Professional Cameras
If you're a professional or a serious amateur you'll want the features a "professional" camera can give you. Most consumer cameras make you go through a series of menus on the LCD screen to do things like switching to manual focus, manual aperture or shutter speed control. Professional cameras have most of these controls on the outside of the camera so that once your fingers get used to where things are you can change the camera's setup very quickly, usually without even having to look at the camera. Professional cameras also give you much higher ISO settings and store pictures more quickly. These cameras also let you use a color profile such as the "Adobe RGB" color profile that captures a wider range of colors than the standard "sRGB" profile used in most consumer cameras. Finally, professional cameras let you shoot in "raw" format, a format that records all the information the camera captures. The advantage in shooting "raw" is that you can adjust things like white balance and exposure later on in Photoshop or Lightroom. Top of the line digital SLRs will let you shoot at a color depth of 14 bits, that's 14 bits for each of the red, green, and blue color channels. With a color depth of 14 bits you end up with a theoretical total of over 4 trillion colors. Your eye can't distinguish 4 trillion colors, and you don't actually see more colors at 14 bits, but the extra data lets you make much wider color and exposure adjustments without introducing noise or losing visible image quality
One problem with a digital camera is the amount of time it takes to store a picture file on its flash memory card. Most professional cameras have a large "buffer," a quickly accessible temporary memory store that goes away when you shut off the camera. When you shoot a picture the camera instantly stores the image in its buffer and then starts the much slower process of transferring the picture from the buffer to the memory card. With a professional camera you may be able to shoot a lot of pictures in rapid succession (burst mode) before you have to stop and wait for some of them to be cleared out of the buffer.
Most professional cameras are single lens reflexes (SLRs). An SLR lets you look through the lens at the picture you're going to take. That can be a big advantage. If you're using a viewfinder camera, unless the viewfinder is an electronic viewfinder (EVF), you have to live with a problem called "parallax." When you get close to your subject, parallax keeps the viewfinder from seeing the same thing the lens is seeing. After you shoot, you find that the subject is way off to the side or the bottom in the picture, even though she was right in the center of the viewfinder. An SLR never has a parallax problem. But an SLR is large, fairly heavy, and obtrusive, and if it's a real SLR like the Nikon D750, when you shoot, the mirror slaps up and down making a very noticeable noise. If you're doing street photography that's a drawback. For street photography you want a camera that's small, quiet, and black, and has an EVF which lets you look out through the lens, the same way an SLR does.
Professional cameras currently on the market have sensor arrays that are several times the size of the sensor arrays on "consumer" point-and-shoot cameras. If two sensor arrays have the same number of pixels and one is several times the size of the other, the large sensor array is going to have much larger individual sensors (photosites), and the larger the photosites the less noise.
Finally, professional cameras let you use interchangeable lenses. That may or may not be a good thing. If you're a professional or a serious amateur it's definitely a good thing, but if you've never hooked up a fixed focal-length lens to a camera with a DX (three-quarter size) sensor you may be surprised when you first do it. With a 35mm film camera or a full-frame digital camera, a 35mm lens is a wide angle lens. That same lens on a camera with a "DX" sensor is the equivalent of about a 52 mm "normal" lens on the 35mm film camera. So if you have a collection of lenses you bought for a 35mm camera you're going to find they're mostly telephoto. The other problem with interchangeable lenses is that when you switch lenses you're liable to get dust on the sensor array. You can get the dust off, but it's a nuisance because even the tiniest dust particle may show up as a problem in the picture.
Professional cameras come at two levels. There's a camera most magazines describe with the wretched word "prosumer," evidently trying to indicate that they're somewhere between a professional camera and a consumer camera. When I began covering this ground in lectures around 2003, cameras that fell into the "prosumer" category included the Canon EOS-10D and the Nikon D100, both at around $1,500 for the body without lenses. Nowadays those cameras have been replaced by Canon and Nikon DSLRs that sell for about the same price, adjusted for inflation, but are much more competent. Earlier Canon and Nikon DSLRs used a sensor that's roughly two-thirds the size of a full-frame 35mm, but a few years ago Nikon came out with the D3, a professional camera with a sensor roughly the same size as 35mm film, and a bit later, the D700, a "prosumer" camera with the same full-frame sensor used in the D3. Canon came out with the 5D, another almost-professional full-frame camera. Both of these are excellent cameras. The 5D is now the 5D III, and a follow-on to the D700, the D750, has been out for some time. I've stopped trying to keep up with the rapid rollout of new cameras.
At a much higher price come the "true" professional digitals. These top-of-the-line cameras are faster and more rugged than their less expensive counterparts, have excellent weather sealing, and have features that speed up a shoot. The Canon EOS-1D X sells for about $6,800 at the time of this writing, and the Nikon D5 goes for about $6,500.
I can vouch for the ruggedness of the D2X, the D3's predecessor. Several summers ago I managed to fall down two steps on a sidewalk in Victor, Colorado while I was shooting pictures and not watching where I was walking. My D2X hit the sidewalk hard enough to bend the lens barrel on my 24-120 zoom and total the lens, but the camera body survived unscathed except for a few scratches. After the local fire department swabbed the gravel out of my forehead I was able to put another lens on the camera and go on shooting. There aren't many cameras out there that can survive that kind of shock.
Recently, several mirrorless interchangeable-lens cameras have been introduced which, in my own estimation, are ideal street cameras. They don't come up to the level of professional cameras in terms of ruggedness, weather sealing, or, at this point, sensor size, but they can produce professional results in the hands of someone skilled in their use and they're small, quiet, and unobtrusive.
