More on Sensors and Crop Factors

In Chapter 10, I described some of the reasons why the large sensor size of a full-frame still camera provides video shooters with some selective focus advantages when compared to the much smaller sensor found on many professional video cameras in the past. I’ll be explaining the concept of crop factor in detail in Chapter 12. Both aspects are important in the video world, but with a few variations caused by the differences in how video is captured and used.

However, unlike the Mark III, the new camera uses a 1.6X crop to give 24p footage and 1.8X crop for 30p. So, while the crop modes are still marked as ‘Super 35,’ it’ll actually be a little more difficult to get a wide-angle field-of-view, even if you resort to dedicated Super 35 or APS-C lenses.

Sensor Size

Sensor size is important because smaller sensors use lenses with shorter focal lengths to fill their frames, and the shorter the focal length, the larger the depth-of-field. That’s why point-and-shoot cameras (or smartphones), with their minuscule sensors, can produce acceptably sharp images for subjects located a few inches from the lens out to infinity. Conversely, because a normal lens on an APS-C camera is in the 38mm range, and on a full-frame camera is roughly 55mm, a full-frame camera like the a7 IV has less depth-of-field for the same field of view.

Selective focus is a definite creative plus for videographers. We’ve all seen shots in which focus initially emphasizes some foreground object that’s sharply rendered, and then the camera operator pulls focus out to a more distant subject, which suddenly appears in great detail. Larger sensors make such techniques easier, which is why current video cameras are often segregated into small sensor and large sensor categories.

Figure 11.1 shows the relative size of the 4K and/or full HD capture area of some typical sensor sizes, starting with the a7 IV’s full-frame sensors at upper left, the “small” sensor of typical pro cameras and the -inch sensor of Sony’s least expensive pro camera at right, and an APS-C sensor and the RED Raven “large” sensor shown at the bottom. Note that the 4K/Full HD Area region shown in the figure applies only when the a7 IV is not set to APS-C/Super 35 mode. Your camera is capable of shooting 4K video using both full-frame and cropped sensor modes; it uses the APS-C/Super 35 crop mode when capturing 60p video. I’ll explain more about the crop factor in the next section.

Crop Factor

The crop factor is important because with any given lens, the field of view will vary depending on how much of that lens’s coverage area is used to capture video. (If you’re completely unfamiliar with crop factors, skip ahead to Chapter 12 and read about them.) Still photos can be shot in both vertical or horizontal orientations, and most often using the 3:2 aspect ratio used outside the Micro Four Thirds (4:3) world. So, the crop factor for stills is calculated by comparing the diagonal measurement of the frame with the diagonal of the traditional 35mm frame.

For video, clips are normally captured with the camera in a horizontal orientation (at least, outside the realm of the smartphone), and the proportions or aspect ratio of the video frame can vary, with 16:9 being the standard for standard HD, full HD, and 4K (Ultra HD) video (and beyond).

The 16:9 proportions work out to roughly 1.78:1, which is close enough to the 1.85:1 widescreen cinema aspect ratio that it’s easy to show movies captured in either aspect ratio on displays compatible with either. Given the 16:9 standard, it’s common to represent the resolution of a video image by its horizontal measurement and scanning method: that is, 720p, 1080p, and 4K (actually 3,840 pixels with your Sony a7 IV camera; 4,096 pixels with some other 4K devices) for progressive scan (p) video.

Your full-frame sensor provides a 1X crop factor for video when shooting Standard HD (720p), Full HD (1080p), or 4K (3840p). Sensors with smaller areas produce various crop factors, based, not on the sensor’s diagonal measurement, but the relative width of the sensor area, compared to the full frame. Super 35 is a popular format for video and is available with your a7 IV. By comparing the widths of the sensor area, we can arrive at a crop factor in APS-C/Super 35mm mode with the a7 IV. (See Figure 11.2.)

There are subtle differences between shooting video in full frame versus Super 35/APS-C modes. Both capture more pixels than needed, but process them differently, using pixel binning and oversampling, respectively. These two processes are different, regardless of what you may have heard, even though they are often incorrectly used interchangeably.

• ■Pixel binning. Video is captured from pixels spanning the full width of the sensor. They are then combined using a process called pixel binning, which takes clumps of red, green, and blue pixels and merges them with others of the same color to create a larger “pixel” at a reduced resolution, resulting in faster capture with reduced noise. The remaining pixels are then demosaiced, which interprets the colors of adjacent pixels to produce a full-color image even though each physical pixel actually is sensitive to only one of the three primary colors.

