Pentax K-3 vs K-S1

The Pentax K-3 and the Pentax K-S1 are two digital cameras that were announced, respectively, in October 2013 and August 2014. Both are DSLR (Digital Single Lens Reflex) cameras that are equipped with an APS-C sensor. The K-3 has a resolution of 24.1 megapixels, whereas the K-S1 provides 20 MP.

Below is an overview of the main specs of the two cameras as a starting point for the comparison.

Headline Specifications

Pentax K-3		Pentax K-S1
Digital single lens reflex		Digital single lens reflex
Pentax K mount lenses		Pentax K mount lenses
24.1 MP – APS-C sensor		20 MP – APS-C sensor
1080/60i Video		1080/30p Video
ISO 100-51,200		ISO 100-51,200
Optical viewfinder		Optical viewfinder
3.2" LCD – 1037k dots		3.0" LCD – 921k dots
Fixed screen (not touch-sensitive)		Fixed screen (not touch-sensitive)
8.3 shutter flaps per second		5.4 shutter flaps per second
In-body stabilization		In-body stabilization
Weathersealed body		not weather sealed
560 shots per battery charge		410 shots per battery charge
131 x 100 x 77 mm, 800 g		121 x 93 x 70 mm, 558 g

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Going beyond this snapshot of core features and characteristics, what are the differences between the Pentax K-3 and the Pentax K-S1? Which one should you buy? Read on to find out how these two cameras compare with respect to their body size, their imaging sensors, their shooting features, their input-output connections, and their reception by expert reviewers.

Body comparison

The side-by-side display below illustrates the physical size and weight of the Pentax K-3 and the Pentax K-S1. The two cameras are presented according to their relative size. Three consecutive perspectives from the front, the top, and the back are available. All width, height and depth dimensions are rounded to the nearest millimeter.

The K-3 can be obtained in two different colors (black, silver), while the K-S1 is available in four color-versions (black, grey, orange, white).

If the front view area (width x height) of the cameras is taken as an aggregate measure of their size, the Pentax K-S1 is notably smaller (14 percent) than the Pentax K-3. Moreover, the K-S1 is markedly lighter (30 percent) than the K-3. It is worth mentioning in this context that the K-3 is splash and dust resistant, while the K-S1 does not feature any corresponding weather-sealing.

The above size and weight comparisons are to some extent incomplete since they do not consider the interchangeable lenses that both of these cameras require. Hence, you might want to study and compare the specifications of available lenses in order to get the full picture of the size and weight of the two camera systems.

Concerning battery life, the K-3 gets 560 shots out of its Pentax D-LI90 battery, while the K-S1 can take 410 images on a single charge of its Pentax D-LI109 power pack.

The following table provides a synthesis of the main physical specifications of the two cameras and other similar ones. In case you want to display and compare another camera duo, you can use the CAM-parator app to select your camera combination among a large number of options.

