How to Get the Best Results from Ultr...

How to Get the Best Results from Ultra-Wide Lenses

从 How to Photograph Fireworks Displays 作者：Kim Brebach

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These days, most kit lenses on consumer DSLRs are wide-angle. 18mm on an APS-C sensor camera (or 27mm in old 35mm speak) is wide enough for most occasions. Ultra-wide angle lenses are those that are shorter than 16mm in focal length. It is here that we’ll strike new creative possibilities and new obstacles.

On cropped sensor lenses, a 30-35mm focal length provides what we call a ‘normal’ Field of View, which is roughly equivalent to what the human eye takes in. At 18mm, the Field of View is almost twice as wide and you can cram lots of things into the frame. At 12mm, you get 50% more FOV again, and now we’re a long way from ‘normal’ – you amost have to turn your head to take in all the detail.

The first thing you notice is the exaggerated perspective, the distorted edges and relationships between foreground and background objects that are ‘stretched’, sometimes unnaturally. Wide-angle scenes can contain many objects at different distances, which helps to draws the viewer into the scene.

There’s plenty of drama in trees and clouds, which are normally innocuous, and there is plenty of distortion as well. With wide-angle lenses, you’ll get a lot of things into the frame, some dark, others light, some near, others far, and all these contrasts push the dynamic range of your DSLR to the limit.

You’ll also get a different perspective from other lenses. As a rule, you’ll find yourself moving much closer to the subject, stepping right into the scene. Think of ultra-wide lenses as the opposite of tele lenses where you tend to back away from objects. Tele lenses tend to flatten depth of field, ultra-wide lenses exaggerate it. This makes background objects appear further from foreground ones than they actually are.

If your camera is even slightly out of the horizontal, verticals will converge. Buildings will develop leans, which adds a sense of drama to otherwise dull scenes like this one:

Sometimes you don’t want this effect, and then it’s best to make sure the horizon is in the centre of the image. You can correct perspective distortions in post-processing but you’ll end up with much smaller images by the time the edges are chopped off.

Because of the exaggerated DOF, sharpness across the whole image is often hard to achieve. Stopping down is the recommended answer but, even at f/11 or f/13, front to back sharpness at 10 or 12mm can remain elusive. In practice, you need to decide on where to focus – infinity, which will make the foreground go slightly soft, or vice versa, which will make infinity go that way. And you need to experiment with aperture to see what works best for your lens and camera.

On ultra-wide lenses, the auto-focus also faces new challenges since objects just a few meters away can be quite small and hard for the AF to lock onto. Beyond the first few meters, ultra-wide lenses tend to take a guess at focus, and that doesn’t help with sharpness – manual focus can often be a better way to go. The main thing is to decide on the visual centre, and focus on that.

Flare is a real pain with ultra-wide lenses, blowing out highlights with little provocation. The broad field of view means you often have a source of bright light not far from the frame, and that’s enough to do the damage. The best times to use these lenses are the magic hours of early morning and late afternoon, outside, or middle of the day inside. They say ultra-wides do better in winter photography where snow cancels out the difference on brightness between sky and ground.

Enter the tripod

By now it’s pretty obvious that point-and-shoot is the wrong technique for ultra-wide photography. Shooting early or late in the day, or inside, and stopping down to f/11 or more, means using a tripod. Add manual focusing and we’re back in the good old days of carefully composing each shot, following a set of rules. Not a bad idea for landscape and architecture photography, but not practical for action or street photography.

When photographing architecture, contrast is more important than resolution, and here it’s important to find and focus on the point on which all those straight lines converge.

Ultra-wides don’t make good portrait lenses unless you’re looking for cartoon-like comic effects. In close-ups, you can get plenty of distortion that exaggerates the bits in the foreground, like noses and foreheads. Ultra-wides are useful though when you want to capture people in their environment, in a shop or office or artist studio, and want to show a lot of their surroundings. Perhaps a bit too much in this case:

I’m reminded here of a friend of a friend I paid a visit to in Nelspruit, South Africa, a faded blonde whose house was full of leopard patterns – leopard skin rugs, leopard cushions, leopard place mats and even leopard coffee cups. Sadly I didn’t have a camera with me, but clearly portraits like these can convey more about the person.

Ultra-wide lenses add drama to your images and can tell stories more forcefully since they exaggerate the perspective. Like good storytellers, they show us scenes in a way we hadn’t seen them before.

