Pentax K-S2 Review

Performance & Burst Mode

Under the hood, the Pentax K-S2 incorporates the PRIME M II CPU, which was launched in 2014 and is thus Pentax's most recent processor as of the writing of this review.  While on the surface, this CPU seems to deliver the same performance and features as the original PRIME M from 2012 (i.e. focus peaking, a moderate burst framerate and a somewhat limited buffer), following testing we discovered that the new chip actually offers a number of perks.

Before we delve deeper into this section, we would like to clarity that Pentax's 12-bit DSLRs (such as the K-50 and K-S2) use a different line of CPUs than the 14-bit DSLRs (such as the K-5 and K-3).  The PRIME M chips are used in 12-bit bodies only.

Typical Filesize

Since the K-S2 has a 20.2 megapixel sensor, its files will typically be larger than those produced by the K-50.  Expect typical JPEGs to be in the 10-12 Mb range, and RAW files (at base ISO) to be in the 19-22 Mb range. Node that the number of megabytes does not directly match the number of megapixels since both JPEG and RAW files are compressed in different ways.

In comparison, typical JPEGs from the 16-megapixel K-50 ranged from 6 to 8 Mb, while its RAW files ranged from 15-17Mb.  If you're upgrading from the K-50 or an older 16-megapixel body, we therefore recommend that you also upgrade to SD cards with twice the capacity of your old cards.  32Gb and 64Gb SDXC cards are perfect for the K-S2.  For optimal performance, also be sure that your SD cards bear the UHS-I rating (details to folow).

Performance

Since the K-S2 works with larger files than previous mid-range cameras, it's no surprise that it needs a more powerful processor.  To put the performance of PRIME M II in perspective, we faced it off head-to-head against the PRIME III processor in the Pentax K-3 and measured how long typical tasks took to complete.  All tests were performed with a Sandisk Extreme Pro card and repeated at least three times.  Median times, rounded to the nearest tenth of a second, are shown in the table below:

Pentax K-3
Pentax K-S2
Startup to 1st shot 0.9s 1.3s
Startup to live view on 1.5s 1.8s
Single file deletion 1.3s 1.3s**
Saving a single JPEG
(time to playback)
1.1s 1.4s
Saving a single RAW
(time to playback)
2.6s 1.7s
Saving a RAW+JPEG
(time to playback)
3.0s 2.2s
Lens correction
processing time
(single file)*
1.1s 0.5s
Shadow/highlight
processing time*
0.1s 0.1s
Clarity enhancement* N/A 1.0s

Pentax K-S2 vs K-3 Performance
*on top of the time it takes to write the file to the card

As you can see, the K-S2 is in fact faster than the K-3 in several areas.  It processes lens corrections more than twice as quickly, which can be seen as a blessing for JPEG shooters.  **Another key improvement is in multiple file deletions.  Unlike the K-3, the K-S2 does not require much additional time to delete multiple files.  Even folder deletions are nearly instant!  However, single file deletions still bring up an annoying progress bar and last about as long as before.

Continuous Shooting and Buffer

Another improvement that isn't apparent based on the K-S2's specifications is the way it handles burst shooting.  Previous generations of Pentax bodies would lock up while files are being written to the card and only allow the photographer to make basic settings changes through the viewfinder. For the most part, the K-S2 allows full menu access while files are being written to its card, as long as a sufficiently-fast card is used. 

Since the K-S2 supports UHS-I card speeds, we recommend the use of fast cards for optimal performance.  If you use a conventional class 10 card you may observe degraded performance, while class 6 cards and below can potentially make the camera outright sluggish.

We of course wanted to quantify how many shots the K-S2 could take at its maximum framerate of 5.4 FPS, and how different card speeds affected this, so we carried out a series of tests using the following memory cards:

For each test, we measured the number of files captured prior to a decrease in framerate, and the number of seconds the camera spent writing files to the card (not counting the burst itself).

Camera
Sandisk Extreme Pro
UHS-I, 90Mb/s write
Sandisk Extreme
UHS-I, 40Mb/s write
Transcend Class 10
10Mb/s write
JPEG Fine 44 frames, 4s 40 frames, 5s 22 frames, 21s
RAW 10 frames, 5s* 10 frames, 6s* 9 frames, 19s
RAW+ 7 frames, 6s* 6 frames, 6s* 6 frames, 24s**
Number of frames at max. FPS

*1 FPS framerate can be maintained for dozens of additional exposures
**camera locks up for several seconds; menus are inaccessible

These results are very positively surprising.  Regardless of file format, the camera finishes emptying its buffer in 4 to 6 seconds with either of the UHS-I cards.  The 90Mb/s card proved to be marginally better.  In this respect the Pentax K-S2 about as fast as the K-3 in RAW mode, and faster in JPEG mode.  However, its buffer size in RAW mode is rather limited.  Fortunately, with UHS-I the camera can keep chugging along at 1FPS almost indefinitely while files are being saved.

