Choosing a Digital Camera 101

Helpful and informative independent filmmaker sources

Choosing the right type of camera

Choosing a camera is best done by having experience with the camera. However, once you become accustomed to a camera, you aren't very likely to change. Changing means relearning, and that often means new shots may not come out well, which means either repeating the shot or living with not so good. But not changing means following behind, and may put you out of the usable window.

The technology for movie cameras is developing very quickly. As theaters turn to digital projection, and digital camera quality becomes nearly the same as film, the camera field is undergoing a rapid transformation.

Film or digital

The great things about digital are that you no longer have to mess with developing, editing, reproducing, and distributing the film, which is enormously expensive for both materials and time. Digital editing is very rapid, and distribution is very quick. Most experts in cinematography feel that digital is comparable. Film is definitely on the way out as a first choice for filming.

Resolution: 1080p or higher

The higher the resolution, the better you can see tiny details in the movie. In general, movies don't emphasize detail. Actors have makeup slathered on thickly so you can't see the flaws in their skin, and if you can see details on the set, these are distracting. Movies are an impressionistic art, not realistic, except when you want to show nitty-gritty detail, warts and all. Short depth of field cameras are commonly used to give the background a softer look (out of focus background). This is called "Bokeh," or blur. The use of "rack focus" changes the focus from element to element within the viewing field, and simply means changing the focus to see one element better while making another out of focus.

There was some question as to whether 720p or 1080p resolution is better. Some have found that a movie captured in 720p, and then the user's viewing device displays (upscales or upconverts) it in 1080p, actually gives a more pleasing picture. This is because there is less distracting detail (it's softer). But you can't really depend on viewing devices since not all devices will upscale the picture to 1080p.

The exception to movies is sports. When people view sports, they want to clearly see the detail. Cameras are coming with higher resolution than 1080p, and these will be good for capturing sports events. However, this also requires more bandwidth.

The real determining factor may be the money you can get. Higher prices are gotten on online sites for higher quality video, and that means 1080p. Even the YouTube and Netflix standard is 1080p, although they will accept less.

Note that at this date, television broadcast in the US is typically 720p or 1080i, including programs on satellite and cable carriers, which requires half the bandwidth of 1080p. Blue Ray discs and online movies are in 1080p. Newer digital televisions generally can display 1080p. Televisions are not expected to have 4K resolution (4x 1080p) for at least another 5 years due to lack of demand, slow technology development, very high price, and lack of 4K content. Forget 4K TVs for five years.

Next page: DSLR or standard digital (camcorders).

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DSLR or standard digital (camcorders)

Both standard digital movie cameras, and DSLR cameras, are electronic and have digital outputs. They have different development paths. The standard digital movie camera was developed specifically for shooting movies. The DSLR camera was developed as a high end digital camera for shooting still pictures. As people with DSLRs have also wanted to shoot videos, the DSLR has slowly evolved into a movie camera. The differences are quickly fading.

Standard movie digital cameras display their output on monitors, so that the cameraman and director can see it, and they typically record to a camcorder inside the camera, or output to a computer. DSLR cameras have a "reflex mirror" that reflects some of the light entering the aperture to a view finder, so that you see directly what the camera sees. DSLRs also have mechanical shutters that momentarily close off the light coming in. They most commonly record to a memory card. They usually have small mounting devices, and smaller lenses. But these characteristics are becoming less true as the still photography cameras are fully developed for shooting video.

DSLR cameras now often only use their electronic portion for shooting video. This means that they use an "electronic" shutter, and the camera electronics sends the picture to a monitor. As with other movie cameras, the monitor may be part of the camera, sitting elsewhere for easy viewing, or both.

For both standard and DSLR movie cameras, the electronic shutter samples the output from the microchip for a brief period, similar to how a mechanical shutter works. The results are similar.

Unlike film, which captures an entire instant at once in a frame, digital cameras sample each row of sensors over a period of time. For this reason they have problems with "rolling shutter." Because they see the subject in rows, they also have problems with problems with moiré.

Rolling shutter is a problem caused sensing parts of the subject image over time. The top row of sensors is read, followed by the next row down, etc. So by the time a vertically oriented subject, such as a pole, is fully scanned, parts of it have already passed. What you see on the output image is a pole that seems to be leaning. Rolling shutter can't be improved in an existing image. Rolling shutter can be improved in cameras by faster scanning, which means the microprocessor in the camera has to operate at a faster speed to check the rows of sensors more quickly, process the image more quickly, and then the cache memory must be able to take information faster (which is a faster type of RAM memory). So the speed of the camera microprocessor is important in selecting a camera.

moiré is an interference pattern caused when the pattern of sensors in the camera overlaps a pattern in the subject image. The resulting interference pattern seen in the output image is a different pattern than exists in the image. moiré is somewhat alleviated by increasing the number of sensors, and can also be reduced in post-production.

