Pentax K-S1 Review

Image Quality

The single most exciting aspect of the Pentax K-S1 is its new 20.2-megapixel sensor.  We do have seven more meaty pages of content prepared for you, but the sensor and image quality is uncharted territory, and that's why we'll be starting the review by taking a closer look at it.

First, a little bit about the sensor as well as our hypothesis: the chip that powers the K-S1 has an increased resolution compared to older entry-level cameras like the 16-megapixel K-50.  Its resolution is still below the 24-megapixel sensor in the K-3 flagship, but since it's a year newer, we might see a little less noise at high ISOs.  It also has no optical low pass filter, which means that everyday photos should appear a more crisp out of the box. 

Custom Image (JPEG Engine)

In the first tab of the image capture menu you'll find a setting labeled "Custom Image". When selected, this option allows you to customize the appearance of your JPEG files by choosing a preset and fine-tuning advanced parameters.

The Custom Image presets are as follows:

• Bright
• Natural
• Portrait
• Landscape
• Vibrant
• Radiant
• Muted
• Bleach Bypass
• Reversal Film
• Monochrome
• Cross Processing

The configurable parameters vary by setting, but for first five (which you'll be using most of the time) they are:

• Saturation
• Hue
• Contrast
• Sharpness
• Clarity (High-key/low-key filtering)

The default "bright" setting is a good starting point, but we recommend that you play around with the settings after taking a few photos and tweak them as desired. An effective way to find the optimal preset is to develop the same RAW file using different settings (via the supplied desktop software) and compare the results.

See this page for a comparison of the various Custom Image presets.

RAW File Formats

The K-S1 can save its RAW files in either .PEF or .DNG format.  In terms of data and filesize, both formats are equivalent.  However, some software may not be able to open .PEF files, so we recommend sticking to .DNGs.  This requires a setting change (via the image capture menu) as the camera defaults to .PEF.

Both formats can be opened by the supplied Pentax software.

Colors and White Balance

You can expect the Pentax K-S1 to produce pleasing images out of the box.  Its default preset renders vivid colors that pleasing to the eye yet still accurate. Contrast and sharpness will obviously vary based on the lens being used, and sometimes editing can make your files even better. However, in many cases you'll be pleased in what the camera come up with on its own.

Unedited out-of-camera photo

Deep reds are just a tad too red out of the box: a characteristic that the K-S1 shares with other Pentax cameras.  We feel that a slight shift in the hue of reds makes images appear more natural, but this is of course a question of taste.  Click on either image below to enlarge.

Original Reds

Corrected Reds

Unfortunately, the K-S1 has not been fitted with Pentax's latest-generation metering system, so its auto white balance sometimes struggles in artificial light: an area in which the K-3 excelled.

In-Camera Image Enhancements

The K-S1 includes a host of settings to enhance images straight out of camera.  These include:

• Lens corrections (vignetting, aberrations, diffraction, distortion)
• Shadow correction
• Highlight correction
• Noise reduction (high ISO and long exposure)

With the exception of highlight correction, these only apply to JPEG files.  They can be accessed via the control panel as well as the main menu.

In general the lens correction work well and can be very effective in compensating for lens imperfections, especially with the kit lenses.

A word of caution: distortion correction adds just over a second of processing time to each photo, which significantly reduces playback speed and can slow down burst shooting.

Moire

Since the K-S1's has no optical low-pass (AA) filter, it's possible for false color patterns to appear in fine repetitive textures, such as textiles or fences.  While it's a rare phenomenon, this can be difficult to remove in post-processing.  Thankfully, the K-S1 has a hardware remedy to this problem thanks for a Pentax-unique feature known as the AA filter simulator.  The AA filter can be activated via the Control Panel when needed and has two strength settings.

Learn more about this system on the Moire page of our Pentax K-3 review.

Stabilization

Pentax's in-camera Shake Reduction system is very effective and enables you to capture sharp photos at slow shutter speeds as low as 1/10s in practice.  Because the stabilization mechanism is located in the body, it doesn't matter what lens you use: they will all benefit.  When using manual lenses, you will be prompted to enter the focal length at start-up.

Detail

The very first thing we observed when we started shooting with the K-S1 is that its files had plenty of detail and were nice and sharp, even with the standard kit lens.  This will allow you to crop more aggressively and get away with less frequent post-processing.  See the enlargement below for an example:

Pentax K-S1 | DA 18-135mm | ISO 100 | Full-Size Image

Daytime Noise

To see how much noise the K-S1 exhibits at higher sensitivity settings, we photographed the scene below in RAW+ at ISO 100 through 1600 at 1-stop increments.  This scene was captured with the 18-55mm kit lens, so the test also doubles as a gauge of what to expect from that particular lens.

