We've seen a stunning revolution in photography since digital cameras were introduced in the 1990's. The quality, convenience, and instant gratification of digital cameras have made them far more popular than film cameras, but the fundamental principle is the same: when you take a photo, light is gathered by a lens and focused onto a light-sensitive material. In the olden days that material was film, with tiny silver halide crystals that have a chemical reaction when exposed to light. In a digital camera the material is an electronic image sensor, with millions of tiny light-sensing components called photosites. Typically, there's one photosite for each pixel in the produced image, so a 16-megapixel camera has 16 million photosites.
Digital Camera Types: DSLR, MILC, and P&S
There are three basic types of digital camera. The most complex type, shown below without a lens, is the digital single-lens reflex camera, or DSLR. The distinguishing feature of a DSLR is its reflex mirror, which reflects light from the lens up to a pentaprism (or a pentamirror) and out through the viewfinder, letting you see exactly what the camera will see. The reflex mirror is semi-transparent in the center, allowing some light to pass through to a secondary mirror and the autofocus sensor, which is a separate sensor used to focus the lens. When you fully press the shutter button, the reflex mirror and secondary mirror flip up out of the way, and a high-speed mechanical shutter opens to let the light go straight through to the image sensor.
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| Light path through a digital single-lens reflex camera (DSLR), with the reflex mirror in place |
The second type of digital camera is the mirrorless interchangeable lens camera (MILC), also called EVIL for electronic viewfinder interchangeable lens. Like a DSLR, a MILC lets you attach a variety of lenses to the camera body. Unlike a DSLR, a MILC has no reflex mirror — with the shutter open, the image sensor is always exposed to light coming though the lens. Also, the image sensor in a MILC is usually smaller than the one in a DSLR. These differences allow a MILC's body and lenses to be much smaller and lighter than those of a DSLR.
However, the MILC has two disadvantages when compared to the DSLR. Without a reflex mirror, the MILC lacks an autofocus sensor, instead using the image sensor to autofocus. This method of autofocusing (called contrast detection) is slower than the method used with an autofocus sensor (called phase detection), especially when trying to focus on a moving subject. With phase detection, the camera can usually estimate the distance to the subject with a single read of the autofocus sensor, and focus the lens accordingly. But using contrast detection, the camera has to read the image sensor at least twice to judge the subject's distance, changing the focus between reads. When shooting roller derby, it's critical to be able to focus on skaters as quickly as possible.
The other disadvantage of the MILC is that it tends to have more visible sensor noise than a DSLR, which gives images a mottled, grainy appearance. The reason for this is the MILC's smaller image sensor, with smaller photosites. When comparing two cameras with the same number of photosites (for example, 16-megapixel cameras), the one with smaller photosites will usually have more visible sensor noise. This is particularly important when shooting in dim light (like most derby venues), because the camera must greatly amplify the signal it gets from each photosite, and the noise gets amplified as well. The level of amplification is called the ISO setting, which I'll discuss more in a later post.
The third type of digital camera is commonly called point-and-shoot (P&S). All P&S cameras have a built-in lens that can't be removed. Like a MILC, the P&S has no reflex mirror or autofocus sensor, so it uses contrast detection to autofocus. And most P&S cameras use even smaller image sensors with tinier photosites, resulting in yet more visible sensor noise. To make matters worse, the lens on a P&S camera is rarely fast enough for action shots in low light (and I'll explain what I mean by "fast enough" when I discuss lenses in the next post). The same drawbacks are even greater in the P&S cameras found in cell phones, where the lens and image sensor are incredibly tiny.
Given the current state of technology, a DSLR is the best choice for shooting derby. Its phase detection autofocus will probably outperform the MILC's contrast detection for a couple more years, and its larger image sensor and photosites will continue to produce less visible noise. In addition, the selection of lenses and flashes is much greater for DSLRs than for MILCs. We might reach a point when MILCs are "good enough" for derby, but it's likely that DSLRs will always be better.
Which DSLR to Use?
So among all the DSLRs, which one should you get? The first decision to make is also the biggest: which manufacturer to choose? This matters a lot because the lenses and accessories you buy can be used only with cameras from one manufacturer. Lenses and flashes for a Canon DSLR can't be used on a Nikon camera, or vice versa. You'll probably end up spending more money on lenses than the camera itself, so in the future when you want to upgrade to a newer camera, you'll be "locked in" to that manufacturer unless you sell everything and start over with new equipment.