8 Rules for Generating Great Results from Ultra-Wide Lenses

Here’s a short list of the basic rules to observe:

1. Include something(s) of interest in the foreground otherwise you will get vast expanses of nothing. In landscape this can mean going low to include foreground flowers for example or getting really close to rocks so that you can see the rock grain.
2. Look for strong compositional lines as this will add drama to your shots. This happens naturally with wide lenses anyway so you are just working with the natural perspective of the lens.
3. Look for interesting skies as ultra-wides capture wide expanses of sky and emphasis the lines in the cloud formations.

1. Try to keep the camera as level as possible when photographing buildings.
2. A polarising filter in clear weather can add more colour, and Neutral Density graduation filters can add a lift in cloudy weather.
3. Move in close: The closer you are to your subject, the more dramatic your images will be. Yes, I mean right up close and personal.
4. Look out for your feet and other extraneous bits that might intrude, like legs of tripods, due to the much wider FOV
5. Use a tripod for landscape shots

That’s about the size of it, or the angle. The rest is practice and experimenting to find out what works best for you and your equipment. That’s half the fun.

I’m indebted to the author of this series which provided some of the advice repeated here: http://www.prime-junta.net/pont/How_to/m_Mastering_Wide-Angle/m_Mastering_Wide-Angle.html?page=3

This article is also very useful, and a fair bit shorter

http://www.kenrockwell.com/tech/how-to-use-ultra-wide-lenses.htm

Post from: Digital Photography School - Photography Tips.

易被忽视的重要曝光知识

易被忽视的重要曝光知识

作者：佚名    来源：网络资料    责任编辑：dplee    日期：2010年06月22日

编者按：数码摄影比胶片摄影方便许多，而有些很简单、很基础、很有用的数码曝光技巧却一直被我们忽略。虽然本文作者以ＲＧＢ色彩值来说曝光并非十分严谨（应用Ｌａｂ色系的Ｌ值），但却是实际经验的总结，更具操作性。 关键字：曝光 知识 技巧

第一步，获得自己相机的曝光数据          每个型号的相机曝光数据其实都是不一样的，即使同一型号的相机曝光也有差异，所以要获得完美的曝光，我们就必须先了解自己手上相机的曝光数据。 1.首先需要一张白纸，白墙也可以，所有白色平整的东西都可以。为了获得良好的光线，最好是白天。 2.将相机设为手动对焦，焦点不用在白纸上，我们不是测镜头没必要拍得那么清楚。 3.将相机内置的对比度、色度、锐化等通通设为0。 4.将相机设为点测光。 5.将相机设为手动档，光圈大概在4到6之间就可以了（其实可以随意设，但不要太小以免碰上倒易率失效）。 6.对着白纸，调整快门令曝光补偿为0EV，按下快门，OK，我们得到一张曝光为0EV的图像。继续调整快门到曝光补偿为+1EV，按下快门，得到一张+1EV的图像。依此类推……一般到+4EV就够了，如果你对你的相机非常这有信心，可以到+5EV、+6EV……+10EV等等。同样的，令曝光补偿为-1EV，按下快门，得到一张-1EV的图像。依此类推……一般到-5EV就可以了。记得每张图像的次序。 7.将拍好的照片导入电脑。测出照片在不同EV值下的亮度。亮度的求法，直接取RGB其中的一个值，或者平均值也可以。在PS里遂张打开图像，用吸管工具吸取中间的象素(就是拍照时点测的位置)记下它的RGB值。每一张都记下来并和它的EV值对应上，整理一下，就可以做成下面这样一张表格。  这是我自己测出的数据：           　　从表格中也可以看出它们的成像风格，D70的宽容度稍小，成像对比高，DP2宽容高，所以成像对比度低，但过渡自然。而且高光位和暗位曲线平缓，能保留更多细节。 　　这就是你相机的曝光数据，这么重要的数据值得花点时间背下来，至少要记住，你的相机加到多档的时候会曝掉(亮度超过255)，或者减到多少档的时候会暗到分不出细节。还有就是在0EV时是什么亮度。最好打印成小卡片随身带着，拍照的时候掏出来看看还是有用的。  　　试想，外拍时你可以说：“你这个曝光出来的亮度值只有116，有点暗哦，如果你加一档曝光让亮度提高到160效果就好好多了。”别人一定会对你刮目相看的。

第二步，训练感觉

　　先作个小小的测试，看中间的灰色方块，你能立刻说出他的亮度（RGB值）吗？

 

 　　如果你能说出它在100~~128之间，恭喜，你可以到一下步了。

 　　如果不行的话，得花点时间训练，在PS里画些不同亮度的方块，然后记下它的亮度值，训练到你能将所有的亮度值猜得差不多的时候，ＯＫ，可以过关了。

 训练的目标是：

 　　一张图片，你只要扫一眼，就能准确说出它的亮度范围，如人脸的RGB亮度是多少，树的亮度是多少，天空的亮度是多少，到能猜个八九不离十的时候,恭喜,你离大师不远了。
当然我们只能猜出一个范围，这个范围有多小，准确度有多高，就看你对曝光的要求有多高，或者说你想离大师有多近。