Another important difference between DSLR and regular digital is the mounting type, lenses, and gear. A very few DSLRs will use some lenses used by their regular digital brothers. And there is a great number of prime and zoom lenses available for DSLRs that aren't too expensive. But the other gear is very different, and there is much less of it. Pulling focus is very different. You can still use a focus puller person, and you generally can still monitor the output on an external monitor. But the gear itself is still often in an early stage of development.

The light weight of a DSLR camera means that moving the camera with gear is much easier, but this can also be a problem as it may not move as smoothly because it is so light.

Next page: How digital affects the image.

 

 

 

 

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How digital affects the image

Digital gets as close as it can to reproducing an exact image of the subject. But the image is analog, the camera sensors are analog, and the camera digital output is an average based on several factors. There really isn't anything true about the image, just as film images are affected by a number of factors besides rolling shutter and moiré.

The sensors in a digital camera cannot recognize color; they only respond to light intensity. A filter is used to channel red, green, or blue light to different sensor sensors in an area. The sensor responds to the intensity of light hitting it, and creates a corresponding analog output for the color of light hitting it. Surrounding sensors are sent a different color of light by the filter.

Everything is averaged. The electronics takes an average of a sensor that sees one color, and its surrounding sensors that see other colors, and from that average determines a color value. By sensing each sensor with its other close sensors, an accurate color representation is found.

Digital technology is affected by a wide variety of factors. The ones that are really important for your consideration are explained in following sections. These include the size of the sensor chip, the frame rate, the number of pixels, the output format (compression used), and the number of encoding code bits.

Sensor chip size

Sensor chips, which are filled with millions of tiny sensors (photo sites), each representing a pixel or a group representing a pixel, come in many different sizes. The physical size of the sensor doesn't necessarily indicate the number of photo sites on it. A 1/3" sensor may have as many photo sites as a full 35 mm sensor. But in general, a larger sensor chip may have more photo sites. Advantages, or disadvantages, come from the size.

Light sensitivity increases with a larger photo site, which can receive more light. Light sensitivity can be very important when operating in low light conditions, and at higher ISOs. It gives you less noise, and a higher quality (truer) result. So in general, larger sensors offer a higher quality image.

Larger sensors actually narrow (crop) the diagonal measure of the area being shot. A wide city scape may be narrowed to only a few buildings when using a larger sensor. This is counterintuitive, but when using the same lens, the focal width at the sensor is the same, but the larger sensor is less covered. So a smaller sensor will give you a wider view. This can be confusing because, for example, Canon® came out with a new 7D camera but the sensor was smaller than in their earlier 5D.

With the diagonal measure being shot being smaller with a larger sensor, this means you may have to be farther away from the subject to get the wider shot. On a set, or for a city scape, you may not be able to back up far enough to get the shot.

Larger sensors have the subject in focus for a greater distance (deeper depth of field), so the subject, someone farther away, and the background may all be in focus at the same time. This can be good, but provides less opportunity for using rack focus and bokeh in your shots.

A smaller and less sensitive sensor may make your shots very subject to lens type and quality. Your zoom lens may not have as good a quality glass (or plastic), as your prime (fixed) lens. If this is so, the larger sensor may give you better light sensitivity in low light conditions (or allow you to use a higher ISO.

A small sensor may give you a picture that is much closer to 35 mm in diagonal size, but not give as good a quality picture as a larger sensor, particularly in low light conditions. This can vary by product by increasing the number of photo sites on a sensor, and by improvements in CMOS sensor technology. A small sensor may give you greater control over focus and bokeh.

Number of pixels

The larger the number of sensors, the more accurate an image can be represented, in color, in resolution, and..., oops, covering up for bad sensors.

When you have a device with millions of sensors, one or more may go bad. But because several sensors are averaged, the effect isn't noticeable.

The more sensors you have, the less the final image can be affected by a bad sensor. To create an HD 1920 x 1080 image, over 2 million sensors are required. More sensors, more accuracy. For example, the Canon 5d Mark III has a 22.3 Megapixel sensor, but its output is 1920 x 1080.

The NIKON® D800 has a 36.3Mp sensor. The Blackmagic® Cinema Camera EF has a sensor resolution of 3.3 Megapixels. The Canon 7D has a 18 Megapixel sensor. The Panasonic® AJ-HPX3000 (HD 1080p broadcast camera) has a 2.2 Megapixel sensor.

Bits: 8 - 32

The number of bits your camera stores information in directly affects the color quality. Cameras with an 8-bit output are only able to store 256 different colors, which is a very low color depth, and very noticeable. For example, when you look at the gradation of colors and shadows on a face using 8-bit color, the face will look splotchy and unreal. You can store a larger variety of colors by buying a camera with higher number of bits used to store the colors.

For example 64-bit computers are able to store and display 16 million colors. But that comes at a price. It takes a lot more bandwidth to send, and a lot more computing power to display. 12-bit cameras store over 14,000 colors, and 14 bit cameras store over 16,000 colors. It is very difficult to do color correction using only 8 bits. High compression often reduces the number of bits, and so reduces the number of colors that get stored and displayed.

The Nikon D800 creates a 14-bit file. The Blackmagic Cinema Camera EF creates a 12-bit file. The Canon 5D and 7D create a 14-bit file. The Panasonic AJ-HPX3000 (HD 1080p broadcast camera) creates a 10-bit file.

Bitrate and bandwidth

Bitrate is the number of computer code bits sent in one second. This affects the bandwidth required to stream or download a video file. The higher the number of bits, the less compression used, and the higher the resolution, the more bits per second are sent, and the more bandwidth required. This is becoming less of a factor for many users. The average broadband user today has a 4 Mbps connection speed (bandwidth). This is the minimum required for 1080p movies.

Conversely, the fewer number of bits, the less compression used, and the lower the resolution, results in a poorer quality image.

Next page: The digital output.

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The digital output

Frame rate

The standard frame rate is 30 frames per second (fps) for NTSC (standard format in the Americas) video production work. (Actually is more commonly 24 fps in the evening.) This means that 30 times a second, the camera sends a complete picture out. This follows the NTSC standard for televisions, even though TVs may be able to scan at 60 fps. This is the frame rate that is best for sports and action movies. Europe follows a different standard (PAL, 25 and 50 fps).

Evening television is often broadcast at 24 fps. This results in a more jumpy image. When shooting movies that will ultimately be seen over broadcast TV, it is good to keep in mind in scenes that if your camera shot is close to the subject so that movements are accentuated (move quickly across the screen) or the speed of movement very fast, the audience will see choppy or jumpy action. But the camera is an intimate tool (is commonly close to the subject, or zoomed in), so not much can be done except to get farther away or change the angle.

Interlaced or progressive

Interlaced is a great standard created by Sony, for television. Instead of sending 24 or 30 fps every second, it scans every other line and so can send only half the lines. Next scan, it sends the other lines. This worked great for vacuum tube (CRT) TVs because the image frame took a long time to fade from the screen. It doesn't work well for modern LED and LCD TVs, and gives the screen a jumpy look. You should not use interlaced formats for movies.

Output: H.264 or other

Most editing programs will edit nearly any common format, especially if they are up to date versions. There are exceptions. Some cameras have proprietary formats that standard editors won't edit. But some of these cameras have a choice of output type. Another exception at times is Apple®, which came out with a new format and it's editor for a while wouldn't edit its old format. The question is, "What is the most useful output from the camera?"

For the most accurate color, and for color correction later in editing, you want as much of the original data produced by the camera as possible.

The RAW output from a camera is the raw output that has not been processed to create a formatted output. It contains the most accurate color and resolution information. But it may take five times as much space on storage discs. Most editing programs will work with RAW.

Other file types remove some color information. Red, green, and blue are stored in bits as 4:4:4, with no subsampling. This is often dropped to 4.2.2, using subsampling of chroma in a block of pixels, as in H.264 HD. The block of pixels may be as small as 4x4. The older MPEG format, MPEG 2, also had a 4.2.2 color space, but it subsampled more blocks, 8, which was less accurate. Is this a problem? The human eyes is more sensitive to brightness than color. So for the eye, it is not a problem. But the more color information is dropped, the more difficult it is to do color correction in editing.

H.264 is the standard for Blue Ray, and is the current best standard for video, unless you work with RAW. The current best standard is 4.2.2 with subsampling of 4 blocks. MPEG Dash is an improvement on H.264, but has similar characteristics. The Panasonic AJ-HPX3000 (HD 1080p broadcast camera) outputs 4.2.2.

Other important factors

Most DSLR cameras do not offer synchronization. So you can't synchronize shots from multiple cameras, and audio recording, with a clap board. This may or may not be important to you. Many people synch audio effectively in editing without camera and audio synchronization.

DSLR cameras have 3/16" stereo plugs for the sound input. These typically require an adapter to work with common microphone cords. The 3/16" ports do not support anything heavy, like adapters, and are very unstable when moving the camera, which can cut off your audio. Devices such as the Beachtek DXA-SLR and Juicedlink DT454 mount underneath the camera and accept two XLR cable inputs, have volume controls, and output to a 3/16" plug. Many people choose to record to a separate device rather than the camera.

Each camera manufacturer has significant technical innovations that improve the performance of their cameras. Some cameras will perform better in low light than others. The best way to tell if a camera is right for your application is to look at or shoot similar footage and see how well it performs. For many standard shots, almost all newer HD 1080p cameras will present a good image.

You may also want to see how much gear is available for the camera you are considering, and how others like it. Many sites on the Internet have comparisons of cameras made by professionals. Some links are below.

Links to related information

- Dorian

End.

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