White Balance

Automatic white balance on the Optio S worked fairly well in natural light but left images looking very orange under artificial light. The preset white balance setting for incandescent light produced a near perfect color balance, however the single fluorescent preset produced an identical result to auto mode. As we would hope manual white balance was the best option for accurate color in any light source.

Outdoors, Auto	Outdoors, Sunny (or Shade)	Outdoors, Manual
Incandescent, Auto	Incandescent, Incandescent	Incandescent, Manual
Fluorescent, Auto	Fluorescent, Fluorescent	Fluorescent, Manual

Macro Focus

We really didn't expect much from the Optio S in the macro department so were pleasantly surprised when we discovered that in fact it is very capable. Switch the camera to Super-Macro mode and the lens is locked at half zoom, at the closest possible focus distance (6 cm) this produced a frame coverage of 35 mm (1.4 in). For an ultra-compact digital camera this is unheard of. Kudos Pentax.

Flash Performance

The flash unit in the Optio S has a specified range (at ISO 200) of 3.5 m (11.5 ft) at wide angle and 2.0 m (6.6 ft) at telephoto. In our tests flash shots exhibited no color cast and fairly good (if conservative) exposure. The Optio S has no provision for flash power compensation.

Skin tone - Good exposure (slightly under exposed), no color cast, natural skin color	Color patches - Good color balance, good flash power, exposure could have done with a little more power

Night exposures

The Optio S has limited night exposure capability because of its maximum 1 second shutter speed even in night scene mode. This is a huge pity because ISO 50 shots at 1 second exhibit hardly any visible noise, if Pentax had allowed exposures of up to 8 seconds the Optio S would have at least a usable night exposure capability. As things stand they only option you have available is to increase sensitivity to ISO 100 or 200, but this unfortunately introduces noise which can be hard to remove.

Night exposure: ISO 100, 1 sec, F2.6
Night exposure: ISO 200, 1 sec, F2.6

Barrel and Pincushion Distortion

It's design may be a technical marvel but the Optio S lens does suffer from noticeable barrel distortion at wide angle, slightly more than we are used to seeing on an ultra-compact digital camera. Luckily things are better at the telephoto end of zoom where there is no measurable pincushion distortion.

Barrel Distortion, 1.4% @ wide angle	Pincushion Distortion, none @ telephoto

Vignetting / Light fall off

Our vignetting / light fall off test is very simple, a shot of a blank wall from two meters away, vignetting will always be most visible at wide angle and maximum aperture and will start to disappear at smaller apertures and/or further zoom. The Optio S exhibited some vignetting at wide angle, specifically on the right hand corners of the image. It is possible that such vignetting could be seen in certain shots.

Slight corner vignetting visible at wide angle and maximum aperture (F2.6)	No vignetting at telephoto

Purple Fringing (Chromatic Aberrations)

The Optio S did exhibit some purple fringing near the corners / edges of images shot at wide angle and maximum aperture (F2.6). As you can see from the crops below it seldom extends more than one or two pixels and isn't particularly strong. This is undoubtedly a consequence of the tiny lens system.

Some fringing visible in the corners of shots with high contrast	Our standard chromatic aberration test shot

Overall Image Quality / Specific Issues

Overall the Optio S delivered relatively good images with very little noise (at ISO 50), moderately good resolution and no major artifact problems. Color balance is good, as is tonal balance which tends towards maintaining shadow detail rather than trying to be too 'punchy', of course you can modify the output from the camera by changing the image processing parameters in the record menu. One note may be that images can occasionally look a little soft and that higher ISO images do look as though they have been processed (noise reduction?).

Bottom of lens softness

One thing I did notice in images taken at wide angle and maximum aperture (F2.6) was a softness along the bottom of the image and most notably in the bottom left or right corners. Anyone who knows a little about lenses will expect the corners of the image to be softer at maximum aperture (especially for such a small lens), however this was more noticeable along the entire bottom of the image and stronger in the bottom corners than the top. It appears as though this issue may vary from one camera to the next as the Casio EX-Z3 (same lens) we had for review didn't suffer quite as noticeably.

Our standard ISO resolution chart	Bottom left corner and bottom 'strip' of image softer than the rest
Note that this image has been rotated 90° clockwise and so softness is now down the left edge	Lens softness along the left edge of the rotated image (this was the bottom of the image before rotation)