Nikon D3X Optics
The Nikon D3X 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 D3X 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 D3X Autofocus
Autofocus is an area where Nikon in the past 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 D3X, D3, D700 and 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.
|Nikon D3X AF Point Selection Options|
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 D3X'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.
With the D3X, 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 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 D3X, D3, D700 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 system 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 so long 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 recent Nikon SLRs 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 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 D3X 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.
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 D3X 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 photographers (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. It also appears that the Nikon D3X's fine-tuning system can 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 Nikon D3X and the D3?
The Nikon D3X and D3 supposedly both use the same Multi-CAM 3500 AF engine, but our tests showed that the D3x was noticeably slower at recognizing accurate focus than was the D3. We have no explanation for this, but the results were confirmed in multiple tests. We'll ask Nikon about this, to see if they can shed any light on the differences in our measurements between the two cameras.
Unfortunately, the Nikon D3X offers no mechanical (ultra-sonic) dust reduction. We're not sure why, as other manufacturers of full-frame DSLR bodies have managed to include this feature. Only Nikon's "Image Dust Off" software solution is provided, where a dust reference photo can be taken and then utilized in Capture NX2 (optional) to remove dust in image post-processing. That said, we've found in-camera dust-removal systems less than perfectly effective. You're still going to need to use a sensor-cleaning kit fairly often, so the advantage of in-body dust removal is perhaps less than it might seem.
Lens Test Results