The K-50 doesn't produce the best photos I've seen from a camera in this class, but they're good enough to please casual photographers.
Lori Grunin
I've been reviewing hardware and software, devising testing methodology and handed out buying advice for what seems like forever; I'm currently absorbed by computers and gaming hardware, but previously spent many years concentrating on cameras. I've also volunteered with a cat rescue for over 15 years doing adoptions, designing marketing materials, managing volunteers and, of course, photographing cats.
The highest I'd use in good light for JPEGs is ISO 800; even at low ISO sensitivities the shadow areas show a little too much noise reduction, but the brighter areas look fine.
(These may look slightly underexposed, but that's a result of the default color settings, which increase contrast and saturation too much.)
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JPEG, high ISO sensitivities
While it can squeak by for ISO 3200, past that it's pretty unusable.
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ISO 100 JPEG
Pentax's processing seems to result in slightly soft photos -- the raw version of this looks a little sharper.
(1/80 sec, f4.5, ISO 100, AWB, spot metering, 18-55mm lens at 42.5mm)
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ISO 200 JPEG
Generally, the photos are acceptably sharp, if not great.
(1/80 sec, f9, ISO 200, AWB, spot metering, 18-55mm lens at 55mm)
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ISO 400 JPEG
At ISO 400, photos still look good, with no excessive noise reduction.
(1/100 sec, f2.8, ISO 400, AWB, spot metering, 18-55mm lens at 40mm)
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ISO 800 JPEG
At ISO 800, it still handles edges pretty well. Color noise in the raw files stays relatively fine-grained until you hit ISO 1600.
Pentax's default color settings -- dubbed Custom Image -- result in the most severe hue shifts and clipped shadows I've ever seen. This really becomes a problem when shooting in low light.
In bright illumination you can usually get away with boosting the contrast and saturation of the colors, but in low light it results in a lot of lost shadow detail and odd color shifts.
Although you can see the artifacts, which include noise-reduction effects and jaggies on high-contrast edges -- JPEG images without fine details can still be usable at ISO 1600.