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White Balance

Although the Optio 550's automatic white balance seemed to work under natural light (outdoors, not too much shade) it couldn't cope with incandescent or fluorescent light. The incandescent preset was too cool for our test lights and so left the image with a cyan cast, none of the three fluorescent presets worked with our fluorescent test lights. 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, Fluor W / N / D Fluorescent, Manual


Macro Focus

The Optio 550 has two macro modes, the first simply named 'Macro' provides a closest focus distance of 15 cm and does allow you to vary zoom, the second 'Super Macro' provides a closest focus distance of 2 cm but locks optical zoom to wide angle (it does allow digital zoom - yuck). The best results were in normal Macro mode at full telephoto zoom, this provided a frame coverage of 40 mm (1.6 in) with virtually no lens distortion. Super Macro mode provided a frame coverage of 27 mm (1.1 in) at its closest focus distance but also introduced a lot of barrel distortion and lighting / reflection problems from the proximity of the lens to the subject.

Macro (lens manually zoomed to full telephoto)

Super Macro (lens fixed at wide angle)


Flash Performance

The Optio 550's built-in flash has a range of 5.2 m (17.1 ft) at wide angle and 3.2 m (10.5 ft) at telephoto. The only question which hangs over those figures (and isn't clear from the Pentax literature) is at what sensitivity they are quoted. Our tests showed no color cast, good white balance, good color balance and good flash exposure metering. Note that the Optio 550 has no provision for adjustment of flash output power.

Skin tone - Good exposure, no color cast, natural skin color Color patches - Good color balance, good flash power


Night exposures

The Optio 550 has a dedicated night exposure mode which allows you to capture images with a shutter speed as slow as 4 seconds, this is actually the camera's slowest shutter speed. It's a pity that Pentax didn't extend this to 8 or 16 seconds as the 550 clearly seems to be capable of capturing long exposures with little visible noise.

Night exposure: ISO 64, 4 sec, F2.8


Barrel and Pincushion Distortion

Normally we test barrel and pincushion distortion at wide angle and telephoto, however I did notice early on that the Optio 550 exhibited mode pincushion distortion at the half-zoom position than it did at telephoto (a very odd set of circumstances). We measured barrel distortion of 0.7% (quite low), half-zoom pincushion distortion of 1.2% (high) and telephoto pincushion distortion of 0.8% (mid to high). With any big zoom lens we expect to see some pincushion distortion at telephoto, and indeed if we hadn't tested half-zoom the Optio 550 would have been looking quite good. However the strong pincushion distortion seen at half-zoom was a surprise and must count against the Optio 550.

Barrel Distortion, 0.7%
At wide angle (37.5 mm equiv.)
Pincushion Distortion, 1.2%
At half-zoom (84 mm equiv.)
 
Pincushion Distortion, 0.8%
At telephoto (187.5 mm equiv.)
 


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. Based on the results we had from our distortion test I decided to also shoot our vignetting / light fall off test at half-zoom. As you can see there is some vignetting at wide angle and half-zoom. We did notice some vignetting in our sample shots (see the gallery).

Some visible vignetting, more visible at bottom
At wide angle (37.5 mm equiv.)
Vignetting still visible
At half-zoom (84 mm equiv.)
 
Virtually no vignetting visible at full telephoto
At telephoto (187.5 mm equiv.)
 


Purple Fringing (Chromatic Aberrations)

As you can see from the shots below the Optio 550 did exhibit some purple fringing around the edges of contrast. This was only visible in shots at wide angle and maximum aperture, and wasn't particularly strong. The is no doubt connected to the rather ambitious five times zoom capability of the lens.

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


Overall Image Quality / Specific Issues

An examination of the Optio 550's image quality shows good resolution and good tonal balance. Images are sharp (if a little over-sharpened) and a browse through several hundred test shots shows that the 550's lens is certainly quite sharp. However, the 550 isn't without a few problems.

As mentioned on the previous page and above the Optio 550 has several noteworthy 'issues', these are image noise from ISO 100 upwards, pincushion distortion in images from half-zoom to telephoto, vignetting from wide angle to half-zoom and mild chromatic aberrations (although this is less serious). The first problem is surely a function of the sensor, data path and image processing. The last three are all connected to the lens system, which I have to say was always going to be the weak link. It's notoriously difficult to make a quality long zoom lens for a digital camera, even more so one that can produce five megapixels of detail and even more so the smaller you make it. Sony achieved a five times zoom lens with a larger five megapixel sensor and a much larger (and higher quality) lens system.

Metering bug (a lemon camera?)

The first camera I had for review also had an unfortunate metering bug which caused the camera to underexpose by about two stops almost any image with a bright highlight in it (it's almost as though the metering system 'panicked'). Subsequent replacement of this camera with another has resolved this issue, however you may still find images in the samples gallery with fairly high EV compensation, they were taken with the first camera.

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