Body Specifications

#		Camera Model	Camera Width	Camera Height	Camera Depth	Camera Weight	Battery Life	Weather Sealing	Camera Launch	Launch Price (USD)	Street Price
1.		Pentax K-3	131 mm	100 mm	77 mm	800 g	560	Y	Oct 2013	1,299	ebay.com
2.		Pentax K-S1	121 mm	93 mm	70 mm	558 g	410	n	Aug 2014	749	ebay.com
3.		Nikon D5500	124 mm	97 mm	70 mm	470 g	820	n	Jan 2015	899	ebay.com
4.		Nikon D7100	136 mm	107 mm	76 mm	765 g	950	Y	Feb 2013	1,199	ebay.com
5.		Nikon D5300	125 mm	98 mm	76 mm	480 g	600	n	Oct 2013	799	ebay.com
6.		Pentax KP	132 mm	101 mm	76 mm	703 g	390	Y	Jan 2017	1,099	ebay.com
7.		Pentax K-70	126 mm	93 mm	74 mm	688 g	410	Y	Jun 2016	649	ebay.com
8.		Pentax K-S2	123 mm	91 mm	73 mm	678 g	410	Y	Feb 2015	749	ebay.com
9.		Pentax K-3 II	131 mm	100 mm	77 mm	800 g	720	Y	Apr 2015	1,099	ebay.com
10.		Pentax K-50	130 mm	97 mm	71 mm	650 g	410	Y	Jun 2013	599	ebay.com
11.		Pentax K-500	130 mm	97 mm	71 mm	646 g	710	n	Jun 2013	549	ebay.com
12.		Pentax K-5 II	131 mm	97 mm	73 mm	760 g	740	Y	Sep 2012	1,099	ebay.com
13.		Pentax K-5	131 mm	97 mm	73 mm	760 g	740	Y	Sep 2010	1,099	ebay.com
14.		Sony A68	143 mm	104 mm	81 mm	610 g	540	n	Nov 2015	699	ebay.com
15.		Sony A77	143 mm	104 mm	81 mm	732 g	470	Y	Aug 2011	1,399	ebay.com
Note: Measurements and pricing do not include easily detachable parts, such as add-on or interchangeable lenses or optional viewfinders.
Convert to Imperial

Any camera decision will naturally be influenced heavily by the price. The listed launch prices provide an indication of the market segment that the manufacturer of the cameras have been targeting. The K-S1 was launched at a markedly lower price (by 42 percent) than the K-3, which puts it into a different market segment. Usually, retail prices stay at first close to the launch price, but after several months, discounts become available. Later in the product cycle and, in particular, when the replacement model is about to appear, further discounting and stock clearance sales often push the camera price considerably down. Then, after the new model is out, very good deals can frequently be found on the pre-owned market.

Sensor comparison

The size of the sensor inside a digital camera is one of the key determinants of image quality. A large sensor will tend to have larger individual pixels that provide better low-light sensitivity, wider dynamic range, and richer color-depth than smaller pixel-units in a sensor of the same technological generation. Further, a large sensor camera will give the photographer additional creative options when using shallow depth-of-field to isolate a subject from its background. On the downside, larger sensors tend to be associated with larger, more expensive camera bodies and lenses.

Both cameras under consideration feature an APS-C sensor and have a format factor (sometimes also referred to as "crop factor") of 1.5. Within the spectrum of camera sensors, this places the review cameras among the medium-sized sensor cameras that aim to strike a balance between image quality and portability. Both cameras have a native aspect ratio (sensor width to sensor height) of 3:2.

In terms of chip-set technology, the K-3 uses a more advanced image processing engine (PRIME III) than the K-S1 (PRIME MII), with benefits for noise reduction, color accuracy, and processing speed.

While the two cameras under review share the same sensor size, the K-3 offers a higher resolution of 24.1 megapixels, compared with 20 MP of the K-S1. This megapixels advantage translates into a 10 percent gain in linear resolution. On the other hand, these sensor specs imply that the K-3 has a higher pixel density and a smaller size of the individual pixel (with a pixel pitch of 3.90μm versus 4.28μm for the K-S1). Moreover, it should be noted that the K-S1 is a somewhat more recent model (by 10 months) than the K-3, and its sensor might have benefitted from technological advances during this time that further enhance the light gathering capacity of individual pixels. Coming back to sensor resolution, it should be mentioned that neither of the two cameras has an anti-alias filter installed, so they are able to capture all the detail the sensor resolves.

The resolution advantage of the Pentax K-3 implies greater flexibility for cropping images or the possibility to print larger pictures. The maximum print size of the K-3 for good quality output (200 dots per inch) amounts to 30.1 x 20 inches or 76.4 x 50.8 cm, for very good quality (250 dpi) 24.1 x 16 inches or 61.1 x 40.6 cm, and for excellent quality (300 dpi) 20.1 x 13.3 inches or 50.9 x 33.9 cm. The corresponding values for the Pentax K-S1 are 27.4 x 18.2 inches or 69.5 x 46.3 cm for good quality, 21.9 x 14.6 inches or 55.6 x 37.1 cm for very good quality, and 18.2 x 12.2 inches or 46.3 x 30.9 cm for excellent quality prints.

