As we’ve seen during our exploration of its features so far, the a6000 is superbly equipped for taking still photographs of very high quality in a wide variety of shooting environments. But this camera’s superior level of performance is not limited to stills. It’s highly capable in the movie-making arena as well. It can shoot Full HD (high-definition) clips. Sony has also provided overrides for controlling all important aspects of a video clip.
So, even though you may have bought your a6000 primarily for shooting stationary scenes, you acquired a device that’s also great for recording high-quality video clips. Whether you’re looking to record informal clips of the family on vacation, the latest viral video for YouTube, or a set of scenes that will be painstakingly crafted into a cinematic masterpiece using editing software, the a6000 will perform admirably.
Recording a video with the a6000 is extraordinarily easy to accomplish—just press the black button with the red dot at the upper right of the camera’s back to start. Sony has tucked it off to the side to minimize the chance that you’ll start recording a movie accidentally. That’s because video can be captured in any exposure mode; there’s no need to activate a special Movie mode. (If you start recording in Sweep Panorama mode, however, the camera will actually use P mode and the video won’t be a panorama.) After you press the button, the camera will confirm that it’s recording with a red REC and numerals showing the elapsed time. Press the button again when you want to stop recording.
Before you start, though, there are some settings to prepare the camera to record the scene the way you want it to. Setting up the camera for recording video can be a bit tricky, because it’s not immediately obvious, either from the camera’s menus or from Sony’s manuals, which settings apply to video recording and which do not. I will unravel that mystery for you, and throw in a few other tips to help improve your movies.
I’ll show you how to optimize your settings before you start shooting video, but here are some considerations to be aware of as you get started. Many of these points will be covered in more detail later in this chapter:
However, the camera can shoot a continuous movie of just under 30 minutes when using AVCHD (Advanced Video Coding High Definition) format, or 20 minutes for MPEG4. If you reach that limit, you can stop recording and start shooting the next clip right away; this assumes there’s enough space on the memory card and adequate battery power. Of course, you will miss about 30 seconds of the action. (Also see the later item about keeping the camera cool.)
Vendors are really cagey about revealing the reason for the seemingly arbitrary/non-arbitrary 29 minute, 59 second limitation on the length of a single video clip—not only with Sony still cameras, but with other brands as well. So, various theories have emerged, none of which have proven to be definitive.
First, here’s what I recommend you do to prepare for your recording session:
If you decide to shoot in MP4 instead, you’ll have only two options, the default 1440 × 1080 12M (for very decent quality) and VGA 3M (for small 640 × 480) videos suitable only for web use).
Which of the many options should you choose? It depends in part on your needs. I have provided a brief hint as to what you can expect with each option in terms of quality. When you have very little remaining space on your memory cards, or if your video clip is intended strictly for upload to a website, you might choose MP4 and VGA. For high quality in a file format that’s widely supported by editing software and by older computers, stick with the high-quality default MP4 setting. The MP4 format is also more “upload friendly”; in other words, it’s the format you’ll want to use if you plan to post video clips on a website, including video sharing sites that can accommodate the 1440 × 1080 video clips. The movies may not look perfect on an HDTV but this won’t be a problem unless you’re a stickler for superb quality.
If your plan is to primarily shoot videos that you’ll show to friends and family on an HDTV set, choose AVCHD. That format gives you the best quality, but can be harder to manipulate and edit on a computer than MP4 videos. I’ll explain the difference between 60/50 and 24 fps (or 25 fps) rates later in this section.
Note
If you don’t have third-party editing software, you’ll be pleased to know that the downloadable Sony PlayMemories Home software can be used for editing of your movies and to write your 60p video clips directly to a Blu-ray disc. Of course, not all Blu-ray players support 1080/60p playback.
If you decide to try this, compose the scene as desired before pressing the record button. Set the Focus Area in the Camera Settings 3 menu to Flexible Spot. Press the lower directional button and the orange bracket will appear on the screen, indicating the current location of the active focus detection point. Move the brackets so they cover the primary subject and press OK (the center button) to confirm. You can now begin recording the video, confident that the focus will always be on your primary subject (assuming it does not move while you’re recording).
