I have Nikon D3300 with Nikon 50mm f1.8G lens. When i try to shoot in AF mode with focus points, i normally get blurry images or out of focus images which is not so sharp, so please help me out to overcome with this issue, this happens mostly while taking group photos.
IMO, your first lesson should be understanding the focus points of your camera.
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What shooting mode are your relying on? Aperture priority? Manual? Auto?
As noted, the aperture (f-stop) you or your camera selected will provide a very shallow depth of field. Think of DOF as a single vertical plane, which it is. Only subjects falling within that one plane will be in "perfect" focus. From that single plane, everything in front and behind that plane will be increasingly out of focus.
By using a very open aperture (f 1.8), you almost guarantee your shot will have out of focus points, even if your shot involves only one individual;
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Depth of field is also a function of the distance between the lens and the subject. An explanation and table for use in determining just how much area will be in sharp focus at various distances and a range of apertures can be found here;
A Flexible Depth of Field Calculator
There are several DOF apps available which you can add to any smartphone. Doing so will place the correct information at your fingertips in any given situation.
As you can calculate, using your 50mm lens and shooting from, say, 5 meters distance will provide a very shallow DOF. Reduce that shooting distance and you also decrease the available DOF for any given aperture setting.
If you are using the wide open aperture to create background blur, use the calculator to determine how far from the lens the background can be before it begins to blur.
Shooting indoors without supplemental light sources forces the camera to select a very slow shutter speed. At 1/15 second shutter speed, you are once again ensuring blur from camera shake or subject movement;
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You can increase shutter speed by raising the ISO value.;
undersyanding shutter speed and subject blur - Google Search
Your Nikon has very wide latitudes in acceptable ISO values before digital noise becomes an issue. Also, remember noticeable noise is relative to the size of enlargement. If your shots are not going to be printed at somewhat large sizes, then noise becomes less of an issue and ISO values can be raised with little concern to image sharpness. What you see on your monitor during post processing is not going to be the image size and quality you will ultimately print. Even an 8 X 10" print has wide latitude in ISO values. It would be wise to consider your final print before you set up your camera's controls.
Once you close down the aperture to increase DOF, you also must compensate for the consequential reduction in light coming into the lens. This is
"the exposure triangle" at work. If you do not raise ISO, the camera will then select an even slower shutter speed as the aperture closes down.
Alternately or collectively, and certainly preferably, you can also introduce supplemental light sources. The easiest and most available source for additional light would be your camera's built in flash unit. Unfortunately, most built in flash units will provide rather harsh light and unnatural shadows. You should do some study on the pro's and con's of using the camera's built in flash;
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The first compensation for problems related to the built in flash is to learn the controls on your camera which adjust the amount of light your built in flash will output;
undersyanding shutter speed and subject blur - Google Search
A preferable alternate or addition to your camera kit would be to purchase a flash head which fits your camera's hot shoe. The options here are numerous and the applications vast. However, indoor photography can only benefit from a high quality flash unit which will allow, at the very least, the ability to bounce the flash output off interior surfaces;
undersyanding shutter speed and subject blur - Google Search
The basic idea is simple; the more light you make available to the camera, the faster the shutter speed for any given aperture. The more stopped down the aperture - to attain a more extensive DOF - the more you need supplemental light sources.
You might also choose flash diffusers to further soften the effect of your flash unit (built in or external);
undersyanding shutter speed and subject blur - Google Search
Female photographic subjects will almost always benefit from a diffused light source.
The use of a monopod or (preferably) a sturdy tripod will hold your camera (relatively) still as you release the shutter. This is not a complete solution as a 1/15 shutter speed will still have subject motion which will still cause blur. Lower quality tripods also have the problem of allowing camera motion while you are depressing the shutter release. Monopods still allow camera movement in one plane. Do not rely on your equipment to substitute for good photographic practices.
You might want to investigate and practice "back button focus" for your camera;
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This will divorce your shutter release button from the function of focusing. IMO this makes the operation of the camera much simpler and effective since you aren't trying to half hold your shutter release in order to focus and compose your shot. It is not, however, a substitute for good photographic technique when it comes to the shutter release itself.
At the very least, learn the proper technique for the shutter release which will not result in camera movement;
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DO NOT "JAB" AT THE RELEASE!
Practice the technique until you are satisfied it is not your shutter technique which is causing any amount of blur, even at faster shutter speeds. With your digital Nikon, each practice shot can easily be deleted from the file.
So fire away!
The more you you practice good technique, the more it will become second nature when shooting your best shots.
Alternates to this would be using the built in timer or a remote shutter release which will make the process of releasing the shutter a mostly hands off affair when the camera is mounted on a tripod. The timer function moves your trigger finger away from the shutter release button if you are hand holding your shot or using a monopod;
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Of course, all of this assumes you are willing to use the more advanced controls included in your camera.