Nikon D40 Optics

Kit Lens

The Nikon D40 ships in kit form with an updated version of the Nikkor 18-55mm f/3.5-5.6G lens that came in kits with the D50. We haven't tested a sample of the 18-55mm f/3.5-5.6G ED AF-S DX II on yet, but don't expect it to be radically different from the earlier model. The 18-55 on the D50 was a fairly typical kit lens, with so-so optical performance wide open, but capable of very good sharpness if you stopped it down one or two f-stops. Kit lenses work well enough for most consumers, and serve their purpose of getting you started without breaking the bank, but a big part of the attraction with SLRs is that you can easily trade up to a better lens when your finances improve, and extend your reach to wider angle, telephoto, or macro photography just by adding to your lens collection.

Nikkor 18-55mm vs 18-55mm II
(Click on image for larger view)


Lens Compatibility

The Nikon D40 marks a bit of a departure for Nikon in the optics department, in that it drops support for the older autofocus lenses whose focus mechanisms were driven from the camera. These lenses have what looks like a little screwdriver slot on their mounting flange, that couples with a protruding, screwdriver-looking shaft on the camera body. A motor in the camera body thus drives the lens mechanics to adjust focus.

More recent Nikkor lenses have motors built into the lens body, which tend to be both faster and quieter than the old-style drive system. These newer lenses carry an AF-I or AF-S designation in their name, and are the only types of lenses the D40 can autofocus with. CPU-equipped lenses lacking built-in focus motors can be used in manual focus mode, and type G or D lens types will also support full 3D color matrix metering for more accurate exposures, particularly when flash is being used. (You can tell CPU-equipped lenses by the set of five electrical contacts arrayed on the side of the lens flange.) The table below (courtesy Nikon Inc) tells the full story of lens compatibility for the D40.

The lack of an onboard focus motor is a key feature distinguishing the D40 from the D80. If you need to use older lenses (or a lot of Nikons current line of prime (non-zoom) lenses with your DSLR, you need the D80 or D200. This is a factor that could turn away current Nikon shooters, but it makes sense for an entry-level camera like the D40. Dropping the AF motor greatly helps with size and weight issues, and probably battery drain as well. Newcomers to the SLR world are likely to be perfectly content sticking with AF-S lenses, and all of Nikon's digital-specific DX lenses are AF-S models, providing a pretty wide range of options.

The lack of an AF motor does give me pause when thinking about photo students though. Students will be drawn to the D40 because of its low price, but I hesitate to recommend a camera for them that wouldn't work with a full range of prime lenses, or that would lock them out of buying and using older, inexpensive lenses purchased on eBay. Bottom line though, I think the D40 would still make a really excellent camera for a photo student. It's very flexible, and all you lose with D- or G-series primes is the autofocus. (And many would say that the discipline of having to slow down and focus manually could be equally as important as learning to shoot with primes in the first place.)

Autofocus System

While the D40 carried over a lot of the capabilities of the D80, its autofocus system is one area where cost-cutting has had a noticeable impact. The previous D50 had a 5-area AF system, and the D80 has 11 active AF points, but the D40 has only three, arranged horizontally across the frame. With the more limited AF array, the D40's ability to track moving subjects will be less than that of the D50 or D80, but the 3-point AF array isn't unreasonable to find in its price bracket.

This is one area where the interests of novice and more experienced shooters may actually converge. Both would benefit from the D80's more sophisticated AF system, and the argument could be made that novices actually need a better AF system than advanced amateurs, as they'll be less accustomed to paying attention to what the camera is focusing on. That said, it's not too difficult to check that one of the 3 AF areas is covering your subject, and it's a relatively small step up to learn to aim the camera and lock focus, and then for the shot itself.

Focus Options

The Nikon D40 offers pretty well all the focus options of its predecessor, the main difference being that options for setting the focus mode are presented on the LCD screen, as opposed to a little single/continuous/manual focus switch on the camera body itself. (Many Nikkor lenses also have an Auto/Manual focusing switch on their barrels. If the switch on the lens barrel is set to "M," focusing will be under manual control, regardless of the setting of the switch on the camera body.) Most AF-S lenses with the built-in Silent Wave focus motor let you manually focus the lens at any time, regardless of the camera's focus setting, so there's less need for a body-mounted focus-mode switch: The menu selection should do fine for most users.