However, if you elect to bypass Movie mode and shoot from within Intelligent Auto or Superior Auto modes instead, you do have access to some overrides. Press the lower directional button and a screen will appear with the Photo Creativity menu superimposed over the live preview of the scene. Scroll left/right among them and the title of the one you’re at will appear. (See Figure 8.1.) These include Background Defocus, Brightness, Color (warm to cool), Vividness (saturation), and Picture Effects. You can preset any of these to the desired level while viewing the live preview to guide you in making the settings that will produce the desired effect. After you start recording however, only the Background Defocus control remains available (also activated with the down directional button).
Figure 8.1 In either of the two Auto modes, you get access to all of the Photo Creativity overrides prior to recording.
In P, A, S, and M mode, all of the functions discussed above work in the same manner as they do when you’re shooting still photos, and they’re discussed in detail in other chapters. Of course, for many purposes you may be content with the default settings, but remember that the a6000 offers great versatility as well. Make the settings before you start recording the movie, using the live preview to decide which will provide the desired effect. After you start recording a movie, you’ll be able to change only the ISO and the level of exposure compensation. (Unless you do so intentionally for a desired effect, avoid changing the exposure compensation during recording since changes in brightness during a movie can be very annoying.)
I find ISO Auto to be fine for most circumstances. If you decide to preset a specific ISO level, be very careful. A low ISO in a dark location can produce an “underexposed” video while setting a high ISO in bright light can produce an “overexposed” clip. Of course, you can preview the effect that any ISO level will produce thanks to live view on the LCD or EVF; set an ISO that will ensure a live view that looks fine. You can change the ISO while recording but remember, changing to a very low or very high ISO will sometimes change the brightness of your video.
By the way, when recording a video in a dark location, it’s possible to get slightly better movie quality, and slightly greater brightness, by activating the Auto Slow Shutter feature in the Camera Settings 7 menu. It is On by default, but if you had set it to Off, I’d suggest turning it back on.
You might prefer to use Aperture Priority (A) mode for full control over the specific aperture; in that case, you can preset a desired aperture and you can also change it anytime while recording. Be careful however, especially if you have set a specific ISO level. If you switch to a very small aperture while recording in low light, your movie clip may darken; this is particularly likely if you’re using a low ISO level. And if you switch to a very wide aperture on a sunny day, especially if using a high ISO, your video will become too bright. Of course, you can see the change in brightness in the live view display before recording a movie and while you’re recording.
Switch to S mode if you want control over the shutter speed; this is a more advanced technique in Movie mode. You can preset a shutter speed and you can change it while recording. Again, be careful as to your settings to avoid a very dark or overly bright video, especially if you have set a specific ISO level. The live view display before and during recording will help to guide you. I don’t recommend using the Manual (M) mode initially but you might want to experiment with it later.
The information display options for the LCD and viewfinder are the same when shooting movies as when shooting stills, except for one aspect: the histogram is not available. Press the DISP button one or more times while recording to switch to another display option when using the LCD or viewfinder. Extra data is provided, including the elapsed recording time, and the time remaining based on the current memory card’s available storage.
Even intermediate movie shooters can be confused by the choice between 24/25 fps and 50/60 fps. The difference lies in the two “worlds” of motion images, film and video. The standard frame rate for motion picture film is 24 fps, while the video rate, at least in the United States, Japan, and other places using the NTSC standard is 30 fps. That’s actually 60 interlaced fields per second; that’s where we get the 60i (60 fps interlaced specification). With interlaced video, the capture device grabs odd-numbered lines in one scan, even-numbered video lines in another scan, and they are combined to produce the final image we view. Progressive scan images (as in 60p) grab all the video lines of an image in order.
Line-by-line scanning during capture and playback can be done in one of two ways. With interlaced scanning, odd-numbered lines (lines 1, 3, 5, 7, . . . and so forth) are captured with one pass, and then the even-numbered lines (2, 4, 6, 8, . . . and so forth) are grabbed. With the 1080/60i format, roughly 60 pairs of odd/even line scans, or 60 fields are captured each second. (The actual number is 59.94 fields per second.) Interlaced scanning was developed for and works best with analog display systems such as older television sets. It was originally created as a way to reduce the amount of bandwidth required to transmit television pictures over the air. Modern LCD, LED, and plasma-based HDTV displays must de-interlace a 1080i image to display it. (See Figure 8.2.)
