Nikon D3 Optics

Nikon D3 Optics

The Nikon D3 is compatible with a wide variety of Nikkor (and third-party) lenses, some dating back to the 1970's. There are some exceptions however. See the table below (provided courtesy of Nikon USA) for details.

In a digital SLR camera, the Optics heading would seem to have more to do with the attached lens than the camera itself. The camera body is responsible for autofocus, though, so it makes sense to talk about autofocus technology here on the "Optics" tab of this review. In the case of the Nikon D3 it turns out that the camera-side of the equation has a lot more to do with image quality than is generally the case.

Nikon D3 Autofocus

Autofocus is an area where Nikon has often been perceived as lagging behind their primary competitor, Canon. Whether they actually have or not, in terms of actual autofocus performance is a matter of fierce debate between loyalists of the respective systems, but there has been no question that Canon's high-end models at least had more AF points than competing designs from Nikon.

With the advent of the Nikon D3 (and D300), Nikon has finally pulled ahead in the AF-point derby, and possibly in the AF-performance race as a whole. We doubt that sheer number of AF-points is so critical, but having a high number opens new opportunities.

The most obvious difference is that the Nikon D3 and D300 now sport no fewer than 51 "precision focus" AF points spread across the frame. (More on that "precision" designation below.) That's just the tip of the iceberg, though, as there are a lot of other changes in the inner workings of the new Multi-CAM 3500FX AF system.

The new AF system also raises the number of cross-type sensors, with a total of 15 AF points sensitive to both horizontal and vertical detail.

The Multi-CAM 3500 AF system offers 9-area, 21-area, 51-area, and 51-area with 3D tracking modes. There's also an option that lets you choose a single active point from a selection of 11, as an aid to users transitioning from the D200's system, or those using both D200 the newer bodies simultaneously.

The reference to "3D tracking" above alludes to the most unusual feature of the Nikon D3's AF system, namely the use of the 1,005-pixel RGB exposure sensor to assist in tracking moving subjects. This is one of those innovations that make you wonder why someone didn't think of it earlier. It's evident that only Nikon was poised to make a move like this, as they're the only SLR maker using such a high resolution sensor in their evaluative AE system. As far as we know, they're also the only ones using an RGB sensor for evaluative metering, something with adds to its usefulness for object recognition.

Tracking autofocus systems are surprisingly adept at interpreting the rather limited data from a handful of AF sensors, and using it to intelligently track moving objects. If you think about it, the amount of information the AF system has at its disposal is very limited: All it has to work with are approximate subject distances at a handful of AF points across the frame. By interpreting changes in the data coming from each, the AF system attempts to pick a subject from the background, then determine the subject's direction and speed.

In fact, AF systems lack almost all the things that our own visual systems use to discriminate objects with: Color, tone, shape and subject size. It's really amazing that AF tracking works as well as it does.

This is where Nikon's innovation in the Multi-CAM 3500 AF system comes in. Nikon has for a long time had a 1,005-pixel RGB sensor in their camera bodies, used by their excellent 3D Matrix Metering system. In matrix metering, patterns of tone and color are used as an index into a large database of "reference scenes" stored in the camera's memory. The camera doesn't directly understand it's snapping a portrait shot, but when it sees a human-shaped blob against a different color background, its scene indexing tells it that it should try to get the exposure of the blob correct, even if it means the overall scene brightness would come out low.

With the D3 and D300, the Nikon engineers have used the data from the 1,005 pixel RGB exposure sensor to help guide the camera's autofocus decisions. We'll have to see how this pans out in actual shooting situations, but the potential is huge. While the RGB sensor provides no distance information, it has much more resolution than even the greatly expanded array of AF points on the new AF sensor. As discussed in the section of this report that covers the AE system, the D3/D300's AE system also incorporates a new Diffractive Optical Element (DOE) designed to improve the effective resolution of the RGB sensor. The 1,005 element AE sensor also captures both tone and color information, which should make it easier to discern where objects are in the field of view and how they're moving.

The net result should be more sure-footed and accurate tracking of subjects as they move about the frame. The relatively high resolution of the RGB sensor should let the camera determine the subject's location more precisely, and therefore develop more accurate measurements and predictions of its motion.

In our discussions with Nikon staff, it also appears that the RGB sensor is contributing some tracking information even when the subject has moved outside the area covered by the AF sensors. At first this didn't seem to make sense. What good would it do to know where the subject is if there aren't any AF sensors there to tell the camera how far away it is, or how fast it's going? It turns out that there are a number of ways the AE sensor could help the AF system outside the active AF area; in my discussions with Nikon engineers, though, I learned that the primary purpose for out-of-area tracking is to reduce the time required by the AF system to re-acquire the subject.

