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Canon A640 Optics


Lens

Zoom
A generous 4x optical zoom range, with good performance.

Canon PowerShot digital camera image Canon PowerShot digital camera image
35mm
140mm
4x Digital Zoom

The Canon A640 zooms 4x over the equivalent of a 35-140mm range, a bit better than the 3x range typical of its class. The 4x digital zoom takes it out to 16x total with a bit less loss of quality than I'm accustomed to seeing from digital zoom.

Macro
A small macro area with good detail and high resolution. Flash does not throttle down well at this range, so plan on using external flash for macro shots.

Canon PowerShot digital camera image
Standard Macro Macro with Flash

The Canon A640's macro setting performs very well, capturing a small minimum area of 0.87 x 0.65 inches (22 x 17 millimeters). Detail is strong and resolution high, with only a moderate amount of softening in the corners from the lens. (Most cameras have some softening in the corners in Macro mode.) The flash doesn't throttle down well, nor can it evenly illuminate the field at such close range. (Plan on using external lighting for your closest macro shots with the A640.)

Distortion
Moderate barrel distortion, low pincushion.

This is the tendency for the lens to bend straight lines outward (like a barrel--usually at wide angle) or inward (like a pincushion--usually at telephoto). The Canon A640's 0.61% barrel distortion at wide angle is lower than average among the cameras I've tested. At the telephoto end, the A640's 0.14% pincushion distortion is also lower than average. An excellent performance.

Barrel distortion at 35mm is 0.61%
Canon PowerShot digital camera image
Pincushion distortion at 140mm is 0.14%
Canon PowerShot digital camera image

Chromatic aberration
Pretty low at both wide angle and telephoto, showing just a small effect on images at edges.

Canon PowerShot digital camera image Canon PowerShot digital camera image
Wide: low, top left @ 200% Wide: low, top right @ 200%
Tele: quite low, top left @200% Tele: quite low, top right @200%

Chromatic aberration is rather low at wide angle, showing very few pixels of moderately bright coloration on either side of the target lines, decreasing to very low levels at telephoto focal lengths. Considering the high resolution, this is another very good performance. (This distortion is visible as a very slight colored fringe around the objects at the edges of the field of view on the resolution target.)

Corner Sharpness
Some softening in the lower corners of the frame, strongest effect in the lower right corner.

Wide: slightly soft
in the lower right corner.
Wide: sharper at center.
Tele: slightly soft
in the lower right corner.
Tele: sharp at center.

The Canon A640 showed only a slight loss of sharpness in the corners of the frame, quite a bit less than is average among cameras of its class. The center of the frame was slightly sharper at wide angle than telephoto, but the difference between the two was minor indeed. This is another impressive result.

Viewfinder

Coverage
Optical viewfinder tight and skewed to the upper right. Very good accuracy from the LCD monitor.

Canon PowerShot digital camera image Canon PowerShot digital camera image
35mm eq., optical viewfinder 140mm eq., optical viewfinder
Canon PowerShot digital camera image Canon PowerShot digital camera image
35mm eq., LCD monitor 140mm eq., LCD monitor

The A640's optical viewfinder was quite tight, showing only about 80% frame accuracy at wide angle and 78% at telephoto lens settings. However, the LCD monitor showed close to about 100% frame accuracy.