DIYFU P2 M3 L3 Cinematography Terminology.docx

Exposure

Exposure, in simple terms, is the amount of light that falls on a unit of photographic medium. In other words, each frame you shoot will have a certain amount of light that has graced the sensor of your DSLR or camcorder. Managing that light is integral to getting a quality image.

What is “Good Exposure”?

Having the appropriate amount of light hit your subject and shooting environment so that the highlights aren’t too harsh or the darkest areas too dark to cause those aspects of your image to be devoid of detail. Once you achieve proper exposure, you can then adjust your image artistically to be more particular to your needs as a filmmaker.

In order to do that, there are some fundamental terms you need to understand. We’ll also talk about how to use a tool designed specifically to properly expose your image.

Sunny 16 Rule

An approximately correct exposure will be obtained on a sunny day by using an aperture of f/16 and the shutter speed closest to the reciprocal of the ISO speed of the film; for example, using ISO 200 film, an aperture of f/16 and a shutter speed of 1/200 second. The f-number may then be adjusted downwards for situations with lower light.

F-Stop

The f-stop of a lens is the minimum and/or maximum number at which the aperture is set. The larger the number the more closed the aperture will be, which means the more light you’ll need to register a quality image.

There are finite f-stop values. The standard f-stop values are: 1.0, 1.4, 2.0, 2.8, 4, 5.6, 8, 11, 16, 22.

To calculate an f-stop, you would divide the lens diameter by the lens’ focal length. So, a 50mm lens with a diameter of 28mm would be f/1.8 (1.78 to be exact).

Steps to calculate an f-stop (for the curious)

1) find your lens diameter (this can typically be found in the literature accompanying your lens when you buy it or on the manufacturer’s website)

2) find your focal length (this should be on the barrel of the lens; if not, it’ll be in the manual for the lens).

3) Divide the diameter by the focal length

d/fl = f-stop

When you decrease the f-stop number, you are widening the area of the lens. Each descending f-number doubles the area (say, f/8 to f/5.6). To double the area, we need to divide the f-number by the square root of 2. The square root of 2 is 1.414.

Example: 2.0 / 1.414 = 1.41

Each increasing f-number effectively halves the amount of light approaching the camera. In this case, you’d multiply the current f-number to the next by 1.414.

Example: 8 * 1.414 = 11.3

A good way to remember how light is affected by the aperture is “larger f-stop number = more closed aperture”.

Many inexpensive zoom lenses have a variable f-stop (or variable aperture), meaning the more you zoom in, the more closed the aperture will become. For instance, the cheaper of the two kit lenses that you can buy with the Canon T2i and T3i is an 18-55mm 3.5-5.6, which means at 18mm (the lens’ widest setting) the aperture is opened further, which allows more light in than it would at its most narrow setting (55mm, 5.6).

https://en.wikipedia.org/wiki/F-number

T-Stop

T-stops (Transmission stops) are numerical values based on the actual light available after absorbency. Even the best lenses absorb some of the light that hits them. Many consumer lenses and photography lenses are rated in f-stop values, whereas cinema lenses are rated in T-stops because of the rapid succession of frames shot, where even the slightest bit of light loss may be noticeable.

You can find out your lens’ transparency ratio from the literature accompanying it. From there, you can calculate the T-stop by dividing the f-number of the lens by the square root of the transparency ratio:

T = f/√t

So, if your lens has an f-stop value of 2 and a transparency ratio of 78% would have a T-stop value of 2.27.

https://en.wikipedia.org/wiki/F-number

Depth of Field

Depth of field (DOF) is the distance in which subjects are most in focus. This can range from several inches (in the case of the 50mm 1.8 mentioned above) to several feet (like a 200mm lens, for instance).

Focal Length

The focal length of a lens determines the field of view of the image being recorded. 10mm, for example, is extremely wide, whereas 1000mm will be extremely narrow in most cases. This also is dependent on what it is you’re shooting. A 50mm lens is often very good for close-ups without a lot of movement (keep in mind the miniscule focal distance with that lens) and a 100mm is good for portraits, medium shots, etc., because the focal distance is much greater. It will allow you to keep your subject in focus and have the background blurred. This is a practical example of depth of field. (see above)

Using a Light Meter

A light meter will be your primary tool for setting your camera to get proper exposure of your scene.

