Nikon D300S Optics
Like other Nikon SLRs, the D300S accommodates a wide range of Nikkor lenses, via the standard Nikon "F" lens mount. Unlike the Nikon D3000 and D5000 consumer models, however (as well as the D40, D40X and D60 before them), the D300S's lens mount includes both a mechanical AF coupling for older "screw-drive" autofocus lenses, as well as AF electrical contacts for the latest AF-IF or AF-S Nikkor lenses with internal focus motors.
The Nikon D300S's lens mount also includes an AI aperture ring connector, a little metal vane located just outside the lens mount flange (at about 1 o'clock), that interfaces with old AI Nikkor manual focus lenses. This engages with the aperture ring on AI-style Nikkor lenses, and lets the D300S support aperture-priority metering mode and provide manual-exposure metering with them. Lower models including the D90 do not have this feature, so the D300S is compatible with a wider range of older Nikkor lenses than its lesser siblings.
With very few exceptions, you can use the Nikon D300S with any F Mount Nikkor lens ever made. See the table and notes below for detailed lens compatibility information extracted from the D300S User's Manual (courtesy of Nikon USA):
Nikon D300S AF Assist
The Nikon D300S has a bright, dedicated autofocus-assist lamp, which also doubles as a self-timer lamp. We prefer this setup over using the flash strobe for AF assist, as this totally decouples autofocusing from flash operation. (The flash does not need to be raised or active.) The AF assist lamp illuminates automatically in poor lighting conditions, and can be disabled via a Custom menu setting.
Nikon D300S Autofocus System
Of the 51 total AF points, 15 (three central columns of 5 points each) are cross-type sensors that are sensitive to detail in both axes, while the remaining 36 points are linear, sensitive to detail in the vertical axis only. Each of the 51 focus areas is individually selectable, allowing precise control over the area of the frame from which focus should be determined. Alternatively, an Auto-area AF mode measures all 51 focus areas, automatically determines which of them are on the primary subject, and then activates only those areas. Nikon says that AF speed has been increased on the Nikon D300S relative to the earlier D300, and we did find some improvement in shutter lag in auto-area mode; other lag times were essentially identical, though.
Like past Nikon DSLRs with built-in flashes, the D300S's AF-assist light is a bright incandescent bulb that emits from the body near the handgrip. We thought to call particular attention to it, because some DSLRs use the flash as an AF-assist light. This would be fine, but they can then also require that the flash be used in the exposure, so there's no way to have AF assist for available-light shots. The D300S doesn't have this limitation.
The D300S lets you choose either auto or manual focus via a small dial on the front of the camera, next to the lens. Setting the switch to "M" puts the camera into Manual focus mode, "S" places it in Single-servo autofocus mode, and "C" places it in Continuous-servo AF. Single-servo AF simply means that the camera sets focus only once, when the Shutter button is first pressed halfway, and is best for stationary objects. Continuous-servo AF means that the camera continuously adjusts the focus, as long as the Shutter button is halfway pressed, and is best for moving objects.
There's an important difference between Single and Continuous Servo modes, although Custom Functions a1 and a2 allow the behavior to be changed. By default, the shutter won't release in Single-servo mode unless the lens is focused, or the lens itself is set to manual focus. (Focus Priority) In Continuous-servo mode however, the camera defaults to firing regardless of the state of focus. (Release Priority) Through the Custom Functions, the Single-servo mode can also offer release priority, while the Continuous-servo mode offers an additional choice which Nikon calls "Release + Focus" priority. This ordinarily defaults to release priority behavior, but automatically switches to focus-priority and slows the camera's frame rate as it deems necessary in low-light or low-contrast conditions where focusing is more difficult.
AF Area Modes
An AF Area Mode lever on the camera's rear panel lets you select between Single-point AF, Dynamic-area AF, and Auto-area AF modes. Single Area AF simply means that the camera judges focus based on one part of the subject, and the user can manually select the AF point by pressing the arrow keys. The other two modes are rather more complex, offering the ability to automatically track moving subjects, determine scene types and even recognize the location of human subjects in a scene.