The market-leading DSLR makers are Canon and Nikon, with Sony in third place, and Pentax and Olympus far behind. Canon and Nikon have the largest variety of cameras and lenses, both at consumer-level quality and professional quality, with prices to match. Sony has a pretty good lineup as well, with one interesting feature: a translucent reflex mirror that's fixed in place to allow continuous use of the autofocus sensor even while shooting a photo or video. But despite Sony's recent advances, I have to recommend either Canon or Nikon. Most pro photographers use one of those two, so they're the brands you're likeliest to find when looking to rent an expensive lens. If you already have another brand of DSLR, it's not the end of the world — stick with it unless you run into problems or limitations that can't be solved.
Between Canon and Nikon, the choice is practically a toss-up. I picked Canon when I bought my 10D camera in 2004, because back then Canon had a slight edge in image quality and sensor noise. Since then, Nikon has caught up and even surpassed Canon in some areas. But overall, it comes down to personal preference. If you really like the feel of a particular camera, or you have a friend who'll help you learn it (and maybe let you borrow a lens or two), those are perfectly good reasons to choose one brand over the other.
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| A favorite shot from my Canon 10D (1/350 sec, f/2, ISO 1600, no flash) |
Each manufacturer divides its cameras into several price tiers, ranging from entry-level to professional. Most features are available in cameras at every tier, but they vary in performance or sophistication. Here are the differences you'll find in the major features, in order from most to least important (in my humble opinion, of course):
- Autofocus performance: More expensive DSLRs use more advanced autofocus algorithms, which can track a moving subject more quickly and accurately than an entry-level camera. They also have more autofocus points, which are the fixed points within the viewfinder frame that the autofocus sensor can "see". Most of the time you'll select a single autofocus point to use, so the actual number of points doesn't matter much. What's more important is that your selected point be of the "cross-type" variety, which can focus on both horizontal and vertical details. The center one is always a cross-type point, but in mid-range and high-end cameras more of the other autofocus points are cross-type, giving you more flexibility.
- Image sensor quality: Camera makers are still packing more megapixels into their higher-end cameras, but for most uses even 10-megapixel resolution is more than enough. The main advantage of having higher resolution is being able to crop a photo and still have enough detail left for a poster or magazine spread. Recent improvements in image sensors have dramatically reduced sensor noise, providing usable image quality up to ISO 6400 or even higher. Even entry-level DSLRs are very good in this respect, but the current models outperform ones from 2 or 3 years ago, and they'll likely get even better in the next few years.
- Image sensor size: The image sensor in most DSLRs is one of two sizes. High-end cameras usually have a full-frame sensor, which is the same size as a 35mm frame of film (36 x 24mm). Entry-level and most mid-range DSLRs have a smaller sensor called APS-C, which is roughly half as large. There are advantages to each size. A full-frame camera has a bigger and brighter viewfinder, and its image sensor either has more photosites (for higher resolution) or larger photosites (for less visible sensor noise).
When using an APS-C camera, the focal length of each lens is effectively multiplied by a "crop factor" of 1.5 (for Nikon) or 1.6 (for Canon). For instance, a 200mm lens on an APS-C camera gives practically the same view as a 300mm or 320mm lens on a full-frame camera. That's handy when you're trying to get a close-up shot, but it works against you for wide-angle shots. Also note that some lenses are designed specifically for APS-C cameras and can't (or shouldn't) be used on full-frame cameras — these are Canon's EF-S and Nikon's DX lenses. But lenses designed for full-frame cameras — Canon's EF and Nikon's FX lenses — can also be used on APS-C cameras. - Burst rate: The burst rate is the number of frames per second (fps) that a camera can shoot in continuous-fire mode. It ranges from 2-4 fps on entry-level cameras to 10-11 fps on professional cameras. I rarely shoot more than 5 fps, because the action in roller derby isn't fast enough to justify it. Note that the burst rate is separate from the shutter speed, which determines how long the shutter is open for each shot. When I'm shooting at 5 fps, the shots are 1/5 second apart, but the shutter is open for only a fraction of that time — often 1/500 second.
