CHOOSING THE RIGHT DOME

By: Todd Winner

玻璃罩还是亚克力罩？ 

There are a lot of decisions when it comes to choosing the right dome port for your camera and lenses. Is a glass dome better than acrylic? What’s the proper size to use with a particular lens? These are just a few of the questions we will cover in this article as well as explain how to use the Nauticam port charts to make an informed decision.

当你需要为自己的相机和镜头选择合适的镜头罩时，你会遇到很多的问题，比如：玻璃罩一定比亚克力罩好吗？指定的镜头需要用多大的尺寸镜头罩？这些将是我们下面会谈到的，并且解释如何使用《Nauticam 镜筒兼容参照表》做出最合适的选择。

GLASS VS. ACRYLIC

Image quality: Both glass and acrylic perform very well and optical are very similar underwater. 

Price: The decisions between the two is often made on price. Acrylic domes tend to be about half the price or less of a similar sized glass dome.

Flare: Glass handles flares and shooting into the sun much better than acrylic. If your shooting style includes the sun in many of your wide angle shots than try to stick with glass. Acrylic domes often show reflections in these type of images.

Depth: Acrylic domes have deeper depth ratings compared to glass domes. Most acrylic domes are capable of 150m compared to 100m for glass. You should always check the actual depth rating of your dome as some, especially the larger domes, can have significantly shallower maximum depths.

Durability: Glass is much harder to nick or scratch but minor damage to acrylic domes can usually be repaired with polishing kits.

Balance: Glass domes tend to be better balanced and weighted underwater. Acrylic domes, especially the larger size ones, tend to tilt port up due to the buoyancy of the port. 

Splits: Glass tends to shed water better for split images but you can still receive good results with acrylic.

玻璃与亚克力的比较

l图像质量：玻璃和亚克力的表现都非常好，在水下的光学性能非常相似。

价格：两者之间的选择通常是取决于价格。亚克力罩的价格往往是同尺寸玻璃罩的一半或更少。

反光：玻璃因为内部有防反射涂层，反光情况比亚克力好的多，基本无反光情况。如果你拍摄的风格是需要在使用广角镜头下且有非常好的光线环境，你需要选择玻璃罩。亚克力罩经常在这些类型的图像中显示反射。

深度：与玻璃罩相比，亚克力罩可以去到更深。大多数亚克力罩的防水深度为150米，而玻璃罩为100米。你应该检查下你镜头罩的的实际深度，因为有些镜头罩，尤其是一些比较大的镜头罩，可能它的潜水深度会更小一些。

耐用性：玻璃很难被划伤，但亚克力罩的轻微损坏比较多通常需要用抛光工具修复。

平衡性：玻璃罩在水下的平衡性和重量更适合。而亚克力罩，特别是较大的亚克力罩，往往由于镜头罩本身的浮力，往往会使镜头罩向上倾斜。

半水面拍摄：半水面拍摄玻璃罩的效果会更好一些，水珠从玻璃材质上滑下的速度更快，但亚克力罩表现也很出色。

 在这张图上你可以看到镜头的反射。这是一个亚克力罩拍摄的。对于这张图片，如果使用玻璃罩效果会更好。

DOME SIZE

All domes are sharp in the center, so when we are comparing the image quality of domes we are concerned more with the corners and edges. In general the larger the dome the better the corner sharpness. Knowing this, it seems like the solution is to use the largest dome possible but this is not always necessary, practical or the best solution. Smaller sensor cameras can use smaller domes and still retain good image quality. This is also more practical as most users of smaller sensor cameras are concerned with size. Fisheye lenses can also use smaller domes and still retain acceptable corners. In fact, in most cases a small dome is preferred over a large dome for a fisheye. This is because fisheye lenses are able to focus extremely close and the smaller dome allows us to get physically closer to our subject. This makes them better suited for close focus wide angle and the smaller size has less drag and is easier to use in tight spaces. Rectilinear lenses will benefit from a larger size dome but you want to use what is appropriate for your sensor size and focal length. Split images also benefit from a larger size dome, creating a thinner meniscus or water line. Whenever your image contains important information in the corners it’s a good idea to stop down to retain good detail. f/8 is recommended for APS-C and M4/3 and f/13 is recommended for full frame sensors.

