The term, "tack sharp" describes an image which shows the main subject in super sharp focus. The image has clean lines, crisp details, and absolutely no blurring. Getting this high level of sharpness is one of the keys to a truly eye catching photo.
1. Use the sharpest aperture
Camera lenses can only achieve their sharpest photos at one particular aperture. This is typically 2-3 stops down from the widest aperture. Look for the lens you are using in a search engine to see if someone has already done the work for you.
Make sure that you take into account the shutter speed and depth of field while trying to stay close to the optimum aperture.
2. Lower your ISO
The higher your ISO, the more digital noise you will get in your photo. Your photo will lack sharp detail and include little specs of fuzz.
Whenever possible, use your camera's lowest ISO setting. on most entry level dslr's that is around 200. If you have to go higher because of light and the movement of the subject, then go higher, just realize that you are sacrificing one for the other.
3. Single point autofocus is your friend
When you use automatic focus, most cameras will try to keep as much of the scene sharp. This is fine when you want to see detail everywhere, but this does not mean that the main subject will be tack sharp.
Switch your camera into single point focus mode to stop the camera from trying to capture the whole image super sharp. In single point autofocus mode your camera will focus sharply on just one point, which is usually the center of the frame. Half press the shutter to get your subject sharp and then move the camera while still holding the button. When you find the perfect composure, press the shutter all the way down.
4. Better lenses
Quality lenses make a huge difference in the sharpness of your photos. Try not to fall into the trap of buying cheap lenses just so you can have a collection. Even if you only invest in one single high quality lens, you will notice the difference from your kit lens. It will be like the heavens are shining down on you and your camera when you see the sharpness and quality and better lens will give you.
5. Lose the lens filters
Filters reduce the sharpness of your lens, which will affect the final image quality. If possible, take them off to improve clarity.
There may be some instances where you need to use a neutral density filter, or polarizer to get the shot just right. That is ok if you are willing to reduce sharpness to get the shot. Sometimes it's best to throw the rules to the wind so you can get the shot.
6. Use a tripod
This should really be the #1 accessory when you are trying to get a sharp picture.
"It's three legs and a camera stuck on top, how complex could it REALLY be?" Get a cheap tripod and find out (just kidding, do research). You'll realize that with a cheap tripod the camera suffers shakes from using the shutter, even when triggering it remotely.
Quality tripods will prevent the camera from the shakes, and moving.Some tripods will let you add accessories and become your second collecting hobby (next to collecting for your camera).
8. Remote cable or timer
Pressing the shutter button with your finger on your camera can cause minute shaking even with a quality tripod. A cable release or remote control is cheap way to avoid this problem (Opteka sells a remote for canon dslr's for about $20). If you don't want to shell out another $20 into your new found (expensive) photography hobby, you can use the camera's timer. The two second timer is generally long enough to avoid shaking from touching the shutter to effect the image.
9. Mirror lock-up
When the mirror flips up to take the picture, it causes your camera to move. You can usually set the MLU to hold the mirror in a retracted position. This can make a big difference on how sharp your photos turn out.
10. Turn vibration reduction off
Many newer dslr cameras and lenses come with a built in vibration reduction system, sometimes called an image stabilizer. When your camera is mounted on a tripod, the camera can get confused and add movement to the phone.
Frolicking along and can't be bothered with a tripod? Here are some quick pointers to get the most out of hand holding.
1. Find/Make a makeshift tripod
You didn't think you'd get away from using a tripod that easily did you? Try resting your camera on a tree branch, a fence post, a rock, or something to keep the camera as still as possible.
2. Increase your shutter speed
A faster shutter speed will capture movement much better. You should stick to the rule of thumb that says that you should use a shutter speed of at least 1/focal length, which means that if you are using a 100mm lens, you want to use a speed of 1/100 or faster.
3. Shoot in burst mode
Rather than taking photos one at a time, just hold down the shutter and snap away. Chances are that one or two will be sharp.
4. Find a way to steady yourself.
Tuck your arms to your sides or lean up against a wall or tree (that you decided not to use as a makeshift tripod. Breathing can cause movements in the camera, so try and relax yourself and not make any jerking movements.
5. Image stabilization - on
Since you're not using a tripod, use the image stabilization. This is what it was made for, the handheld warrior.