparency must be switched off before it can be used comfortably. The magnifying glass size can be changed, and its position can be either in a fixed place on the screen or following the mouse.
The default action is for the magnifying glass to follow the mouse pointer around the screen, but not obscure it. This means there are two mouse pointers on the screen - the unmagnified one and another inside the magnifying glass. The glass shifts its position relative to the pointer if it approaches the edge of the monitor, which can be off-putting.
ZoomIt
ZoomIt was created for use during technical presentations. It has a simple magnifier called Live Zoom which works in Windows Vista and 7. Live Zoom can be toggled on and off with Ctrl + 4, and a magnification level then chosen with Ctrl + Up/Down. No other magnification features are available.