• ■Oversampling. In this mode, video is also captured over the full width of the sensor. However, it oversamples, grabbing more pixels than required for the final video frame. That large number of pixels is demosaiced first, and then downsized to the required size. Because oversampling happens after the RGB pixels have been analyzed and demosaiced, the process allows for better capture of details for a sharper final image. The a7 IV uses 7K oversampling to capture 4K 30p 10-bit 4:2:2 video, with no pixel binning. However, to record 4K 60p 10-bit 4:2:2 video, a Super 35/APS-C crop is used with a full pixel readout over the cropped width with 4.6K oversampling.

In practice, the image quality difference is not great, but still can be important when capturing ultra-high-definition 4K video. You’ll probably want to shoot in full-frame mode to avoid the crop factor under most circumstances, and switch to Super 35/APS-C mode when you actually need the 1.5X field-of-view crop.

But should you be shooting full high-definition movies, or ultra-high-definition (4K) video? If your memory card (which should be a 64GB or larger CFe or SDXC card) or external recorder like the Atomos Shogun, can handle the data rates, 4K is alluring, even if your movies will never be viewed in anything other than 1080p format. All that extra detail is hard to resist.

Other Important Parameters

But wait, as they say, there’s more! The last sections of this chapter will explain some of the other technical details of shooting video, providing enough detail, I hope, to get you reading more complex tomes that cover this information in depth.

Frame Guides

Frame guides are a useful way of visualizing the area that will be captured within a larger visible display. In ancient times, interchangeable-lens rangefinder film cameras that used an optical viewfinder would have bright frame outlines appear, often automatically when a particular lens was mounted on the camera, and sometimes through the use of an attachment that fit over the built-in viewfinder. In the digital age, frame guides have been popular with digital cameras that use an optical viewfinder, providing a masked-off display to preview the actual image area that will be captured in crop or video modes. Cameras with electronic displays, like the a7 IV, don’t necessarily need frame guides, because the capture area can be enlarged and masked off electronically to show only the actual image area.

Even so, frame guides are a popular tool for videographers, because they allow viewing the area outside the actual frame that will be captured (the “look-around area”) so you can monitor moving subjects before they enter the frame. In professional productions, it’s useful to look at the region outside the captured frame to detect when boom microphones, careless crew members, or other objects threaten to intrude on the frame.

The a7 IV cameras offer a variety of frame guides that can be turned on or off in the Shooting > Marker Display group. They include grid lines, aspect ratios, frame center markings, and “safety” areas. These markers appear only on the EVF or LCD monitor, and not in the captured video itself. The Marker Display group has five entries (see Figure 11.3).

• ■Marker Display. This setting has On and Off options, and simply enables or disables marker display. You can turn any, all, or none of the markers described next on or off independently.
• ■Center Marker. This crosshair can be used to determine whether your subject is placed in the exact center of the screen. (See Figure 11.4, upper left.)
• ■Aspect Marker. Use these guides to frame your image so the important subject matter is contained within a desired aspect ratio, or to frame the image for later cropping to that aspect ratio. You can select from 4:3, 13:9, 14:9, 15:9, 1.66:1, 1.85:1, or 2.35:1. These conform to various movie formats in common use. (Star Wars, for example, was filmed in CinemaScope, with a 2.35:1 aspect ratio.) (See Figure 11.4, upper center and upper right.)
• ■Safety Zone. It’s common to shoot movies knowing in advance that they will be cropped down eventually for display in a slightly different format. The director simply makes sure that the important parts of the frame are included in the “safety zone” that will never be cropped out. For example, you wouldn’t want to put two characters who are talking to each other at opposite ends of the entire frame but would instead locate them in the safety zone so both would be visible. Your camera’s safety zone display can be set for 80 percent or 90 percent of the frame to represent the area that will always be shown when the movie is viewed on a standard HDTV.
• ■Guideframe. This grid is used to help you determine whether horizontal and vertical lines are skewed and can also be used as a Rule of Thirds guide for composition.