镜头罩尺寸选择

所有镜头罩的中心都是清晰的，所以当我们比较不同镜头罩的图像质量时，我们更关心的是边角的成像。一般来说，镜头罩越大，边角的清晰度越好。知道这一点，似乎要想边角效果好的解决办法就是选择最大的镜头罩，但是这不一定，实用的或许才是最好的解决方案。

较小传感器的相机可以使用较小的镜头罩，仍然可以保持良好的图像质量，而且这也更实用，因为大多数小型传感器相机的用户都关心镜头罩尺寸。鱼眼镜头也可以使用较小的镜头罩，仍然有可以接受的角落画质。事实上，在大多数情况下，鱼眼镜头喜欢小的镜头罩而不是大的，这是因为鱼眼镜头能够非常近距离对焦，而较小的镜头罩可以让我们身体越发接近拍摄的主体，这使得它们更适合近焦广角。更小尺寸的镜头罩阻力更小，更容易在狭小空间使用。

直线镜头受益于尺寸大一定的镜头罩，但你需要考虑哪种尺寸才是最适合相机传感器大小和焦距。半水面的拍摄需要比较大一点的镜头罩。当你需要图片角落包含更多重要信息，最好将光圈数值提高，，APS-C和M4/3建议使用f/8，全帧传感器建议使用f/13。

小镜头罩与鱼眼镜头配合的好，可以让你更接近所拍摄对象，并用它填充大部分画面。

EXTENSIONS

Using the correct extension has a huge impact on image quality. Each lens is different so it is important to know the proper length for each of your lenses. Luckily for us Nauticam is constantly testing lenses and publishes their recommendations for extensions, ports and gears in their port charts.

延伸环

使用正确的延伸环对图像质量有很大的影响。每个镜头长短都是不同的，所以知道每个镜头适当长度是很重要的。对我们来说幸运的是，Nauticam一直在测试各种镜头，并在Portchart里面不断更新，不断发布对不同镜头使用的延伸环、镜筒和变焦环/对焦环的建议。

大尺寸的镜头罩通常是拍摄半水画面的最佳选择

REMOVABLE SHADE

Circular fisheye lens like the popular Canon EF 8-15mm f/4L Fisheye USM and Nikon AF-S Fisheye Nikkor 8-15mm f/3.5-4E ED require a dome port with a removable shade. The shade must be removed before shooting at the 8mm end of the zoom range.

可拆卸遮光罩 

像常用的的佳能EF 8-15mm f/4L fisheye USM和尼康AF-S fisheye Nikkor 8-15mm f/3.5-4E ED这样的圆形鱼眼镜头需要一个可拆卸的遮光罩。在拍摄变焦范围的8毫米端之前，必须去掉遮光罩。

鱼眼图像需要一个带有可拆卸的遮光罩

PORT OPENINGS

Nauticam makes five different size port openings. Typically you will use the same size ports as the opening on your housing but there are are a number of step-up and step-down rings to use ports with different openings. This is most common with mirrorless systems that can use DSLR lens from other manufactures with adapters.

N200 found on some Cinema housings 

N120 found on DSLR, some full frame Mirrorless housings, Medium Format and some Cinema housings

N100 found on Sony full frame Mirrorless housings

N85 found on APS-C and M4/3 Mirrorless housings

N50 found on some compact housings

镜头罩开口尺寸

Nauticam有5种不同大小的镜头罩尺寸。通常情况下，需要使用与防水壳开口尺寸相同的镜头罩，但同时有很多转接环可以来使用另外不同尺寸的镜头罩。比如最常见的无反系统，可以通过其他制造商的转接环来使用DSLR的镜头

N200    主要针对于专业视频机防水壳

N120    主要针对于DSLR, 部分全画幅微单相机防水壳, 中画幅和部分视频机防水壳

N100    主要针对于Sony 全画幅微单相机防水壳 

N85      主要针对于APS-C 和 M4/3 微单相机防水壳

N50      主要针对于便携卡片机防水壳

NAUTICAM PORT CHARTS

This is a great resource to get the necessary information needed to set up a lens correctly. You can find the port charts in the learn section or in the footer of the nauticam.com site. Here is direct link: https://www.nauticam.com/pages/port-charts This is also a good place to start if you are thinking about purchasing a lens for underwater use. Chances are if it is a lens that performs well underwater it has already been tested and is on the chart. Start by finding the correct chart for the housing you are using.

Nauticam 镜筒兼容参照表

这是Nauticam厂家的资源，如果你需要为使用的镜头选择所需搭配的镜头罩以及其他配件，可以从这上面选择对应的信息。你可以通过访问https://www.nauticam.com/pages/port-charts找到portchart（镜头搭配图），这是你水下拍摄之前一个准备工作。如果您的镜头在水下会有不错的效果，那么它可能已经被测试过并且相关的信息已经在portchart中有体现。

Below is a page from the N120 Canon system Port chart. The first column shows the lens. The second shows zoom and focus gears. The third shows port bases like a step up extension. The fourth has the recommended extension length. The fifth has the recommended port often designating one as the most optimal with an asterisk if there is more than one choice. The last column shows accessories that work with that set up like flip adapters or the wet wide lens.

下面一页是通过N120佳能系统portchart举例。第一列显示镜头。第二列是对应所需要到的变焦/对焦环。第三列为镜筒底座。第四列为延伸环。第五列为推荐的镜头罩，如果有多个选择，通常用星号标注的镜头罩为最佳推荐。最后一列中还展示了与该搭配配合使用的配件，如翻转支架或者各种光学镜头等。