A kit lens might not be ‘fast’, but you can still achieve a shallow depth of field
Kit lenses are limited by their maximum (largest) aperture. The 18-55mm f/3.5-5.6 that typically comes bundled with the D3400 has a variable maximum aperture – f/3.5 at the wide, 18mm end of the zoom and f/5.6 when it’s at 55mm. Compare this with the maximum aperture of two classic kit lens upgrades: a ‘nifty fifty’ 50mm f/1.8, and an 85mm f/1.8. At 55mm, the kit zoom is more than three stops ‘slower’. This doesn’t mean it takes three times longer to focus, but when the kit lens is used at its maximum aperture, the smaller opening lets in less light, and consequently a much slower shutter speed is required for a correct exposure. Slower shutter speeds can lead to blurred images, whether that’s because the subject moved during the exposure or the camera did.
There are ways to get around this light loss (as you’ll see over the page), but there’s another side effect of the smaller maximum aperture: it’s much harder to blur out backgrounds. Depth of field is a measure of how much front-to-back sharpness an image appears to have, and it varies according to the type of camera used, the focus distance and – crucially – the size of the aperture. The smaller the aperture, the greater the depth of field, and vice versa. This is one of the reasons that portrait pros use ‘fast’ lenses with large maximum apertures, as they make it easier to achieve a shallow depth of field, with the subject’s eyes sharp and the foreground and background beautifully blurred. Embrace blur Although you might not be able to achieve the waferthin depth of field and soft, creamy blur of an 85mm f/1.4 lens that costs more than a grand (though see page 83 for a brilliant secondhand option), there are some simple steps you can take to get the shallow depth of field look with an inexpensive kit lens. For a start, make sure that there’s a considerable distance between the subject and the background, so that the backdrop is pushed far beyond the depth of field. Shooting towards a ‘clean’ background that’s devoid of distractions will heighten the effect, as will zooming the lens to its longest setting.
The closer you focus the lens, the shallower the depth of field, so move in as close to the subject as appropriate. As a final touch, include features that are close to the front of the lens to provide a diffuse foreground and make the sharp subject ‘pop’ from the image (see above). Wildlife photographers often use this technique by shooting through grass and other vegetation, but it can be used for portraits and action images too. Of course, when you’re dealing with a shallow depth of field there’s less room for error when it comes to focusing. To ensure sharp shots, choose an autofocus point, position it over the most important feature (such as the eyes in a portrait) and magnify the image on the rear screen to check for sharpness.
Set a large aperture, get up close to objects in the foreground and focus beyond them to sandwich your sharply-focused subject between a diffused foreground and a distant, blurred backdrop