Beginner's Guide to High Speed Video

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You have a cool high speed camera. Now what?

You have extensive photographic experience. That's great! You already understand shutter speed, aperture, depth of focus, ISO etc. On the other hand you may simply want to use the camera but don't understand all that mumbo-jumbo. Either way, this guide will provide a quick introduction to high speed video and how to successfully use the edgertronic camera.

Exposure: An Exercise in Tradeoffs

Modern digital cameras use shutter, aperture and sensitivity settings to control exposure (how bright or dark the image is). These settings might be automatic in a Point-and-Shoot camera, or they might be manually overridden in a high end SLR. The edgertronic high speed camera provides manual control of these settings, allowing the user to optimize the settings for the task at hand. Most of these settings are tradeoffs: changing a particular setting will improve one characteristic and simultaneously degrade another. Furthermore, these settings often interact with each other. An understanding of these tradeoffs and interactions will help you pick the best balance, of these settings, for your unique application.

Aperture: Light vs Depth-of-Field

The aperture is the part of the lens (iris) that can be opened or closed to let in more or less light. Turn the aperture ring and you'll see the iris open and close, admitting more or less light. Apertures are specified in F-stops like f2.8. The Nikon lens supplied with the edgertronic has an aperture range of f1.8 (large iris, most light) to f22 (small iris, least light). Here's the second tradeoff: there's a range of distances where objects are in focus, called Depth-of-Field (DOF). Large apertures like f1.8 let in the most light, but the DOF is very small. Conversely, smaller apertures like f22 let in less light, but the DOF is much larger.

Todd Vorenkamp at B&H Photo and Video has written a fantastic tutorial on this subject: Understanding Aperture

Shutter: Light vs Motion

A shutter is a mechanical or electronic device that controls how long light is captured for each frame. For historical reasons, the shutter is specified in fractions of a second like 1/60. The edgertronic has an electronic shutter, and the shutter can be set from 1/10 to 1/250,000. Here's the first trade off you must manage: long shutters let in more light, but short shutters are better at freezing motion and allow higher frame rates.

Todd Vorenkamp at B&H Photo and Video has written a fantastic tutorial on this subject: Understanding Shutter Speed

ISO: Sensitivity vs Noise

The ISO rating is a number that indicates how sensitive the camera is to light. In the old film days, different films had different ISO ratings. The films with low ISO ratings were generally sharper and had less visible grain compared to those with higher ISO ratings. The edgertronic camera is electronic, and the ISO rating can be adjusted from 1600 - 25600 (color) and 6400 - 102400 (monochrome). You guessed it .. ISO is the third trade off. You will get the best image quality at low ISO settings. Higher ISO settings electronically increase the light sensitivity, but also increase noise.

Todd Vorenkamp at B&H Photo and Video has written a fantastic tutorial on this subject: Understanding ISO

Lenses: What's in your camera bag?

The edgertronic ships with a Nikon 50mm f1.8D lens. This single lens suits the widest range of customer applications. If you could pick only one lens, then this is the one to have. Some customers will have special requirements that require a different lens.

Here are some articles from B&H Photo and Video that explains the differences between standard, wide angle telephoto and macro lenses:

ROI: Resolution vs Frame Rate

The ROI (Region Of Interest) is the rectangular region, set by the user, that defines the image sensor region read out each frame. The edgertronic camera reads 756Mpix/sec from the image sensor. Although ~12x faster than a typical video camera, it's still finite. All High Speed video cameras let you trade off the size of the ROI and frame rate. A 1280x1024 ROI has 1.31Mpixels and can be read out at 494 frames/sec. By setting a smaller ROI, 192x96, for example, the frame rate can be increased to 17.791 frames/sec. Of course many intermediate ROI and frame rates are possible as well.

Capture Buffer

The Capture Buffer is an 8GB (16GB optional) high speed memory, that holds the RAW data form the image sensor because you can't compress 756 Mpix/sec to an h.264 file. Depending on the settings, the capture buffer will hold at least 9.8 seconds of video. The UI allows the user to set a shorter buffer length (faster encode) as well as a pre-trigger percentage. After the camera is setup, and before a trigger occurs, the image sensor data is continuously written into the capture buffer. Once full, the oldest frames are discarded to make room for newer frames. When a trigger event occurs, a post-trigger frames, are saved to the capture buffer. When this save completes, the camera switches to encoding the frames, in the capture buffer, into an h.264 video file. Note that the pre-trigger lets the user capture events that occur prior to the trigger.

You Can't Have Too Much Light

Let's say you are trying to take a high speed video of a baseball being hit. You want to freeze the fast motion, so you'll need a fast shutter setting. You want everything to be in sharp focus, so you'll need a small aperture for good DOF. You want the image quality to be as good as possible, so you'll need a low ISO setting. A fast shutter needs more light, so does a small aperture and low ISO setting. Now, you need a lot of light, far more than you've ever needed. Even daylight may be insufficient.

Why does high speed video require so much light? The simple answer is shutter speed. A normal video might be shot with a 1/60 equivalent shutter speed. The edgertronic is a high speed video camera and you'll rarely use shutter speeds slower that 1/500. In the baseball example above, you might use a shutter speed of 1/3,000. That requires 50x more light (5.7 F-stops) than a 1/60 shutter. That's a big difference. Now turn the shutter to it's fastest setting: 1/250,000. Now you need 4167x more light (12 F-stops). Sunlight might not be enough.

Artificial Lighting and Flicker

If you are using the edgertronic indoors, you are likely to need artificial light. Most light sources will flicker at 2x the power line frequency. The severity of the flicker depends on the type of light: Discharge lamps with magnetic ballasts (florescent, mercury, sodium and HID) are the worst in terms of flicker. Tungsten, Halogen and lights that have electronic ballasts (CFL's, general illumination LED's), which are somewhat better in terms of flicker, but may still be objectionable. Electronic lights that run off of a regulated power supply are the only ones that are truly flicker free. The edgertronic is calibrated for daylight (5500K). Keep this in mind when choosing artificial lights.

Lights, Camera Action

Enough talk, let's setup the camera by referring to Quick start guide. Now you should be connected to the camera and you see the settings window. If you want to change any setting(s), just enter them in the Desired column, and the values in the Allowed column will be recalculated. In general, a setting has priority over the settings below. Further, unspecified (blank) settings are automatically set to the highest speed possible based on the other settings. At this point, the settings are just a "what if" and haven't actually changed the camera settings. When you want to try out the settings, click the X in the upper right corner of the settings window, or click outside the settings window. At this point the camera will automatically Calibrate and then show a Live Preview.

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