Live View Framerate and Exposure

The K-S2 also delivers a much smoother live view framerate than the original PRIME M bodies.  It is virtually impossible to get live view to slow down, even at high ISOs or low light with focus peaking enabled.  This makes for an enjoyable shooting experience in live view and video mode.

In M mode, rather than forcing an accurate exposure, the camera does its best to deliver a preview of the actual exposure based on the selected shutter speed, aperture, and ISO.

Speaking of the LCD screen, it has 921k dots, the typical resolution found in higher-end cameras.  This makes the view view picture clear and keeps the menu text sharp.

Mirror in Live View

The first several Pentax bodies with live view would always drop the mirror and exit live view whenever the user accessed a menu or changed the shooting mode.  Fortunately, the K-S2 improves on this somewhat: while changing modes via the mode dial, the mirror stays up and the camera remains in live view.  But Pentax engineers didn't quite go far enough:  the mirror comes down whenever you try to access the main menu or the control panel.  This not only slows things down in the field, but makes the camera noisier than it ought to be.

Shake Reduction Sound

It is perfectly normal for the SR mechanism to produce a faint sound while in live view and while the viewfinder meter is enabled, even if stabilization is off.  This is because the SR system must remain active simply to lock the sensor in place.  In addition, when the camera is off, the sensor floats semi-freely inside the body, which leads to the infamous "clunk" sound whenever the camera is moved around.  We would like to stress that this is not a defect, though it might catch beginners off guard.

Dust Removal

When enabled, the K-S2's sensor-shift dust removal system generates a very brief rumbling sound.  Unlike flagship models, the K-S2 does not have the ultrasonic DR II system which is nearly silent.

Battery Life

The Pentax K-S2 can only be powered by the rechargeable D-LI109 battery, which is the same battery used in the past three generations of mid-range/entry-level DSLR models.This battery has a relatively low capacity (1050 mAh) and with moderate playback and live view usage, it lasted for 350-450 shots during our tests.  This is around half the battery life of the flagship models, which use a larger 1860 mAh battery.

The K-S2 does not support the Pentax AA battery holder, nor does it have a dedicated battery grip.  We therefore recommend purchasing and carrying an extra D-LI109 or two while out in the field.  Users employing the K-S2 for studio use can also power it via the K-AC109 adapter.  The adapter is hard to find outside of Japan.

For best results we recommend the use of genuine Pentax batteries, though third-party batteries can prove to be much more affordable alternatives for backup batteries.  We recommend checking user reviews prior to the purchase of any third-party battery, as many cheap batteries deliver lower than advertised capacities.

Desktop File Transfer

The K-S2 only has a USB2 port, which means that file transfers using a USB cord may not be able to utilize the card slot's maximum speed.  If your PC has a USB3 card reader, we recommend using it instead for large file transfers.

Shutter Sound

Users of the Pentax K-5 series and now the K-3 series have long been enjoying one of the quietest shutter mechanisms among APS-C DSLRs.  Unfortunately, one area in which the Pentax K-S2 makes a few compromises is the shutter.

The shutter sound is comparatively loud and the K-S2 sounds just like the K-30 and K-50 before it.  You can get accustomed to the way it sounds, but even entry-level cameras from competitors will be quieter.

The video above demonstrates the K-S2's shutter sound across a variety of modes.

Performance Verdict

The Pentax K-S2 delivers very impressive everyday performance and we are happy to report that it is among the fastest Pentax DSLRs currently available.  It speeds up tasks that were once very sluggish and is simply a pleasure to use in the field, because it almost never gets in the way of what you want to do.

It would be a big improvement if the camera could refrain from exiting live view while its menus (or at least the control panel) are being accessed.  Similarly, the loud shutter can be a bit discouraging, but this is really only an issue when you're indoors or up close and personal with your subject.

We would have also liked to see a faster burst framerate for the sake of bragging rights— it's a little disappointing to see a new model have a slower framerate than the older K-50— but in practice the difference between 5.4 FPS and 6FPS (of the K-50) is negligible.  A larger RAW buffer would have been a bigger improvement.


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