The Pentax K-3 has a native sensitivity range from ISO 100 to ISO 51200. The Pentax K-S1 offers exactly the same ISO settings.

Technology-wise, both cameras are equipped with CMOS (Complementary Metal–Oxide–Semiconductor) sensors. Both cameras use a Bayer filter for capturing RGB colors on a square grid of photosensors. This arrangement is found in most digital cameras.

Since 2007, DXO Mark has published sensor performance measurements that have been derived using a consistent methodology. This service is based on lab testing and assigns an overall score to each camera sensor, as well as ratings for dynamic range ("DXO Landscape"), color depth ("DXO Portrait"), and low-light sensitivity ("DXO Sports"). The Overall DXO ratings for the two cameras under consideration are close, suggesting that they provide similar imaging performance. The adjacent table reports on the physical sensor characteristics and the outcomes of the DXO sensor quality tests for a sample of comparator-cameras.

Sensor Characteristics

#		Camera Model	Sensor Class	Resolution (MP)	Horiz. Pixels	Vert. Pixels	Video Format	DXO Portrait	DXO Landscape	DXO Sports	DXO Overall
1.		Pentax K-3	APS-C	24.1	6016	4000	1080/60i	23.7	13.4	1216	80
2.		Pentax K-S1	APS-C	20.0	5472	3648	1080/30p	23.5	13.0	1061	78
3.		Nikon D5500	APS-C	24.0	6000	4000	1080/60p	24.1	14.0	1438	84
4.		Nikon D7100	APS-C	24.0	6000	4000	1080/60p	24.2	13.7	1256	83
5.		Nikon D5300	APS-C	24.0	6000	4000	1080/60p	24.0	13.9	1338	83
6.		Pentax KP	APS-C	24.1	6016	4000	1080/60i	23.9	13.2	1699	81
7.		Pentax K-70	APS-C	24.0	6000	4000	1080/60i	23.8	13.1	1639	80
8.		Pentax K-S2	APS-C	20.0	5472	3648	1080/30p	23.6	12.9	1514	79
9.		Pentax K-3 II	APS-C	24.1	6016	4000	1080/60i	23.6	13.6	1106	80
10.		Pentax K-50	APS-C	16.1	4928	3264	1080/30p	23.7	13.0	1120	79
11.		Pentax K-500	APS-C	16.1	4928	3264	1080/30p	23.7	13.1	1087	79
12.		Pentax K-5 II	APS-C	16.1	4928	3264	1080/25p	23.8	14.1	1235	82
13.		Pentax K-5	APS-C	16.1	4928	3264	1080/25p	23.7	14.1	1162	82
14.		Sony A68	APS-C	24.0	6000	4000	1080/60i	24.1	13.5	701	79
15.		Sony A77	APS-C	24.0	6000	4000	1080/60p	24.0	13.2	801	78
Note: DXO values in italics represent estimates based on sensor size and age.

Many modern cameras are not only capable of taking still images, but also of capturing video footage. Both cameras under consideration have a sensor with sufficiently fast read-out times for moving pictures, but the K-3 provides a higher frame rate than the K-S1. It can shoot video footage at 1080/60i, while the K-S1 is limited to 1080/30p.

Feature comparison

Apart from body and sensor, cameras can and do differ across a variety of features. The K-3 and the K-S1 are similar in the sense that both have an optical viewfinder. The latter is useful for getting a clear image for framing even in brightly lit environments. The viewfinders of both cameras offer the same field of view (100%), as well as the same magnification (0.63x). The adjacent table lists some of the other core features of the Pentax K-3 and Pentax K-S1 along with similar information for a selection of comparators.