As the diagram above shows, the 1,005 element RGB sensor covers a somewhat greater portion of the frame than do the 51 active AF points. (When I asked the engineers just what portion of the frame area the RGB AE sensor covered, however, they politely but firmly declined to say.) The wandering red line drawn on the figure shows the path followed by a hypothetical subject during a continuous burst of exposures. Note that a portion of the subject's path (the part between the two blue "X" marks) is outside the active AF area, yet still within the area covered by the 1,005 pixel sensor. In previous Nikon AF systems, and those of competing manufacturers, the AF system would have no idea where the subject was once it passed beyond the active AF area. As a result, it would take more time to re-acquire the subject when it re-entered the active AF area near the bottom of the frame. In the Nikon D3 and D300, though, the AF system will remain aware of the position of the subject, even if it doesn't know its range while it's outside the AF area. When it re-enters the AF area, the camera can quickly determine its range, and doesn't need to spend any processing cycles figuring out which AF point is covering it.

It's easy to imagine how this capability could help in the tracking of difficult subjects: While I'm sure it's less of a problem for pro shooters, I myself have often encountered situations in sports or wildlife shooting where it was a challenge to keep a rapidly- or erratically-moving subject framed within the AF area. If the camera were able to track such subjects when they wandered slightly outside the AF area, I'd expect I'd have had more "keepers" when I came back from the shooting sessions.

This edge-of-frame tracking ability isn't a panacea though. While the engineers declined to say just how much of the frame the RGB sensor covered (and I did press them on this point), it seems that it doesn't extend too far beyond the edges of the AF array. In our discussions, they were clear that the D3/D300 could only track objects a small distance outside the AF area. They seemed much more emphatic about the impact of improved tracking accuracy within the active AF area than outside it. Still, the ability to reduce re-acquisition time, even in a limited percentage of cases, is a very worthwhile feature. In the case of the D300, the Matrix metering sensor is likely to cover almost the entire frame, so the D300 has a slight advantage.

One question of course, is why Nikon waited until now to develop such an AF system. After all, the 1,005 element RGB sensor has been in use in Nikon SLRs for something like 10 years now. When I asked the engineers about this, they said that a key factor was the speed of the CPU used for camera management, the chip that handles autofocus, autoexposure, and user interface operation, as opposed to image processing. The control processor used in the D3 and D300 is considerably faster than similar processors in earlier models, and now has sufficient throughput to do meaningful image processing with the 1,005 element sensor data in real-time, where earlier units did not. Secondarily, the newly-added Diffractive Optical Element brings greater imaging precision to the 1,005-element sensor, permitting more accurate discrimination and localization of objects within the AE area.

These days, most improvements in camera functionality are incremental, basically taking what had been done before, only now doing it a bit faster, a little more precisely, etc. In contrast, Nikon's use of RGB exposure sensor data to assist AF operation stands out as a more radical innovation, bringing an entirely new approach to the problem of AF tracking, different from any we've seen before. It's an exciting development, and one that we'll be watching eagerly as the first production samples hit the market: It's a very clever idea, but we won't know how successful it is until we hear the experience of practicing photographers using the new system in the field.

Nikon D3 AF "Fine Tuning"

The microscopic pixel dimensions of modern digital sensors have placed more extreme demands on autofocus accuracy than was ever the case in the film era. This has revealed a lot of shortcomings in autofocus systems, not the least of which have been the frequent "near-miss" mismatches between particular lens/camera combinations. A lens that focuses fine on one body may front-focus on another and back-focus on a third. Change bodies and the problem may move to another lens.

Solving this sort of mismatch problem has often meant shipping your entire complement of lenses and bodies to the manufacturer to have them all fine-tuned to match each other. This was and is a costly and time-consuming process, and if any of the lenses in question were made by someone other than the camera manufacturer, you were simply out of luck: If you returned them to the lens maker, chances are you'd hear back that they were in perfect working order. (And well they might be: Attached to a different body, they might focus just fine.)

Ideally, there'd be a way to tell the camera to tweak its focus forward or back just a tad, depending on the lens you were using. In fact, this is just what the Nikon D3 provides: You can register up to 20 different lens "types" with the camera (more on "types" in a moment), and make micro-adjustments to the AF system for each.

This is an area where Nikon has followed Canon's lead. The Canon EOS-1D Mark III first introduced the idea of AF micro-adjustment when it was introduced back in late February 2007. Both can keep track of 20 different "registered" lenses.