Newer displays work better with a second method, called progressive scanning or sequential scanning. Instead of two interlaced fields, the entire image is scanned as consecutive lines (lines 1, 2, 3, 4, . . . and so forth). This happens at a rate of 30 frames per second (not fields), or, more precisely, 29.97 frames per second. (All these numbers apply to the NTSC television system used in the United States, Canada, Japan, and some other countries; other places use systems like PAL, where the nominal scanning figures are 50/25 rather than 60/30.)
One problem with interlaced scanning appears when capturing video of moving subjects. Half of the image (one set of interlaced lines) will change to keep up with the movement of the subject while the other interlaced half retains the “old” image as it waits to be refreshed. Flicker or interline twitter results. That makes your progressive scan (p) options a better choice for action photography.
Computer-editing software can handle either type (although AVCHD may not be compatible with the programs you own), and convert between them. The choice between 24 fps and 60 fps (or 25 fps and 50 fps) is determined by what you plan to do with your video. The short explanation is that, for technical reasons I won’t go into here, shooting at 24 fps (or 25 fps) gives your movie more of the so-called “cinematic” look that film would produce, excellent for showing fine detail. However, if your clip has moving subjects, or you pan the camera, 24 fps (or 25 fps) can produce a jerky effect called “judder.” The 60 fps (or 50 fps) option produces a home-video look that some feel is less desirable, but which is smoother and less jittery when displayed on an electronic monitor. I suggest you try both and use the frame rate that best suits your tastes and video-editing software.
Figure 8.2 The inset shows how lines of the image alternate between odd and even in an interlaced video capture.
Movies captured with MP4 format can’t be burned to disk with Sony’s PMB (Picture Motion Browser) software. However, if you capture using AVCHD, you can create Blu-Ray Discs, AVCHD Disks, or DVD-Video discs using the PMB software.
Once you have set up the camera for your video session and pressed the Movie button, you have done most of the technical work that’s required of you. Now your task is to use your skills at composition, lighting, scene selection, and, perhaps, directing actors, to make a compelling video production.
Indeed, the a6000 allows you to choose any exposure mode, including manual exposure, auto ISO, shutter speed, and aperture. You can change settings while shooting, and lock exposure with the AEL button.
Autoexposure works very well, modifying the exposure as the scene brightness changes; the method used depends on the metering mode that you’re using. You can zoom to your heart’s content (though I recommend that you zoom sparingly). Best of all, AF-C autofocus works like a charm; the camera can track moving subjects and quickly snap them back into sharp focus with speedy continuous AF. Manual focus is also available, with focus peaking to help you zero in on a focus plane. Don’t limit yourself based on the weaknesses of past cameras; the a6000 opens up new horizons of video freedom.
If the preview display suggests that your movie will be dark (underexposed) and if it does not get brighter after you set plus compensation, there’s another problem: the camera cannot provide a good exposure for the movie at the ISO that you have set (as discussed earlier). Switch to a higher ISO level until the brightness is as desired or switch to ISO Auto to enable the camera to set a higher ISO level to prevent the “underexposure.”
Why would you need this feature? Let’s say you’re filming entertainers against grass and foliage but you’re moving the camera and will soon be filming a second group against a white sky. As soon as you do so, the backlighting will cause the video to get darker. Don’t let that happen. Before pointing the lens toward the backlit area, press AEL and keep it depressed. This will prevent the exposure from changing as you point the lens toward the backlit part of the scene. This is preferable to waiting until an underexposure problem starts and then setting plus exposure compensation that suddenly makes the video brighter.
You might think that setting your A6000 to a faster shutter speed will help give you sharper video frames. But the choice of a shutter speed for movie making is a bit more complicated than that. As you might guess, it’s almost always best to leave the shutter speed at 1/30th or 1/60th second, and allow the overall exposure to be adjusted by varying the aperture and/or ISO sensitivity. We don’t normally stare at a video frame for longer than 1/30th or 1/24th second, so while the shakiness of the camera can be disruptive (and often corrected by image stabilization), if there is a bit of blur in our subjects from movement, we tend not to notice. Each frame flashes by in the blink of an eye, so to speak, so a shutter speed of 1/30th or 1/60th second works a lot better in video than it does when shooting stills.
Higher shutter speeds actually introduce problems of their own. If you shoot a video frame using a shutter speed of 1/250th second, the actual moment in time that’s captured represents only about 12 percent of the 1/30th second of elapsed time in that frame. Yet, when played back, that frame occupies the full 1/30th of a second, with 88 percent of that time filled by stretching the original image to fill it. The result is often a choppy/jumpy image, and one that may appear to be too sharp.
