Cameras are improving amazingly quickly, year after year for the past 20 years, since digital cameras became widely available. During the first half of this development period, the emphasis was on improving resolution: the number of pixels. This trend was complemented by improvements in computers – CPUs, memory and storage, and internet bandwidth – to handle larger and larger image and video files. At the same time, sensors were being miniaturized; all those millions of pixels were being compressed into smaller and smaller spaces. In the past 7 years or so, the emphasis has shifted more towards sensor sensitivity; cameras can see in the dark almost as well as human eyes now.

These rapid changes make deciding on a new camera difficult. Whatever you choose, a better camera will come along within a year for the same cost. Such is the price of progress. One aspect has not changed: you’ll have to pay more for a wider range of features, and even more for the ability to control all those features directly, which is what you’ll need for flow vis.

On this page, we’ll go over six types of cameras: DSLRs, mirrorless, point-and-shoot, phone cameras, video and high-speed video. In each category, you’ll find that some cameras offer the basic controls you need, and some may not, or the controls are so buried in menus that they are useless. What you want to look for in a camera for flow vis is manual control over focus, focal length (zoom), aperture, shutter speed, and sensitivity (ISO). If you are shooting video, you’ll want control over frame rate too. It’s also nice to have the ability to use high-quality file formats, but that’s not an absolute requirement. If some of these terms are mysterious to you, don’t worry, we’ll go over each in depth in the next few sections.

Once you know what kind of control you want over your camera, you MUST RTFM: Read the *ahem* Freaking Manual for your camera. All cameras are different, even within one manufacturer’s products, and you’ll want the details for your exact model. Yes, you can probably find out certain details from YouTube, but they won’t be as comprehensive as your specific camera’s manual.  Artists and engineers alike must know their tools.

DSLR: Digital Single Lens Reflex

This is the standard type of camera for serious photographers. They come in an astonishing variety of quality, features and prices. They have two features that distinguish them from other types of cameras. One is that the photographer can look through an optical viewfinder to see exactly what will be in the image, although most cameras also have an LCD screen on the back for viewing and menu controls. Figure 1 shows where the name comes from. During composition, the image comes in through the lens, bounces up from an angled mirror, is formed on a ground glass screen and then bounces through a pentaprism make the image right side up. When the shutter button is pressed, the mirror snaps up out of the way (that’s the reflex part), the shutter opens and the image goes straight through onto the sensor.

Image stabilization is an increasingly common feature; this will compensate for small amounts of shake caused by humans holding the camera. If the shutter is open for more than 1/30 of a second, camera motion can make the image smear on the sensor. Also, the stronger the zoom you are using, the more the image is likely to smear even at short shutter times. Manufacturers compensate for camera motion in one of two ways; by moving elements inside the lens to counteract the motion (Canon and Nikon) or by moving the sensor itself (Sony and Pentax) . Of course, you can always use a tripod to hold the camera steady, but be sure to lock the mirror up or the reflex action itself will shake the camera.

The other feature that all DSLRS share is that the lens is interchangeable with other lenses having the same mount type. Each manufacturer has a unique mount type to try to force users to buy lenses from them, although there are third-party manufacturers who make compatible lenses. Be careful when shopping for third-party lenses; image stabilization may or may not be included and may or may not be compatible with your camera.

The advantages of DSLRs over smaller cameras are many. The optical viewfinder works well even in bright sunlight. There are tons of lenses of varying focal lengths and quality available.  Most importantly for flow vis, DSLRs allow manual control over focus, aperture, shutter speed and sensor sensitivity. They all have various automatic exposure and focus modes. They may also shoot great video, including a limited slo-mo capability and may have a time lapse capability (but not commonly). They may have Bluetooth or WiFi connectivity. They may be able to store files in a high resolution uncompressed form (also good for flow vis). They all have a 1/4-20 threaded hole on the bottom to attach a tripod. Many have a built-in flash, and all have some sort of sync connection for external flash.

I’m not going to talk about megapixels of resolution, or the highest sensitivities available because that info will be obsolete long before you read this. But I do want to point out that all those pixels are fit onto sensors of specific sizes, as shown in Figure 2. ‘Full frame’ refers to the size of a ’35 mm’ film image, the previous standard for general photography. The next row down shows typical DSLR sensor sizes, and on down to the 1/2.5 inch common in cellphones. This is important because large sensors collect a lot of light, and this means large sensors have a better signal-to-noise ratio than small ones and so perform better in low light, another plus for the DSLR.

The primary disadvantage of DSLRs is that they are large, heavy and often expensive, especially the lenses. Surprisingly, smaller cameras may be better for macros because of how optics scale. DSLRs can certainly shoot excellent macro (close up) photographs, but will require special lenses and attachments to do so.

Another caveat is that generally you are stuck with the software that your larger cameras come with, although there are some hack projects that let you change the firmware, especially for Canon cameras .