What does lens "type" mean here? Basically, a lens "type" is a lens model. For instance, if you have a 70-200mm f/2.8 and a 100mm f/2.8 Micro, the camera would recognize each lens when it was attached to the camera, and automatically load the appropriate fine-tuning setting. If you had two 70-200mm f/2.8s though, the camera would have no way to distinguish between them, and would load the same fine-tuning settings for either one.

While there may be some photgraphers (particularly pros) who have more than 20 lenses in their kits, the 20-lens "fine-tuning library" will cover the needs of the vast majority of shooters. And while we'll need to test it with third-party lenses, it seems likely that the Nikon D3 and D300's fine-tuning systems should be able to recognize lens types, regardless of who manufactured them. This is a huge step forward in focus accuracy, giving photographers the tools they need to maintain and calibrate their own equipment.

Autofocus differences between the D3 and the Nikon D300?

The Nikon D3 and D300 both use the same Multi-CAM 3500 AF engine, but there's been a little confusion over the implementation in the two cameras. For the record, the two systems are identical, but there's one unavoidable difference: The smaller image sensor in the D300 means that the AF area covers a rather larger portion of the overall frame area. This strikes us as an entirely good thing, it'd actually be nice if the D3's AF sensor array were larger, to give the same frame coverage as on the D300.

Other than this one difference resulting from the different frame sizes of the two cameras, the AF systems in both are identical, though the D3 has much quicker autofocus according to our tests. Nikon has also limited the number of lenses registered for AF micro-adjustment on the D300 to 12, while the D3 supports 20 lenses.

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Nikon D3 Chromatic Aberration Correction

One of the more unusual aspects of the Nikon D3 is its ability to correct image artifacts arising from lateral chromatic aberration (CA) in the lenses used with it. This isn't strictly the first time we've seen a camera able to correct for optical shortcomings in the lenses used with it. That distinction goes to Olympus, whose E-1 SLR offered the capability to correct for a range of lens distortion and artifacts.

In the case of the Olympus E-1, though, the distortion correction was preprogrammed, based on information communicated from the Olympus Zuiko "digital-specific" lenses to the camera. That is, each lens carried information regarding its distortion characteristics, which it communicated to the camera when it was attached. Based on what we've been told though, the D3 appears to be able to figure out how much lateral CA a lens is creating at each focal length and correct accordingly.

Lateral CA correction is something that's relatively easy to do digitally, at least to a reasonable degree of approximation. CA arises from the varying refraction of light of different wavelengths (colors) as it passes through an optical system. Some colors are refracted (bent) more than others, so light of different colors coming from a single point may not fall on the same spot on the sensor. This produces the red, purple, blue or green fringes you see around contrasting objects, particularly at the edges of the field of view.

Given that digital cameras naturally separate light into red, green, and blue color components, it's possible to do some color-based processing to make at least approximate corrections for the effects of chromatic aberration. This is what the Olympus E-1 did, and what DxO Optics Pro and other software programs do, including the Lens Correction filter in Adobe Photoshop CS3.

What's unusual in the D3 though, is that the camera is figuring out on its own what correction is needed, rather than being told what to do by the lens (as with the Olympus E-1), applying a precalculated correction (as with DxO Optics Pro), or having a user dial it in interactively (as in Photoshop). When pressed, Nikon said that best results would be obtained with Nikon lenses, but that the system would work with third-party lenses as well. We specifically asked a panel of Nikon engineers whether there was any database of Nikon lens characteristics involved, and they replied that there was not -- the camera figures out what lateral CA is present and corrects for it all on its own, irrespective of the lens involved. We've confirmed that the D3's CA correction works in-camera for non-Nikon lenses, although it's hard to say how well or poorly: We'd need examples of a Nikon and third-party lens with the same CA behavior to say whether the correction is equal or not. That said, it certainly appears to be as effective, as far as we can tell.

One place where there may be a difference between Nikon and third-party optics is in the area of RAW file processing. In keeping with the philosophy of a RAW file representing exactly what the sensor captured, the Nikon D3 only applies the chromatic aberration correction to JPEG images, not to the RAW files themselves. Using Nikon Capture NX software (an added-cost, optional software package), the user can then choose to apply the same correction the camera would have. Nikon said that this post-capture correction would be made in Nikon Capture using the same algorithms as employed by the camera in adjusting the JPEG data, but we haven't tried Capture NX with third-party lenses yet.

The images above were taken from our standardized test shots. For a collection of more pictorial photos, see our Nikon D3 Photo Gallery .