It's a common frustration for new photographers and one that I have felt many times. You think you're doing everything right, but the images are coming out all wrong. "Why aren't my photos sharp?" Here's a rundown of the things that might be affecting your photo's sharpness.
Starting with the obvious, check your focus. This isn't always easy -- especially in low light. Autofocus or back button focus can do a decent job in most situations, but it is far from foolproof. If sharpness is critical, I recommend switching to manual focus. And if your camera offers assistance options such as focus peaking, all the better.
For portraits, you should focus on the subject's closest eye. This draws attention right where you want it to be. When it's too dark to see through the viewfinder, increase your ISO during composition to give you some night vision. If you recompose after focusing, be sure your subject hasn't gone fuzzy -- especially important when using a wide aperture with a short depth of field. And don't forget to keep your equipment clean; dirt and smudges can make parts of your image appear out of focus.
Focus is the first step in getting a sharp image, and it's really helpful to practice nailing it.
Motion blur occurs when your shutter remains open for long enough to capture movement. This movement can be from either the camera or the subject (or both), and the blur is exacerbated by a slow shutter speed.
Camera Motion Blur
To avoid motion blur, your first step is to minimize camera movement. This is achieved by either using a tripod or turning up your shutter speed. Low shutter speeds absolutely require a tripod. What's a low shutter speed? The general (but not absolute) rule is any speed below the reciprocal of your focal length. For example, a 50 mm focal length without a tripod will require a shutter speed of at least 1/50 s. Always round up if you don't have that exact shutter speed. In this case, 1/60 s will do. A 100 mm focal length will need a shutter speed of at least 1/100 s. Anything less than the reciprocal means a tripod becomes necessary.
This rule is complicated somewhat by crop sensors. If you are not using a full frame camera, your focal length should be adjusted to the full frame equivalent before determining shutter speed. In other words, if your camera has a crop factor of 1.5x, your effective focal length for a 100 mm lens becomes 150 mm. Base your shutter speed calculation on the latter value.
Consider also whether your camera or lens has built-in stabilization. This corrects for the shakiness of our less-than-stable hands and allows us to use a lower shutter speed. The amount of correction varies among models and manufacturers -- some claiming up to four stops. Usually it is safe to drop at least one or two stops of shutter speed with these systems. Remember, when using a tripod, you should turn stabilization off. On a tripod, the stabilization mechanism will detect the movement of itself and create a positive feedback loop of (in)correction. Some cameras are smart enough to turn stabilization off automatically, but you shouldn't rely on that assumption.
Subject Motion Blur
If your subject is in motion, a tripod won't help much. Your only option here is to increase shutter speed until you can capture your subject frozen in time. The appropriate value varies depending on the subject's speed. For people walking, 1/125 s is a good starting point. For running, bump up to 1/250 s. To freeze falling water, start at 1/180 to 1/250 s. Kids and sports present their own special challenges and generally require even higher shutter speeds. Experiment beforehand to find a good setting for your situation. When in doubt, err to the faster side.
Of course, simply increasing shutter speed is easier said than done. If we could do that for any shot, we wouldn't need tripods at all. While increasing your shutter speed, you may have to compromise on your ISO and aperture settings. Ideally, you should introduce more light to compensate. Daylight, strobes, flashes, lamps... But that's a post for another day.
Depth of Field
The aperture setting determines your depth of field. That's the short story. The less short story is that there's a range, or slice, of "acceptably sharp" depth a certain distance from your camera's sensor. This depth is affected by aperture, sensor size, distance to subject, and, to a lesser degree, focal length. The definition of "acceptably sharp" is subjective, and the sharpness and sharpness falloff within your depth of field can vary quite a bit. If you want to get technical, there's some super fun math involved.
But to keep it simple, ensure your depth of field is long enough to capture your subject as sharply as you desire. If you are too close to your subject with a too-wide aperture, much of it will be out of focus. This is frequently desired, especially in portrait and macro photography, but if you want more of your subject in focus, try stepping back or stopping down your aperture setting. Break out the tripod if you have to!
This is especially important to keep in mind with moving subjects which are slipping into and out of your depth of field "slice". If you need to get shots quickly (street photography, for example), shoot on aperture priority with a higher aperture setting. This gives a longer depth of field that captures more of a subject in focus, and that frees you up to adjust other exposure settings more quickly.
At one point in time, it was only adjustable by changing rolls of film. Now ISO is easily changed on digital cameras with the flick of a dial. This gives you much more flexibility, but you also need to be aware of the effects of higher ISO settings.
The ISO setting determines how sensitive your sensor is to light. A higher ISO pulls more light and allows for a faster shutter speed or smaller aperture. This is useful, for example, when you need to capture moving objects in low light. The caveat is that higher sensitivity introduces noise or grain into the image. The higher the ISO, the more noise there will be and, consequently, the less the sharpness.
Ideally, you should always shoot at the lowest ISO possible. It's more of a last ditch option for when your situation absolutely will not allow for the image to be taken. That said, if a lower ISO will sacrifice the shot, then definitely adjust away! In cases such as indoor or night photography, it is unavoidable. Just be aware of how much sharpness you are losing with each stop of the dial.
Light does funny things, and it's important to keep those things in mind when shooting. After all, photographers are really just manipulating and capturing light. Diffraction causes light to bend when it passes through a small opening. One example of a small opening is a stopped down aperture in your camera's lens. Contrary to the advice given above for depth of field, stopping down your aperture setting can actually make things worse! Beyond a certain setting, the effects of diffraction can reduce the sharpness of your photo and make it appear soft instead of crisp.
