{"slug":"astro-beginner-guide-2","title":"星空摄影技巧全揭秘，包括星轨拍摄与星空降噪技法! (下)","author":"Thomas看看世界","date":"2018-04-17","wechat":"https://mp.weixin.qq.com/s?__biz=MzI4NDA5MzE5NQ==&mid=2247486697&idx=1&sn=c5ce0453ea66fea0a538808ef142ba33&chksm=eb81f28ddcf67b9b7819fbb15b6da44cb1006c92c56179f2cfb4abf9da93e185ec062ae9fd08&scene=21#wechat_redirect","blocks":[{"t":"h","x":"本篇教程是星空摄影技巧揭秘的下篇，将从以下几方面系统讲解：","xe":"This tutorial is Part 2 of Astrophotography Techniques Revealed, systematically covering the following:"},{"t":"h","x":"（阅读前建议先学习上篇，以确保知识的连贯性）","xe":"(We recommend studying Part 1 first to ensure continuity)"},{"t":"h","x":"阅读上篇: 这可能是最详细的星空摄影入门教程，果断收藏！ (上)","xe":"Read Part 1: This May Be the Most Detailed Astrophotography Beginner's Guide — Save It! (Part 1)"},{"t":"img","f":"img-01","w":737,"h":419},{"t":"img","f":"img-02","w":1080,"h":828},{"t":"img","f":"img-03","w":433,"h":640},{"t":"img","f":"img-04","w":1080,"h":1080},{"t":"img","f":"img-05","w":753,"h":1024},{"t":"h","x":"（文中星空照片全部为作者本人拍摄，更多照片请看图虫个人主页","xe":"(All night-sky photos in this article were shot by the author. For more, see my Tuchong homepage:"},{"t":"p","x":"https://tuchong.com/957710/ 或微信：JingshuZhu）","b":true,"xe":"https://tuchong.com/957710/ or WeChat: JingshuZhu)"},{"t":"h","x":"一. 降噪处理","xe":"I. Noise Reduction"},{"t":"p","x":"由于星空拍摄的高感光度和长时间曝光，随之而产生的噪点对画质的影响是极大的，降噪成为星空摄影必不可少的一个环节。在多种降噪大法中，选用哪种方式最适宜，我们要先来了解噪点是如何产生以及种类和特征才能对症下药。","b":false,"xe":"Because night-sky shooting uses high ISO and long exposures, the resulting noise has an enormous impact on image quality, making noise reduction an essential step. Among the many noise-reduction methods, which is most suitable? We first need to understand how noise is produced, and its types and characteristics, to prescribe the right remedy."},{"t":"p","x":"数码相机的感光元件尺寸是影响噪点表现的重要因素之一，噪点的多少因传感器构造以及处理器差异而不同，各品牌各种型号的相机对噪点的控制能力也不尽相同， 但噪点问题是现在所有数码相机都没能完全克服的问题。","b":false,"xe":"Sensor size is one of the key factors in noise performance. The amount of noise varies with sensor design and processor, and every brand and model controls noise differently — but noise remains a problem no digital camera has fully overcome."},{"t":"p","x":"数码相机的噪点主要是指CCD/CMOS将光线作为接收信号并输出的过程中所产生的图像中的粗糙部分，也指图像中不该出现的外来像素，经常由电子干扰产生，使图像看起来就像布满细小的糙点。亮部接收到的信号多，信噪比高，所以噪点少，反之暗部噪点多。所以暗光环境是噪点产生的根源，使用高ISO拍摄其实并没有真正提高相机的感光度，只是将原定的电子信号放大，同时噪点也会被放大。","b":false,"xe":"Digital camera noise mainly refers to the rough parts of the image produced when the CCD/CMOS receives light as a signal and outputs it — foreign pixels that shouldn't be in the image, often caused by electronic interference, making the image look covered in fine grit. Bright areas receive more signal and have a high signal-to-noise ratio, so noise is low; dark areas, conversely, are noisy. Dark environments are therefore the root of noise. Using a high ISO doesn't actually increase the camera's sensitivity — it merely amplifies the existing electronic signal, and the noise gets amplified along with it."