第三步，测光

 

  

　　举个例子，以DP2数据为例，拍一白墙,要求在照片里的亮度是116左右，方法是点测物体，设曝光补偿为0拍摄就可以了。想让他更亮一点到207左右，就要加两档曝光；反过来图像要暗点就减曝光。就象摇控器上的亮度按钮一样。

　　现在我们可以通过曝光来精确控制墙的亮度了，但另一个又问题来了，这面墙的正确亮度应该是多少？116？或是207？

　　答案是都对，或者都错。

　　因为摄影是门创作，并非只是单纯的记录，所以我们要自己决定这面墙的亮度，这也是第二步训练的目的。我们不仅要看出照片上的亮度，还要决定照片上物体的亮度。创作的意思就是你要自己作主，而不是让相机为你作决定，除非你认为相机比你更聪明。

　　那么怎样决定照片中物体的亮度？这个话题说起来有点长，但有个笨办法，就是多看图，不一定是照片，油画水彩素描什么的都可以拿过来看，电影电视画面也可以。特别是多看大师的作品，看看大师是怎样安排物体间的亮度的。

　　记住，你要学习的是图像中的亮度关系！

 　　如果你有心，可以记下一些亮度关系，如人的脸部在亮度116时是怎么样，在207时是怎么样，在44时又是怎么样。又如一般情况下，天空的亮度是多少，树木的亮度是多少，水面的亮度是多少等等。当然记下来只是为了参考，当你按这种情况曝光时就知道是什么效果了。

　　俗话说熟读唐诗三百首，不会作诗也会吟。图片看多了你自然知道一个物体该有什么样的亮度，每次你举起相机，脑里应事先浮现一幅将要拍好的图像，你要做的就是调节相机的光圈快门使拍出来照片与你脑中的图像吻合，然后按下快门，一件作品便诞生了。对你来说这是真正的作品，因为这是你按自己意愿拍出来的，不是相机自动计算的结果。

最后再聊聊几种常用的曝光方式：

1.最亮细节保留曝光方式：

 　　这种方式适合于主体比较亮的状况，如下图花朵亮而背景暗，普通曝光模式往往会令白色的花朵过曝而丢失细节，如何保留花的亮度层次而又不能过曝？

  

　　分析一下这个场景，不能过曝就是说照片中最亮的部分不能超过255。看回我们的曝光数据表，当曝光为+3EV时亮度243，既足够亮又没有过曝，是理想的曝光值。所以拍摄前先寻找白色物体中的最亮的部分，用点测，调整曝光补偿到+3EV，按下快门，这就是最佳曝光了。

  

　　同样上面这种情况也适合，这种大面积白色如果曝光处理不好就容易令画面发灰，要保留雪的亮度而且不丢失细节，只要对雪最亮的部分点测并+3EV就可以了。

2.最暗细节保留曝光方式：   　　和最亮细节保留曝光方式类似，但是是以保留暗部的细节为主，适合于拍黑色物体。  　　不一样的是，亮度细节保留只要不超过255就可以了，但人眼的生理状态是对暗部变化不敏感，从曝光数据也可以看出，当RGB亮度值降到20以下，它们之间的差别就很难分辨，加上数码相机固有的噪点，所以最暗细节的保留不是大于0就可以了，而是尽可以将曝光后的亮度提高到一点，最好到20以上，当然指的是被拍摄主体的亮度。     　　一个黑色的镜头放在黑色的背景上，理论上它们都是黑色的是不是，但我们却不能拍成全黑的，象这种情况是，点测镜头中比较暗的部分调整补光补偿在到-3EV左右进行拍摄。这样拍出来的照片就算黑也黑得有层次。  3.保证主体曝光方式：   　　这种多用于人像拍摄或者产品拍摄， 拿mm作例子吧。   　　拍人像特别拍mm的时候，就是要拍得漂漂亮亮白白净净的是不是，如果拍成黑脸小心mm找你算帐（就算长得黑也不行），如上图，将图拖到PS里用吸管量一下mm的脸，亮度是216，对应的曝光补偿应该是在+2.3EV左右，若你下次想拍这种效果，外拍时脸皮厚点，将相机直接对到模特脸上点测+2.3EV，然后走开另找角度拍摄。放心，曝光值不会因为你的距离改变。