Generally, diffraction is only an issue for large format photographers who use lenses with very small aperture settings. Think f/45. However, diffraction effects are still noticeable in less extreme photography. At f/11, you may see softness in your photos. Up to f/16, this effect will be minimal, but if you can avoid it, you should. At f/22 is when it really kicks in. Shorter focal lengths are more affected by this phenomenon, too; the aperture opening is smaller than that of a longer focal length at equal aperture settings.
In short, if sharpness is critical but you need a long depth of field, I recommend making f/8 or f/11 your minimum aperture setting. That's not a firm rule though, and it's always important to consider the desired outcome. Sometimes a bit of softness is necessary to get everything into focus.
Your lens is the interface between the world and your camera's sensor, and many photographers argue that it's your most important piece of equipment by far. Indeed, the quality of the optics in your lens has a huge impact on image quality and sharpness. If you are considering buying third party lenses, be aware that many of them are cheaper for a reason. Some are great, but most are inferior to first party lenses. This is fine for the casual shooter who only wants something good enough, but if you are more demanding and can't seem to get tack sharp photos no matter what you try, your lens may be to blame.
Where lens quality has the greatest effect is when shooting with wide apertures. To be clear, almost all lenses are less sharp at the widest aperture settings. Yes, I know, I'm flip-flopping all over the place on aperture. But if you've been paying attention, you'll see we are narrowing into a range of aperture settings that offer the highest sharpness. We already have a minimum: f/11. The maximum however depends largely on the quality of your lens. Extremely high-quality (and expensive!) lenses can pull super sharp images even when fully opened. However, most lenses don't offer the sharpest images until they are brought down two or three stops from full open. Lenses of lower quality need to be dropped even further to get acceptable sharpness.
Zoom lenses present this problem, too. In order to give the versatility of a range of focal lengths, quality tends to be reduced. Zoom lenses are more complex, and there's more room for optical error. This is why many photographers still opt to use prime, or single-focal-length lenses. Even though zooms are more convenient, they usually cannot match the image quality of a similarly priced prime lens.
Additionally, distortion, vignetting, and chromatic aberration are at their worst with wider apertures, and lower quality typically means more of each. Some cameras automatically correct these issues, but the results aren't always the best.
Lenses can also vary from unit to unit. It's not unusual to find one that has been damaged or poorly calibrated. Always thoroughly test your lenses in a controlled environment to make sure they are acceptably sharp before taking them out into the wild. It's much easier to determine early if a lens is bad. Of course, you should make sure all other potential sharpness issues are accounted for.
Lighting affects sharpness? In a roundabout way, yes! This is due to the way sensor information is stored in a digital image file. Instead of recording the data linearly throughout the brightness levels of the image, the brightest pixels get more room to store their data.
Each "stop" on a camera represents a halving or doubling of light. This is an exponential change. Likewise, the amount of data in an image file that is allocated to each stop within a sensor's dynamic range is exponential. The brightest recorded stop gets half of all the data -- even if you've recorded twelve stops in total! Each stop down gets only half of the data of the stop above it until you're at the bottom, darkest stop which only gets the scraps after everyone else is done.
What does this mean to you as a photographer? It means that darker areas of your photos will have less data and less detail associated with them. To avoid this, try increasing your exposure as much as possible without blowing your highlights. This practice is known as exposing to the right thanks to the way it pushes your histogram to its right edge. There's a higher risk of overexposing with this technique, but as long as you watch your histogram, you should be okay.
This is more problematic for high contrast scenes in which you have a large range of tones and a lot of dark areas. Landscapes in particular, with a very bright sky and a dark foreground, can have mushy shadow areas even when the overall image is well-exposed. In this case, you may have to find a different angle with a better-lit foreground, or wait for the sun to start setting to get a more subdued light (golden hour!).
In any case, always try to expose to the right, and bring the exposure down a bit in post. This will give you more data to work with during editing as well as less noise in the shadows. And if you've been advised to err on the side of underexposure, take that with a grain of salt. While it is easier to pull detail from underexposed areas, that data will be quite noisy. It's always best to get the exposure right in camera.
- Use a timer or remote shutter. Even on a tripod, the movement from engaging the shutter by hand can cause enough motion to blur your photo.
- Hang weights or other equipment from the hook on your tripod. This gives it greater stability and is excellent for windy conditions.
- If you don't have the luxury of a tripod, try to keep the camera as steady as possible by any means necessary. Keep it close to your body, and take a wide stance to steady yourself. You can also rest the camera against other objects like a tree or railing.
- If your camera has the option, lock up the mirror. A DSLR's mirror can easily cause vibration during an exposure.
- Adjust the diopter. This is the tiny dial near the viewfinder. It determines the amount of magnification of the eyepiece and allows those with poor vision to use the finder without glasses. If all of your photos come out blurry even when they look sharp in the finder, this could be your issue.
- Increase sharpness of raw images in post-production. Raw images are usually dull and lack sharpness. This is normal; no processing has been done on them to boost contrast, color, or sharpness. Raw capture leaves that job to you, the photographer.
The most important takeaway I hope to give with this post is that all elements of photography are deeply intertwined and affect each other in various ways. There is much more happening behind the scenes of a "tack sharp photo" than simply changing shutter speed, aperture, and ISO settings. Initially, this can be very overwhelming to a beginner, but if you practice these principles for long enough, they will become second nature. If you are having trouble, take them one at a time, and make each one a habit. Whatever your method, the best advice is to keep shooting and to learn from your results.