},{"t":"img","f":"img-06","w":821,"h":1024},{"t":"h","x":"噪点类型及特征","xe":"Noise Types and Their Traits"},{"t":"h","x":"1) 明度噪点","xe":"1) Luminance noise"},{"t":"p","x":"明度噪点呈现为颗粒状，没有颜色，和传统胶片上的颗粒十分相近。","b":false,"xe":"Luminance noise appears as grain — colorless, very similar to grain in traditional film."},{"t":"img","f":"img-07","w":1000,"h":903},{"t":"h","x":"2) 彩色噪点","xe":"2) Color noise"},{"t":"p","x":"彩色噪点的大小会是亮度噪点的数倍至数十倍，呈现为色斑，通常为洋红色或绿色，由于信噪比决定了彩色噪点的多少，导致这类噪点主要存在于图像中的暗部。","b":false,"xe":"Color noise blobs are several to dozens of times larger than luminance noise, appearing as color blotches, usually magenta or green. Because the signal-to-noise ratio determines how much color noise there is, this kind of noise mainly lives in the dark areas of an image."},{"t":"img","f":"img-08","w":1000,"h":663},{"t":"h","x":"3) 热噪点","xe":"3) Hot-pixel (thermal) noise"},{"t":"p","x":"热噪点呈现为带有颜色的亮点状，它是由于长时间曝光产生，","b":false,"xe":"Thermal noise appears as colored bright dots, produced by long exposures:"},{"t":"p","x":"感光元件长时间运作，致使温度升高，图像就会于某个固定位置出现光点。","b":false,"xe":"as the sensor operates for a long time and its temperature rises, bright dots appear at fixed positions in the image."},{"t":"img","f":"img-09","w":1000,"h":682},{"t":"p","x":"以上三种噪点中，明度噪点和彩色噪点均为随机噪点，其位置和分布皆为随机；而热噪点为固定噪点，相近的拍摄情况下，出现的位置是相同的。","b":true,"xe":"Of these three types, luminance noise and color noise are random — their positions and distribution are random; thermal noise is fixed — under similar shooting conditions it appears in the same positions."},{"t":"h","x":"五种常见降噪方法","xe":"Five Common Noise-Reduction Methods"},{"t":"h","x":"1.机内降噪","xe":"1. In-camera noise reduction"},{"t":"p","x":"机内降噪分为高ISO降噪和长曝光降噪，高ISO降噪只适用于JPEG格式，而且损失细节，对RAW格式不起作用。长曝光降噪对减少噪点有一定作用，但是拍摄时间会增加一倍。例如：打开长曝光降噪功能，30秒曝光，之后相机马上会进行30秒降噪；如果五分钟曝光，就意味着要再等待五分钟降噪时间。所以如果计划拍摄多张堆栈降噪，不可同时开启长曝光降噪功能，否则拍摄间隔时间过长，后期图像无法对齐。","b":false,"xe":"In-camera noise reduction comes in two flavors: high-ISO NR and long-exposure NR. High-ISO NR only works for JPEGs, costs detail, and does nothing for raw files. Long-exposure NR reduces noise to a degree but doubles the shooting time: with it enabled, after a 30-second exposure the camera immediately runs a 30-second dark-frame reduction; a five-minute exposure means waiting another five minutes. So if you plan to shoot multiple frames for stacking, do not enable long-exposure NR — the gaps between frames would become too long and the images couldn't align in post."},{"t":"img","f":"img-10","w":1024,"h":1481},{"t":"p","x":"《枯树与银河》由于照片中的树从湖中一直延伸至天空，很难分离地景与银河，多张平均值堆栈降噪不适宜这种场景，所以采用单张拍摄，机内降噪和后期插件降噪相结合，也可以得到不错的画质。","b":false,"xe":"In \"Dead Tree and the Milky Way\", the tree stretches from the lake all the way into the sky, making it hard to separate foreground from sky — multi-frame average stacking is unsuitable for such scenes. A single exposure combined with in-camera NR and post-plugin NR can still deliver good image quality."