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Not surprisingly, the M40's overall performance is identical to the M30. It starts up in just over two and a half seconds and shuts down in just under two, and in single-shot mode it has an average shot-to-shot cycle time of just over three seconds. In continuous mode it averages 1.5 seconds per shot, although in both tests I was using a high-speed SanDisk SD card. The video mode is also unchanged, offering VGA resolution at 30fps with mono sound. The camera is of course powered by the same 740mAh Li-ion rechargeable as the M30, and the battery duration is the same at 230 shots. As usual I tested this and found it to be fairly accurate.
Of course the whole point of upgrading the sensor is to produce better image quality, and here the M40 succeeds, although only just. There is a small but noticeable improvement in overall detail, but some of that comes from the apparently much lower file compression at the highest quality setting. While the M30 produced image files of about 2.5MB, similar shots taken on the M40 are over 3MB, a greater difference than I'd expect between a 7MP and an 8MP sensor. Dynamic range and colour reproduction are about average for this class of camera. Unfortunately the lens is still the same, and produces significant barrel distortion at wide angle, pincushion distortion at telephoto and poor corner sharpness. Noise control is as good as ever though, with acceptable image quality at 400 ISO and usable results at 800. Even at the highest setting of 3200 ISO I have seen worse performance from more expensive cameras.
The Optio M40 is only a marginal improvement over the M30, but it is not a bad little camera. It is well made, has good handling for an ultra-compact, and is extremely easy to use. It performs fairly well, and apart from the lens distortion the image quality is pretty good, especially its noise control at higher ISO settings. As before though, weak points are poor low light ability and lens distortion, but for the price it is certainly worth considering.