Nikon D3100 vs Pentax K-S2

The Nikon D3100 and the Pentax K-S2 are two digital cameras that were announced, respectively, in August 2010 and February 2015. Both are DSLR (Digital Single Lens Reflex) cameras that are equipped with an APS-C sensor. The Nikon has a resolution of 14.2 megapixels, whereas the Pentax provides 20 MP.

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

Headline Specifications

Nikon D3100		Pentax K-S2
Digital single lens reflex		Digital single lens reflex
Nikon F mount lenses		Pentax K mount lenses
14.2 MP – APS-C sensor		20 MP – APS-C sensor
1080/24p Video		1080/30p Video
ISO 100-3,200 (100 - 12,800)		ISO 100-51,200
Optical viewfinder		Optical viewfinder
3.0" LCD – 230k dots		3.0" LCD – 921k dots
Fixed screen (not touch-sensitive)		Swivel screen (not touch-sensitive)
3 shutter flaps per second		5.4 shutter flaps per second
Lens stabilization only		In-body stabilization
not weather sealed		Weathersealed body
550 shots per battery charge		410 shots per battery charge
124 x 96 x 75 mm, 505 g		123 x 91 x 73 mm, 678 g

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Going beyond this snapshot of core features and characteristics, what are the differences between the Nikon D3100 and the Pentax K-S2? 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 Nikon D3100 and the Pentax K-S2. 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 D3100 can be obtained in two different colors (black, red), while the K-S2 is available in six color-versions (black, grey, pink, orange, green, white).

If the front view area (width x height) of the cameras is taken as an aggregate measure of their size, the Pentax K-S2 is notably smaller (6 percent) than the Nikon D3100. However, the K-S2 is markedly heavier (34 percent) than the D3100. It is noteworthy in this context that the K-S2 is splash and dust-proof, while the D3100 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 D3100 gets 550 shots out of its Nikon EN-EL14 battery, while the K-S2 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	Street Price
1.		Nikon D3100	124 mm	96 mm	75 mm	505 g	550	n	Aug 2010	US$ 599	ebay.com
2.		Pentax K-S2	123 mm	91 mm	73 mm	678 g	410	Y	Feb 2015	US$ 749	ebay.com
3.		Nikon D40	124 mm	94 mm	64 mm	522 g	470	n	Nov 2006	US$ 499	ebay.com
4.		Nikon D40X	124 mm	94 mm	64 mm	522 g	520	n	Mar 2007	US$ 729	ebay.com
5.		Nikon D60	126 mm	94 mm	64 mm	522 g	500	n	Jan 2008	US$ 629	ebay.com
6.		Nikon D3000	126 mm	97 mm	64 mm	536 g	500	n	Jul 2009	US$ 599	ebay.com
7.		Nikon D3200	125 mm	96 mm	77 mm	505 g	540	n	Apr 2012	US$ 599	ebay.com
8.		Nikon D5000	127 mm	104 mm	80 mm	590 g	510	n	Apr 2009	US$ 749	ebay.com
9.		Nikon D5100	128 mm	97 mm	79 mm	560 g	660	n	Apr 2011	US$ 749	ebay.com
10.		Nikon D7000	132 mm	105 mm	77 mm	780 g	1050	Y	Sep 2010	US$ 1 499	ebay.com
11.		Pentax K-3	131 mm	100 mm	77 mm	800 g	560	Y	Oct 2013	US$ 1 299	ebay.com
12.		Pentax K-3 II	131 mm	100 mm	77 mm	800 g	720	Y	Apr 2015	US$ 1 099	ebay.com
13.		Pentax K-70	126 mm	93 mm	74 mm	688 g	410	Y	Jun 2016	US$ 649	ebay.com
14.		Pentax KP	132 mm	101 mm	76 mm	703 g	390	Y	Jan 2017	US$ 1 099	ebay.com
15.		Pentax K-S1	121 mm	93 mm	70 mm	558 g	410	n	Aug 2014	US$ 749	ebay.com
16.		Sony NEX-5N	111 mm	59 mm	38 mm	269 g	460	n	Aug 2011	US$ 699	ebay.com
17.		Sony NEX-C3	110 mm	60 mm	33 mm	225 g	400	n	Jun 2011	US$ 599	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 D3100 was launched at a somewhat lower price (by 20 percent) than the K-S2, which makes it more attractive for photographers on a tight budget. 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. All other things equal, a large sensor will have larger individual pixel-units that offer better low-light sensitivity, wider dynamic range, and richer color-depth than smaller pixels 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, but their sensors differ slightly in size. The sensor area in the K-S2 is 3 percent bigger. They nevertheless have the same format factor of 1.5. Both cameras have a native aspect ratio (sensor width to sensor height) of 3:2.

