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[摄影技巧] How to Take Sharp Photos (ZT)

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发表于 2015-11-4 05:44:43 | 显示全部楼层 |阅读模式
https://photographylife.com/how-to-take-sharp-photos



Home / Photography Tutorials / How to Take Sharp Photos

How to Take Sharp Photos
September 24, 2009 By Nasim Mansurov305 Comments
One of the things that makes photography frustrating, is softness and blur in pictures. Sharp photos are much more appealing than soft images. It is very disappointing when you take a picture at a special moment and images come out soft/blurry or out of focus. In this article, I will go through the techniques that I use to make sure that my images always come out tack sharp.

Let’s start with the reasons why an image might come out blurry:
  • Slow shutter speed could cause camera shake, which would produce a blurry image
  • Poor focus acquisition would result in a soft image
  • Your subject could be moving and causing a motion blur
  • You might have a bad lens or a lens that is not capable of producing sharp photos
  • Your ISO could be set to a very high number, resulting in lots of noise and loss of detail
NIKON D300 @ 300mm, ISO 200, 1/500, f/8.0

In order to resolve these issues, you need to address them all at the same time, which will help achieve optimal sharpness.
How to take sharp pictures
  • Start with setting your camera to the lowest ISO “base” value (in my Nikon camera it is ISO 200). Remember that the camera base ISO will produce the highest quality images with maximum sharpness. The higher the ISO (sensor sensitivity), the more noise you will see in the image. I suggest reading my article on understanding ISO.
  • If you have an “Auto-ISO” feature in your camera, set it to “On” with the following settings:  ISO sensitivity auto control: “On”, Maximum sensitivity: 1600, Minimum shutter speed: 1/100. What this does, it basically tells the camera to automatically change the sensitivity of the sensor based on light availability. If the amount of light entering the lens decreases and the shutter speed goes below 1/100 of a second, the camera automatically increases ISO to keep the shutter speed above 1/100 of a second. If you have shaky hands, I would recommend bumping up the “Minimum shutter speed” to something like 1/200-1/250 (I will go through proper camera hand-holding techniques so that you could shoot at even lower shutter speeds in a separate article). If you do not have Auto-ISO, then you would have to adjust it manually in low-light between the lowest value and ISO 1600. Why ISO 1600 is the maximum I recommend? Because anything higher than that in an entry-level DSLRs produces too much noise, which has a negative impact on overall image quality. On older-generation DSLRs such as Nikon D40/D80/D200, you might want to keep the maximum ISO to 800.
  • Hand-holding rule: If you have a zoom lens that goes beyond 100mm, I would recommend applying the general hand-holding “rule”, which states that the shutter speed should be equivalent to the focal length set on the lens. For example, if you have your lens zoomed at 125mm, your shutter speed should be at least 1/125 of a second. Keep in mind that this rule applied to 35mm film and digital cameras, so if you own an entry-level DSLR with a crop factor (not full frame), you need to do the math accordingly. For Nikon cameras with a 1.5x crop factor, just multiply the result by 1.5, whereas for Canon cameras, multiply by 1.6. If you have a zoom lens such as the 18-55mm (for Nikon DX sensors), set the “Minimum Shutter Speed” to the longest focal range of the lens (135mm), which is 1/200 of a second. Here are some examples:
    • 50mm on Nikon DX (D3000/D5000/D90): 1/75 (50mm x 1.5)
    • 100mm on Nikon DX (D3000/D5000/D90): 1/150 (100mm x 1.5)
    • 150mm on Nikon DX (D3000/D5000/D90): 1/225 (150mm x 1.5)
    • 200mm on Nikon DX (D3000/D5000/D90): 1/300 (200mm x 1.5)
    • 300mm on Nikon DX (D3000/D5000/D90): 1/450 (300mm x 1.5)
    NIKON D300 @ 280mm, ISO 200, 1/1600, f/4.0
  • 99% of the time, I shoot in Aperture-Priority mode and set aperture to the lowest value when I shoot in low light. In aperture-priority mode, you tell the camera what the lens aperture should be (the “f” number, for example f/3.5), while the camera automatically meters and guesses what the shutter speed should be to properly expose the image. So, set your camera to aperture-priority mode and lower the aperture to the lowest possible number.
  • Set your metering to “Matrix” on Nikon or “Evaluative” on Canon, so that the whole scene is assessed to estimate the correct shutter speed.
  • After you set the right metering mode and your lens to aperture priority, point it to the subject that you want to photograph and half-press the shutter. Doing so should show you the shutter speed on the bottom of the viewfinder. If the shutter speed is showing 1/100 or more, you should be good to go. Snap an image or two and see if you are getting any blur in your image. I typically review my images on the back of the camera at 100% and make sure that nothing is blurry. If the shutter speed is below 1/100, it means that you simply do not have enough light. If you are indoors, opening up windows to let some light in or turning the lights on will help to increase your shutter speed.