In Auto-area AF mode, the camera chooses which AF points to use automatically, with the selected points shown briefly in the viewfinder for reference when in Single-servo AF mode. The camera automatically determines the subject type, and bases AF point selection on its decision of the main subject in the scene. When using either G- or D-type lenses, this becomes rather more intelligent, with the camera able to use its 1,005 pixel exposure/white balance sensor to distinguish human subjects from the background. This allows the D300S to automatically select the focus points located over your human subject(s)
|Nikon D300S AF Point Selection Options|
Dynamic Area AF is relevant only when in Continuous-servo AF mode, with its behavior mirroring that of Single-point AF when in Single-servo mode. Dynamic Area AF employs all or a subset of the autofocus points, though you can still manually select the starting point for AF operation. When Dynamic Area focusing is enabled, the camera first focuses on the subject in the primary focus area. When the subject moves to a different AF area, the camera shifts the focus to "follow" the subject. This is great for irregularly moving subjects. (Sports and kids come to mind.) As well as allowing tracking across all 51 AF points, at the user's option the camera can limit subject tracking to only a small area of 9 or 21 points including the user-selected starting point. The illustrations above show the three different Dynamic-area options, with the point arrays grouped around the central AF point. As noted, you can manually select different starting points, and the cluster of Dynamic-area points will follow your selection. As an aid to users transitioning from the earlier D200's system or using the D200 with newer bodies simultaneously, there's also also an option that lets you choose a single active point from a selection of 11, matching the AF point layout of the D200.
Starting with the D3 and the original D300, the Nikon engineers have used the data from the 1,005 pixel RGB exposure sensor to help guide the camera's autofocus decisions. While the RGB sensor provides no distance information, it has much more resolution than even the large array of AF points on the Multi-CAM3500 AF sensor. As was the case in the D3/D300, the D300S's AE system also incorporates a Diffractive Optical Element (DOE) designed to improve the effective resolution of the RGB sensor by optically aligning the red, green, and blue pixel planes with each other. The 1,005 element AE sensor also captures both tone and color information, making it easier to discern where objects are in the field of view and how they're moving.
With this RGB-assisted AF approach, when an AF point initially acquires a lock on a particular subject, the camera immediately notes the pattern of light and color found at the corresponding point on the RGB array. Then, as the subject or camera moves, the camera can track the light/color pattern corresponding to the subject across the face of the RGB array. This provides much finer-grained position information than could ever be obtained from the sparse AF array. The RGB sensor doesn't provide any distance information, but by more precisely tracking subject information, it permits a much surer hand-off of the subject between AF points.
The use of the RGB sensor as part of its AF tracking is unusual enough to warrant a little additional discussion. Back when the D3 and original D300 were announced, we had an opportunity to query the chief engineer responsible for the new AF system fairly closely, in the course of which we learned some important details of how the system worked. The following is taken from our review of the D3, but all the information is directly applicable to the Nikon D300S, as the same AF technology is used in that model as well.
In our discussions with Nikon staff, we learned that the RGB sensor contributes 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? While 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 a 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 with any specificity.) The wandering red line drawn on the figure shows the path followed by a hypothetical subject during a continuous-shooting burst. 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 remains 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.
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 D300S, the Matrix metering sensor is likely to cover almost the entire frame, so the D300S has a slight advantage over Nikon's full-frame cameras using this system.
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. It's no kind of a scientific test, but in shooting with the D3 and D300 and now the new D300S and D3s, I have indeed been very pleased by how few shots were lost due to blown focus. I'm personally a little leery of camera AF systems in general, but have had consistently good results with this advanced system from Nikon.
One question of course, is why Nikon waited until now to develop such an AF system. After all, the 1,005 element RGB sensor had been in use in Nikon SLRs for over 10 years before Nikon linked it to the AF system in the D3/D300. 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 was considerably faster than similar processors in earlier models, and so had 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 brought 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 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.
Changing AF Points & Locking Focus
In any of the AF modes, you can change the primary focus area by unlocking the focus area selector (the Four-Way Arrow pad on the back panel) and then shifting the focus area using the up, down, right, or left arrow directions on the control rocker. You can lock the focus area selection by turning the switch back to the lock position. By default, the Nikon D300S does not "wrap" the focus area selector as you scroll between focus areas. Custom Setting a7 lets you opt for a "Wrap" function. What this means is that if you press the right arrow key again, after the right focus area is already selected, the selection will immediately jump to the left focus area. The same thing happens when moving the focus area selection vertically as well.
There are several methods by which you can lock focus on the D300S. The first is to half-press the Shutter button to lock the focus, placing your subject in the selected focus area, halfway pressing the Shutter button, then realigning the composition and firing the shutter. Alternatively, when using Single Servo AF, you can press the AF-L/AE-L button (or through Custom Function F5, the Function button) to lock focus, even if the Shutter button is released. This lets you recompose the photograph without keeping your finger on the Shutter button, but on the AE-L/AF-L button instead. (Reducing the chance that you'll accidentally trip the shutter when you don't intend to.) Finally, the AF-ON button acts in the same manner as half-pressing the shutter button (but without engaging Vibration Reduction if a compatible lens is attached, and without determining exposure, which the shutter button can do if Custom Function c1 is set to "On").