To select between the three types of AF, you just navigate to the Focus Mode option on the camera's shooting display (or to the identical Focus Mode option in the Custom Settings Menu system) and choose between AF-A (Auto Servo), AF-S (Single Servo), and AF-C (Continuous Servo). Manual focus is the fourth option. Single Servo simply means that the camera sets focus only once, when the Shutter button is first pressed halfway, and is best for still objects. Continuous Servo means that the camera continuously adjusts the focus, as long as the Shutter button is halfway pressed, and is best for moving subjects. The Auto setting (added to Nikon's D-series SLR line with the earlier D50) lets the camera select the servo mode, depending on the movement of the subject.

The Nikon D40 is similar to the D50 in how it behaves in out-of-focus conditions. Some SLRs will let you fire the shutter in Continuous Servo mode if the lens hasn't achieved focus, but not in Single Servo mode. The D40 never fires the shutter if the lens isn't focused. (Unless of course, you have the camera or lens set to manual focus operation.) This more restrictive shooting could be an inconvenience to more experienced shooters, but will almost certainly be a benefit to novices, as the camera itself will guard against capturing out-of-focus images.

Focus can be confined to one of the three specific focus points in both Single Area mode, and in Dynamic Area which offers focus tracking. Single Area AF simply means that the camera sets focus based on the specific area you've designated. Dynamic AF employs all three of the autofocus areas. When Dynamic Area focusing is enabled, the camera first focuses on the subject in the chosen focus area. After the camera has initially "locked on" to the subject, if it moves to a different AF area, the camera will shift its focus to "follow" the subject. This is great for irregularly moving subjects. (Sports and kids come to mind.) In both Dynamic and Single Area AF modes, you can change the primary focus area using the right or left directions on the Multi-Selector pad. Closest Subject Priority is a third option, selected via either the AF-Area mode option on the shooting screen or by a custom settings menu item. Closest Subject Priority means that the camera will focus on the closest object that falls under one of the three focus points.

There are two methods by which you can lock focus on the Nikon D40. The first is via the Shutter button, placing your subject in the selected focus area, halfway pressing and holding 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 to lock focus (and exposure, unless the button is set for focus-only in the Custom Settings menu). Keeping this button pressed will maintain the focus and/or exposure lock, even if the Shutter button is released. This lets you recompose the photograph without having to keep your finger on the Shutter button, but rather on the AE-L/AF-L button instead. (Reducing the chance that you'll accidentally trip the shutter when you don't intend to.)

There are several options available for the AE-L/AF-L button, which can be set via the Custom Settings Menu. 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. (No need to keep the button pressed down.) Finally, you can set the AE/AF lock button so it alone controls the autofocus system, meaning the autofocus won't actuate when the Shutter button is half-pressed, only when the AE/AF lock button is pressed instead.

If you're a novice user considering purchasing a Nikon D40, and all this focus/exposure lock mumbo-jumbo sounds confusing, don't let it worry you: The camera's default operation is very straightforward, but the availability of features like these is really liberating for more advanced users.

AF Assist

Like past Nikon DSLRs, the D40'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 competing cameras (notably the Canon Digital Rebel series) use the flash as an AF-assist light. This would be fine, but they also require that the flash be used in the exposure, so there's no way to have AF assist for available-light shots. The D40 doesn't have this limitation.

Sensor Cleaning!

Everyone understands that lenses sometimes get dust on them and need to be cleaned, and there are a lot of lens-cleaning cloths, solutions and other accessories on the market that work well. BUT, what do you do when your sensor gets dusty? Dust specks on the sensor tend to show up when shooting at very small apertures, appearing as dark blobs on your images. They're distracting at best, a terrible nuisance at worst, if you end up having to retouch every image to rid of them.

