How do I choose a prime lens to get blurred backgrounds for full-body street photography shots?

Question

I like to shoot street photography, say with the subject far enough away in the image that I can capture the full body, and still get focal blur in the background. My kit lens gives a decent effect of this when shooting portraits but loses the focal blur when the subject is farther away and the whole image is basically in focus at one depth of field.

Correct me if im wrong but this is due to the kit lens' limited depth of field or higher f-stop number? So a friend recommended I go for a lens with a smaller f-stop. Is a lens such as the Nikon 35mm f/1.8G ideal for this type of scenario? And what would be more preferable in this situation with the crop factor taken into account a 30mm or a 50 mm? Or something else entirely.

I have a Nikon D3400 and I am looking to upgrade from the 18-55 kit lens. I realize that it has a crop sensor but I am still learning about manual photography so hopefully one day soon I will upgrade to a full sensor camera when I am more knowledgeable about shooting.

Obviously not looking for a lens thats more expensive than the camera but also would still work on a full sensor camera should I upgrade.

Answer 1

Any 35mm or 50mm prime lens with f/1.8 or better should work. If you plan to learn to use your camera manually, you have even more options. But beware: Don't just buy a non-AF lens because you might want to have one later. Nikon 35/1.8 or 50/1.8 should be around 200€ new. Nikon 50/1.4 are about 300-400€ new. Older, used lenses should be about 100€ cheaper.

But there also 50/1.4 for 100€ (used). But be aware of the condition of the lens. I, myself, would NEVER buy a lens with fungus. I have to much fear of spreading into other lenses.

Some little scratches on cheap, used lenses are not that bad. Most tiny scratches are not visible in the final photo.

Answer 2

On crop sensors, 35mm is easier to use (than 50mm) because it is a normal focal length (approximately equal to the length of the diagonal of the frame), but 50mm will get you more blur because of the longer focal length when the camera-subject distance is kept the same.

If you're open to trying some sharp, manual-focus lenses, 35/2.8 and 50/1.8 lenses tend to produce reasonably good background blur at normal distances (about 180cm). Lenses with M42 mounts that can be adapted to Nikon bodies are pretty inexpensive, so you can get one of each focal length to try. Then when you have more experience, you can spend more on your dream lens.

Increased background blur is associated with the following:

• Larger apertures (smaller n for f/n).
• Longer focal lengths.
• Subjects much closer to camera than to background.

You are able to get good background blur for portraits with the kit lens because the aperture is large enough (f/5.6) for the focal length (55mm) when the subject is close to the camera. However, when the subject moves away from the camera, the aperture becomes inadequate. When you zoom out (18-24mm), the aperture doesn't get large enough (f/3.5) to compensate for the change in focal length.

Just getting lenses with larger apertures doesn't necessarily solve the problem. The focal length still has to be long enough, and the subject still has to be close enough. That is why compact cameras with tiny focal lengths don't get good background blur at normal subject distances despite having f/2 apertures. This issue with smaller focal lengths doesn't affect you too much now since you ask specifically about 30-50mm, but you should be aware of it for when you start looking at lenses shorter than 28mm.

There's also subject-background separation (or isolation), which is somewhat related to background blur. I'm not sure of all of the factors involved, but increased background blur is not necessary, nor sufficient, to produce good subject-background separation. For instance, I had an old Tokina-made 35/2.8 lens that produced surprisingly good subject-background separation at f/5.6, though it was a bit soft wide open. The bokeh characteristic of that particular lens was a medial highlight with a lateral smear. Bokeh "balls" looked like "popped" bubbles. This seemed to be able to emphasize the subject while de-emphasizing the background.

Answer 3

The easiest way to increase background blur is to increase the distance between your subject and the background. More specifically, you should increase the ratio between the camera-to-background and the camera-to-subject distances. This works with any lens.

The biggest difference between lenses in terms of background blur is about the way that blur is rendered. Is it "harsh" or "busy", or is it "smooth" or "creamy? " We call the quality of the blur "bokeh".

Lenses intended for portraiture tend to have smoother "bokeh" at the expense of edge-to-edge sharpness when imaging a flat test chart.

Other lenses, such as those meant for flat field work such as macro photography or art/document reproduction use are more highly corrected for field curvature and tend to render a flatter field of focus. The design of such a lens usually means the "bokeh" of the out-of-focus areas is less smooth.

In the end it comes down to being able to assess a particular lens' design and understanding how that will affect the way photos made with that lens will look. Flat field lenses are good for certain types of portraits - typically those shot in a studio with a backdrop specifically made to be used as a portrait background. In such cases the lens is usually stopped down enough that almost any lens will do.

When, on the other hand, you're shooting portraits outdoors and need to smooth out the background, the last thing you need is a "macro" type of lens. In general, prime lenses with very large apertures and higher numbers of aperture blades are designed with portraiture as at least one possible use case. Macro lenses or other flat field types of lenses tend to be a tad slower than other lenses with similar focal lengths. For example, most 90-100mm "macro" lenses tend to be f/2.8 or slower. Other 85-105mm lenses better suited to narrow depth of field portraits tend to be f/1.8 or f/2.

One thing to pay attention to if you intend to move to FF one day is that Nikon makes both full frame FX 35m f/1.8 and an APS-C only DX 35mm f/1.8 lens.