A reliable method for finding the appropriate f-stop for your lens is to get light readings of your subject where the light is even, where it is hottest (brightest) and where it is darkest and average the f-numbers by dividing by three.

So, if your highlights are at 1.8, your midtones are at 2.8 and your shadows are at 3.5, you’d add them up:

1.8 + 2.8 + 3.5 = 8.1

Then divide that by 3:

8.1 / 3 = 2.7 (which we’ll round up to 2.8)

This number will give you a good overall exposure in this hypothetical situation.

A light meter should be your best friend, especially when just starting as a filmmaker/cinematographer. It’s a device that measures the temperature of light and will give you a numerical reading to use to set your f-stop based on the frame rate you’re shooting at, shutter speed and ISO. It’s a very handy tool to have. They range in price, and I would recommend picking one up that is capable of calculating for digital standards. You can usually find a light meter for relatively cheap on eBay; just remember to test it when it arrives and contact the seller if there’s a problem.

Shooting Tips

When outside in sunlight, it’s best to set your camera to the least sensitive ISO and use a neutral density filter to generate a better quality image

ISO/ASA

ISO is an abbreviation for the International Organization for Standardization. Why it’s not IOS is another issue. ASA stands for American Standards Association. There’s your history lesson.

ISO (or ASA) is the numerical rating of photographic film stock based on its sensitivity to light. The higher the number, the more sensitive it will be to light. This applies to digital as well, since the sensor and the computer within the camera attempts to mimic this aspect of filming.

This is the difference between using organic and digital ISO values. Organic ISO values are ISO settings traditionally found when using film – 100, 200, 320, etc. Digital ISO values have been added to DSLR cameras to bring more variety and increase the diversity of shooting environments for users. Once you push your ISO past 800 on most cameras, you will be able to see a good deal of grain and digital noise. ISO 400 is ideal for inside photography, but there can be slight noise visible as well.

This, too, has to do in part with the size of your camera’s sensor. The smaller the sensor, the more light it needs to create a quality image. That means, too, that low light performance is affected (take the Canon T3i and Panasonic GH2, for example).

Ideally, to avoid excessive digital noise, you should attempt to set your ISO to the lowest setting that will still generate a quality image in the environment in which you’re shooting. It’s best to play around with your camera to find out what ISO setting begins to create the most grain and digital noise. That is the number you should avoid exceeding, if possible.

Shutter Speed

The shutter is the eyelid of your camera’s lens. The shutter speed, then, is the time in seconds or fractions of seconds it takes to close, thereby capturing an image.

Ideal overall shutter speed is determined by frame rate, though a number of factors influence it. For instance, if you’re shooting at 24p (digital’s equivalent to film – 24 frames a second), your ideal shutter speed would be double the frame rate, so 1/48 of a second.

Shutter speed can be manipulated for a number of stylistic reasons. If you’re looking to achieve a stuttering effect in motion, like 28 Days Later, you would want to increase your shutter speed to something like 1/250 of a second. You would then have to “stop down” your f-stop on your lens to compensate for the sensitivity to light.

Shutter Angle

The angle of the shutter will affect your image. Typically, the shutter is a semicircle and is set to 180 degrees. Adjusting this to 270, for instance, will cause the shutter to be open longer in its revolution, allowing more light in. This will also affect the natural feel of motion in footage captured.

Standards -- NTSC and PAL

This has to do with the rating of electricity and the difference in television technical standards.

NTSC stands for the National Television System Committee and is the standard used in North America, South America, the Phillipines and some Pacific islands. NTSC uses frame rates of 60i or 30p, which offers 20% more fluid motion than PAL.

For folks shooting in PAL (which stands for Phase Alternating Line and is used in European markets), the frame rate is 50 frames/sec, so the ideal overall shutter speed would be 1/50 of a second. Because of its technology, PAL offers more accurate color representation.

The Cinematography Triangle

Let’s briefly go over this, because these three factors influence your image.

At the top is your ISO. At the first corner is your f-stop and the second corner is your shutter speed. For digital filmmaking, each of these variables can be adjusted.

Here’s an example of how this triangle works. Let’s say you’re shooting at ISO 200, with an f-stop of 3.0 and shutter speed of 1/48; you see that your ISO setting is too sensitive even at 200 and you pull back to ISO 100. You would then have to adjust your f-stop to 2.8 (“stopping down”) to keep a quality image.

Another example: if you’re set at ISO 800 (which means you’re probably in a fairly dim environment, since you’re using a much more sensitive “film stock”) and have a shutter speed of 1/48 and an f-stop of 1.8, you should probably adjust your shutter speed to 1/24 of a second, which will brighten your image because your shutter will be open longer to capture your image. (This is most effective in environments in which there’s no movement, since you’re liable to pick up light traces and blurry subjects if there’s action)

Keep in mind, though, that with most cameras, if you’re using a highly sensitive ISO, adjusting shutter speed may result in a grainy image, moreso than it will be already. In the case of digital filmmaking, you’ll end up with digital noise, which will make for an ugly picture.

All of these elements work in tandem to create a great image. Though you should avoid blowing out the details of your scene, the more light you use, the better image you’ll get.

Frames Per Second

For the purposes of this example, I will be describing frames per second as it relates to speed of motion in your film.

If you’re looking to achieve fast motion, you’ll want to shoot fewer frames per second (fps). With film, 12 fps would be double speed; 8 fps would be 2/3 as fast. Unfortunately, I know of no camera currently that accomplishes this. More filmmakers are looking for true slow motion rather than fast motion.

In order to accomplish decent fast motion, you could use something like Time Remapping in After Effects or transcode your footage to the appropriate frame rate.

Shooting slow motion is the opposite; you’d employ more frames. The more frames per second you shoot, the more footage you have and the slower it will play. There are cameras on the market that can accomplish far higher frame rates, but they are often outside the budget of most filmmakers initially. Besides, slow motion is only ever used for stylistic purposes, so if you have a sequence that requires it, you might as well rent the camera for that sequence rather than buying one for occasional use.

A good number of cameras have the capability of shooting 60fps, like the Canon T2i and T3i, though, with those two cameras, you’re limited to 720p instead of full HD (1920x1080).

Since we’re on the topic, I suppose I should go into aspect ratios now…

Aspect Ratio and Resolution

Aspect ratio has to do with the shape of the frame and television standards mostly.

Films are shot in a number of different aspect ratios. Some of the common ones used are 1.85:1 and 2.35:1.

The frame of an image shot in the 1.85:1 aspect ratio is 1.85 times as wide as it is high; 2.35:1 is 2.35 times as wide and is called anamorphic.

There are others, like 1.77:1, 1.66:1, etc.

So frame-wise, standard definition footage is shot at 4:3 (1.33:1). HD is 16:9. This means the frame is four units wide and three units high and 16 units wide/9 units high, respectively.

When you hear about footage being 640x480, for example, you’re hearing someone describe the resolution of an image per thousands of pixels. The smallest high definition resolution is 720x480. Film resolution is 4k once it’s transferred to a digital medium for effects work and editing.

Resolution and aspect ratio matter a good deal when deliberating as to what kind of project you’re making and how it’s going to be delivered. There are far more things to consider when taking these things into account. For a thorough technical education, pick up “The Filmmaker’s Handbook: A Guide to the Digital Age” (see the Resources section).

Progressive vs. Interlaced

Might as well briefly cover this, too…

If you’ve ever seen a “p” next to some numbers in filmmaking or electronics (like televisions, for example) it indicates a “progressive” image, meaning each frame is one image, there are no fields to it.

An interlaced image (indicated by an “i” – 1080i, for instance) has fields. It is not one single image but two images interlaced by their fields. If you were to examine interlaced footage, you’d see that it’s made up of interwoven lines.

Style

So then, stylistically, what is it you’re going for? Do you want everything in focus like a comedy or the action scenes in action films (deep focal length)? Will you rely heavily on lenses with shallow depth of field that will keep your subjects in focus but obscure the background? This can be good in intimate moments with your characters.

Do you plan on using fast motion or slow motion at all? These are all things to consider when planning and shooting your film.