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Nikon D70

The Nikon D70 is an "entry-level" SLR loaded with features at a sub-$1,000 price.

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Page 7:Exposure

Review First Posted: 04/14/2004

Exposure

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Available exposure modes include Program AE, Manual, Aperture Priority, and Shutter Priority modes. Also new are full Auto and Digital Vari-Program modes (similar to the Scene modes on Nikon's consumer digicams), including Portrait, Landscape, Close up, Sports, Night landscape, and Night portrait. Shutter speeds from 30 seconds to 1/8000 second are available, plus bulb for exposures up to 30 minutes. In Program mode, you can use the Main command dial to adjust the camera's selection in favor of a higher shutter speed and a larger aperture, or vise versa if the options are available, handy for when you want to emphasize shutter speed or aperture.

ISO sensitivity ranges from 200 to 1600, adjustable by pressing the ISO button and turning the Main command dial to change the setting on the Status LCD. It can also be changed in the menu. A Noise Reduction mode in the settings menu reduces fixed-pattern image noise when shooting at the higher sensitivity settings at longer exposure times. White balance modes include Auto, which covers almost the entire range from 3,500K to 8,000K. It can also be set manually for Incandescent (3,000K), Fluorescent (4,200K), Sunlight (5,200K), Flash (5,400K), Cloudy (6,000K), Shade (8,000K), or Preset, which the user sets based on a white or gray object in the scene or a pre-captured photograph. I found the auto white balance generally did a good job, and the Preset option was very accurate under a wide range of lighting conditions. My biggest gripe is that neither Auto nor Incandescent reach down far enough to handle the household incandescent lighting that's so common in the US. (Although Incandescent can be tweaked enough to almost get there.) Why can't digicam companies make auto white balance options with enough range to cover this very common light source?

White balance can be fine tuned by pressing the WB button and turning the sub-command dial. It can be adjusted from -3 to +3 in increments of 1, but the actual step size varies as a function of the white balance mode that's selected. See table below for details, which shows the lighting color temperature that each setting corresponds to. 

 

Camera Display--> -3 -2 -1 0 1 2 3
Direct Sunlight 5600 5400 5300 5200 5000 4900 4800
Shade 9200 8800 8400 8000 7500 7100 6700
Overcast 6600 6400 6200 6000 5800 5600 5400
Incandescent 3300 3200 3100 3000 2900 2800 2700
Fluorescent 7200 6500 5000 4200 3700 3000 2700
Flash 6000 5800 5600 5400 5200 5000 4800

The D70 has three metering options, 3D Matrix, Center Weighted, and Spot. The 3D Matrix setting integrates exposure information from 1,005 areas across the entire screen, as opposed to most multisegment sensors that have from 10 to 35 areas to analyze. The scene viewed by the metering sensor is compared to a database of common photographic situations to help the camera decide whether the image consists of a backlit subject, for example, or else a dark foreground object. This information is enhanced (essentially made "3D") by the focus distance information shared from the microchip in the D- and G-series lenses. All Nikon SLRs use some form of matrix metering, but the D70 is the first time that the full 1,005-element RGB sensor originally introduced in the flagship F5 film-based model has been deployed in an "entry level" d-SLR. It's by far the most sophisticated metering system of any d-SLR currently on the market for less than $3,000. The net result of all this is a more frequently accurate metering response than that produced by center weighted metering, especially if the subject is off-center. In practice, I found the D70's metering to generally be quite accurate. It seemed to have a tendency to slightly underexpose most shots by 0.3 to 0.7 EV, but it was pretty consistent in this, leading me to believe that this might represent a deliberate choice by its designers, to avoid losing highlight detail. Overall, I felt pretty confident of getting the exposure I expected with the D70, after relatively little time spent with the camera.

As to the other metering options for the D70, center-weighted metering takes a light reading from the entire image area, but places the greatest emphasis on a circular area in the center. In an unusual feature for an "entry level" d-SLR, as Custom Function menu option lets you select how large an area contributes toward the center-weighting. Options are 6, 8, 10, and 12 mm, with 8mm being the default. Spot metering in the D70 takes a reading from the center one percent of the image area, excellent for quick measurements from a face without having to close the distance much.

The D70's Exposure compensation adjustment lightens or darkens the overall exposure anywhere from -5 to +5 EV units, in one-third step increments. It can also be adjusted to work in half step increments. Note though, that exposure compensation does not work in any of the Digital Vari-Program modes. As noted above, I found the D70 to fairly consistently underexpose shots by about 0.3 EV, since most of my shots were better when set from +0.3 to +0.7 EV. By default, test shots captured under harsh lighting showed the D70 to be quite a bit more contrasty than I'd personally prefer, although the color from the D70 is excellent. There is a variable contrast control buried in the shooting menu that lets you adjust the contrast level to low, normal, or high. I found that this worked fairly well, but a little differently than some. Rather than leaving the midtones at the same brightness and pulling in or pushing out the shadow and highlight values, the contrast adjustment on the D70 leaves the highlight values undisturbed, and adjusts the midtone and shadow levels to affect the contrast. This is good in that it means the camera will hold onto essentially the same highlight detail, regardless of how you have the contrast set, but it also means that contrast adjustments have a pronounced effect on overall image brightness. At the end of the day, the results are the same as a more conventional approach, but it might take a little different approach to understanding exposure and contrast adjustment than many amateurs are accustomed to. (The D70's behavior in this regard will actually be well-suited to pro shooters, who are accustomed to metering for the highlights first and foremost. Here, the approach that's implemented is to expose for the highlights, then use the contrast adjustment to control how you want the midtones and shadows to appear.)