Mirrrorless

A mirrorless camera is just like a DSLR, without the optical viewfinder, so no mirror, no reflex. You’ll find the same interchangeable lenses and features (though the lenses themselves are not always interchangeable between a DSLR and a mirrorless camera, even from the same manufacturer). This type of camera is gaining rapidly in popularity; it’s more compact and lighter than DSLRs. If you are OK without the optical viewfinder (maybe you rarely shoot outdoors), then this is a good choice.

Point-and-Shoot

These are compact cameras with lenses that you cannot swap out. They may have a great range of focal lengths (superzooms) to compensate. They may have an optical viewfinder, but it won’t be through the lens that goes to the sensor, so exact framing may not be possible. They are generally lightweight, rugged and cost-effective, but cellphones are competing hard for this end of the market. They are sometimes called PHD cameras, an acronym for Push Here Dummy, meaning that they have automatic features to get you great images of friends and pets with no effort on your part. Probably not so great for flow vis. Look for those manual control options mentioned above, and check that the controls are reasonably accessible.

Cellphones

The cameras in cellphones have to be tiny and flat; lenses that stick out from the phone are just not acceptable, and the sensors have to match the lenses. This leads to certain limitations. One is that the aperture is fixed, i.e., the diameter of the hole that the light enters the camera through cannot change size. This is in contrast to all other types of camera. Besides affecting the amount of light that the camera captures, the depth of field remains fixed, too (more on that later). The range of zoom is limited, too, but it may seem large because of ‘digital zoom;’ the lens doesn’t change but software makes it seem like it does. To get around these limitations, manufacturers are starting to include multiple cameras on phones, up to five, with different focal length lenses and different sensors to match . Some of these cameras include monochrome (black and white) sensors that are better in low light, or infrared time-of-flight cameras for depth sensing. Information from the multiple cameras are combined automatically, transparent to the user.

Smartphone cameras are also different because there are apps you can get that allow you better control over your photos. The apps for phones are inexpensive ($10 to $20) and give you good control over focus, shutter speed and ISO. If you are going to use your phone camera for flow vis, I highly recommend you invest in one of these.

One more benefit to phone cameras comes from the tiny sensors and short focal length lenses; these make amazing macro photographs possible.

Video Cameras

All of the cameras described above generally come with video capability. Cameras older than 5 years or so may not, so check for this if you are shopping the used markets. Video-only cameras for the consumer and prosumer markets are a thing of the past. All digital cameras will shoot at 30 frames per second but newer cameras and higher-end cameras are starting to come with higher frame rates for slow motion video, and may have a feature for time-lapse as well. If you want to see clouds flow across the sky (Figure 4) you’ll want one frame every 3 to 5 seconds, for example. Again, if you are shooting with a cellphone, there are apps that make this possible, if you are willing to set your phone outside for the couple of hours it takes to acquire enough frames. For larger cameras, they’ll need to have the high frame rates built in, but there are external timers available for time-lapse for almost any camera.

Then there are the action cameras,  primarily used for video, epitomized by the GoPro Hero series. These are tiny, shockproof, waterproof cameras (handy for shooting underwater). They have image stabilization, good resolution, and both time-lapse and limited slo-mo capability. Their primary drawback is that they have a fixed, wide angle lens; not interchangeable. However, there are new competitors coming on the market, so look for that limitation to go away.

Figure 4: A time-lapse taken September 4th facing the Front Range north of Colorado Springs. 1,672 pictures were taken from 10:20 AM to 12:40 PM and played back at 30 FPS. Cumulus clouds are shown building in a stable atmosphere over the mountains. Ryan Daniel, Clouds First 2016.

High-Speed Video Cameras

The last category we’ll talk about is high-speed cameras. These are not in the consumer or prosumer category; they start at $15K and go up from there. My prosumer Canon 90D can shoot full HD (1920X1080 px) video at 120 fps (frames per second) maximum. The entry-level 2016 Vision Research VR Miro C110 that CU Boulder students can use can shoot 915 frames per second at its full resolution of 1280×1024 in color, and 52,445 fps at a very reduced resolution of 128 x 8 pixels. So notice: after a certain point, the high frame rate is achieved by sacrificing resolution. This is because the buffers can only transfer data from the sensor into memory at a limited speed. Also notice that 1/54,445th of a second is a very short shutter time; your lighting needs to be very bright to be seen by the sensor in that short of a time. The camera sensitivity goes up quite a bit if it’s switched to monochrome mode, and cameras that are designed to be only monochrome are even faster.

Happily, such extreme frame rates are not often required for flow vis. Many phenomena can be captured at less than 3000 fps, allowing both color and reasonable resolution. Figure 5 is a lovely example, shot at 1600 fps.

Figure 5: Water streaming from a spinning open cell sponge forms spiral trails. Anonymous Student, Rob Vancleave, Luke McMullan and Joanna Bugajska. Team Third 2015.

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