Detail and Moiré K-5 II vs. K-5 IIS

Those seeking extra detail in their shots might be tempted by the K-5 IIS's lack of a low-pass filter, something we’re seeing more companies drop from their SLRs as resolutions increase. Anti-aliaising filters are designed to slightly blur the final image, so in very simple terms, removing a sensor's AA filter should increase sharpness. What’s the risk? Primarily aliasing artefects moiré patterning, which is created when the frequency of patterns in your subject begins to exceed the frequency of the grid of pixels on the cameras' sensor.

Moiré is commonly seen in the repeating patterns of fabric, but nature has its repeating patterns as well, including palm fronds, grasses, feathers, and even fine ripples on water. 

We worked on this question of the relative benefits extensively with the Nikon D800 and D800E and found that as we'd expect, using a good prime lens both cameras delivered best central sharpness between around F3.5 to F5.6 (note that lenses typically achieve the best evenness of sharpness at slightly smaller apertures). Given that the pixel pitch of the K-5 II is about the same as the D800E (which offers an output resolution of 15MP in DX crop mode) we were not surprised to find the same thing with the K-5II and IIS.

During the course of this review, we shot comparison samples at various apertures - large and small - and consistently saw more moiré in images from the K-5 IIS. Within this optimum aperture range of F3.5 to F5.6, we found that where moiré was visible from images with one camera, it was also present in shots from the other, but the patterning was more intense in the pictures shot with the K-5 IIS. As we left this aperture range and shot between F5.6-11, the K-5 II lost the tendency toward moiré likely thanks to relative increase in diffraction, while the K-5 IIS still showed the effect in some scenes.

Fabric

K-5 II, 18-135mm lens, 1/20, F4.5, ISO 100 K-5 IIS, 18-135mm lens, 1/15, F4.5, ISO 100

As you can see from the JPEGS above, taken at F4.5, moiré made an appearance in images from both cameras. This is a particularly moiré-prone fabric, but it's a fairly common Glen-plaid design any event photographer is likely to encounter. Fashion photographers will be all too familiar with the effect.

K-5 II, 43mm lens, 1/100, F7.1, ISO 100 K-5 IIS, 43mm lens, 1/100, F7.1, ISO 100

We were more surprised to find moiré in a far darker coat, the blue blazer captured in this shot at portrait distances, at a relatively small aperture of F7.1.

Studio Comparisons

Looking at our Studio Comparison Scene, shot at F8, the K-5 IIS plainly shows moiré in some feathers, currency samples, and the focus scale. All crops below are at 100%.

This is our studio test scene. With APS-C format cameras we shoot this scene at F8 at an equivalent focal length of ~85mm (or as near as possible). This aperture is selected because it generally provides good edge-to-edge sharpness, and enough depth-of-field to render the main image area in focus.
K-5 II - JPEG  K-5 IIS - JPEG 
 K-5 II - Raw   K-5 IIS - Raw 
 K-5 II - JPEG   K-5 IIS - JPEG 
 K-5 II - Raw   K-5 IIS - Raw 

We see moiré from both cameras, even at F8, which is most intense where we'd expect - the areas of finest detail. The blue feather shows moiré in the K-5 II's Raw shot, but in both the K-5 IIS's JPEG and Raw shots (the blue arcs radiating out from the left of the feather's center rib). The etching cropped above shows color moiré in the vertical lines, which are only slightly visible in the K-5 II images. As percentages of the overall Studio Comparison Scene, though, this effect is minor; were these frequencies to become more dominant in the scene, we might have more of a problem.

K-5 II, 50mm F5.6, 1/50, ISO 100  K-5 IIS, 50mm F5.6, 1/50, ISO 100 
K-5 II, 50mm F5.6, 1/50, ISO 100  K-5 IIS, 50mm F5.6, 1/50, ISO 100 

The crops above show areas from our new (forthcoming) studio scene, shot at F5.6 for best central sharpness. Exposures were captured in Raw mode, with sharpening turned off in Adobe Camera Raw and a basic USM (amount 100%, radius 0.6, threshold 0) added in Photoshop. The K-5 IIS gives crisper results, with fractionally more detail visible on very close examination. The fine text is better defined (especially visible the low-contrast black-on-gray) but pretty intense moiré can be seen in the white text on the black background. That said, the K-5 II also gives some moiré but it's less intense.

