Canon PowerShot S90 Optics
A fairly wide, 3.8x optical zoom lens with good performance. Average digital zoom performance.
|28mm eq.||105mm eq.||4x Digital Zoom|
The Canon PowerShot S90's lens covers the equivalent of a 28-105mm zoom on a 35mm camera, with a fairly typical zoom ratio of about 3.8x. Details are pretty good across the frame at full wide-angle, with minor blurring and coma distortion in the corners. Moderate levels of chromatic aberration are visible in the corners, as well as some flare around the brighter areas of the scene. Results at full telephoto are somewhat soft overall, but with only small amounts of chromatic aberration and flare (see the User Report for a different telephoto shot that is considerably less soft, with the subhead "Range."). The Canon S90's 4x digital zoom did a pretty good job of maintaining fine detail despite the typical blurring and loss of resolution associated with 4x digital zoom.
A slightly larger than average macro area, with excellent detail and resolution. Flash had a lot of difficulty throttling down, and is partially blocked by lens.
|Standard Macro||Macro with Flash|
The Canon PowerShot S90's macro setting captured a slightly larger than average area of 2.54 x 1.91 inches (65 x 48 millimeters). Detail and resolution were both excellent, though there's some softening in the corners from field curvature of the lens. (Most cameras have some softening in the corners in macro mode. What we can see here is a bit better than average.) The Canon S90's flash had a lot of difficulty throttling down at this distance, causing extreme overexposure where the flash wasn't blocked by the lens. The overexposure plus the shadow from the lens resulted in a very unevenly lit image. Plan on using external lighting for the closest macro shots with the S90.
Lower than average barrel distortion at wide-angle and telephoto in JPEGs. Higher distortion in RAW files.
|Camera JPEG: Barrel distortion at 28mm is 0.4%|
|Camera JPEG: Barrel distortion at 105mm is 0.1%|
The Canon S90's 0.4% barrel distortion at wide-angle is lower than average among the cameras we've tested, and quite good considering its 28mm equivalent focal length. This distortion is only slightly noticeable in some of its images. At the telephoto end, the S90's 0.1% barrel distortion is very low and hardly noticeable. Distortion 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).
|Uncorrected RAW: Barrel distortion at 28mm is 3.5%|
|Uncorrected RAW: Barrel distortion at 105mm is 0.2%|
With such good numbers from JPEGs, we suspected the camera may be correcting for geometric distortion in JPEGs. We were right. After converting RAW files using dcraw, which doesn't apply any distortion correction, barrel distortion at wide-angle was much higher, at about 3.5%. Barrel distortion at telephoto was only slighter higher than the JPEG, at about 0.2%. Incidently, Adobe Camera Raw 5.6 beta doesn't correct for distortion in the S90's RAW files (see crops above), but we wouldn't be surprised if it did in subsequent versions of the software. Canon's own Digital Photo Professional software (included) corrects it.
It's interesting to note that we didn't see this behavior with the Canon G11. Its uncorrected RAW images had essentially the same amount of geometric distortion as its JPEGs. The PowerShot S90 has a much smaller lens, however, which is likely why it requires correction while the G11's lens does not.
Chromatic Aberration and Corner Softness
Moderate C.A. at wide-angle, lower C.A. at telephoto. Moderate blurring in the corners of the frame at wide-angle, but only slight blurring at telephoto.
Chromatic Aberration. Chromatic aberration is moderate at wide-angle, showing about 8-10 pixels of moderately bright coloration on either side of the target lines. The color extends fairly deep into the frame, but the width and intensity of the fringes reduce as you move toward the center. At telephoto, the extent of the chromatic aberration is about the same, perhaps even slightly higher, but it's not nearly as bright and therefore much less noticeable. There's also some noticeable red lens flare or chromatic aberration in the center of the frame at telephoto. The Canon S90 appears to be applying some correction for C.A. in its JPEGs, as uncorrected RAW files have higher amounts. Chromatic aberration is a type of distortion visible as a slight colored fringe around the objects at the edges of the field of view on the resolution target.
Corner Softness. The Canon PowerShot S90's lens produced mild to moderate corner softness at full wide-angle. Blurring was strongest in the upper right corner, but didn't extend very far into the frame, and is likely exacerbated by geometric distortion correction. Corners at full telephoto were only slightly soft, though there was a loss of contrast across the image compared to wide-angle. Overall results are pretty good, especially considering that these shots were taken at maximum aperture (f/2.0 is pretty fast at wide-angle!), as sharpness generally improves as the lens is stopped down to smaller apertures.