Core Features

#		Camera Model	Viewfinder (Type or 000 dots)	Control Panel (yes/no)	LCD Specifications (inch/000 dots)	LCD Attach- ment	Touch Screen (yes/no)	Max Shutter Speed *	Max Shutter Flaps *	Built-in Flash (yes/no)	Built-in Image Stab
1.		Pentax K-3	optical	Y	3.2 / 1037	fixed	n	1/8000s	8.3/s	Y	Y
2.		Pentax K-S1	optical	n	3.0 / 921	fixed	n	1/6000s	5.4/s	Y	Y
3.		Nikon D5500	optical	n	3.2 / 1037	swivel	Y	1/4000s	5.0/s	Y	n
4.		Nikon D7100	optical	Y	3.2 / 1229	fixed	n	1/8000s	6.0/s	Y	n
5.		Nikon D5300	optical	n	3.2 / 1037	swivel	n	1/4000s	5.0/s	Y	n
6.		Pentax KP	optical	n	3.0 / 921	tilting	n	1/6000s	7.0/s	Y	Y
7.		Pentax K-70	optical	n	3.0 / 921	swivel	n	1/6000s	6.0/s	Y	Y
8.		Pentax K-S2	optical	n	3.0 / 921	swivel	n	1/6000s	5.4/s	Y	Y
9.		Pentax K-3 II	optical	Y	3.2 / 1037	fixed	n	1/8000s	8.3/s	n	Y
10.		Pentax K-50	optical	n	3.0 / 921	fixed	n	1/6000s	6.0/s	Y	Y
11.		Pentax K-500	optical	n	3.0 / 921	fixed	n	1/6000s	6.0/s	Y	Y
12.		Pentax K-5 II	optical	Y	3.0 / 921	fixed	n	1/8000s	7.0/s	Y	Y
13.		Pentax K-5	optical	Y	3.0 / 921	fixed	n	1/8000s	7.0/s	Y	Y
14.		Sony A68	1440	Y	2.7 / 460	tilting	n	1/4000s	8.0/s	Y	Y
15.		Sony A77	2359	Y	3.0 / 921	full-flex	n	1/8000s	12.0/s	Y	Y
Note: *) Information refers to the mechanical shutter, unless the camera only has an electronic one.

One feature that is present on the K-3, but is missing on the K-S1 is a top-level LCD. While being, of course, smaller than the rear screen, the control panel conveys some of the essential shooting information and can be convenient for quick and easy settings verification.

The Pentax K-3 has an intervalometer built-in. This enables the photographer to capture time lapse sequences, such as flower blooming, a sunset or moon rise, without purchasing an external camera trigger and related software.

Concerning the storage of imaging data, both the K-3 and the K-S1 write their files to SDXC cards. The K-3 features dual card slots, which can be very useful in case a memory card fails. In contrast, the K-S1 only has one slot. Both cameras can use UHS-I cards, which provide for Ultra High Speed data transfer of up to 104 MB/s.

Connectivity comparison

For some imaging applications, the extent to which a camera can communicate with its environment can be an important aspect in the camera decision process. The table below provides an overview of the connectivity of the Pentax K-3 and Pentax K-S1 and, in particular, the interfaces the cameras (and selected comparators) provide for accessory control and data transfer.