Outdoor, organic and non-organic detail

K5 II, 40mm lens - F7.1, 1/125, ISO 100 - Click to download raw (DNG) file K5 IIS, 40mm lens - F7.1, 1/125, ISO 100 - Click to download raw (DNG) file
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Landscape elements do indeed show more detail in the K-5 IIS, but some elements with repeating patterns show moiré and other artifacts from both cameras. Detail in the trees is better, though, and moiré only occurrs in a few locations; it was difficult to find at first.

Analysis

After looking at the above images, it should be pretty obvious which camera most people should choose for the lion's share of photographic situations: The Pentax K-5 II. Having more detail in a camera is always desirable in theory, except when that detail comes with colors and patterns that aren't there in the actual scene. Moiré patterning can be created by many things, but in this case it's caused by the interaction between the grid of pixels on the sensor and a pattern in the scene, and is unequivocally more of a problem in images from the K-5 IIS.

In our Nikon D800 review, we went over the situations in which the D800E (which also effectively has no low-pass filter) suffered moiré and decided that since both cameras exhibited the same artifacts to differing degrees, people would have to deal with them one way or another, and the Nikon D800E's images - particularly the JPEGs - were improved enough in terms of detail to warrant the risk for the sake of detail. After all, with the D800E's extremely high pixel count, most of the artifacts we saw made up a small enough percentage of the frame that it wasn't as big a risk. Here, as well, we see both cameras, the K-5 II and K-5 IIS, exhibiting moiré with good lenses at optimal apertures. We also see more apparent detail. But with the K-5 IIS the moiré is intense enough in those high detail areas where a suitable pattern is present to greatly diminish the advantage for general photographic purposes. This becomes quite apparent in our Resolution target.

We don't think it will be as great an issue in outdoor landscape photography, where repeating patterns are less prevalent, but wildlife photographers should take note of the potenital for moiré in hair and feathers. The problem with moiré is not just the rainbow patterns that emerge, because you can minimize or remove the color with filters; it's the pattern they leave behind even after you effectively remove the color that concern us. The blue patterns in the blue feather of our Studio Comparison Scene are an example of moiré that is very difficult to remove by just changing or blurring the colors.

In portrait photography you're less likely to shoot at apertures that give you too much detail, so stopping down out of the F3.5-5.6 danger range might make sense, but there are always exceptions, and the K-5 IIS is more likely to give you color errors right in the plane of focus on hair and clothing should you want to shoot at a wider aperture to accent an eye or other feature. Landscape photographers are less likely to shoot at wide apertures, as they usually seek the greatest depth of field. Shooting at smaller apertures can minimize moiré thanks to diffraction limiting, as we see in the camera with the very light AA filter (the K-5 II), but you have to stop down even more to eliminate it from the K-5 IIS, to the point where the slight benefit in resolution is negated.

As usual, which camera is better for general photography is open to interpretation; as such, we've tried to provide as many images as possible to help you make an informed choice. Likewise, what purposes are suited to the K-5 IIS's increased detail-gathering potential are also a matter of opinion. The good news is we had to look pretty closely to find the issues we've highlighted above, save for those in the Glen-plaid jacket; granted, we were looking there too, but we think the colorful rainbows are obvious enough in this case, and would appear in a larger print. Many will look at these and think the differences are negligible. As such, we'll stop short of not recommending the K-5 IIS in favor of the K-5 II; we just advise that readers consider carefully which is for them. Most of us would prefer to avoid the moiré as much as possible, as the K-5 II's detail is pretty good as it is, but note that none of our images were affected by moiré enough that we hesitate to shoot with the K-5 IIS.

For those who'd like to see for themselves whether shooting without a low-pass filter is better or worse, the K-5 IIS represents an inexpensive way to find out, compared to the D800E or medium-format cameras that the pros use.