Pentax K-S1 Review

February 4, 2015 | Jack Baker | |
thumbnail

Image Quality

The Pentax K-S1’s new 20.1-megapixel APS-C sensor isn’t quite as pixel packed as the 24.2MP chip in the D3300, but it’s a marked increase over the old 16.3MP K-500, and the difference is boosted by the new camera not having an optical low pass filter.

Detail is impressively well resolved, even at ISO3200, and it’s only at ISO6400 where grain and noise reduction processing start to obscure very fine detail. Grain and colour speckling are more obviously visible at ISO12800, but the setting is still perfectly usable, as is ISO25600 if you’re prepared to downsize images a bit to minimise the level of visible grain. However, ISO51200 is very much a last resort for use in very low light due to high noise and low detail levels.

When you’re not scrutinising detail, the Pentax K-S1 still produces impressive images thanks to its vibrant colour reproduction and excellent dynamic range. Images are accurately exposed, and, unlike some of Pentax’s DSLRs of old, the K-S1 is less prone to underexpose high contrast scenes.

Of course your choice of lens has a big impact on the camera’s image quality, but the 18-55mm kit lens performs well. Sharpness is high, right to the corners of frame. Minor barrel and pincushion distortion is visible at either end of the focal range, but activating the K-S1’s automatic distortion correction feature instantly and effectively resolves this. Chromatic aberration is also evident on high contrast boundaries, and whilst the camera can automatically correct lateral chromatic aberration, it does leave some visible fringing.

Noise

Just as with the K-500 before it, the Pentax K-S1 has a sensitivity range of ISO100-51,200, which is a stop higher than bother the Canon EOS 100D, Nikon D3300 and the D5500. You can set the sensitivity in 1, 1/2 or 1/3 EV increments and the upper ISO limit for Auto ISO can also be user defined from ISO51200 right down to ISO200.

JPEG

RAW

ISO 100 (100% Crop)

ISO 100 (100% Crop)

iso100.jpg iso100raw.jpg
   

ISO 200 (100% Crop)

ISO 200 (100% Crop)

iso200.jpg iso200raw.jpg
   

ISO 400 (100% Crop)

ISO 400 (100% Crop)

iso400.jpg iso400raw.jpg
   

ISO 800 (100% Crop)

ISO 800 (100% Crop)

iso800.jpg iso800raw.jpg
   

ISO 1600 (100% Crop)

ISO 1600 (100% Crop)

iso1600.jpg iso1600raw.jpg
   

ISO 3200 (100% Crop)

ISO 3200 (100% Crop)

iso3200.jpg iso3200raw.jpg
   

ISO 6400 (100% Crop)

ISO 6400 (100% Crop)

iso6400.jpg iso6400raw.jpg
   

ISO 12800 (100% Crop)

ISO 12800 (100% Crop)

iso12800.jpg iso12800raw.jpg
   

ISO 25600 (100% Crop)

ISO 25600 (100% Crop)

iso25600.jpg iso25600raw.jpg
   

ISO 51200 (100% Crop)

ISO 51200 (100% Crop)

iso51200.jpg iso51200raw.jpg

Focal Range

The Pentax K-S1 is available body only, or in a kit with an 18-55mm lens giving a 3x optical zoom equivalent to 27-82.5mm in 35mm camera terms.

27mm

82.5mm

focal_range1.jpg focal_range2.jpg

File Quality

The Pentax K-S1 will capture JPEG images in fine, normal and basic quality settings. It’ll also record RAW files in the widely compatible DNG format, and will shoot RAW+JPEG with any JPEG compression setting.

Best (12.5Mb) (100% Crop)

Better (5.68Mb) (100% Crop)

quality_fine.jpg quality_standard.jpg
   

Good (2.72Mb) (100% Crop)

RAW (29.2Mb) (100% Crop)

quality_basic.jpg quality_raw.jpg

Macro

Although the standard 18-55mm kit lens is not a dedicated macro lens, it’ll still focus as close as 11cm from your subject and will do so even when using a 55mm focal length. Consequently it’s surprisingly easy to capture detailed close-up shots with a smooth background bokeh blur.