- Burst buffer: When you take a series of photos, they're temporarily stored in the camera's buffer memory before being written to the flash memory card. The buffer size determines how many continuous-fire shots you can take before the buffer memory fills up and the burst rate slows down. A typical entry-level camera has a buffer size of 5 to 10 shots, whereas a high-end camera can shoot 20 to 30. My burst sequences are rarely longer than 5 shots (one second of continuous shooting at 5 fps), so even a small buffer size should be fine. Note that cameras have different buffer sizes — and sometimes different burst rates — for RAW and JPEG images. For reasons I'll explain in a future post, you should plan to shoot in RAW mode, not JPEG.
- Viewfinder brightness and coverage: As mentioned above, a DSLR with a full-frame image sensor has a bigger and brighter viewfinder than one with an APS-C sensor. Another factor that affects the viewfinder quality is whether a pentaprism or a pentamirror is used to direct the image from the reflex mirror to the viewfinder. A pentaprism is a solid block of glass that produces a brighter and more accurate viewfinder image than a pentamirror, which is lighter in weight and found in entry-level cameras. Higher-end cameras also tend to have greater viewfinder coverage, which is the percentage of the captured scene that's visible in the viewfinder. In a camera with 100% coverage, the image sensor captures exactly what you see in the viewfinder. In one with 95% coverage, the image sensor captures an extra 5% of the scene beyond the edges of the viewfinder. But these effects are relatively minor compared to the big difference between full-frame and APS-C viewfinders.
- Build quality: Entry-level DSLRs are built to be lightweight and inexpensive, which means using plastic bodies and light-duty moving parts such as the shutter and reflex mirror. Mid-range and especially pro cameras sacrifice lightness for durability, using metal bodies — often with weatherproof seals — and heavy-duty moving parts that last longer before they break. Unless you plan to use your camera in the rain or shoot more than 100,000 photos before upgrading to the newest model, it's not worth paying extra for higher build quality.
- Live view: Live view mode lets you compose a shot using the camera's LCD screen instead of the viewfinder, by raising the reflex mirror and opening the shutter to let light onto the image sensor continuously. It can be useful for shots that would otherwise be hard to compose, such as holding the camera overhead or down at floor level. But the camera uses the image sensor to autofocus in this mode, because the secondary mirror is also raised and can't direct any light to the autofocus sensor. As with a MILC, contrast detection is used instead of phase detection, so the autofocus becomes slower and less accurate for moving subjects. I seldom use this feature.
- Video capability: Video recording with DSLRs is a relatively new feature, having first appeared just a few years ago. I'll admit that I almost never shoot video, since the skills required are vastly different, and I'm not very good at it. Technically, it works in a similar fashion to live view, using contrast detection to autofocus. Due to the "rolling shutter" nature of the image sensor, the subject may look distorted when you pan the camera. I'm sure DSLR video capability will be improved in future models, but frankly it just doesn't interest me. If video is important to you, please look elsewhere for advice.
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| A recent favorite from my Canon 1D Mark IV (1/500 sec, f/3.2, ISO 3200, three remote flashes) |
I spent over a year shooting derby with my Canon 10D before I started feeling limited by it, particularly by the speed of its autofocus. On the advice of fellow derby photographer Michael Coyote, I decided to upgrade to a professional camera and in 2007 I bought a Canon 1D Mark III. The improvement was noticeable immediately, and although I still had many out-of-focus shots, I gradually got better at tracking skaters in the viewfinder to maintain focus. Coincidentally, that model was plagued with autofocus problems (compared to Canon's previous pro models), and last year I upgraded again to a 1D Mark IV. The differences are subtle, but I find myself getting more razor-sharp images and fewer almost-sharp images.
Despite my experience, I'm not recommending that you run out and buy a professional camera. I don't even recommend that you buy the best camera you can afford. You should buy a DSLR with the understanding that digital camera technology is rapidly advancing, but lens technology is relatively mature. If you buy a new DSLR today, future improvements will probably tempt you to replace it within 5 years. But a high-quality lens will satisfy your needs for 10 years or more, even if you replace your camera — provided that your new camera is from the same manufacturer as the old one. So plan to spend at least as much on lenses as on your camera, and divide your budget accordingly. In my next post, I'll write about the qualities to consider when selecting a lens.
I hope this overview has been helpful. Please let me know if it's too technical, not technical enough, or just right. And if anything I've said is unclear or incorrect, please call it out in the comments below. Jam on!