With 20MP, the K-S2 offers a higher resolution than the D3100 (14.2MP), but the K-S2 has smaller individual pixels (pixel pitch of 4.28μm versus 5.01μm for the D3100). Yet, the K-S2 is a much more recent model (by 4 years and 5 months) than the D3100, and its sensor will have benefitted from technological advances during this time that enhance the light gathering capacity of its pixel-units. Coming back to sensor resolution, it should be mentioned that the K-S2 has no anti-alias filter installed, so that it can capture all the detail its sensor resolves.

The resolution advantage of the Pentax K-S2 implies greater flexibility for cropping images or the possibility to print larger pictures. The maximum print size of the K-S2 for good quality output (200 dots per inch) amounts to 27.4 x 18.2 inches or 69.5 x 46.3 cm, for very good quality (250 dpi) 21.9 x 14.6 inches or 55.6 x 37.1 cm, and for excellent quality (300 dpi) 18.2 x 12.2 inches or 46.3 x 30.9 cm. The corresponding values for the Nikon D3100 are 23 x 15.4 inches or 58.5 x 39 cm for good quality, 18.4 x 12.3 inches or 46.8 x 31.2 cm for very good quality, and 15.4 x 10.2 inches or 39 x 26 cm for excellent quality prints.

The Nikon D3100 has a native sensitivity range from ISO 100 to ISO 3200, which can be extended to ISO 100-12800. The corresponding ISO settings for the Pentax K-S2 are ISO 100 to ISO 51200 (no boost).

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 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.		Nikon D3100	APS-C	14.2	4608	3072	1080/24p	22.5	11.3	919	67
2.		Pentax K-S2	APS-C	20.0	5472	3648	1080/30p	23.6	12.9	1514	79
3.		Nikon D40	APS-C	6.0	3008	2000	none	21.0	11.0	561	56
4.		Nikon D40X	APS-C	10.0	3872	2592	none	22.4	11.4	516	63
5.		Nikon D60	APS-C	10.0	3872	2592	none	22.5	11.4	562	65
6.		Nikon D3000	APS-C	10.0	3872	2592	none	22.3	11.1	563	62
7.		Nikon D3200	APS-C	24.1	6016	4000	1080/30p	24.1	13.2	1131	81
8.		Nikon D5000	APS-C	12.2	4288	2848	720/24p	22.7	12.5	868	72
9.		Nikon D5100	APS-C	16.1	4928	3264	1080/30p	23.5	13.6	1183	80
10.		Nikon D7000	APS-C	16.1	4928	3264	1080/24p	23.5	13.9	1167	80
11.		Pentax K-3	APS-C	24.1	6016	4000	1080/60i	23.7	13.4	1216	80
12.		Pentax K-3 II	APS-C	24.1	6016	4000	1080/60i	23.6	13.6	1106	80
13.		Pentax K-70	APS-C	24.0	6000	4000	1080/60i	23.8	13.1	1639	80
14.		Pentax KP	APS-C	24.1	6016	4000	1080/60i	23.9	13.2	1699	81
15.		Pentax K-S1	APS-C	20.0	5472	3648	1080/30p	23.5	13.0	1061	78
16.		Sony NEX-5N	APS-C	16.0	4912	3264	1080/60i	23.6	12.7	1079	77
17.		Sony NEX-C3	APS-C	16.0	4912	3264	720/30p	22.7	12.2	1083	73
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-S2 provides a faster frame rate than the D3100. It can shoot movie footage at 1080/30p, while the Nikon is limited to 1080/24p.