Input-Output Connections

#		Camera Model	Hotshoe Port	Internal Mic / Speaker	Microphone Port	Headphone Port	HDMI Port	USB Port	WiFi Support	NFC Support	Bluetooth Support
1.		Pentax K-3	Y	mono / mono	Y	Y	mini	3.0	-	-	-
2.		Pentax K-S1	Y	stereo / mono	-	-	micro	2.0	-	-	-
3.		Nikon D5500	Y	stereo / mono	Y	-	mini	2.0	Y	-	-
4.		Nikon D7100	Y	stereo / mono	Y	Y	mini	2.0	-	-	-
5.		Nikon D5300	Y	stereo / mono	Y	-	mini	2.0	Y	-	-
6.		Pentax KP	Y	stereo / mono	Y	-	-	2.0	Y	-	-
7.		Pentax K-70	Y	stereo / mono	Y	-	mini	2.0	Y	-	-
8.		Pentax K-S2	Y	mono / mono	Y	-	micro	2.0	Y	Y	-
9.		Pentax K-3 II	Y	mono / mono	Y	Y	mini	3.0	-	-	-
10.		Pentax K-50	Y	mono / mono	-	-	micro	2.0	-	-	-
11.		Pentax K-500	Y	mono / mono	-	-	-	2.0	-	-	-
12.		Pentax K-5 II	Y	stereo / mono	Y	-	mini	2.0	-	-	-
13.		Pentax K-5	Y	stereo / mono	Y	-	mini	2.0	-	-	-
14.		Sony A68	Y	stereo / mono	Y	-	micro	2.0	-	-	-
15.		Sony A77	Y	stereo / mono	Y	-	mini	2.0	-	-	-

It is notable that the K-3 has a microphone port, which is missing on the K-S1. Such an external microphone input can help to substantially improve the quality of audio recordings when a good external microphone is used.

Studio photographers will appreciate that the Pentax K-3 (unlike the K-S1) features a PC Sync socket, so that professional strobe lights can be controlled by the camera.

Both the K-3 and the K-S1 have been discontinued, but can regularly be found used on ebay. The K-3 was replaced by the Pentax K-3 II, while the K-S1 was followed by the Pentax K-S2. Further information on the features and operation of the K-3 and K-S1 can be found, respectively, in the Pentax K-3 Manual (free pdf) or the online Pentax K-S1 Manual.

Review summary

So how do things add up? Is there a clear favorite between the Pentax K-3 and the Pentax K-S1? Which camera is better? Below is a summary of the relative strengths of each of the two contestants.

Advantages of the Pentax K-3:

• More detail: Offers more megapixels (24.1 vs 20MP) with a 10% higher linear resolution.
• Better jpgs: Has a more modern image processing engine (PRIME III vs PRIME MII).
• Better video: Provides higher movie framerates (1080/60i versus 1080/30p).
• Better sound: Can connect to an external microphone for higher quality sound recording.
• Better sound control: Has a headphone port that enables audio monitoring while recording.
• Easier setting verification: Features an LCD display on top to control shooting parameters.
• Larger screen: Has a bigger rear LCD (3.2" vs 3.0") for image review and settings control.
• More detailed LCD: Has a higher resolution rear screen (1037k vs 921k dots).
• Faster shutter: Has higher mechanical shutter speed (1/8000s vs 1/6000s) to freeze action.
• Faster burst: Shoots at higher frequency (8.3 vs 5.4 flaps/sec) to capture the decisive moment.
• Easier time-lapse photography: Has an intervalometer built-in for low frequency shooting.
• Longer lasting: Can take more shots (560 versus 410) on a single battery charge.
• Better sealing: Is weather sealed to enable shooting in dusty or wet environments.
• Faster data transfer: Supports a more advanced USB protocol (3.0 vs 2.0).
• Better studio light control: Has a PC Sync socket to connect to professional strobe lights.
• Greater peace of mind: Features a second card slot as a backup in case of memory card failure.
• More heavily discounted: Has been on the market for longer (launched in October 2013).

Arguments in favor of the Pentax K-S1:

• More compact: Is smaller (121x93mm vs 131x100mm) and will fit more readily into a bag.
• Less heavy: Has a lower weight (by 242g or 30 percent) and is thus easier to take along.
• More affordable: Was introduced into a lower priced category (42 percent cheaper at launch).
• More modern: Was introduced somewhat (10 months) more recently.

If the count of individual advantages (bullet points above) is taken as a guide, the K-3 is the clear winner of the match-up (17 : 4 points). However, the relevance of individual strengths will vary across photographers, so that you might want to apply your own weighing scheme to the summary points when reflecting and deciding on a new camera. A professional wildlife photographer will view the differences between cameras in a way that diverges from the perspective of a family photog, and a person interested in architecture has distinct needs from a sports shooter. Hence, the decision which camera is best and worth buying is often a very personal one.