The reason for that is more social imprinting than scientific: we’ve all grown up accustomed to seeing the look of Hollywood productions that, by convention, were shot using a shutter speed that’s half the reciprocal of the frame rate (that is, 1/48th second for a 24 fps movie). Movie cameras use a rotary shutter (achieving that 1/48th second exposure by using a 180 degree shutter “angle”), but the effect on our visual expectations is the same. For the most “film-like” appearance, use 24 fps and 1/60th second shutter speed.
Faster shutter speeds do have some specialized uses for motion analysis, especially where individual frames are studied. The rest of the time, 1/30th or 1/60th of a second will suffice. If the reason you needed a higher shutter speed was to obtain the correct exposure, use a slower ISO setting, or a neutral-density filter to cut down on the amount of light passing through the lens. A good rule of thumb is to use 1/60th second or slower when shooting at 24 fps; 1/60th second or slower at 30 fps; and 1/125th second or slower at 60 fps.
Once upon a time, the ability to shoot video with a digital still camera was one of those “gee whiz” gimmicks camera makers seemed to include just to have a reason to get you to buy a new camera. That hasn’t been true for a couple of years now, as the video quality of many digital still camera has gotten quite good. The Sony a6000 is a stellar example. It’s capable of HD quality video and is actually capable of outperforming typical modestly priced digital video camcorders, especially when you consider the range of lenses and other helpful accessories available for it.
Producing good quality video is more complicated than just buying good equipment. There are techniques that make for gripping storytelling and a visual language the average person is very used to, but also pretty unaware of. After all, by comparison we’re used to watching the best productions that television, video, and motion pictures can offer. Whether it’s fair or not, our efforts are compared to what we’re used to seeing produced by experts.
Although this book can’t make you a professional videographer in half a chapter, there is some advice I can give you that will help you improve your results with the camera.
For example, one thing beginners sometimes forget is that movies need to move. Even if you’re shooting a static landscape or architectural scene, like the one in Figure 8.3, you should try to incorporate motion in some way. I waited until the powered parasail moved into the picture before capturing my clip of the Alcázar in Segovia, Spain.
Figure 8.3 If possible, incorporate motion into otherwise static scenes.
Camera shake’s enough of a problem with still photography, but it becomes even more of a nuisance when you’re shooting video. While the stabilizer found in lenses with the OSS designation can help minimize this, it can’t work miracles. Placing your camera on a tripod will work much better than trying to hand-hold it while shooting. One bit of really good news is that compared to pro dSLRs the a6000 can work very effectively on a lighter tripod, due to the camera’s light weight. On windy days however, the extra mass of a heavy tripod is still valuable.
A shooting script is nothing more than a coordinated plan that covers both audio and video and provides order and structure for your video. A detailed script will cover what types of shots you’re going after, what dialogue you’re going to use, audio effects, transitions, and graphics.
A storyboard is a series of panels providing visuals of what each scene should look like. While the ones produced by Hollywood are generally of very high quality, there’s nothing that says drawing skills are important for this step. Stick figures work just fine if that’s the best you can do. The storyboard just helps you visualize locations, placement of actors/actresses, props and furniture, and also helps everyone involved get an idea of what you’re trying to show. It also helps show how you want to frame or compose a shot. You can even shoot a series of still photos and transform them into a “storyboard” if you want, such as in Figure 8.4.
Figure 8.4 A storyboard is a series of simple sketches or photos to help visualize a segment of video.
Today’s audience is used to fast-paced, short scene storytelling. In order to produce interesting video for such viewers, it’s important to view video storytelling as a kind of shorthand code for the more leisurely efforts print media offers. Audio and video should always be advancing the story. While it’s okay to let the camera linger from time to time, it should only be for a compelling reason and only briefly.
It only takes a second or two for an establishing shot to impart the necessary information. For example, many of the scenes for a video documenting a model being photographed in a Rock and Roll music setting might be close-ups and talking heads, but an establishing shot showing the studio where the video was captured helps set the scene. (See Figure 8.5.)
Provide variety too. Change camera angles and perspectives often and never leave a static scene on the screen for a long period of time. (You can record a static scene for a reasonably long period and then edit in other shots that cut away and back to the longer scene with close-ups that show each person talking.)