Feature comparison

Apart from body and sensor, cameras can and do differ across a variety of features. The D3100 and the K-S2 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 viewfinder in the K-S2 offers a wider field of view (100%) than the one in the D3100 (95%), so that a larger proportion of the captured image is visible in the finder. In addition, the viewfinder of the K-S2 has a higher magnification (0.63x vs 0.53x), so that the size of the image transmitted appears closer to the size seen with the naked human eye. The adjacent table lists some of the other core features of the Nikon D3100 and Pentax K-S2 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.		Nikon D3100	optical	n	3.0 / 230	fixed	n	1/4000s	3.0/s	Y	n
2.		Pentax K-S2	optical	n	3.0 / 921	swivel	n	1/6000s	5.4/s	Y	Y
3.		Nikon D40	optical	n	2.5 / 230	fixed	n	1/4000s	2.5/s	Y	n
4.		Nikon D40X	optical	n	2.5 / 230	fixed	n	1/4000s	3.0/s	Y	n
5.		Nikon D60	optical	n	2.5 / 230	fixed	n	1/4000s	3.0/s	Y	n
6.		Nikon D3000	optical	n	3.0 / 230	fixed	n	1/4000s	3.0/s	Y	n
7.		Nikon D3200	optical	n	3.0 / 921	fixed	n	1/4000s	4.0/s	Y	n
8.		Nikon D5000	optical	n	2.7 / 230	full-flex	n	1/4000s	4.0/s	Y	n
9.		Nikon D5100	optical	n	3.0 / 921	swivel	n	1/4000s	4.0/s	Y	n
10.		Nikon D7000	optical	Y	3.0 / 921	fixed	n	1/8000s	6.0/s	Y	n
11.		Pentax K-3	optical	Y	3.2 / 1037	fixed	n	1/8000s	8.3/s	Y	Y
12.		Pentax K-3 II	optical	Y	3.2 / 1037	fixed	n	1/8000s	8.3/s	n	Y
13.		Pentax K-70	optical	n	3.0 / 921	swivel	n	1/6000s	6.0/s	Y	Y
14.		Pentax KP	optical	n	3.0 / 921	tilting	n	1/6000s	7.0/s	Y	Y
15.		Pentax K-S1	optical	n	3.0 / 921	fixed	n	1/6000s	5.4/s	Y	Y
16.		Sony NEX-5N	optional	n	3.0 / 920	tilting	Y	1/4000s	10.0/s	n	n
17.		Sony NEX-C3	optional	n	3.0 / 920	tilting	n	1/4000s	5.5/s	n	n
Note: *) Information refers to the mechanical shutter, unless the camera only has an electronic one.

One feature that differentiates the K-S2 and the D3100 is in-body image stabilization (IBIS). The K-S2 reduces the risk of handshake-induced blur with all attached lenses, while the D3100 offers no blur reduction with lenses that themselves do not provide optical image stabilization.

The Pentax K-S2 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 D3100 and the K-S2 write their files to SDXC cards. The K-S2 supports UHS-I cards (Ultra High Speed data transfer of up to 104 MB/s), while the D3100 cannot take advantage of Ultra High Speed SD cards.

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 Nikon D3100 and Pentax K-S2 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.		Nikon D3100	Y	mono / mono	-	-	mini	2.0	-	-	-
2.		Pentax K-S2	Y	mono / mono	Y	-	micro	2.0	Y	Y	-
3.		Nikon D40	Y	- / -	-	-	-	2.0	-	-	-
4.		Nikon D40X	Y	- / -	-	-	-	2.0	-	-	-
5.		Nikon D60	Y	- / -	-	-	-	2.0	-	-	-
6.		Nikon D3000	Y	- / -	-	-	-	2.0	-	-	-
7.		Nikon D3200	Y	mono / mono	Y	-	mini	2.0	-	-	-
8.		Nikon D5000	Y	mono / mono	-	-	mini	2.0	-	-	-
9.		Nikon D5100	Y	mono / mono	Y	-	mini	2.0	-	-	-
10.		Nikon D7000	Y	mono / mono	Y	-	mini	2.0	-	-	-
11.		Pentax K-3	Y	mono / mono	Y	Y	mini	3.0	-	-	-
12.		Pentax K-3 II	Y	mono / mono	Y	Y	mini	3.0	-	-	-
13.		Pentax K-70	Y	stereo / mono	Y	-	mini	2.0	Y	-	-
14.		Pentax KP	Y	stereo / mono	Y	-	-	2.0	Y	-	-
15.		Pentax K-S1	Y	stereo / mono	-	-	micro	2.0	-	-	-
16.		Sony NEX-5N	Y	stereo / mono	-	-	mini	2.0	-	-	-
17.		Sony NEX-C3	Y	stereo / mono	-	-	mini	2.0	-	-	-

It is notable that the K-S2 offers wifi support, which can be a very convenient means to transfer image data to an off-camera location. In contrast, the D3100 does not provide wifi capability.

Both the D3100 and the K-S2 have been discontinued, but can regularly be found used on ebay. The D3100 was replaced by the Nikon D3200, while the K-S2 does not have a direct successor. Further information on the features and operation of the D3100 and K-S2 can be found, respectively, in the Nikon D3100 Manual (free pdf) or the online Pentax K-S2 Manual.

Review summary

So how do things add up? Is there a clear favorite between the Nikon D3100 and the Pentax K-S2? Which camera is better? Below is a summary of the relative strengths of each of the two contestants.

