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ISO (Sensitivity) Adjustment

ISO equivalence on a digital camera is the ability to increase the sensitivity of the CCD to allow for faster shutter speeds and/or better performance in low light. The way this works in a digital camera is by "turning up the volume" on the CCD's signal amplifiers, nothing is without its price however and doing so also amplifies any noise that may be present and often affects colour saturation.

The Optio 430 has two ISO sensitivity choices of ISO 100 and ISO 200. There is also Auto ISO which will vary the sensitivity automatically depending on available light. It's a shame Pentax didn't include an ISO 400 option. The crops below are taken from three patch positions on our standard colour patches shot at ISO 100 and 200.

ISO 100, 1/40 sec, F4.2
ISO 200, 1/80 sec, F4.2

These patches don't tell the whole story, if you look closely at the middle grey patch you can see some slight mottling at ISO 100, more visible mottling and noise can be found in every day images around areas of detail (see the watch crops on the previous page). It appears as though the Optio 440 is using a fairly strong noise reduction algorithm.

White Balance

The Optio 430 has a good set of white balance choices including manual preset white balance which we really wouldn't expect to find on an ultra-compact digital camera. As you can see from the results below the Auto white balance worked best in natural light. The pre-programmed white balance settings were excellent, indeed the incandescent and fluorescent settings are probably the best I've seen on any consumer digital camera. Manual preset white balance also worked very well.

Outdoors, Auto Outdoors, Cloudy Outdoors, Manual
Incandescent, Auto Incandescent, Incan. Incandescent, Manual
Fluorescent, Auto Fluorescent, Fluorescent Fluorescent, Manual

Low Light Focus

This test measures the minimum amount of light under which the camera can still focus. The focus target is our lens distortion test chart (shown here on the right), camera is positioned exactly 2 m (6.6 ft) away.

Light levels are gradually dropped until the camera can no longer focus. This is carried out at both wide angle and telephoto zoom positions (as more light reaches the focusing systems with a larger aperture).

This test target is the optimum type of subject for most "contrast detect" AF systems (as it has a vertical line at its center), you should consider the results below the best you could expect to achieve.

Lens position Aperture Lowest light focus
Wide angle (37 mm) F2.6 1.4 EV (6.6 Lux, 0.6 foot-candle)
Telephoto (111 mm) F4.8 1.8 EV (8.7 Lux, 0.8 foot-candle)

Light intensity (Lux) = 2.5 x 2^EV (@ ISO 100), 10.76391 Lux = 1 foot-candle (fc)

Overall a fairly good performance, the Optio 430 appears to have the tuned firmware which Optio 330 users got a little later on. This newer firmware manages to grab focus even in fairly low light levels.

Flash Performance

The Optio 430's internal flash has a specified range of 0.14 - 3.7 m (0.5 - 12 ft) at wide angle and 0.4 - 2.0 m (1.3 - 6.6 ft) at telephoto. In our tests it repeatedly produced underexposed or strongly blue cast images. This is a sign of either an inaccurate white balance (which should really be locked for flash photographs in low light) and / or poor flash exposure metering.

Skin tone test: Flash brighter at the left than the right. Slightly cool blue cast on the white balance. Wide angle 2 m wall test: As we'd expect the camera's flash doesn't have enough power to fill the frame, note the drop-off in the corners. Again not a bad exposure but a notable blue cast white balance.

Barrel and Pincushion Distortion

The Optio 430 lens barrel distortion at full wide angle was measured at 1.2%, this is towards the high end of what we'd expect. The news is better at full telephoto, no measurable pincushion distortion.

Barrel Distortion, 1.2% @ wide angle Pincushion Distortion, 0% @ telephoto

Purple Fringing (Chromatic Aberrations)

Overall the 430 did as well as its three megapixel brother the 330. Purple fringing was almost undetectable even in very extreme images. About the only thing worth mentioning was a certain amount of blooming radiating from overexposed areas into image detail.

Hard pressed to find evidence of chromatic aberrations in "every day" shots
Our now standard chromatic aberration test shot - mostly blooming

Overall Image Quality / Specific Issues

Generally speaking the Optio 430's image quality was good if you're going to use downsampled images (for web posting / email) and below average if you print at large sizes or are like me and examine all your images at least 100% magnification. Colour balance was good, as was mid to high-tone grayscale, but things got muddier in the shadows (see below). The 430's internal noise reduction system can also lead to some strange artifacts, super smooth areas bordered with noisy detail. To my eye the 430 doesn't gain a lot from its 4 megapixel sensor.

Underexposure / Contrast

The Optio 430 seems to have the same "heavy contrast" as its brother the 330. That is that (a) the camera tends to underexpose by default and (b) shadow areas end up almost black. The shot on the left below was taken with a +1.0 EV exposure compensation. As you can see the top end of the grayscale now looks acceptable, however the bottom (shadow) end looks dark and muddy. A slight curve adjustment in Photoshop brings the shadow detail back out again. This is a shame because I wouldn't expect the average user of the 430 to (a) use exposure compensation to compensate for the metering system or (b) post-process their images to ensure correct shadow detail.

Shot with +1.0 EV compensation Same image with a slight curve adjustment

Noise Artifacts

Another trait which became visible fairly early on in my testing are what I can only describe as noise artifacts. These patterns (artifacts) of noise appear around areas of detail on an otherwise smooth surface. What I can only assume is that the camera has a built-in noise reduction algorithm (a bit like a "smart blur") which is cleaning up noise from smooth areas but stopping when it reaches areas of detail. The clearest example of this can be seen around the seconds digits on the watch face crops below.

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