Macro

Macro (100% Crop)

macro1.jpg macro1a.jpg

Flash

The Pentax K-S1’s built-in flash has an approximate power rating of GN10. Our testing revealed the flash produces only minor vignetting when shooting a white scene from a distance of 1.5m at an 18mm focal length. Red-eye is also successfully eliminated, even without using red-eye reduction.

Flash Off - Wide Angle (27mm)

Flash On - Wide Angle (27mm)

ISO 64 ISO 64
   

Flash Off - Telephoto (202.5mm)

Flash On - Telephoto (202.5mm)

ISO 64 ISO 64

And here are some portrait shots. As you can see, neither the Flash On setting or the Red-eye Reduction option caused any amount of red-eye.

Flash On

Flash On (100% Crop)
flash_on.jpg flash_on1.jpg
   

Red-eye Reduction

Red-eye Reduction (100% Crop)

flash_redeye.jpg flash_redeye1.jpg

Night

The camera’s Night Scene mode seems to offer little benefit over using conventional Auto mode, as both modes work by raising the sensor sensitivity. This scene is captured in Night Scene more, but with auto ISO capped at ISO400, giving a 1.5-second shutter speed at f/4.

Night

Night (100% Crop)

night1.jpg night1a.jpg

Shake Reduction

Pentax’s Shake Reduction system does a great job of compensating for camera movement and allows you to use up to a 4-stop slower shutter speed than would be possible with the system switched off. Shake Reduction is less essential when shooting at the short focal lengths of the 18-55mm kit lens, but it comes into its own in low light and when using telephoto lenses.

Shutter Speed / Focal Length

Shake Reduction Off (100% Crop)

Shake Reduction On (100% Crop)

1/10th / 27mm antishake1.jpg antishake1a.jpg

Effects

Turn the Pentax K-S1’s mode dial to ‘Effects’ and ten colour filters are available to help spice up your shots. Choose from: Faded Color, Clear Tone, Brilliant Color, Unicolor Bold, Vintage Color, Cross Processing, Warm Fade, Bold Monochrome, Infrared Filter and Vibrant Color Enhance effects. All are applied at full resolution.

Faded Color

Clear Tone

effects_01.jpg effects_02.jpg
   

Brilliant Color

Unicolor Bold

effects_03.jpg effects_04.jpg
   

Vintage Color

Cross Processing

effects_05.jpg effects_06.jpg
   

Warm Fade

Bold Monochrome

effects_07.jpg effects_08.jpg
   

Infrared Filter

Vibrant Color Enhance

effects_09.jpg effects_10.jpg

Anti-Aliasing Filter Simulator

The Pentax K-S1 follows in the wake of cameras like the K-5 IIs and Nikon D810 by not including an optical low pass filter. These are fitted to most cameras to eliminate the problem of moiré. If you’ve ever seen someone on television wearing a pinstripe shirt, chances are strange wavy coloured bands (moiré) may appear across it.

This effect is produced when repetitive detail patterns are too fine for an image sensor’s pixel array to capture accurately. Fitting an optical low pass filter in front of the sensor guards against the phenomena by blurring an image ever so slightly, but just enough to take the edge off fine patterns and eliminate moiré. Trouble is, the filter blurs every single shot, yet most scenes you snap are unlikely to feature moiré-inducing patterns.

Nowadays larger, high-megapixel sensors are less susceptible to moiré, hence the potential to capture more detail by removing the optical low pass filter outweighs the rare instances where moiré may be visible. In reality, the extra detail benefits are very subtle and you’ll probably need to shoot using a tripod, low ISO sensitivity and a high quality lens set at its optimal aperture to see a difference.

But on the flip side, any problems with moiré are so uncommon you’re only likely to encounter them when shooting resolution test charts in a studio environment. If you do ever spot some interference in the real world, the K-S1 has a simulated optical low pass simulator. This works using the sensor’s Shake Reduction mechanics, which minutely vibrate the sensor to create the same level of blur as a conventional optical low pass filter provides. But the beauty of this system is you can choose when to use it.