How about other alternatives? Do the specifications of the Pentax K-3 and the Pentax K-S1 place the cameras among the top in their class? Find out in the latest Best DSLR Camera listing whether the two cameras rank among the cream of the crop.

In any case, while the comparison of the spec-sheets of cameras can offer a general idea of their imaging potential, it says little about, for example, the shooting experience and imaging performance of the K-3 and the K-S1 in practical situations. At times, user reviews, such as those published at amazon, address these issues in a useful manner, but such feedback is on many occasions incomplete, inconsistent, and unreliable.

Expert reviews

This is why hands-on reviews by experts are important. The adjacent summary-table relays the overall verdicts of several of the most popular camera review sites (amateurphotographer [AP], cameralabs [CL], digitalcameraworld [DCW], dpreview [DPR], ephotozine [EPZ], photographyblog [PB]). As can be seen, the professional reviewers agree in many cases on the quality of different cameras, but sometimes their assessments diverge, reinforcing the earlier point that a camera decision is often a very personal choice.

Expert Camera Reviews

#		Camera   Model	AP   score	CL   score	DCW   score	DPR   score	EPZ   score	PB   score	Camera Launch	Launch Price (USD)	Street Price
1.		Pentax K-3	4/5	..	..	83/100	5/5	5/5	Oct 2013	1,299	ebay.com
2.		Pentax K-S1	4/5	..	..	..	4.5/5	4/5	Aug 2014	749	ebay.com
3.		Nikon D5500	5/5	+	..	79/100	4.5/5	4.5/5	Jan 2015	899	ebay.com
4.		Nikon D7100	5/5	+ +	..	85/100	4.5/5	4.5/5	Feb 2013	1,199	ebay.com
5.		Nikon D5300	4/5	+ +	..	79/100	4.5/5	4.5/5	Oct 2013	799	ebay.com
6.		Pentax KP	4/5	..	3/5	82/100	5/5	4.5/5	Jan 2017	1,099	ebay.com
7.		Pentax K-70	4.5/5	..	4/5	79/100	4.5/5	4.5/5	Jun 2016	649	ebay.com
8.		Pentax K-S2	4.5/5	..	..	..	5/5	4.5/5	Feb 2015	749	ebay.com
9.		Pentax K-3 II	4.5/5	..	..	..	5/5	5/5	Apr 2015	1,099	ebay.com
10.		Pentax K-50	5/5	..	..	..	5/5	4.5/5	Jun 2013	599	ebay.com
11.		Pentax K-500	..	..	..	..	4.5/5	4.5/5	Jun 2013	549	ebay.com
12.		Pentax K-5 II	5/5	..	..	80/100	5/5	4.5/5	Sep 2012	1,099	ebay.com
13.		Pentax K-5	4/5	..	..	83/100	5/5	4.5/5	Sep 2010	1,099	ebay.com
14.		Sony A68	3/5	..	..	..	4/5	4/5	Nov 2015	699	ebay.com
15.		Sony A77	5/5	91/100	..	81/100	..	5/5	Aug 2011	1,399	ebay.com
Note: (+ +) highly recommended; (+) recommended; (o) reviewed; (..) not available.

The above review scores should be interpreted with care, though. The ratings were established in reference to similarly priced cameras that were available in the market at the time of the review. Thus, a score needs to be put into the context of the launch date and the launch price of the camera, and comparing ratings of very distinct cameras or ones that are far apart in terms of their release date have little meaning. Also, kindly note that some of the listed sites have over time developped their review approaches and their reporting style.

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Check K-S1 offers at
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Other camera comparisons

Did this review help to inform your camera decision process? In case you are interested in seeing how other cameras pair up, just make a corresponding selection in the search boxes below. Alternatively, you can follow any of the listed hyperlinks for comparisons that others found interesting.

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