There are several options available for the AE-L/AF-L button, which can be set via Custom Settings Menu f4. You can program it to lock either focus or exposure separately, or both together (the default). You can also change its operation so a single press locks and holds the exposure setting. A second press or -- optionally -- a shutter release will then reset the focus / exposure locks, as will the camera's metering system powering down. You can also disable the AE-L/AF-L button altogether, have it mirror the AF-ON button, or set it to preview depth of field, lock flash exposure, disable flash, trigger a burst of bracketed photos with one shutter button press, select the metering mode, jump to playback mode or the top of the My Menu, or change the file type. While pressed and in concert with rotating the command dials, the AE-L / AF-L button can control the dynamic AF area, auto bracketing or non-CPU lens number, or be disabled. The Function button can mirror all of these behaviors too, with the exception of serving as a secondary AF-ON button, and with an added ability to change to a 1EV step size when controlling aperture or shutter speed with the command dials and pressing the Function button. (Phew -- that's a lot of customization!)
Nikon D300S 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 D300S provides: You can register up to 12 different lens "types" with the camera (more on "types" in a moment), and make micro-adjustments to the AF system for each, across a range of +/-20 (arbitrary) increments.
While there may be some photgraphers (particularly pros) who have more than 12 lenses in their kits, the 12-lens "fine-tuning library" will cover the needs of the vast majority of D300S users. We've found that this system also recognize lens types for third-party lenses as well, so its utility extends to essentially any CPU-containing AF lens the Nikon D300S can work with.
The lens-based AF tuning function can also be disabled altogether, if you want to revert to the standard focus tuning for all lenses. It should be noted that AF fine tuning only affects phase detection autofocusing, having no effect over contrast detection AF in Live View mode. (It's also an option best left disabled unless you know you have a front- or back-focusing issue with one or more of your lenses, because the system can also be used to manually introduce a focusing error, perhaps making it impossible to focus to infinity, or the the ordinary macro focusing distance of a lens.)
AF fine-tuning has by now become a fairly standard feature on higher-end SLRs. That doesn't diminish the fact that it's a huge step forward in focus accuracy, though, giving photographers the tools they need to maintain and calibrate their own equipment.
Nikon D300S Anti-Dust Technology
To help combat dust particles that can enter the camera when changing lenses, the Nikon D300S includes an ultrasonic dust cleaning system to automatically vibrate the low-pass filter over the sensor each time the camera is turned on or off (programmable). There is also an immediate mode where cleaning takes place on demand, and of course, there's a manual cleaning mode, where the camera lifts the mirror and opens the shutter, allowing access to the low pass filter with a blower or other cleaning device. You can also capture an "Image Dust Off Reference Photo," and use the optional Capture NX2 software to remove dust shadows from your images via post-processing.
While ultrasonic dust removal systems can increase the interval between manual cleanings, it bears noting that no such system system can completely eliminate the need to occasionally clean the sensor manually. Copper Hill Images is an advertiser of ours, but we'd recommend their wet/dry cleaning system even if they weren't (it's what we use in our own lab): See the Copper Hill website for details.
Lens Test Results - Automatic CA Correction
The D300S usually ships without a standard "kit" lens, so this section would normally be left blank intentionally. We felt that Nikon's in-camera chromatic aberration correction deserved some special notice, though. See the text below...
Nikon In-Camera CA Correction
200% Crop from Nikon D90,
18-105mm lens at 18mm
Converted from RAW,
no CA correction applied
200% Crop from Nikon D90,
18-105mm lens at 18mm
Automatic CA correction applied
Like most of their recent higher-end SLR models, the Nikon D300S incorporates Nikon's in-camera chromatic aberration correction technology, which is automatically applied to all JPEG images. RAW files are left untouched (as they should be), so they serve as a useful reference for the effectiveness of the correction.
We didn't have a lens with particularly bad CA in-house when we tested the Nikon D300S, so reached back to our review of the Nikon D90 for a good example of what the technology can do. The D90's 18-105mm kit lens had quite a bit of CR in the corners of the frame at some focal lengths, but you'd never know it from looking at its JPEGs. The crops above (at 200% size, to make it easier to see just how good the CA correction actually is) show results from the corner of a frame shot at 18mm on the D90. The results are pretty amazing: The rather pronounced CA seen in the uncorrected image at left (taken from a RAW file) is almost entirely invisible in the in-camera JPEG.
This CA-correction technology will work for both Nikon and third-party lenses, although Nikon claims it works better on Nikon-branded optics. We haven't verified that claim; in our informal evaluation it has worked pretty well with most lenses we've looked at.