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了解物镜
Match your objective to your imaging task
A microscope objective is composed of a complex set of lenses and optics, and different objectives are designed for different imaging tasks. Capturing good images relies on choosing the correct objective.
Learn the correct magnification for your experiment and how to tell if your objective can be used with air, oil, or other immersion media.
 | 为您的成像靶标选择最合适的物镜显微镜的物镜由一套复杂的镜片和光学元件组成，不同的目镜针对不同的成像目的而设计。能否捕获良好的图像，取决于物镜的选择是否正确。 您可以在本节学习到如何在实验中正确校正放大倍率，以及如何在空气、油或其他浸没介质之中使用物镜。 |
Topics in this section
Understanding your objective
The objective is an essential part of the microscope and can greatly influence image quality. Objectives come with lots of information written on them, and most of it is written in code. But don’t worry; it’s easy to decipher.
Figure 1. Common notations found on objectives and what they mean.
Selecting the right magnification
Magnification tells you the optical magnification the objective provides
Magnification tells you the optical magnification the objective provides. The magnification you choose depends on what you want to see. The usefulness of magnification will be limited by your resolution. Making a big fuzzy blob of light even bigger won’t give you a better picture. Provided you have similar resolution at different magnifications, using higher magnification will allow you to see smaller things (such as organelles inside a cell) better. On the other hand, using a lower magnification will give you a better image of the big picture—such as a field of cells or interactions between cells.
Figure 2. Same field of cells captured at different magnifications. Each magnification can offer different information, and the best choice for your experiment will vary depending on what you want to know.
Matching immersion medium to objective
The Immersion medium is what's between the objective and the coverslip (or the bottom of the dish or flask that holds your sample).
Each objective is designed for a specific immersion medium, which is marked on the objective. The main types of immersion media are air, oil, and water. It is important that you never put air objectives in oil or other liquids. Doing this will make the person in charge of the microscope really angry! The main purpose of using different types of immersion media is to minimize the refractive index differences that are present in the space between the objective and the sample. This includes the substrate (i.e., glass coverslip) that the sample is on and the imaging medium (i.e., buffer) that the sample is in. Minimizing this difference will result in better image resolution.
Figure 3. Use of immersion media matched to the objective can minimize the refractive index differences between the objective and the sample.
Refractive index
Light will travel through different types of materials at different rates. When light travels through one material (such as air) and into another (such as water), the light is refracted. It appears bent. For instance, when you put a pencil in a glass of water and view the glass from the side, the pencil will look bent. This is because air has a different refractive index than water.
Numerical aperture and the refractive index of immersion medium
Numerical aperture is a property of the objective that indicates how good the resolution can be in the image you collect (basically how much fine detail you can see).
Lots of times, you will hear people talk about the “NA” of an objective. “NA” stands for numerical aperture and its value partly depends on the refractive index of the material that is between the objective and the glass coverslip that your sample is on. In general, objectives with higher NA give you better resolution. Higher NA objectives often have higher magnification and use some sort of immersion medium. Immersion medium is used to alter the refractive index of the space between the objective and glass coverslip so that it is closer to the refractive index of the glass coverslip itself. This minimizes refraction and loss of light, ultimately giving you a better image.
Figure 4. The pencil appears bent or broken because the refractive indexes of water and glass are different than that of air.
了解物镜
物镜是显微镜的基础组件，对成像质量有着很大的影响。物镜上写有很多信息，多数为代码的形式，但您也不必担心，这些内容破译起来并不困难。
图 1. 物镜上常见的标识及其含义。
选择合适的放大倍数
放大倍数表示物镜提供的光学放大倍率
放大倍数表示物镜提供的光学放大倍率。具体选择哪一种放大倍数，取决于您希望观察的样本。放大倍数的使用情况也要受到分辨率的限制。将一大片模糊的光团放大，并不一定会使图片的清晰度更好。假定您在不同放大倍率下具有相似的分辨率，则提高放大倍率能让您观察到更微小的对象（例如细胞内的细胞器）。但另一方面，使用低放大倍率则能获得更清晰的大图 – 如细胞视野或细胞间相互作用。
图 2. 在不同放大倍数下捕获的细胞视野。每一放大倍数均可提供不同的信息，最适合的选择很大程度上依赖于您希望观察的内容。
为物镜选择合适的浸没介质
浸没介质是物镜和盖玻片（或者您盛放样品的培养皿或培养瓶底部）之间的物质。
每一种物镜都针对某一种浸没介质而设计（物镜上有所标注）。主要的浸没介质类型有空气、油和水。因此，您务必要注意，切勿将适用于空气的物镜放在油或其他液体之中。否则会令显微镜的管理人员发狂！之所以要使用不同类型的浸没介质，目的是为了最大限度降低物镜和样品之间的空隙内存在的折射率差异，这其中就包括放置样品的基底（例如，盖玻片）以及样品所处的成像介质。最大限度降低这种折射率差异，才能实现更好的图像分辨率。
图 3. 使用适合于物镜的浸没介质可以最大限度降低物镜和样品之间折射率差异。
折射率
光线通过不同类型的材料时，会存在不同的速率。当光线穿过某一种材料（例如空气）进入另一种材料（例如水）时，会出现折射。在此过程中，光线会有所弯曲。例如，当您将一根铅笔放入一玻璃杯水中时，从玻璃杯的另一侧观察，您会发现铅笔好像已经弯曲了。这是因为空气和水的折射率不同所致。
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是指为了实现不同类型相差提高分辨率，物镜中含有多少组矫正镜片。矫正镜片有助于校正光线穿过物镜时的光线弯曲路径等，以确保视野边缘和中间一样清晰；此外，在不同波长的光线穿过物镜内的镜片时，它们还可校正光线的不同行为。
样品通常封固在玻璃盖玻片上。最常见的的玻璃盖玻片名为#1.5盖玻片，厚度为0.17 mm。印在物镜上的盖玻片厚度数值表示物镜设计的最佳玻璃盖玻片（或任何您放置样品的基底，例如，塑料底器皿）厚度。
有些物镜具有较长的工作距离，这就表示该物镜可以在较大的盖玻片厚度范围内获得良好的图像。如果您希望透过塑料底器皿和T-75培养瓶等比玻璃底器皿更厚的器皿观察成像，这一类物镜较为适合。为获得最佳的成像效果，在制造长工作距离物镜内的镜片时，需考虑如何适应不同厚度的镜片。
有些物镜带有手动调节环。您可以将调节环转到与您的样品盖玻片厚度对应的特定数字，但并非所有的长工作距离物镜都有调节环。
The working distance is the distance between the objective and the cover glass, or between the objective and the top (or bottom) of whatever vessel you are imaging through, when your sample is in focus. When you are imaging through something thin, like a cover glass, you can use objectives with shorter working distances. But when you are imaging samples that are in a thicker vessel, such as a plastic plate or dish, you will probably need an objective that has a longer working distance. The working distance of an objective is often written on the objective. The working distance of the objective in this example is 7.4 mm. It is considered to have an ‘extra-long working distance’ and is abbreviated as ELWD on the objective.
仅供科研使用，不可用于诊断目的。