Most of us are naturally leery about the idea of poking around inside the delicate innards of our DSLRs to wrestle with recalcitrant dust specks. Gently blowing the sensor surface (actually, the surface of the anti-aliasing filter) with compressed air gets rid of some dust, but there's invariably a lot that just stays stuck, no matter what. So what do you do?

If you've got dust specks on your sensor (and sooner or later you will), you're going to need to clean it. There are a lot of products out there intended to address this need, but a distressing number of them work poorly (if at all), and many are grossly overpriced. Advertising hype is rampant, with bogus pseudo-scientific jargon and absurd product claims run rampant. And prices - Did I mention prices? How about $100 for a simple synthetic-bristle brush?

So how do you know what product to use?

We don't pretend to have used everything currently on the market, but can tell you about one solution that worked very well for us. The "Copper Hill" cleaning method is straightforward and safe, and in our routine usage here at Imaging Resource, highly effective. Better yet, the products sold by Copper Hill Imaging are very reasonably priced. Best of all, Nicholas R (proprietor of Copper Hill) has put together an amazingly detailed tutorial on sensor cleaning, free for all.

Sensor cleaning is one of the last things people think about when buying a d-SLR, but it's vital to capturing the best possible images. Take our advice and order a cleaning kit from Copper Hill right along with your d-SLR, so you'll have it close at hand when you need it: You'll be glad you did!

(Other than a few backlinks on their site, we receive no promotional consideration from Copper Hill. We just think their sensor cleaning products are among the best on the market, and like their way of doing business. - We think you will too. Check them out.)



Good performance from the 18-55mm kit lens when stopped down.

18mm 55mm

The Nikon D40 comes bundled with a Nikkor 18-55mm lens, which covers the basic zoom range most commonly used. Results were quite good in these shots, where the programmed exposure stopped the lens down to f/8.0. Wide open, some softness appears in the corners, but the lens performs quite well when stopped down one or two f-stops.

A small macro area with great detail and high resolution. Flash performs well up close.

Standard Macro Macro with Flash

The Nikon D40's 18-55mm kit lens performed well in macro mode, capturing a minimum area of 2.76 x 1.84 inches (70 x 47 millimeters). Detail and resolution were both quite good, though there was a fair amount of softening in the corners, most likely the result of spherical aberration in the lens. (Most cameras have some softening in the corners in macro mode.) The flash produced reasonably even results, with only minimal falloff in the corners of the frame.

Moderate barrel distortion at wide angle with the kit lens.

This is the tendency for the lens to bend straight lines outward (like a barrel -- usually at wide angle) or inward (like a pincushion -- usually at telephoto). The Nikon D40's 18-55mm kit lens produced about 0.83% barrel distortion at wide angle. Though this is about average among the cameras we've tested, we still find it a little high to our eyes. At the telephoto end, the lens produced about one pixel of barrel distortion, or 0.04%, which is quite low.

Barrel distortion at 18mm is 0.83%
Barrel distortion at 55mm is less than 0.04%

Chromatic aberration
Fairly bright at wide angle, almost none at telephoto.

Wide: low but bright,
top left @ 200%
Wide: bright,
top right @ 200%
Tele: low and much less bright,
top left @200%
Tele: very low,
top right @200%

Chromatic aberration is low at both wide angle and telephoto settings with the 18-55mm kit lens. At wide angle, there's about 3-4 pixels of bright coloration on either side of the target lines. However, at telephoto, the pixels aren't nearly as bright. (This distortion is visible as a very slight colored fringe around the objects at the edges of the field of view on the resolution target.)

Corner Sharpness
Some softening in the corners of the frame with the kit lens.

18mm: some softening in the
corners (upper right)
18mm: sharper at center
55mm: only slightly soft in the
corners (upper right)
55mm: sharper at center

The Nikon D40's 18-55mm kit lens produced slightly soft corners in a few shots, mainly at the full wide angle setting and wide open (as shown above). At telephoto, corners showed slight blurring, but overall results were pretty good. (In the wide angle shot above, you can also see the D40's tendency to over-sharpen images at its default settings. Note the white halos around the black target elements in the center crop.)


The images above were taken from our standardized test shots. For a collection of more pictorial photos, see our Nikon D40 Photo Gallery .

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