},{"t":"h","x":"2. Adobe Camera Raw /Lightroom降噪","xe":"2. Adobe Camera Raw / Lightroom noise reduction"},{"t":"p","x":"Adobe Camera Raw (ACR) 和 Lightroom 的降噪设置和参数是一致的，一般情况下，彩色噪点的参数默认设置不需要更改，明度噪点的参数不超过20，过高的参数会影响图像的锐度和细节。","b":false,"xe":"ACR and Lightroom share identical noise-reduction settings and parameters. Generally, the default color-noise settings need no change, and luminance NR should stay under 20 — higher values hurt sharpness and detail."},{"t":"img","f":"img-11","w":576,"h":1252},{"t":"h","x":"3.插件降噪","xe":"3. Plugin noise reduction"},{"t":"p","x":"Nik Dfine, Noiseware, Topaz Denoise都是不错的降噪插件，界面均提供了更为精细的手动选项，操作简单，其中Nik Dfine可以免费下载使用。","b":false,"xe":"Nik Dfine, Noiseware, and Topaz DeNoise are all good noise-reduction plugins with finer manual options and simple operation; among them, Nik Dfine is free to download and use."},{"t":"h","x":"4.多张平均值堆栈降噪","xe":"4. Multi-frame average stacking"},{"t":"p","x":"本文中提及的所有降噪处理中，这是一种操作复杂但是效果最好的方法，这种技术在深空摄影中早已被广泛使用。机位不动的情况下，连续拍摄6-10张，堆栈的照片越多效果越好，但是它的效应是递减的，前四张照片堆栈降噪后画质大幅提升，5-6张以后的效果就没有那么明显了，所以没有必要耗费时间拍摄太多张，我通常用4-6张堆栈降噪。由于星空的相对转动，要利用蒙版分别对天空和地面降噪，否则地面对齐后，星星就成了拉线状。","b":false,"xe":"Of all the noise-reduction methods in this article, this is the most complex to execute but the most effective — a technique long used in deep-sky photography. With the camera fixed, shoot 6-10 consecutive frames; the more frames you stack the better, but the benefit diminishes: the first four frames bring a huge quality gain, and beyond 5-6 the improvement is marginal, so there's no need to shoot too many. I usually stack 4-6 frames. Because the sky rotates relative to the ground, you must use masks to reduce noise on sky and ground separately — otherwise, once the ground is aligned, the stars become trails."},{"t":"img","f":"img-12","w":972,"h":1000},{"t":"p","x":"降噪前，放大400%细节图","b":false,"xe":"Before noise reduction, detail at 400%"},{"t":"img","f":"img-13","w":978,"h":1000},{"t":"p","x":"六张堆栈降噪，放大400%细节图","b":false,"xe":"Six-frame stacked noise reduction, detail at 400%"},{"t":"h","x":"5.拍摄暗场降噪","xe":"5. Dark-frame noise reduction"},{"t":"p","x":"这种降噪方式主要针对长时间曝光产生的热噪点，拍摄完成后，在同一环境，扣上镜头盖，使用相同参数再拍摄一张暗场照片。拍出的照片就是一张全黑图片，但仍会有热噪点的彩色亮点。利用热噪点是固定噪点的特性， 在Photoshop中导入两张照片，正常照片在下，暗场照片在上，然后的图层模式选择“差值”，就可去除热噪点。","b":false,"xe":"This method targets thermal noise from long exposures. After finishing the shoot, in the same environment, put the lens cap on and shoot one dark frame with the same settings. The resulting image is a fully black picture that still contains the colored bright dots of thermal noise. Exploiting the fact that thermal noise is fixed, import both photos into Photoshop — the normal photo below, the dark frame above — and set the layer blend mode to \"Difference\" to remove the thermal noise."},{"t":"p","x":"注意：暗场虽然只是一张全黑的照片，但必须和其它照片在同一时段同一环境拍摄，因为热噪点的产生和拍摄环境温度以及传感器温度有直接关系。","b":false,"xe":"Note: although a dark frame is just a fully black photo, it must be shot in the same session and environment as the other photos, because thermal noise is directly related to ambient and sensor temperature."},{"t":"img","f":"img-14","w":1000,"h":948},{"t":"p","x":"以上几种降噪技术是我在过去几年的拍摄中总结出比较行之有效的方法，通常会视情况结合2-3种使用以得到更好地画质。","b":false,"xe":"These are the noise-reduction techniques I've found most effective over years of shooting; I usually combine two or three of them depending on the situation for even better image quality."},{"t":"img","f":"img-15","w":1080,"h":409},{"t":"h","x":"堆栈降噪实例","xe":"A Stacking Noise-Reduction Example"},{"t":"p","x":"以上提及的五种降噪处理中，堆栈降噪是最有效，但也是操作最复杂的方法，需要精湛的前期拍摄和后期处理技术共同完成。为了便于更为直观地理解，这里用例图列举常规操作的主要步骤：","b":true,"xe":"Of the five methods above, stacking is the most effective but also the most complex, requiring refined field and post technique together. To make it easier to understand, here are the main steps with example images:"},{"t":"p","x":"1.在Adobe Bridge中选择同一机位连续拍摄的六张照片（四张-八张都可以）在工具中选择“在Photoshop中做为图层打开”。","b":false,"xe":"1. In Adobe Bridge, select six consecutively shot photos from the same camera position (anywhere from four to eight works), and under Tools choose \"Open in Photoshop as Layers\"."},{"t":"img","f":"img-16","w":1000,"h":693},{"t":"p","x":"2.在Photoshop中六张照片已做为图层被放在一个文件中，首先要做的是对齐图像，但是由于星空的相对运动，对齐地景后星星是拖尾的，所以先要给天空做选区，用蒙版把每一张照片的地景盖住，这样星空部分才可以对齐。","b":false,"xe":"2. The six photos are now layers in one Photoshop file. The first step is aligning the images — but because the sky moves relative to the ground, aligning the ground leaves the stars trailed. So first make a selection of the sky and use a mask to cover each photo's ground, allowing the sky portions to align."},{"t":"img","f":"img-17","w":1000,"h":606},{"t":"p","x":"3.在“编辑”菜单中选择“自动对齐图层”。","b":false,"xe":"3. Under the Edit menu, choose \"Auto-Align Layers\"."},{"t":"img","f":"img-18","w":1000,"h":624},{"t":"p","x":"窗口弹出，选择默认的“自动”方式。","b":false,"xe":"In the dialog that pops up, choose the default \"Auto\" method."},{"t":"img","f":"img-19","w":1000,"h":607},{"t":"p","x":"4.选中所有图层，然后从“图层”菜单中选择“转换为智能对象”。","b":false,"xe":"4. Select all layers, then from the Layer menu choose \"Convert to Smart Object\"."},{"t":"img","f":"img-20","w":1000,"h":623},{"t":"p","x":"这时六个图层合并为一个智能对象图层。","b":false,"xe":"The six layers now merge into one Smart Object layer."},{"t":"img","f":"img-21","w":1000,"h":603},{"t":"p","x":"5.接下来进行堆栈降噪的核心部分，从菜单中选择图层-智能对象-堆栈模式-中间值，完成对天空的降噪。重复上面所有步骤对地景降噪，不同的只是在第二步中用蒙版隐藏天空部分。","b":false,"xe":"5. Next comes the core of stacking noise reduction: from the menu choose Layer - Smart Objects - Stack Mode - Median to finish denoising the sky. Repeat all the steps above for the ground — the only difference is using masks to hide the sky in step 2."},{"t":"img","f":"img-22","w":1000,"h":628},{"t":"p","x":"6.由于堆栈过程中“对齐”图层这一步，不能做镜头校正，所以降噪之前未对照片做任何修改。将降噪之后的天空和地景做为图层放在一个文件中，合并后的常规调整与其它星空照片相同。","b":false,"xe":"6. Because the alignment step makes lens correction impossible, no adjustments are made to the photos before denoising. Place the denoised sky and ground as layers in one file; the routine adjustments after merging are the same as for any other night-sky photo."},{"t":"img","f":"img-23","w":1000,"h":605},{"t":"h","x":"这里提供星空原图的百度云下载链接供大家进行堆栈练习：","xe":"Here's a Baidu Netdisk download link to the original night-sky files for stacking practice:"},{"t":"p","x":"链接:https://pan.baidu.com/s/1wLPcTTWA3uofPR56ktVmiw","b":false,"xe":"Link: https://pan.baidu.com/s/1wLPcTTWA3uofPR56ktVmiw"},{"t":"p","x":"密码:u2wz","b":false,"xe":"Password: u2wz"},{"t":"h","x":"二.星轨拍摄技法","xe":"II. Star-Trail Technique"},{"t":"p","x":"拍摄星轨的原理就是由于地球的自传，星星的位置会相对旋转，利用长时间曝光，拍摄出星星在夜空中运动的轨迹。由于肉眼不可能看到这样的景象，所以拍出的画面令人感觉很神奇玄妙。","b":false,"xe":"The principle of star trails: as Earth rotates, the stars' positions rotate relative to us, and a long exposure captures their paths of motion across the night sky. Because the naked eye can never see this, the resulting images feel magical and mysterious."},{"t":"h","x":"拍摄时间","xe":"Shooting Time"},{"t":"p","x":"首先要选择晴朗无云的夜晚，其次要考虑月亮的影响，尽量在没有月亮或峨眉月前后的夜晚拍摄，月光太强会使星轨数量减少，拍出的星轨稀疏暗淡。","b":false,"xe":"First choose a clear, cloudless night; then consider the Moon — try to shoot on moonless nights or around the crescent phase. Moonlight that is too strong reduces the number of visible trails, leaving them sparse and faint."},{"t":"p","x":"有一个小技巧就是精确算好月升月落时间，利用月光给地景补光。比如月升前1-2小时开始拍摄星轨，之后机位不动等月亮升起后拍摄地景；或者在月落前约半小时拍摄地景，之后机位不动拍摄星轨。","b":false,"xe":"One trick is to calculate moonrise and moonset precisely and use moonlight to light the foreground. For example, start shooting star trails 1-2 hours before moonrise, then keep the camera fixed and shoot the foreground once the Moon is up; or shoot the foreground about half an hour before moonset, then keep the camera fixed and shoot the trails."},{"t":"p","x":"同理，机位不变前提下，也可利用日出前或日落后的蓝调时段（Blue Hour）拍摄地景，再和星轨照片后期合成在一起。","b":false,"xe":"By the same token, with the camera fixed, you can use the Blue Hour before sunrise or after sunset to shoot the foreground and composite it with the star trails in post."},{"t":"h","x":"拍摄方位","xe":"Shooting Direction"},{"t":"p","x":"尽量在远离城市光污染的地区，虽然晴朗的夜晚在城市也可拍出星轨，但是星轨数量极为稀疏，缺乏吸引力。","b":false,"xe":"Stay as far from city light pollution as possible. You can capture star trails in a city on a clear night, but they'll be extremely sparse and unappealing."},{"t":"p","x":"拍摄方向决定了星轨的形态，如果想拍出同心圆星轨必须北半球面向正北（南半球正南）拍摄，得到以北极星为圆心的星星运动轨迹。如果不能识别北极星，用指南针找准正北（南半球正南）方向拍摄即可。面向东西方拍出的星轨呈弧线。","b":false,"xe":"The shooting direction determines the trails' shape. For concentric-circle trails you must face due north in the Northern Hemisphere (due south in the Southern Hemisphere), producing star motion centered on Polaris. If you can't identify Polaris, use a compass to find due north (due south in the Southern Hemisphere). Trails facing east or west appear as arcs."},{"t":"h","x":"拍摄器材","xe":"Shooting Gear"},{"t":"p","x":"星轨拍摄的器材要求相对较低，广角中焦长焦镜头均可拍摄，超广角镜头可以拍出同心圆星轨，长焦镜头拍出的星轨呈弧线。其它附件和拍摄银河是大致相同的（详见上篇），只是快门线的作用尤其重要。","b":false,"xe":"Gear requirements for star trails are relatively low — wide, standard, and telephoto lenses all work. Ultra-wide lenses can capture concentric-circle trails; telephoto trails appear as arcs. The other accessories are largely the same as for shooting the Milky Way (see Part 1), except the shutter release is especially important."},{"t":"p","x":"拍摄银河即使没有快门线也可以完成拍摄，但是拍摄星轨最好使用具有编程功能的快门线。可以设定每张曝光时间，拍摄张数等，按下快门后相机会执行程序自行拍摄，直到程序结束。如果按照传统拍摄方法单张出片必须B门拍摄，也需要快门线才能开启B门。","b":false,"xe":"You can shoot the Milky Way without a shutter release, but for star trails a programmable intervalometer is best. You can set each frame's exposure time, the number of frames, and more; after pressing the shutter, the camera executes the program by itself until finished. The traditional single-frame method requires Bulb mode, which also needs a shutter release to engage."},{"t":"p","x":"拍星轨比较特殊的一个附件是防雾片，当拍摄地区比较潮湿，夜晚镜头长时间暴露在外容易起雾，导致拍摄失败，拍摄前用防雾片擦拭镜头可在一段时间内适当防止起雾。","b":false,"xe":"One accessory special to star-trail shooting is an anti-fog wipe. In humid regions, a lens exposed to the night air for a long time fogs up easily and ruins the shoot. Wiping the lens with an anti-fog cloth beforehand helps prevent fogging for a period of time."},{"t":"img","f":"img-24","w":600,"h":900},{"t":"h","x":"拍摄方法","xe":"Shooting Method"},{"t":"p","x":"传统拍摄方法是单张长曝光一次成片，形成同心圆星轨要至少拍摄30分钟左右，通常一小时以上才会好看，超长时间的曝光会带来大量噪点，无论是打开机内降噪还是后期降噪都是难以解决的，而且有时会导致地景过曝，同时对电池的性能也是考验。","b":false,"xe":"The traditional method is a single long exposure: concentric-circle trails need at least about 30 minutes, and usually an hour or more to look good. Such ultra-long exposures bring heavy noise that neither in-camera nor post NR can fully solve, sometimes overexpose the foreground, and also test battery performance."},{"t":"p","x":"数码时代比较流行的方法是连续拍摄多张30秒至几分钟曝光的照片，后期堆栈叠加。例如计划一小时曝光，设定单张拍摄时长5分钟，那么总共需要连续拍摄12张照片；每张曝光3分钟，需要连续拍摄20张照片；每张曝光30秒，需要连续拍摄120张照片；以此类推。那么怎样才是单张的最佳拍摄时长呢？这个问题关系到你的电脑图像处理速度。对于硬件配置一般的电脑，试想120张照片同时导入Photoshop计算会有怎样的后果，不但处理速度极为缓慢，而且很有可能发生死机的情况。而一次导入12张照片则是不同的情况，一般的电脑配置都可以应付，但弊端是只要其中一张照片拍摄出现问题，就不能连接成完整的星轨，可能会导致拍摄失败，而且不同型号相机对于长曝光产生的热噪点控制能力也大有不同。所以并没有所谓的最佳拍摄时长，要根据自己的情况自行决定。","b":false,"xe":"The popular method in the digital era is shooting a continuous series of frames from 30 seconds to several minutes each and stacking them in post. For example, planning a one-hour total exposure: at 5 minutes per frame you need 12 consecutive photos; at 3 minutes per frame, 20 photos; at 30 seconds per frame, 120 photos; and so on. So what's the best per-frame duration? That depends on your computer's processing speed. For an average-spec computer, imagine importing 120 photos into Photoshop at once — not only would processing be painfully slow, a crash is likely. Importing 12 photos at once is a different story that any ordinary computer can handle; the downside is that if any single frame has a problem, the trails can't connect into a complete whole, possibly ruining the shoot — and different camera models vary greatly in how well they control thermal noise from long exposures. So there is no single best frame duration; decide based on your own situation."},{"t":"p","x":"个人经常采用适合地景正常曝光的快门速度，我会先测试几张确定构图并得到一个最佳参数组合。具体方法是先用大光圈和高感光度短时间曝光试拍，根据拍出的图像和直方图调整构图并确定所需曝光量，再调整到合适的光圈和ISO，然后根据互易率计算出实际需要的快门速度。比如试拍曝光组合ISO12800/F4/4S拍摄到的地景和天空既有充足的细节又不会过曝，把这组参数做为正常曝光参数，调整感光度和光圈为ISO400/F5.6, 根据互易率计算出曝光时间为4分钟， 那么我就连续拍摄15张以到达总曝光时长一小时。","b":false,"xe":"I personally often use a shutter speed appropriate for a normally exposed foreground: I shoot a few test frames to lock the composition and find the best parameter combo. Specifically, I first test with a wide aperture, high ISO, and short exposure; adjust the composition and confirm the needed exposure from the resulting image and histogram; then set a suitable aperture and ISO, and calculate the actual shutter speed required via the reciprocity law. For example, if a test at ISO 12800 / f/4 / 4s captures both foreground and sky with ample detail and no overexposure, I take that as the normal exposure, then adjust to ISO 400 / f/5.6, and the reciprocity law gives a 4-minute exposure — so I shoot 15 consecutive frames for a total of one hour."},{"t":"img","f":"img-25","w":1024,"h":683},{"t":"p","x":"注意用多张堆栈叠加拍摄方法，要关闭相机的长时间曝光降噪功能，否则由于降噪要耗费一倍时间，拍出的星轨不连贯。","b":false,"xe":"Note: with the multi-frame stacking method, turn off the camera's long-exposure noise reduction — otherwise, since NR doubles each frame's time, the trails will be discontinuous."},{"t":"p","x":"光圈F2.8-F5.6之间较为常见，光圈越大拍出的星轨越明亮。ISO我通常会根据环境光情况，设置在200-800之间，低ISO拍出的画面噪点较少，画质干净。","b":false,"xe":"Apertures between f/2.8 and f/5.6 are common; the wider the aperture, the brighter the trails. I usually set ISO between 200 and 800 depending on ambient light — low ISO produces less noise and cleaner image quality."},{"t":"p","x":"和拍摄银河一样，自动对焦无法在暗光环境聚焦，需要转换为手动对焦模式（具体方法详见上篇）。","b":false,"xe":"As with shooting the Milky Way, autofocus can't lock on in the dark, so switch to manual focus (see Part 1 for details)."},{"t":"h","x":"多种堆栈叠加法的后期处理","xe":"Post-Processing for Various Stacking Methods"},{"t":"p","x":"星轨的后期合成并不复杂，有专门的合成软件，也有在Photoshop手动操作，这里介绍一个简单易学的方法。","b":false,"xe":"Star-trail compositing is not complicated — there is dedicated stacking software, and you can also do it manually in Photoshop. Here's a simple, easy-to-learn method."},{"t":"p","x":"1) 在Adobe Camera Raw 或 Lightroom对照片的明度和颜色做常规调整，包括色温，曝光，对比度，饱和度和降噪等。","b":false,"xe":"1) In Adobe Camera Raw or Lightroom, make routine brightness and color adjustments to the photos, including white balance, exposure, contrast, saturation, and noise reduction."},{"t":"p","x":"2) 将调整应用到所有的照片上，可以用批处理以保证所有调整一致。","b":false,"xe":"2) Apply the adjustments to all photos — use batch processing to keep everything consistent."},{"t":"p","x":"3) 在Photoshop中选择文件>脚本>统计，将照片载入堆栈。","b":false,"xe":"3) In Photoshop, choose File > Scripts > Statistics to load the photos into a stack."},{"t":"p","x":"4) 堆栈模式执行“最大值”，根据照片数量和电脑的硬件配置，处理速度会有所不同，可能要等一会，完成计算后，星轨就形成了。","b":false,"xe":"4) Run the \"Maximum\" stack mode. Processing speed varies with the number of photos and your hardware — you may need to wait a while. Once the calculation completes, the star trails are formed."},{"t":"p","x":"本文知识点，部分节选于笔者朱静姝 (Jingshu Zhu) 的新书《追光之路》，预计今年五月出版。","b":true,"xe":"Parts of this article's content are excerpted from the author Jingshu Zhu's (朱静姝) new book \"Chasing the Light\" (《追光之路》), expected to be published this May."},{"t":"img","f":"img-26","w":800,"h":620}],"titleEn":"Astrophotography Techniques Revealed: Star Trails and Noise Reduction (Part 2)"}