Figure 8.5 An establishing shot from a distance sets the stage for closer views.
When editing, keep transitions basic! I can’t stress this one enough. Watch a television program or movie. The action “jumps” from one scene or person to the next. Fancy transitions that involve exotic “wipes,” dissolves, or cross fades take too long for the average viewer and make your video ponderous.
In movie shooting, several factors restrict your composition, and impose requirements you just don’t always have in still photography (although other rules of good composition do apply). Here are some of the key differences to keep in mind when composing movie frames:
Figure 8.6 Movie shooting requires you to fit all your subjects into a horizontally oriented frame.
Here’s a look at the different types of commonly used compositional tools:
Figure 8.7 A medium shot is used to bring the viewer into a scene without shocking them. It can be used to introduce a character and provide context via their surroundings.
Figure 8.8 A close-up generally shows the full face with a little head room at the top and down to the shoulders at the bottom of the frame.
Figure 8.9 An extreme close-up is a very tight shot that cuts off everything above the top of the head and below the chin (or even closer!). Be careful using this shot since many of us look better from a distance!
Figure 8.10 A “two-shot” features two people in the frame. This version can be framed at various distances such as medium or close up.
Figure 8.11 An “over-the-shoulder” shot is a popular shot for interview programs. It helps make the viewers feel like they’re the one asking the questions.
Much like in still photography, how you handle light pretty much can make or break your videography. Lighting for video can be more complicated than lighting for still photography, since both subject and camera movement are often part of the process.
Lighting for video presents several concerns. First off, you want enough illumination to create a useable video. Beyond that, you want to use light to help tell your story or increase drama. Let’s take a better look at both.
You can significantly improve the quality of your video by increasing the light falling in the scene. This is true indoors or out, by the way. While it may seem like sunlight is more than enough, it depends on how much contrast you’re dealing with. If your subject is in shadow (which can help them from squinting) or wearing a ball cap, a video light can help make them look a lot better.
Lighting choices for amateur videographers are a lot better these days than they were a decade or two ago. An inexpensive incandescent video light, which will easily fit in a camera bag, can be found for $15 or $20. You can even get a good-quality LED video light for less than $100. Work lights sold at many home improvement stores can also serve as video lights since you can set the camera’s white balance to correct for any color casts. You’ll need to mount these lights on a tripod or other support, or, perhaps, to a bracket that fastens to the tripod socket on the bottom of the camera.
Much of the challenge depends upon whether you’re just trying to add some fill light on your subject versus trying to boost the light on an entire scene. A small video light will do just fine for the former. It won’t handle the latter. Fortunately, the versatility of the a6000 comes in quite handy here. Since the camera shoots video in Auto ISO mode, it can compensate for lower lighting levels and still produce a decent image. For best results though, better lighting is necessary.
While ramping up the light intensity will produce better technical quality in your video, it won’t necessarily improve the artistic quality of it. Whether we’re outdoors or indoors, we’re used to seeing light come from above. Videographers need to consider how they position their lights to provide even illumination while up high enough to angle shadows down low and out of sight of the camera.
When considering lighting for video, there are several factors. One is the quality of the light. It can either be hard (direct) light or soft (diffused) light. Hard light is good for showing detail, but can also be very harsh and unforgiving. “Softening” the light, but diffusing it somehow, can reduce the intensity of the light but make for a kinder, gentler light as well.
While mixing light sources isn’t always a good idea, one approach is to combine window light with supplemental lighting. Position your subject with the window to one side and bring in either a supplemental light or a reflector to the other side for reasonably even lighting.
Some lighting styles are more heavily used than others. Some forms are used for special effects, while others are designed to be invisible. At its most basic, lighting just illuminates the scene, but when used properly it can also create drama. Let’s look at some types of lighting styles:
Figure 8.12 With three-point lighting, two lights are placed in front and to the side of the subject (45-degree angles are ideal) and positioned about a foot higher than the subject’s head. Another light is directed on the background in order to separate the subject and the background. There’s also a supplementary hair light above, behind, and to the left of the model.
Figure 8.13 Flat lighting is another approach for creating even illumination. Here the lights can be bounced off of a white ceiling and walls to fill in shadows as much as possible. It is a flexible lighting approach since the subject can change positions without needing a change in light direction.
