April 28, 2011

Getting Equipped: Cameras

I'm often asked what equipment I use for shooting derby, or what equipment I recommend. This is a tricky topic to discuss, because it requires an understanding of technical subjects such as autofocus behavior, sensor noise, lens apertures, and more. In future posts I'll cover those subjects in greater detail, but here I'll try to provide just enough background to explain the basic differences between types and price levels of equipment.

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.

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.

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.
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!


mcwheely said...

I am glad you wrote this because it means that I do not have to write it on my blog now, but rather can just link to it. :)

Peter Djordjevich said...

Don't count out MILCs because of contrast AF. Some might argue contrast AF is more accurate since it is based on what the sensor truly sees. The argument that it is slower because it requires two reads instead of one is only true if you are using the same processor to compare contrast against phase. A faster processor fixes this issue. The disadvantage is your IR focus assist lamp in the flash will not work because the sensor has an IR filter built on it. Take a look at the Panasonic GH2, really the first pro-ish MILC. It outperforms most DSLRs in the same price range.

To argue that MILCs don't have enough lenses in the portfolio is also inaccurate. All of the Olympus 4/3 and Pan/Leica 4/3 lenses work with their micro43 cameras. The adapter will allow AF to work with not impact on focus speed. The motor is in the lens, so the adapter just passes the signal along. Agains focus speed is purely dependent upon the motor speed in the lens and the processors speed.

One thing you might want to add as an advantage specifically for micro43 cameras is you can hold the camera plus 300mm equivalent lens in one hand. Plus, the doubled depth of field is a huge advantage in low light if you don't care about bokeh. Sensor crop does not affect aperture size ability to gather light. The depth of field and focal length is doubled. This is where you see the price saving when buying micro43 or 4/3 lenses. Of course, you pay a penalty going with super wide angle.

nocklebeast said...

This is a great article, really good if I were to start over with a digital SLR.

I just gotta point out that "mirror-less cameras" existed in the film era as well.... Some of them were called rangefinders back then. Only Epson and Leica have made digital rangefinders.

Anyway, a while back I wrote a blog post in the voice of a slightly over-the-top fanboy about shooting derby with a rangefinder (perhaps I'm the only derby photog that does?)


I'd hesitate to actually recommend rangefinders to a prospective derby photog, as I focus manually. About a year ago I had a conversation with a very enthusiastic photog new to derby... he had one of those fancy Canons or Nikons. The conversation began with "Hey, is that a Leica?" and ended with "It has a lot of manual controls, then, huh?" "Um... yeah," I replied.

Joe Rollerfan said...

Peter, great comments. I agree that autofocus using contrast detection has the potential to be more accurate then phase detection. And for stationary subjects, it might already be better.

My concern about the speed of contrast detection is that it will always require more lens movements. Both types of autofocus are iterative feedback systems, in which multiple readings are made. In phase detection, the first reading gives the camera a very good estimate of the distance, so after it moves the lens the second reading is usually very close to the correct focus. In contrast detection, the camera can't infer anything from the first reading — it can't tell the distance to the subject, and it can't tell whether the lens is focused too far or too close. It has to move the lens once and make a second reading just to get that initial distance estimate. I agree that the processor speed will make the extra processing time inconsequential, but the extra lens movement will always be necessary. Yes, with fast enough lens motors, this limitation can also be addressed. I expect that DSLRs and MILCs will both eventually have very capable contrast detection autofocus.

With regard to lens selection, you're right that I overlooked the Four Thirds lenses when looking at Micro Four Thirds. A few of those lenses sound interesting, particularly the 35-100mm F/2 and the 50-200mm F/2.8-3.5. If you're saying that MILCs are already "good enough" for shooting derby, you might be right. Are there any options for using off-camera flash with MILCs?

Joe Rollerfan said...

Nocklebeast, thanks for the rangefinder comments. You've captured some great shots, although I shudder (or maybe shutter) to imagine using manual focus for action shots. As an aside, phase detection autofocus in DSLRs works very similar to the focus patch in a rangefinder — the autofocus sensor "sees" bits of two images, and the discrepancy between them indicates the distance to the subject and how much to move the lens.

Peter D said...

All of the dedicated Olympus and Panasonic flashes will still work the their micro43 cameras. The only thing that doesn't work is the IR focus assist lamp. The IR lamp is normally used in extremely low light situations where ambient light isn't enough to detect focus. I use the FL-36R regularly with my E-P1 when I can't get the proper exposure at ISO 1600 or less. The new Panasonic GH2 has a built in focus assist lamp that is used instead of the external flash's.

"The Contrast Auto-Focusing system is amazingly quick in good light and the camera achieves focus almost all of the time indoors or in low-light situations, helped by the AF assist lamp. The GH2 also doesn't have any notable problems locking onto the subject in low-light situations.".

Hopefully, the upcoming pro-ish micro43 from Olympus will have something similar.


Peter D said...

Another benefit is you can adapt virtually any lens to micro43 because the mount and sensor is smaller than other manufactures. The auto focus will not work with other non-43 lenses, but you can get AF confirmation chips built into the adapter. I have a collection of Nikon FX lenses and Minolta MC/MD lenses that I use occasionally with my E-P1. Olympus has in-body image stabilization, which helps greatly when using adapted lenses.

Peter D said...

Here is a good article on how you should set your AF settings for action shots.


One thing to be aware of is the first generation Olympus E-P1 does not have AF tracking. That probably affected many reviewers opinion about slow auto focus with first generation MILCs. The E-PL1 and newer models all have AF tracking.

Peter D said...

I'm too sure about "10-megapixel resolution is more than enough". It depends on if you plan on making prints or just posting to the web. This is also why I don't like cropping even though I crop more than 90% of my shots.

