How can I take a photo with everything in focus with my DSLR?

Question

I am quite new to DSLRs and one of the first things I noticed was the incredible focus points and appearance of depth that you can achieve. That is great in a lot of scenarios, but not in all. When filming a landscape as a whole, I do not want to have the focus on that single tree, but on the whole skyline.

Is there a way by which you can sort-of "disable" the focus, so that the raw image is recorded without any added blur? I suppose something as simple as this is only a small function you can turn off, but I can't seem to find it in the manual of my camera.

Answer 1

What you are looking for is large depth of field. This is an optical property, not something applied as a special effect, so it's not something you can turn on or off. The raw image captures the light focused by the lens, and inevitably there will be parts of the scene which are either too far or too close — out of the range where the rays are tightly organized by the lens. In fact, the fashion of shallow depth of field with blur as a key compositional element is relatively recent — traditionally, many photographers' concern was the same as yours: getting more of the scene in focus.

The good news is that you can affect this: a smaller aperture will give you greater depth of field. That means larger f numbers, like f/16 or f/22. This won't give you infinite focus, but will greatly increase the range which appears sharp. The "price" is that you'll need either higher ISO or longer shutter speed. For highest image quality, longer shutter is usually the better option — which is why tripods are common for landscapes.

For a given aperture, you can find the hyperfocal distance, which is the distance at which you can set the focus to get the largest depth of field. (There are a number of online calculators which can figure this out for you, although without an distance scale on the lens you kind of have to guess when focusing.)

If you use a pinhole lens the aperture will be so small that you will have effectively have infinite depth of field. But, with this approach, or even with any small aperture like f/11 or up, you sacrifice a little of the top possible sharpness of the in-focus area in exchange for greater overall depth across the scene.

To add to some of the confusion here: compact point & shoots and phone cameras use small sensors. That correspondingly means that the real aperture is smaller for the same field of view (see Why does a bigger sensor lead to a shallower depth of field? for details), which means that these cameras often have very high depth of field when focused on anything not right next to the lens. Because shallow DoF is trendy these days, some cameras and phones actually have a software-based effect to add the appearance of blur due to limited DoF. So, for these cameras, it is a software blur effect that can be turned off. For bigger cameras like your DSLR, though, it's natural and unavoidable.

Finally, there is an emerging field called "computational photography", where unfocused light rays are recorded without a traditional lens. With this approach, focus is applied after the fact, just as you were thinking. However, this technology is in its infancy — the only commercial camera to work this way is the Lytro, and its resolution is so low that it's really just a toy (and a sort of "tech preview").

Answer 2

When filming a landscape as a whole, I do not want to have the focus on that single tree, but on the whole skyline.

mattdm's answer about depth of field is spot-on, so I'll just add a few practical points:

1. Depth of field depends in part on focal distance. That is, for any given aperture setting, depth of field will increase as the distance to the subject increases. If you're taking a photo of a landscape, you're probably focusing on something that's pretty far away; in that case, just about everything that's not close to the camera will probably be in focus even with just a medium aperture. Example: On a Canon 7D (i.e. crop sensor), a 50mm lens set to f/4 focussed on a subject 50 ft. from the camera, objects at distances between 34 ft. and 92 ft. will be in focus -- a total depth of field of 59 feet. If the subject is 100 ft away, on the other hand, you get a total DOF of 1283 ft.! Try your own scenarios using this online depth of field calculator to get a feel for how distance, aperture, and DOF are related.

2. Your DSLR will let you choose a particular autofocus point. Putting that point on your subject will ensure that the subject is in focus, but it doesn't mean that everything else in the image will be out of focus. (This may be obvious, but I could see how a beginner could misconstrue the meaning of the selected AF point.)

3. Your DSLR can automatically select which AF points to use. If you're used to manually selecting the AF point yourself, try the auto setting and let the camera choose. The Nikon AF system is pretty smart -- if you're shooting a landscape, it's not going to focus on just one tree.

4. You can preview the image by using the depth of field preview button on your camera. This causes the camera to stop the lens down to the selected aperture so that you can see exactly what is and isn't in focus at your selected aperture.

Answer 3

To expand on the both excellent answers by mattdm and Caleb, I should add that depth of field is distinct from background blur. This means that if the image is printed / viewed as small, there can be more acceptably in focus than what is said by the depth of field.

Given equal framing and maintaining the same camera crop factor, depth of field is proportional to F-number, and background blur is proportional to focal length divided by F-number.

There is one and only one strategy to increase the depth of field given equal framing, assuming changing crop factor of the camera is not an option:

1. Increase the aperture F-number, i.e. stop down

Focal length does not affect depth of field if you move closer or further away to keep equal framing at the same time focal length is changed.

Now, if you want to both maximize depth of field and minimize background blur given equal framing, you should also:

2. Decrease the focal length (zoom out) and walk closer to the subject

Sometimes you cannot do (2) while at the same time maintaining the F-number, because the maximum F-number can vary depending on the focal length of a zoom lens.

For example, with a slightly stopped down 24mm f/2.8 crop lens (equivalent to slightly stopped down 38.4mm f/4.4 on full frame camera), nearly everything is in focus and those elements that are out of focus don't have much blur, unless the subject is VERY close. If you are not satisfied with the results, stop it down more.

On the other hand, on a 85mm f/1.8 crop lens that has not been stopped down, the depth of field is very small and the out-of-focus elements are very blurred.

These strategies can be used to your advantage if you want everything in the subject to be in focus (acceptably large depth of field), and background blur to be large at the same time. For example, for portrait photographs, it may be better to use 85mm f/1.8 crop lens and stop it down a little than to use 50mm f/1.8 crop lens wide open, to have good depth of field AND desirable background blur at the same time. Of course, this means you need to step back and can hit a wall in the process if shooting indoors!

Oh, and when stopping down, you need to compensate it somehow in exposure:

1. Use a flash, if feasible, but this may not be feasible if the subjects are very far away
2. Or increase the exposure time, while at the same time using a tripod or image stabilization, if feasible, but this may not be feasible if the subjects are fast-moving