Time Codes and User Bits

The Time Code (TC) and User Bit (UB) settings are information that can be embedded and used to sync clips and sound when editing movies. Advanced video shooters find SMPTE (Society of Motion Picture and Television Engineers)-compatible time codes embedded in the video files to be an invaluable reference during editing. To oversimplify a bit, the time system provides precise hour:minute:second:frame markers that allow identifying and synchronizing frames and audio. The time code system includes a provision for “dropping” frames to ensure that the fractional frame rate of captured video (remember that a 24 fps setting actually yields 23.976 frames per second while 30 fps capture gives you 29.97 actual “frames” per second) can be matched up with actual time spans.

Using time codes and user bits is a college-level film school class on its own, but I’m going to provide a quick overview to get you started. If you’re at the stage where you’re using time codes, you don’t need this primer, anyway. However, the a7 IV’s (Movie) Shooting > TC/UB Group has six entries. (See Figure 11.5.)

• ■Time Code Preset. Sets the time code. If you’ll be shooting 60i/50i, you can choose time codes from 00:00:00:00 (hours, minutes, seconds, frame) to 23:59:59:29 or 23:59:59:24, respectively. With 24p, you can set multiples of four from 0 to 23 frames. If you own the RMT-VP1K remote commander, the time code can be reset to zero using a button on the controller.
• ■User Bit Preset. Sets the user bit, which is a marker you can insert in your video, say to designate a scene or take. There are four digits in each user bit (for example, 01:02:03:04), and the digits are each hexadecimal in nature, so you could create a code like C0 FF EE if you were feeling facetious. Everyone will know you’re joking because user bits aren’t in general use anymore.
• ■Time Code Format. Sets the recording method for the time code. You can choose from DF (drop frame) or NDF (non-drop-frame) formats. Drop frames are a way of compensating for the discrepancy between the nominal number of frames per second and the actual number (for example, 30 fps yields 29.97 actual frames per second, and 60 fps gives you 59.95 frames per second). In drop-frame format, the camera will skip some time code numbers at intervals to eliminate the discrepancy. The first two frame numbers are removed every minute except for every tenth minute (think of it as a leap year). You may notice a difference of several seconds per hour when using the non-drop-frame option.
• ■Time Code Run. Sets the count up format for the time code. You can choose Rec Run, in which the time code counts up only when you are actually capturing video; or Free Run (also known as Time of Day), which allows the time code to run up even between shooting clips. The latter is useful when you want to synchronize clips between multiple cameras that are shooting the same event. When using Free Run, even if the cameras record at different times, you’ll be able to match the video that was captured at the exact same moment during editing.
• ■Time Code Make. Sets the recording format for the time code on the recording medium. Choose Preset to record a new time code, or Regenerate to read the previous time code setting and record the new time code consecutively. When Regenerate is selected, the time code advances no matter what TC Run setting has been selected.
• ■User Bit Time Rec. Sets whether or not to record the time as a user bit.

As explained in Chapter 9, the Setup > Display Option > TC/UB entry allows you to determine which of three options are displayed during review. It has nothing to do with what actually is recorded onto the Time Code track; it determines how the information is shown:

• ■Counter. When this default value is chosen, the display will include the time counter, which starts at zero and is shown as H:MM:SS (hours, minutes, seconds).
• ■TC. The SMPTE (Society of Motion Picture and Television Engineers) time code is displayed as HH:MM:SS:00 (hours, minutes, seconds, frames, but the frames are always shown as 00).
• ■U-Bit. A four-character string used to identify the camera that captured the video.

Picture Profiles

If you’ve been taking photos for a while, you’re probably familiar with all the fixes and tweaks you can do with your still images within image editors like Photoshop. It’s relatively easy to adjust color tones, contrast, sharpness, and other parameters prior to displaying or printing your photo. Movies are a little trickier, because any given video typically consists of thousands of individual photos, captured at 24 frames per second (or faster), with the possibility that each and every frame within a particular sequence might need fixes or creative adjustments.

Shooting video does not preclude doing post-processing during editing. Indeed, many videographers deliberately shoot relatively low-contrast video in order to capture the largest dynamic range possible, and then fine-tune the rendition later using their editing software. Picture Profiles let you do that—and also allow you to adjust your camera so that the video you capture is pre-fine-tuned in order to reduce or eliminate the amount of post-processing you do later.

The a7 IV camera is furnished with eleven “canned” picture profiles, which you can think of as Creative Looks for movies. The parameters included in these profiles can be further adjusted by you to better suit the “look” you are striving for in your videos. You can connect your camera to a TV or monitor using the HDMI Out connector and an HDMI cable, view the image produced by the camera on the larger screen, and then make adjustments to the picture profile. I described the process in how-to form briefly in Chapter 7.

