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Manual Control Options
The Nikon D40 has full manual control of exposure, white balance, ISO and focus. Most other Nikon DSLRs offer two control dials for exposure and have other interface refinements that make manual shooting easier. The D40 relies on one control dial for all of these adjustments.
Focus
Auto Focus (4.5)
The Nikon D40 has 3 auto focus sensor sites, arrayed in a row across the center of the frame. This arrangement is inferior to the auto focus systems on previous Nikon DSLRs that have 5-11 sites. It's unusual to see a manufacturer take a backward step like this. Many DSLR users of even very advanced cameras focus, then recompose, which is what D40 users will have to do. The difference is, with more sensors, the shifts can be smaller, and in cases where that is impossible, such as when the sensors should be tracking a moving object, it doesn't work at all.
The auto focus system is accurate but slow. We found that it handled dim indoor light, as long as the subject was contrasted. The D40 is noticeably inferior to the D70 and D80 in focusing on our low-contrast subjects.
Manual Focus (7.0)
The Nikon D40's focusing screen is bright and contrasted. We found it easy to focus with the D40 even in subdued light. The kit lens is mechanically sloppy, so it's not as easy to focus with it as it would be with a better-quality Nikon lens.
Exposure (9.25)
In addition to setting exposure completely manually, the D40 can set exposure compensation. For normal exposures, the D40 can be set to shoot up to 5 EV above or below the metered reading, in 1/3-EV steps. A button on the camera accesses the exposure compensation feature. Exposure compensation for flash is available only through the camera menu, and runs from 1 EV above to 3 EV below the metered setting.
Metering (8.0)
 The general specs of the D40 metering system aren’t as impressive as other Nikon DSLRs – the metering system uses a 420-segment RGB sensor. The D50 and D80 use this same sensor, but other Nikons such as the D70s use a 1,005-segment RGB sensor. Nikon calls its evaluative metering mode “Matrix Metering,” which indicates that the D40 compares many separate light readings from across the frame to establish the ideal exposure. The hope is that evaluative systems will recognize backlighting or other difficult lighting situations and compensate for them, getting the exposure right on the subject. As with other Nikons, we found that the Matrix system can be fooled with typical backlit scenes and with bright subjects on black backgrounds. To an extent, that's to be expected: The system will deliver more usable images if it compromises a bit, rather than trying to guess perfectly every time. Few pictures will be perfect, but even fewer will be completely wrong. The D40 also offers center-weighted and spot metering, which are useful for manual shooting. The center-weighted metering option favors the central 75 percent of the frame, while the spot option meters from about a spot that represents about 2.5 percent of the total frame and is centered on the active focus area.
White Balance (7.5)
The D40's Auto white balance setting works well, which is good, because that's likely what the target market for the camera will use. The presets are incandescent, fluorescent, direct sun, flash, cloudy and shade. The D40 has an option for fine-tuning the presets. The manual white balance system can take a measurement from a white surface or pick up a balance from existing shots.
ISO (7.5)
Nikon shies away from using the number “3200” for its maximum ISO setting, so the D40 has a “HI 1” ISO setting that's a full stop above ISO 1600. The D40's conventional ISO range is 200-1600, in full-EV steps. It's too bad that it doesn't offer 1/3-EV steps because small jumps in ISO can get the exposure into a useful range without degrading image quality as much as full-stop jumps. The Nikon D50 has the same full-stepped range, but 1/3 increments are available on the D70 and pricier models.
Shutter Speed (8.0)
An impressive 1/500-second flash sync speed is the big news with the D40. Its full shutter speed range, from 1/4000-30 seconds, plus Bulb for time exposures, is typical of DSLRs, and it's a completely serviceable range. The D40's shutter speeds are selectable in 1/3-EV steps, which is typically a fine enough interval to get exposure just about perfect.
Aperture (0.0)
The D40 controls aperture settings on compatible lenses through electronic connections in the lens mount. It can adjust the f-stop in 1/3-EV increments, which is typical for DSLRs and also good enough for even very careful users. The kit lens has maximum apertures of f/3.5 when zoomed wide and f/5.6 when zoomed in.
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