  • If you are still getting blurry images, try to hold the camera steady without shaking it too much and take another picture. If it doesn’t help, try increasing the “Minimum Shutter Speed” value to a higher number in your “Auto-ISO” settings. For those without the “Auto-ISO” feature – try to bump up your ISO all the way to ISO 800 or even 1600 and see if you can get faster shutter speeds.
  • While hand-holding your camera, there is a direct correlation between the camera shutter speed and blurry images. The lower the shutter speed (below 1/250 of a second), the higher the chance for blurrier images. Why? Because while hand-holding a camera, factors such as your stance, breathing, camera hand-holding technique all play a huge role in stabilizing the camera and producing shake-free images. Think of it as holding a rifle on your hand. You wouldn’t want to move around while trying to shoot – you need to stand as steady and stable as possible, pull the stock tightly into the shoulder, exhale and then shoot. The same technique works great for your photography, especially when you have to deal with slow shutter speeds. As I said above, I will post another “how-to” on proper camera hand-holding techniques, but for now, I recommend holding the camera just like you would hold a rifle (except your right hand goes on the shutter instead of the trigger), with one of your legs on the front and your body balance spread across both legs. I personally exhale when I shoot very slow shutter speeds and it does help me to get sharper images, so try it and see how it works for you. The difference between shooting a camera versus a rifle, is that you can at least adjust the shutter speed to a higher number and avoid camera shake, whereas you cannot do the same on a gun.
  • Learn how to focus correctly and deal with focusing issues. This one is very important, as your camera focus directly impacts image sharpness. The first thing you need to learn is how to differentiate between a camera shake/motion blur and a focus problem. When a subject in your image is soft or out of focus, while something else in the foreground or background is perfectly in focus and sharp, it is a focus issue. If the whole image is blurry and nothing is sharp, it is most likely a slow shutter speed or improper camera holding technique that is the issue. If you are having problems acquiring a good focus, here are some things that I recommend for you:
    • Lack of light can cause auto-focus malfunction, resulting in inaccurate focus acquisition by the camera. Make sure there is plenty of light for your camera to properly focus.
    • The center focus point is generally the most accurate in cameras. If you are having problems acquiring focus because your focus point is elsewhere, I recommend moving it back to the center. Many cameras allow having a separate button for focusing, without touching the shutter. I set my camera this way, focusing exclusively with my thumb, while pushing the shutter trigger with my index finger. This way, I can use the center focus point (which almost never has any issues with acquiring correct focus), acquire correct focus, then recompose without moving my body and then shoot. If you have such a feature in your camera, I recommend enabling it in low-light situations. In all other cases, leaving the shutter to both focus and shoot is the best option for convenience reasons.
    • The camera auto-focus system works by looking at the contrast around the focus area. For example, if you try to focus your camera on a clean white wall, it will never be able to acquire focus, because the camera will not see any areas of contrast. On the other hand, if you have a white wall with a dark object on it and you put your focus point in between the wall and the object, your camera will instantly acquire correct focus. My recommendation is to place the rectangular focus area to an area with the most contrast. Examples are: edges of objects, lines separating different colors, numbers and letters printed on objects, etc.
    • Focus multiple times until you can clearly see in the viewfinder that the object is in focus. For this one, you need to have a good viewfinder and a good vision. Some entry-level DSLRs have a very small viewfinder, making it hard or sometimes even impossible to see if you are getting correct focus. Unfortunately, there is not much you can do if you cannot tell if the subject is in focus by looking into the viewfinder, so just take multiple pictures while constantly re-adjusting the focus and review images on the camera LCD.
  • Make your subject freeze. If you are photographing a person, have them freeze and not move while you take their picture. When you work with slow shutter speeds, even if you do everything right, your images might still come out blurry just because your subject moved while the shutter was open. This is called motion blur. Sometimes people like the effect of the motion blur, especially for high-speed objects like cars. To reproduce this effect on your camera, set your camera to Shutter-Priority mode, then set your shutter to 1/100 of a second or less. Ask your subject to move his/her hand quickly, while not moving the body. The result should be a sharp picture of the person’s body, while having a motion blur on his/her hand.