Needless to say, creating and using Picture Profiles is a highly technical aspect of video making, at least in terms of the amount of knowledge you need to have to correctly judge what changing one of the parameters will do to your video. I hope to get you started with a quick description of what those parameters do, so you’ll have a starting point when you start to explore them.

More on 4K Video

It’s probably a great time for you to start working with 4K video, especially since 8K video is already on the way. In practice, shooting 4K is not much different than shooting full HD or standard HD. The only changes you might make involve your realization that as long as you are capturing higher-quality video, you might as well upgrade your technique (and, perhaps, your auxiliary equipment).

While 4K video still seems new and exotic, given the usual pace of technology, it’s very likely that your next HDTV will have 4K capabilities (if your current set does not), and cable/satellite/streaming systems as well as Blu-Ray discs will all make the leap sooner than any of us expect.

Shooting in 4K is still in its infancy: few of us own 4K high-definition televisions that allow playing back 4K content at its full resolution. However, the number of 4K-capable TVs is growing all the time, and there are some definite benefits to shooting ultra-high resolution now, even before the ability to take advantage of the format is widespread. Simply speaking, if you shoot 4K and then convert it to conventional full HD, your video will generally be much higher in quality than if you originated in 1920 × 1080 resolution. All you need is editing software like Adobe Premiere Pro, Final Cut Pro, or Corel Video Studio that can work with and edit your 4K clips.

The key thing to know is that your a7 IV can record 4K video internally, export 4K video to an external recorder, or to both simultaneously. If you want to record only to the memory card, you don’t need to do anything special other than select XAVC S 4K or XAVC HS under the File Format entry and your desired frame/bit rate under Record Setting.

If you prefer to output your 4K video to the HDMI port (say, to a video recorder or other device), or HDMI port and the memory card, you need to visit the Setup > External Output > HDMI Output Settings entry described in Chapter 9. Set the Still/Movie/S&Q dial to Movie and attach your camera to the external device using an HDMI cable. Since the length of your recording time is essentially limited only by the a7 IV’s ability to dissipate heat and avoid shutdown from high sensor temperatures (potentially a problem when shooting 4K video), the extra storage of an external monitor can come in handy.

As I mentioned in Chapter 10, you will probably want to use an external microphone, either plugged into the a7 IV’s microphone jack or connected through the multi-interface shoe on top of the camera. As I noted, a move to professional microphones using the XLR interface might also seem prudent. Sony offers the XLR-K3M adapter kit, a dual-channel device that can be mounted in the multi-interface shoe and used to connect XLR mics and other audio sources to the a7 IV. It’s pricey at almost $600, but includes a Sony ECM-XM1 shotgun microphone.

Using an External Recorder

If you’re truly becoming an advanced videographer, you’ll probably be working with the a7 IV’s ability to output “clean” non-compressed HDMI video to an external monitor or video recorder, including the Atomos Shogun lineup, which includes versions that are quite affordable, at least in terms of professional video gear. You can choose models both with and without an external LCD monitor, and capture to solid-state drives (SSD), a laptop’s internal or connected hard drive, or to CFast memory cards (the latter chiefly as a nod to those still using the “fast” version of Compact Flash cards). Such equipment allows very high transfer rates and is certainly your best choice if you’re shooting 4K video.

Probably the best of the lot for a7 IV owners is the Atomos Ninja V, an extremely portable unit with a 5.2-inch screen and a $695 price tag that’s currently the lowest for this type of device. Its size is a definite plus—if you’re shooting video with a smaller, lightweight camera, you’re going to need an equally compact recorder/monitor, such as the roughly 13-ounce Ninja V. Add a battery, HDMI cable, and a 2.5-inch solid-state drive, and you’re ready to go.

The Ninja V has HDMI input and output jacks on its left edge, which you can see in Figure 11.6. The latter allows you to daisy-chain an even larger monitor or other device. A power button, headphone jack, microphone/audio input, and remote jack reside on the other edge. The touch screen enables you to view your video and access the monitor/recorder’s menus and controls, which is convenient (except outdoors in cold weather when you’re wearing gloves and might wish you had a few buttons to press instead). The only other “defect” of the unit is the noise produced by its fan; even when you’re using an external microphone with your a7 IV, the fan noise may be picked up in a quiet room.