An auto-bracketing feature takes three shots of the same subject with varying exposure values determined by either the photographer in manual mode or by the camera in all other modes. The exposure steps for bracketing can vary across a range of -2 to +2 EV (values are added to the already chosen exposure compensation value), in increments of either one-third or one-half. Through the Custom Settings menu, the Bracketing function can also be set to adjust white balance or flash exposures only. (By default, both ambient and flash exposures are bracketed.)

The D100 also offers Sharpness, Tone Compensation (Contrast), and Hue adjustments, accessed through the Shooting menu. I mentioned the contrast adjustment feature above, but its Custom option deserves special mention. What's unusual here (for an entry-level d-SLR at least) is that the Custom tone compensation option accepts downloaded tone curves from a computer. (If no curve is downloaded, the Custom setting defaults to the Normal setting.) This lets you completely define the camera's tonal characteristics via the computer, something that has heretofore only been available on the highest-end d-SLR models.

For those familiar with the concept of the "color wheel", which arranges visible colors in a circle, Nikon's Hue adjustment will make sense: It offers a range of adjustment from -9 to +9 degrees around the color wheel. (A complete circuit of the wheel being 360 degrees.) If you don't carry a degree-calibrated color wheel in your head, I've provided the illustration of a color wheel at right. The dark bars show the total shift that the full 18 degree range of adjustment offered by the D70's hue control can produce. - As you can see, it's a fairly subtle adjustment. Note too, that the effect on any given color will depend on where that color is around the wheel. For red colors, a positive adjustment will shift the red toward orange, while a negative adjustment will shift it toward purple. For blues though, positive adjustments shift the color toward purple, while negative adjustments shift it toward cyan. The rollover image below shows the effect of going from -9 to +9 on the Hue adjustment - The -9 shot is visible by default, move your cursor over the image to see the effect of the shift to +9 degrees.

When reviewing images on the LCD monitor, you can call up a histogram and a highlight function to give you a complete readout on the exposure. This is a useful tool to examine your exposure in the camera instead of waiting to download images and then deciding to reshoot. As I noted in my discussion of these features in the Viewfinder section of this review, I'd like to see the Highlight function be a little more restrained in its reporting of overly-strong highlights. (Actually, the ideal would be to let the user select at what brightness level the highlight warning should activate. Why hasn't any manufacturer done this yet?)

Continuous Shooting Mode
Nikon claims that the D70's Continuous Shooting mode captures 3 frames per second, depending on the amount of image information and available Compact Flash space. In practice, I clocked it at 2.92 fps, quite close. When using a fast Compact Flash card, like a SanDisk Extreme or Ultra II or presumably one of the even faster Lexar 80x cards that are coming (May, 2004), the buffer doesn't fill very quickly. One can watch the counter move down to about a five-frame capacity and slowly move down then back up again. The faster the card, the more quickly the buffer can offload the data, and in the case of high resolution with "normal" or "basic" compression, the buffer may never fill at all. This is truly amazing, and a first with any digital camera I've seen. Do note though, that this effect requires a card of 60x or more. (Finally, a camera that really takes advantage of fast memory cards!)

Image Noise
Overall, the D70 has very good noise characteristics. The chart below shows a plot of noise magnitude vs ISO value for the D70 and Canon Digital Rebel, but as usual, the chart tells only a small portion of the story. While the D70 shows numerically higher noise levels, particularly at very high ISO settings, in actual fact, the noise pattern of the D70 is a good bit finer-grained. This makes it noticeably less objectionable to the eye. Bottom line, I found the D70's images shot at ISO 1600 to be thoroughly acceptable for all but the most critical applications. For routine shooting of family memories, I have no qualms about running the D70 at its maximum ISO setting on a routine basis.

 

What's up with RAW?

Like many high-end digicams, the has a "RAW" file format as an option. If you're new to the world of high-end digital cameras, you may not be familiar with the concept of the "RAW" file format. Basically, a RAW file just captures the "raw" image data, exactly as it comes from the camera's CCD or CMOS image sensor. So why would you care about that? - RAW files let you manipulate your images post-exposure without nearly as much loss of image quality as you'd get with JPEG files. A full discussion of RAW file formats is way beyond the scope of this article, but Charlotte Lowrie of MSN Photo has written an excellent article describing the benefits of the RAW format, titled A Second Chance to Get It Right. Check it out, it's one of the clearest tutorials on RAW formats I've seen yet.

 

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