The images above are from each camera zoomed-in to their longest focal lengths and the Canon A640’s 140mm equivalent shows a slight edge over its rivals. It’s handy for getting in a little tighter, although if you’re after a more significant difference from a PowerShot as standard you’ll need to go for the 6x optical range of the A710 IS, or the 12x range of the super-zoom S3 IS; both of these models also boast Image Stabilisation to combat camera shake whereas the A640 does not.
The A640 does however support the optional WC-DC58N wide angle and TC-DC58N tele-converter lens attachments which multiply the focal length by 0.7x and 1.75x respectively. To attach these you first press the button to the lower right of the lens to release the housing surrounding it. You must then fit the optional LA-DC58F conversion lens adapter onto which either a filter or the converter lenses can be mounted.
The PowerShot A640 also boasts excellent macro facilities and can focus as close as 1cm when zoomed-out to wide angle. This gives the A640 amazing close-up opportunities, although beware at this sort of distance it’s difficult not to cast a shadow on the subject. See our Results and Gallery pages for examples.
In a market where an increasing number of new compacts only offer composition using their main colour screens, the A640 is unusual in that it also provides an optical viewfinder. These may seem old-fashioned compared to using a nice, big colour screen, but there are benefits.
The main one is having an alternative means of composition when the colour screen becomes hard to view, such as under direct sunlight. Since you’re not using any power to illuminate a colour screen when composing with the optical viewfinder, you’ll also extend your battery life – indeed Canon claims up to three times as many shots can be taken with the viewfinder alone compared to using the screen.
Of course it’s highly unlikely you’d use the viewfinder exclusively for composition and unlike the screen it won’t show 100% coverage, exposure information nor focus indication beyond a light, but it’s still good to have it as an option. If your battery's running too low to run the screen for much longer, it could mean the difference of missing a crucial shot or grabbing it.