    As you can see from the above image, everything in the image is sharp, while the fan is blurred through motion blur, that I specifically created by shooting the image in low shutter speed of 1/20 of a second (the image was shot hand-held).
    Here is another example of motion blur that I shot at night on a tripod (shutter speed is 2 seconds):
    NIKON D700 @ 70mm, ISO 200, 2/1, f/8.0
  • Make sure that your vibration reduction (VR on Nikon) or image stabilization (IS on Canon) is set to “On” on your lens, if you have it. Many of the consumer zoom lenses have some sort of anti-shake/vibration reduction technology in them, allowing one to shoot at lower shutter speeds and still get sharp images. If you have one of those lenses, go ahead and try lowering your shutter speed to a lower value. You can even lower down the “minimum shutter speed” in your Auto ISO settings to something like 1/50 of a second and still get sharp images.
  • Get a good fast prime lens such as the Nikon 35mm f/1.8 DX or 50mm f/1.4 / f/1.8 lenses. These prime lenses are relatively inexpensive, ranging between $200 to $400 for the f/1.4 model. Very few zoom lenses can achieve the same optical quality as the prime lenses, because prime lenses have simpler design and are optimized to perform for only one focal range. Although you lose the ability to zoom in and out, prime lenses are much faster than most zoom lenses and are excellent choices for low-light and portrait photography. Because of the shallow depth of field, they are also capable of producing pictures with beautiful bokeh (nicely blurred backgrounds). When I got my hands on my first prime lens, I just could not believe how much of a difference it made in terms of sharpness. If you have never used a prime lens before, give it a try and you will not regret it.
  • When photographing people or animals, always focus on the closest eye to you. This is very important, especially when dealing with large apertures between f/1.4 and f/2.8. As long as the eye of the subject is sharp, the image will most likely be acceptable. Take a look at this photograph of my son Ozzy:
    Normally, I delete images like this, but I’m glad I kept it for this article. As you can see from the above image, I failed to acquire correct focus on Ozzy’s eye and somehow focused on his hair instead.
    Now, compare it to this image:
    NIKON D700 @ 50mm, ISO 200, 1/320, f/2.0

    Such a big difference between the two. The second image looks much sharper, although I was using the same camera settings.
  • Aperture also plays a big role in achieving optimal sharpness. For landscape photography, I mostly use apertures between f/8 and f/10, while for portraits, I use apertures of f/1.4 to f/8, depending on what I want to do with the background. Most lenses are sharpest between f/5.6 and f/8, so if you are shooting during a bright sunny day, try increasing your aperture to a number between f/4 and f/8 and see if it makes a difference. Just keep in mind that playing with aperture changes the depth of field and will have an impact on the lens bokeh.
  • Clean your lenses! An amateur photographer approached me once and asked for advice on what he could do to bring more contrast and sharpness to his images. When I saw the front element of his lens, I immediately made a suggestion to clean his lens. It was so dirty that I couldn’t believe he was still able to take pictures. A dirty and a greasy front element of the lens is a guarantee to inaccurate camera focusing and poor image contrast. If you don’t know how to do it properly, check out my article on how to clean DSLR lenses.
  • Get a tripod for low-light situations (see my article on how to choose a tripod). For shooting lightning storms, fireworks, city lights and other cool stuff at night, a sturdy tripod is a must! Don’t buy a cheap tripod designed for point and shoot cameras, but rather invest in a heavy duty, sturdy tripod that can handle your DSLR. Having a self-timer mode or a cable/wireless shutter release is also very helpful, to minimize camera shake. The below image would not be possible to capture without a tripod:
    NIKON D700 @ 40mm, ISO 100, 5/1, f/16.0
  • Shoot in bursts. Set your camera to AF-C (Auto Focus in Continuous Mode), then photograph your subject in bursts by just holding the shutter button. Shooting moving subjects continuously (especially children) helps improve the odds that you’ll get a shot that is spot-on. Firing off 3 or 5 shot bursts can also help freeze the motion of your subject, especially when with a bit of panning. Sometimes you’ll get just enough of the face (of say a happily-running kid) in focus then everything else gets blurred because of the motion, leaving you with a nice isolation that highlights the emotion of that moment. This valuable tip was provided by our reader Eric.




发表于 2015-11-4 09:01:35 | 显示全部楼层
老满说,我们很多社员还停留在把照片拍清楚的阶段。。。。
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 楼主| 发表于 2015-11-4 14:43:54 | 显示全部楼层
moonbay 发表于 2015-11-4 09:01
老满说,我们很多社员还停留在把照片拍清楚的阶段。。。。

惭愧啊,我还在这阶段摸索呢,追赶老满是没希望了
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发表于 2015-11-5 02:32:14 | 显示全部楼层
俺已经过了这阶段了。

远近看不清楚
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发表于 2015-11-5 14:27:44 | 显示全部楼层
好文章。
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