When it comes to making a successful video, audio quality is one of those things that separates the professionals from the amateurs. We’re used to watching top-quality productions on television and in the movies, yet the average person has no idea how much effort goes in to producing what seems to be “natural” sound. Much of the sound you hear in such productions is actually recorded on carefully controlled sound stages and “sweetened” with a variety of sound effects and other recordings of “natural” sound.
Your a6000 has a pair of stereo microphones on its front surface, able to capture Dolby Digital Audio. There is no way of plugging in an external microphone with the unadorned camera. You must use an adapter plugged into the Multi Interface shoe, or a microphone designed specifically for Sony cameras, such as the Sony ECM-XYST1M mic. If you stick with the built-in microphones, you must be extra careful to optimize the sound captured by those fixed sound-grabbers. You will find an Audio Recording entry in the Camera Settings 7 menu (it just turns sound on or off), as well as a Wind Noise Reduction on/off switch. But that’s as far as your camera adjustments go.
Since recording high-quality audio is such a challenge, it’s a good idea to do everything possible to maximize recording quality:
WIND NOISE REDUCTION
The a6000 does offer a low-cut filter feature that can further reduce wind noise; it’s accessed with the Wind Noise Reduction item of the Camera Settings 7 menu, discussed in Chapter 3. However, this processing feature also affects other sounds, making the wind screen far more useful.
I’ll cover the use of lenses with the a6000 in more detail in Chapter 9, but a discussion of lens selection when shooting movies may be useful at this point. In the video world, not all lenses are created equal. The two most important considerations are depth-of-field, or the beneficial lack thereof, and zooming. I’ll address each of these separately.
Have you wondered why professional videographers have gone nuts over still cameras that can also shoot video? The producers of Saturday Night Live could afford to have Alex Buono, their director of photography, use the niftiest, most expensive high-resolution video cameras to shoot the opening sequences of the program. Instead, Buono opted for a pair of digital SLR cameras. One thing that makes digital still cameras so attractive for video is that they have relatively large sensors; that provides two benefits compared to cameras with a smaller sensor. In addition to improved low-light performance, the large chip allows for unusually shallow depth-of-field (a limited range of acceptable sharpness) for blurring the background; this effect is difficult or impossible to match with most professional video cameras since they use smaller sensors.
Figure 8.14 provides a comparison of the relative size of sensors. The typical size of a professional video camera sensor is shown at lower left. The APS-C sized sensor used in the a6000 is shown just north of it. You can see that it is much larger, especially when compared with the sensor found in the typical point-and-shoot camera and many other compact camera models (at right). Of course, the full-frame sensors found in some cameras, including the Sony Alpha SLT-a99 and Alpha a7r, are even larger. But, compared with the sensors used in many pro video cameras, and the even smaller sensors found in the typical camcorder, the a6000’s image-grabber is larger.
Figure 8.14 Sensor size comparison.
As you’ll learn in Chapter 9, a larger sensor calls for the use of longer focal lengths to produce the same field of view, so, in effect, a larger sensor allows for making images with reduced depth-of-field. And that’s what makes cameras like the a6000 attractive from a creative standpoint. Shallow depth-of-field makes it easier to blur a cluttered background to keep the viewers’ eyes riveted on the primary subject. Your a6000, with its larger sensor, has a distinct advantage over consumer camcorders in this regard, and even does a much better job at offering selective focus effects at wide apertures than professional video cameras.
When shooting still photos, a zoom is a zoom is a zoom. The key considerations for a zoom lens used only for still photography are the maximum aperture available at each focal length (“How fast is this lens?), the zoom range (“How far can I zoom in or out?”), and its sharpness at any given f/stop (“Do I lose sharpness when I shoot wide open?”).
When recording video, the priorities may change, and there are two additional parameters to consider. The first two I listed, lens speed and zoom range, have roughly the same importance in both still and video photography. Zoom range gains a bit of importance in videography, because you can always/usually move closer to shoot a still photograph, but when you’re zooming during a shot, most of us don’t have that option (or the funds to buy/rent a dolly to smoothly move the camera during capture). But, oddly enough, overall sharpness may have slightly less importance under certain conditions when shooting video. That’s because the image changes in some way many times per second (30/60 times per second), so any given frame doesn’t hang around long enough for our eyes to pick out every single detail. You want a sharp image, of course, but your standards don’t need to be quite as high when shooting video.
Here are the remaining considerations, and the two new ones:
