T356 Spring 2013 - Week 2

Agenda

• Cameras & lenses (cont)
• Video signal
• Lab this week: Studio 5 Profile / Directing Challenge. Simple floor plans & lighting plots

Announcements/Reality Check

• Critical Viewing Assignment due today
• Because of MLK day we have no lecture or labs next week
• Camera Quiz (Quiz #1) the week after next.
• PSAs- Should find a client by our next lab, as initial PSA Proposals are due in a few weeks.
• Special guests (Nicole Schönemann & Andrew Libby) from the Service-Learning Program are in this week. Nicole and Andrew have some clients from the Office of Service Learning who would like PSAs produced for them.
• Don't forget about other major production assignments. Now is the time to be thinking about your demonstration video and dramatic scene.

Lecture

- Review camera terms from last week's notes -

Major parts of video cameras: lens, beam splitter, CCDs/CMOS, & viewfinder

Sensors

The lens focuses the light onto an imaging or pickup device. In the old days cameras used tubes, these days CCDs (Charge Coupled Device) or CMOS (Complementary Metal-Oxide Semiconductor) sensors are used. CMOS sensors are beginning to become more widely used as they are a bit easier to manufacture and use less power than CCDs. The tiny camera in your laptop or cell phone most likely uses a CMOS imaging device.

Most professional video cameras use a beam splitter, which consists of prisms. The incoming light is split into its primary components, Red Green & Blue and recorded onto three separate CCD or CMOS imaging elements. These elements are about the size of a postage stamp and convert the light energy into an electric charge. While the industry norm has been to use three imaging elements, a growing number, such as the Red One, are using a large, single CMOS sensors.

Here's a nice picture of a prism block from Adam Wilt's amazing and informative website:

CCD and CMOS sensor sizes

Most sensors are made in different sizes such as 1/4", 1/3", 1/2", and 2/3". Some of the new HD video cameras use larger CMOS sensors that more closely match standard film sizes such as 35mm. This allows DPs to use their existing collection of 35mm lenses and attachments.

Consumer cameras usually have only one pickup device or three very small CCDs. (1/4" for example.) As the price and quality goes up, so does the size of the CCD. Professional studio cameras generally have larger CCDs. (The Canon HXL1 uses 1/3" CCDs while the Grass Valley cameras in Studio 5 use 2/3" CCDs.) Lens mounts are standardized and matched to the corresponding CCD size. (You'd use a 2/3" lens mount with a camera with 2/3" CCDs.) The bigger the lens mount, the bigger the CCD and the more room for more pixels. Generally speaking, bigger is better and the more pixels a CCD or CMOS sensor has on it the higher the resolution or detail that can be delivered by the camera.

Bandwidth & Resolution

How much detail does the camera show, or how much signal detail can we carry? Bandwidth is refers to how much signal a device can carry and is typically given in megahertz (MHz). Resolution refers to how well the camera resolves the image. With the proper test charts and monitors, it's possible to measure the resolution of VCRs, TVs, and other video devices.

To determine resolution you need to use a resolution chart. The most important parameter is horizontal resolution.

Horizontal Resolution: The number of vertical lines that can be seen when placed side by side.

A test chart can be used to determine the camera's resolution.
	This close up shows the chart's convergence lines. The point at which the lines are no longer individually discernable is the resolution of the camera.

Approximate resolution of various formats.

• VHS can resolve about 240 lines
• DVDs about 400 lines
• DV about 500 lines
• HD - XDCam is about 900 lines

Sensitivity

How much light does the camera need to operate? This is called minimum illumination or sensitivity. It’s measured in foot-candles (American) or lux (European) usually along with the required f-stop and gain needed to capture an image. For example Panasonic's AJ-SDX900 reported minimum illumination is 0.01 lux (F 1.4, +48dB +20dB gain).

Aspect Ratio

The aspect ratio should always be provided in width to height. Before the advent of HD, TV was broadcast in 4:3. HD is always broadcast in 16:9.

• 4 x 3 (or 1.33:1)
• 16 x 9 (or 1.78:1) This is closer to standard widescreen movies.

Other parts of a studio camera include:

Filter wheel. It usually holds a couple of neutral density (ND) filters and a color correction filter (3200 degrees Kelvin for indoor, 5600, 5600 + 1/4 ND, etc)

Viewfinders: small video monitor mounted on top of the camera. Typically will be either CRT (Cathode Ray Tube) or LCD (Liquid Crystal Display). CRTs are used in most standard TVs and video monitors. (Black and white CRTs provide higher resolution than color, so are better to focus with.) LCDs are used in flat displays (like laptops).

Tally lights: turn on when the camera is on-line

Power supply: 12 volts- conveniently the same voltage a car runs on.

Gain: The gain feature boosts the level of the video signal electronically. Since the video is "amplified", it's done so in dBs. (+3 db, +6 db, + 9 db, etc.) Turning on the gain adds noise and excessive amounts will produce noticeable graininess.

Lenses:

Focal length: the distance from the optical center of the lens to the target (CCD or film) Measured in millimeters. An 18mm lens would generally be considered a wide angle lens. A 200mm lens could be considered a telephoto lens.

Angle of view: Wide angle lenses have a wide angle of view. When you zoom in all the way to a CU you have a very small angle of view.

Zoom ratio: Most video lenses have variable zoom lenses or focal lengths. The range is the zoom ratio. You can say that a lens provides a 10:1 or a 17:1 range, but this still doesn't’t tell you much about the focal length in terms of actual numbers (how many millimeters is is?)

So to solve this zoom ratios on lenses usually have two numbers. The first refers to the minimum focal length. The second is the multiplier.

• 9.5x17 (9.5mm x 161.5mm)
• 10x10? (10 mm x 100 mm)
• 12 x 20? (12 mm x 240 mm)
• 8 x 80 (Some lenses have the mm marked as the 2nd number)

Depth of Field

Good camera operators know how to precisely control the depth of field, which is the area that is in focus. Depth of field is affected by two major factors: focal length and aperture.

Wide angle lenses (such as 20mm) will tend to have a very large depth of field. In other words when you are zoomed out to a wide shot, everything will look like it's in focus. Telephoto lenses (such as 200mm) create a much smaller depth of field. When you are zoomed in, it's much trickier to track objects, such as people, moving toward or away from the camera.

F-stop - A number that represents the size of the aperture in an inverse manner. A large f-stop corresponds to a small aperture, or opening in the iris. A small f-stop represents a large opening. You should know your standard f-stops: 1.4, 2.0, 2.8, 4, 5.6, 8, 11, 16, 22. Increasing one f-stop will cut the light in half. Decreasing the f-stop by one will double the light.

The relationship between F-stop and depth of field: The larger the f-stop (or smaller the opening) the greater your depth of field will be.

Think about this. Imagine you are in the studio zoomed in on a MCU of your talent with a chart in the background. The background is out of focus. What could you do to make it sharper?

Answer: You could add light, reducing the aperture. You could also move the camera closer so that you are using a shorter focal length.

Part II: You are in the studio zoomed in on a MCU of your talent with a chart in the background that is distracting. You want to make the background out of focus. What could you do to make it fuzzier?

Answer: You could reduce light, increasing the size of the aperture. Turning on the shutter will achieve a similar result. You could also move the camera farther away, increasing the focal length.

Selective focus: the process of using limited depth of field to throw areas of the image out of focus

Rack focus: varying the focus from one object to another

Follow focus: Keep focus on an object moving towards or away from the camera. (Separates the amateurs from the pros.)

Macro focus - an adjustable ring at the base of the lens, near where it attaches to the camera. Allows the operator to focus on items a few inches from the lens.

Auto focus - A feature found on consumer cameras. Typically not found or used on professional cameras.

Auto iris - automatically controls the iris to maintain the proper exposure. This can often lead to problems. If something bright enters the frame- the camera will iris down causing a noticeable darkening of the image.

Smear & moiré patterns: Certain bright colors tend to smear, especially red. Moiré patterns show up when you are shooting a small, highly contrasting pattern (say a herringbone jacket) The pattern of the image interacts with the pattern of the imaging pixels to create the moiré patterns.

White balance - adjusts the Red Green & Blue signals to be of equal intensity. (In the RGB color system, white is made up of equal components of red, green and blue.) Many camera operators prefer to work with a camera's built in preset instead of white balancing.

Black balance - irises the lens down all the way to black and sets the pedestal/black level at 7.5 IRE.

Studio Gear

What are the cameras in the studio connected to?

CCU: camera control unit. Controls all aspects of the camera's operation. (except the lens)

Camera Shading - the engineer operating the CCU manually adjust the iris from shot to shot.

Other terms and pieces of equipment include:

Sync generator: produces an electronic synchronization signal. This is used to time all the cameras together so their electronics are working in unison.

Vectorscope: A device that shows color information.