Advantages of the Nikon D3100:

• Better moiré control: Has an anti-alias filter to avoid artificial patterns to appear in images.
• Less heavy: Is lighter (by 173g or 26 percent) and hence easier to carry around.
• Longer lasting: Can take more shots (550 versus 410) on a single battery charge.
• More affordable: Was introduced into a lower priced segment (20 percent cheaper at launch).
• More heavily discounted: Has been available for much longer (launched in August 2010).

Arguments in favor of the Pentax K-S2:

• More detail: Has more megapixels (20 vs 14.2MP), which boosts linear resolution by 19%.
• Maximized detail: Lacks an anti-alias filter to exploit the sensor's full resolution potential.
• Better video: Provides higher movie framerates (1080/30p versus 1080/24p).
• Better sound: Can connect to an external microphone for higher quality sound recording.
• More complete view: Has a viewfinder with a larger field of view (100% vs 95%).
• Larger viewfinder image: Features a viewfinder with a higher magnification (0.63x vs 0.53x).
• More detailed LCD: Has a higher resolution rear screen (921k vs 230k dots).
• More flexible LCD: Has a swivel screen for odd-angle shots in portrait or landscape orientation.
• More selfie-friendly: Has an articulated screen that can be turned to be front-facing.
• Faster shutter: Has higher mechanical shutter speed (1/6000s vs 1/4000s) to freeze action.
• Faster burst: Shoots at higher frequency (5.4 vs 3 flaps/sec) to capture the decisive moment.
• Easier time-lapse photography: Has an intervalometer built-in for low frequency shooting.
• Better sealing: Is splash and dust sealed for shooting in inclement weather conditions.
• Sharper images: Has stabilization technology built-in to reduce the impact of hand-shake.
• Easier file upload: Has wifi built in for automatic backup or image transfer to the web.
• Easier device pairing: Supports NFC for fast wireless image transfer over short distances.
• Faster buffer clearing: Has an SD card interface that supports the UHS-I standard.
• More modern: Reflects 4 years and 5 months of technical progress since the D3100 launch.

If the count of individual advantages (bullet points above) is taken as a guide, the K-S2 is the clear winner of the contest (18 : 5 points). However, the relative importance of the various individual camera aspects will vary according to personal preferences and needs, so that you might like to apply corresponding weights to the particular features before making a decision 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 Nikon D3100 and the Pentax K-S2 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 D3100 and the K-S2 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	Street Price
1.		Nikon D3100	5/5	+ +	..	72/100	4.5/5	4.5/5	Aug 2010	US$ 599	ebay.com
2.		Pentax K-S2	4.5/5	..	..	..	5/5	4.5/5	Feb 2015	US$ 749	ebay.com
3.		Nikon D40	..	81/100	..	+ +	o	4.5/5	Nov 2006	US$ 499	ebay.com
4.		Nikon D40X	..	79/100	..	+ +	4/5	4/5	Mar 2007	US$ 729	ebay.com
5.		Nikon D60	..	80/100	..	+ +	4/5	4.5/5	Jan 2008	US$ 629	ebay.com
6.		Nikon D3000	..	+	..	72/100	4/5	4.5/5	Jul 2009	US$ 599	ebay.com
7.		Nikon D3200	5/5	+ +	..	73/100	4.5/5	4.5/5	Apr 2012	US$ 599	ebay.com
8.		Nikon D5000	..	+ +	..	75/100	4/5	4.5/5	Apr 2009	US$ 749	ebay.com
9.		Nikon D5100	5/5	+ +	..	76/100	4.5/5	4.5/5	Apr 2011	US$ 749	ebay.com
10.		Nikon D7000	4/5	..	..	80/100	4.5/5	4.5/5	Sep 2010	US$ 1 499	ebay.com
11.		Pentax K-3	4/5	..	..	83/100	5/5	5/5	Oct 2013	US$ 1 299	ebay.com
12.		Pentax K-3 II	4.5/5	..	..	..	5/5	5/5	Apr 2015	US$ 1 099	ebay.com
13.		Pentax K-70	4.5/5	..	4/5	79/100	4.5/5	4.5/5	Jun 2016	US$ 649	ebay.com
14.		Pentax KP	4/5	..	3/5	82/100	5/5	4.5/5	Jan 2017	US$ 1 099	ebay.com
15.		Pentax K-S1	4/5	..	..	..	4.5/5	4/5	Aug 2014	US$ 749	ebay.com
16.		Sony NEX-5N	3/5	+ +	..	79/100	4.5/5	4.5/5	Aug 2011	US$ 699	ebay.com
17.		Sony NEX-C3	3/5	+ +	..	74/100	4.5/5	4/5	Jun 2011	US$ 599	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. It should also be noted that some of the review sites have over time altered the way they render their verdicts.

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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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