Why use an external monitor/recorder like the Ninja V, when your a7 IV has its own nifty monitor and can store quite a lot of video on UHS-II-compliant memory cards? From a monitor standpoint, an external unit’s screen is larger, easier to see, and offers more flexibility in positioning. The a7 IV’s screen tilts up or down; mounted on a ballhead like the one in the figure, you can adjust an external screen to any angle, including reversing it to point in the same direction as the lens, so vloggers can monitor themselves as they record or stream their video blog.

But the best value may come from the recording capabilities of such a device. Internal video is saved to your memory card in the standard H.264/MPEG-4 Part 10 format, which compresses that stream of images as much as 50X. That video has only 8 bits of information: good, but somewhat limited in the dynamic range that can be included. Depending on your scene, you may lose some detail in the highlights or shadows.

Fortunately, the a7 IV can also direct its video output through the HDMI port in “clean” uncompressed 4:2:2 8-bit UHD (ultra-high-definition) resolution. That’s correct. Sony still doesn’t offer external 10-bit output, which is unfortunate: 8-bit output gives you 16.8 million possible colors; 10-bit output is capable of more than 108 billion hues. Nor is 60p 4K video available. However, for most of us who aren’t professional videographers, the a7 IV’s output should be sufficient, especially since the available Picture Profiles include four HLG (hybrid log gamma) curves suitable for HDR (high dynamic range) recording.

The HDMI port on the a7 IV accepts an HDMI cable. I prefer to purchase value-priced third-party cables, which I buy in convenient lengths of 3 feet, 6 feet, 10 feet, or longer. The cable can be connected to the monitor, recorder, or other device of your choice. (Some of the screen shots in this book were output to a Blackmagic Intensity shuttle that allowed capturing stills of the a7 IV’s menus, live view, and video.)

When it comes to saving your 4K video files, you have three destination combinations to choose from:

• ■Capture to memory card (only). You can output your 4K video to a memory card in your a7 IV, but it really should be a fast CFe card. Because 4K video files can be so massive, you’ll want a 64GB to 128GB (or larger, when they become affordable) card to store your movies. This option is the least expensive, but it comes at a cost. The camera compresses your 4K video, using a maximum 100MB/second transfer rate, so a bit of quality is lost. If you’re planning on editing the video and ending up with 1080p HD clips, you probably won’t notice the difference, especially since your 4K-to-HD conversion will usually have more detail than a straight 1080p movie.
• ■Capture to an external recorder (only). If you’re really serious about video, you’ll want to consider using an external recorder, linked through the a7 IV’s HDMI port. The video is not compressed, and you can take advantage of the fastest transfer rates to optimize quality. You’ll want to visit Setup > External Output > HDMI Settings > Record Media during HDMI Output and choose Off.
• ■Capture to both. If you’re equipped with a very fast memory card and external recorder, you can opt to save your video to both destinations. Set Setup > External Output > HDMI Settings > Record Media during HDMI Output and choose On.

Audio Settings

I’m going to wind up this chapter with an explanation of the Audio Recording options available in the Shooting menu when the Shooting/Movie/S&Q dial is set to a movie position. There are six entries, shown in Figure 11.7.

• ■Audio Recording
• ■Audio Recording Level
• ■Audio Out Timing
• ■Wind Noise Reduction
• ■Multi-interface Shoe Audio Settings
• ■Audio Level Display

Audio Recording Level

Options: Levels from 0 to 31 (Default: 26)

My preference: N/A

You can adjust the recording level of the camera’s built-in or external microphones using this entry, which also enables/disables the audio level overlay on the screen while movies are captured.

To use this feature, just follow these steps:

• 1.Rotate the Still/Movie/S&Q dial to the Movie position.
• 2.Navigate to the Audio Recording group, highlight Audio Rec Level, and press the center button.
• 3.The screen shown in Figure 11.8 appears. Rotate the front or rear dials or control wheel or use the left/right controls to adjust the volume level up or down. There are 32 different levels, from 0 to 31.

• 4.Press the center button to confirm and exit the screen.
• 5.Alternatively, you can use the up/down buttons to highlight Reset to return the recording level to the default value. Then press MENU to exit.
• 6.If Audio Recording and Audio Level Display are set to On, an overlay appears at the lower left of the EVF or LCD monitor showing the current audio levels for the left/right channels (Ch1/Ch2).