10MP = 3872 x 2592 = 12.91" x 8.64" @ 300ppi
12MP = 4290 x 2800 = 14.30" x 9.34" @ 300ppi
Film Scan = 5380 x 3620 = 20MP = 17.93" x 12.06" @300ppi

If you truly want the equivalent to film quality you need about 20MP, which doesn't exist yet in a DSLR unless you include Medium Format like the Leica S2.

Interestingly, digital cinema projectors in large movie theaters only project at around 12MP. Ultra High Definition is defined as 7680×4320 or about 34MP. I think that's where the MP race will end, or at least until they defind super ultra HD.

Joe Rollerfan said...

Peter, you'll note that I said "for most uses" 10 megapixels is more than enough. I've made many 8x12" prints from 10-megapixel images, and they look fantastic. A digital film scan is limited by the grain of the film, which looks terrible even at ISO 400. For shooting derby, digital surpassed film quality years ago.

Peter D said...

I was just using film scan as an example of what to strive for because I can't see stock photography houses demand more than what film can give you. Their criteria is usually based on print size vs. web size. If your image fits their print criteria, it can be used for web, which only increases your odds of selling it. Have you tried selling derby photos on stock sites?

Some stock photography places don't allow upconverted images. 10MP looks to be the minimum today for stock photography. And you figure that minimum will probably raise to 12MP in another year or two. Alamy has a good list of what camera's are recommended for professional use.


I'm curious how do you upconvert cropped images to maintain maximum detail?

Joe Rollerfan said...

I don't use stock photo sites. I've always sold my photos myself, through e-mail. If I've cropped an image so tightly that it's too low-res for print, I won't use/sell it.

Peter D said...

The shot above is amazingly sharp for ISO3200. Why did you choose such a high ISO and wide aperture when using 3 strobes? And how did you keep from over exposing the shot?

Joe Rollerfan said...

Peter, I'll discuss this more in a future post, but there are three reasons I use high ISO and a wide aperture even when using flash: to use some of the ambient light, to reduce the flash power, and to minimize the flash recycle time. I set the flash exposure with a combination of ETTL mode and trial-and-error.

Peter D said...

Interesting interview from Panasonic talks about the AF speed.

"Now the GH2 has the world's fastest AF speed of 0.1 secs and we have incorporated the same system in the G3 with 14-140mm 10x lens. So it's as fast as the GH2. And with the kit lens 14-42mm, AF is 0.18 seconds, and with the 45-200mm it is 0.105 seconds, so our AF speed is very fast and accurate. We have exceeded all other DSLR cameras. AF contrast system is not only famous for speed but also for accuracy. If we look at auto focus probability at aperture f/1.4 we have 90% success, but conventional phase difference AF has only 60%."


Djipal said...

Great shots!
I photograph Roller Derby too (in France, Bordeaux). The main problem is the lack of light, and, of course, the lack of obturation speed. On my Nikon D3S, with fast lenses, I am often using f/3.2, 1/200s and 3200 ISO...
So I am very impresed with your pictures. Congratulations.

I have a question. On the second picture of this post, you wrote: 1/500s with 3 remote flashes. I thought the synchro flash speed of the Canon 1D mkIV was 1/300 sec. How did you used a 1/500 s speed?
Tank you very much in advance.

Joe Rollerfan said...

Excellent question, Djipal. There are two different ways to use a flash with a shutter speed that's faster than the X-sync speed.

The first and more common way is to use the high-speed sync (HSS) mode of the flash. In this mode, the flash bulb actually flickers very rapidly instead of firing just one burst of light. This produces fairly even light while the shutter curtains are moving, but it's more of a power drain than the regular X-sync mode, and it takes longer to recycle the power between shots. Using high-speed sync mode, you can shoot up to the maximum shutter speed of your camera, which is usually 1/4000 or 1/8000 sec.

The other method, and the one that I use, depends on the HyperSync feature of the PocketWizard remote flash triggers. In HyperSync mode, the trigger fires a single flash burst just as in X-sync mode, but it uses very precise timing to fire the flash exactly as the shutter curtains begin moving. (In X-sync mode, the flash doesn't fire until the first curtain is fully open.) This trick lets me use a 1/400 or 1/500 sec shutter speed on the Canon 1D4 instead of 1/300, but on other cameras there isn't as big a benefit.

Hope that helps explain things a bit. Eventually, I'll get back to this blog and write about lighting and other important stuff.

Djipal said...

Hello Joe,
Thank you very much for this detailed answer.
I knew the HSS, but I also knew that the power of the obtained light reduces hugely in this mode. So I supposed it was not the solution you used.

However, I didn't know the Pocket Wizard possibility.
It seems very intersting.
Many thanks for this information!

Joe Rollerfan said...

One more thing to consider is that in relatively dark venues, where your flash is significantly brighter than the ambient light, you don't need a fast shutter speed to freeze the action -- the X-sync speed of 1/250 or 1/300 sec should be fine. That's because the flash itself lasts such a short time, usually 1/1000 sec or less, and there's not enough ambient light to cause noticeable motion blur.

It's counterintuitive, but the darkest venues are the easiest ones to light. The most difficult venues are the ones with relatively bright light but poor color or directionality. In those venues, you need more powerful strobes to overpower the crappy ambient light, or else use faster shutter speeds to avoid motion blur.

Djipal said...

Yes, you are right, and it is important to keep it in mind.
Thank you very much.

Eugene K said...
This comment has been removed by the author.
Eugene K said...

Joe, As you mentioned, I find live view very useful for shooting from high or low position. To make it more usable, most (or all) Canon cameras can be configured to use the "Quick" Auto Focus mode in live view. With this setting the mirror temporarily drops during Auto Focus to allow phase detection sensor to be utilised.

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