Waveform Monitor: A device for measuring brightness (luminance) levels and timing information. (Studio engineers use this when shading the cameras.) The scale is in IRE units. In this country (NTSC) the black level is set at 7.5 IRE. (In Europe using the PAL system, it's set at 0.) The brightest portion of the video signal (ie. white clouds on a sunny day) should not exceed 100 IRE. So the darkest portion of a video signal will register at 7.5 IRE and the brightest possible white will be 100 IRE.

If you look at the display of a waveform monitor, you'll see registration lines, which are spaced at 20 IRE intervals. Each step up the grid on a waveform monitor (20 IRE) is equal to one f-stop.

Contrast ratio: The range between the darkest & brightest portions of the image. Compared to real life contrast ratios (what we see with our eyes) and film, video has a very narrow contrast ratio. This is one of the reasons video looks thin (not as good) compared to film. In a studio you try to maximize use of camera's limited contrast ratio by limiting the difference between the darkest dark and the brightest bright. A light meter and waveform monitor are great tools to help light a scene correctly, taking advantage or maximizing the available contrast ratio.

The Video Signal --------------

Fields & Frames

Like film, the moving TV image we see is really a series of still frames. In a standard definition TV system these frames are taken and presented approximately 30 times a second. (The actual rate is 29.97 frames per second.) However each frame is actually made up of two interlaced fields. Field one displays all of the odd lines and field two displays all of the even lines. Together the two fields make up an interlaced frame of video.

It's important to understand that one field is the smallest sample of light (unless a different shutter rate is used) and that they are taken every 1/60th of a second. If you use a light meter with a camera shooting standard interlaced video, you'll set the frame rate on the light meter to 1/60th of a second. (Or 30 if the light meter offers a "cinema" mode.)

Interlaced scanning & CRT displays:

When a CRT displays a video signal, the electron beam scans all odd numbered lines from left to right & top to bottom to show field 1. Then the beam jumps back up to the top & scans the even lines for field 2. These two fields make up a complete TV picture (a frame)

Horizontal retrace - is when the beam jumps back to start another line

Vertical retrace - is when the beam jumps back up to the top of the screen.

Electronic shutters: Camera shutters by default take a picture every 1/60 of a second. (This is the interval of a field of video) You can see a blur in fast-moving objects. (baseballs etc) You can increase the shutter speed to capture fast-moving things better. As with still cameras, the faster the shutter speed, the more light is required.

Remember: even if you use a faster shutter speed, your fields will still be sampled 60 times a second. It's just sampling the image for a shorter duration of time.

DTV (Digital TV)

Broadcasters have begun transmitting their video digitally. Digital TV supports a number of new video formats including HDTV. Some of these new formats use progressive scanning instead of an interlaced frame.

Progressive Scanning: The electron beam scans each line (not skipping even or odds etc)

Common formats supported by Digital TV include:

• 480i uses 480 scan lines at (approximately) 30 frames per second or 60 fields per second
• 480p uses 480 lines scanned at 60 frames per second
• 720p uses 720 lines at 60 frames per second (HDTV) 1280 x 720
• 1080i uses interlace scanning (HDTV) 1920 x 1080

 

Lab------------------------

• Look at floor plans & lighting plots.
• Review rotation exercise
• Review director's and the AD's job.
• Think about where the Floor Director should be
• Carry out rotation exercise

Designing simple floor plans and light plots.

Today we'll construct & light a simple set to use for our directing exercise.

Floor plans & lighting plots should be driven by what the producer wants to see inside the frame. In other words design your set through the eyes of the camera. Once you determine what you want to see inside the viewfinder or on the monitor, you can think about how to build and light the set to achieve the desired image.

Pass out floor plan/lighting plot examples

Review roles of director and assistant director.

• Both should talk clearly. (No-one else should talk unless necessary)
• Always address the person you're talking to. (Camera 1- please tilt up")

AD duties:

• Get's folks prepared. Makes sure Floor Director quiets set before shooting.
• Times the show. Counts down out loud and presses the timer start at "0". Do not rush!.
• Runs the Teleprompter
• Helps set up shots
• Keeps track of time. Knows how to backtime. Tells the director when to wrap.
• Makes sure to end timer at after fade to black.

Director duties:

• Stay calm
• Schmoozes the talent. Always make them comfortable.
• Should brief and "ready" the TD, audio, graphics, etc. BEFORE COUNTDOWN STARTS.
• Be able to say "Mic & CUE talent"
• Focus on getting good shots and a good performance.
• Should be able to look ahead and line up shots well before they are needed.
• Don't freeze. When in doubt, cut to another good shot.
• Keep directions accurate and concise. "Ready downstream key." "Ready 1....... Take 1"
• Thanks everybody at end.

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