Pentax K-S1 | ISO 100 | DA L 18-55mm | Full-Size Image

For each of the two locations, we present three 100% crops.  The first set is from unedited JPEG files straight out of the camera.  We used the default Bright custom image mode with auto noise reduction, no lens corrections, and no AA filter simulator.  The second set consists of RAW files sharpened & de-noised  (25% and 0-15%, respectively) in Adobe Camera RAW.  The final set was developed from RAW with no additional sharpening and no luminance noise reduction to illustrate the sensor's natural noise.

	Summit
ISO	JPEG (Defaults, NR Auto)	Processed RAW	Unedited RAW
100
200
400
800
1600
	Roof
100
200
400
800
1600

We can draw the following conclusions from these tests:

• Noise levels are very low overall
• Detail loss is negligible through ISO 800
• RAW files are considerably more detailed than out-of-camera JPEGs

The results look promising so far, but now, let's see how the K-S1 fares side-by-side with the K-50 and K-3.

Low-Light High ISO

We photographed the scene below with the Pentax K-S1, K-50, and K-3 to compare their resolution and noise levels side by side.  Each camera was placed on a tripod and fitted with the same copy of the DA L 18-55mm kit lens.  The exposure was kept constant and other shooting settings were identical to those used above.

Night Test Scene - Click for original RAWs & JPEGs

The images in the grid below are full-size crops of the circled area in the test scene.  The RAW files were developed with the same (conservative) sharpening and noise reduction presets at each ISO.  For the JPEG set, K-S1's white balance system seems to have been fooled, most likely due to a small variation in the orientation of the camera.

	RAW Files
ISO	K-3	K-S1	K-50
100
200
400
800
1600
3200
6400
12800
25600
51200
	JPEG Files
ISO	K-3	K-S1	K-50
100
200
400
800
1600
3200
6400
12800
25600
51200

We can make some interesting observations based on these images.

First of all, it's evident that shooting in RAW in low-light scenarios holds a considerable advantage over JPEGs with auto noise reduction. Our remaining remarks are therefore based exlusively on the RAW results.

The K-S1's sensor renders considerably more detail than the K-50.  Noise levels are very low until ISO 3200, and though the K-50 is slightly less noisy near/above that threshold, its photos still aren't as detailed at the end of the day.  Bottom line: the K-S1 is better in low light.

Finally, in terms of detail, the K-S1 is actually neck-and-neck with the K-3 through ISO 3200, were the K-3's 4 extra megapixels only have a small effect on the final product.  At ISO 6400 the K-S1 is a little bit more noisy than the K-3 but still manages to bring out similar levels of detail.  Finally, at ISO 12,800, the K-3 clearly pulls ahead in all aspects, likely thanks to its 14-bit color depth combined with the added resolution. The K-S1, like the K-50, only captures 12-bit RAW files and thus has less shadow detail in extreme scenarios.

ISO 6400 Comparsion: K-3 (left) vs K-S1 (right) - Click for full size

Dynamic Range

When it comes to dynamic range, all photographers agree that shadows are easier to recover than highlights.  The same holds true for the K-S1, which means that you will be better off under-exposing than over-exposing an image when in doubt.  To an extent, the in-camera shadow and highlight correction options can automate this for you, but to truly gain control over the camera's dynamic range, it is necessary to shoot in RAW.

While we did not attempt to quantify the K-S1's dynamic range in terms of stops, based on subjective tests it is very similar to that of the K-50.  Shadows can typically be recovered even when you underexpose by 5 stops, albeit with visible grain.  Hilights typically won't be fully recoverable above 1 stop of overexposure.  The K-3 has an edge over the K-S1 thanks to its higher bit depth, which again is no surprise.

Feel free to download the .DNG RAW file of the photo below to experiment with the shadows and highlights:

Dynamic Range Sample - Click for RAW file

Verdict

The Pentax K-S1 takes great pictures.  Whether you're shooting on full auto mode or in RAW with manual settings, you can expect the K-S1 to deliver satisfying images that will hold their ground against other comparable cameras currently on the market.

In-camera auto noise reduction is quite aggressive in JPEG mode and can cause considerable detail loss at high ISOs.  We therefore recommend disabling noise reduction or using the "low" setting at ISO 3200 or above.

Compared to 16-megapixel Pentax K-50, the K-S1 is a considerable upgrade in terms of image quality. Thanks to a higher resolution and lack of a low-pass filter images will be sharper and details will be clearer, giving you more room to crop when needed.

Not unexpectedly, the K-S1 still falls short of the image quality of the K-3 flagship, and our hypothesis about its noise level has been disproved.  A lot of the time the two cameras come very close to each other, but in harsh lighting and at very high ISOs, the flagship triumphs.