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February 20, 2013 9:42 AM
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10 Basic Things Indie Filmmakers Need to Know about Digital Cinematography Before Shooting

7. Frame Rate

Frame rate is the frequency with which your DSLR captures consecutive images. This typically corresponds to the number right before a “P” in the case of progressive images, so that 24p is 24 frames per second, 30p is 30 frames per second, and 60p is 6,000,000 frames per second. Just kidding. Different frame rates have very different motion rendering characteristics, which, combined with different shutter speeds, produce images that behave very differently. Motion pictures have had a standard frame rate of 24 frames per second since the 1920s, and audiences have come to associate this frame rate with cinematic content, so being able to shoot in 24p is essential if you’re planning on shooting narrative material. However, you don’t always have to shoot at the same frame rate at which you’re planning on distributing your material. For example, if your DSLR can shoot 60p, this is a very effective way of acquiring slow-motion footage — anything shot at 60p can be played back at 40% speed in a 24p timeline for a flawless slow-motion effect, and can generally be slowed down further in your editing system.

8. ISO & Noise

ISO is actually the International Organization for Standardization, which is why you see it used in lots of places beyond photography — many businesses are certified ISO:9001, for example. As cinematographers we’re concerned with just one “standardization,” however — the one that pertains to measurement of noise in photography. ISO as it relates to digital photography is based on analog standards of film speed — while we won’t be shooting a frame of actual film with our DSLRs, our cameras are calibrated so that an ISO of 400 on our camera is somewhat equivalent to a film SLR’s ISO 400. ISO is a logarithmic measurement, so ISO 400 is twice as sensitive to light as ISO 200, ISO 200 is twice as sensitive as ISO 100, and so on and so forth.

The relationships between sensitivity and noise is basically linear, however, so the higher the ISO, the brighter the image — and the more noise contained in the image. However, thanks to sophisticated noise reduction and other processing tricks, DSLRs have managed to dramatically reduce noise at higher ISOs, and can often blow film stock out of the water (this depends on which camera you’re shooting with, which we’ll cover in the next chapter).

9. Progressive vs. Interlaced

Interlacing was a workaround invented for oldertech CRT monitors in the 1930s that has lived far too long. In the early days, video bandwidth was more limited than today, and so engineers found a way to divide a frame into two images and display it using alternating fields. As you can see in this image of a tire wheel, interlacing can cause motion artifacts (as well as a host of other problems). We’re lucky to live in a predominantly progressive society today — in the imaging sense if not the political. Progressive scanning is a method that captures and displays the lines of an image in sequence, which is akin to motion picture film with regards to motion rendering. Compared to interlaced images, progressive images have a higher vertical resolution, lower incidence of artifacts, and scale better (both spatially and temporally). Friends don’t let friends shoot interlaced! Luckily, while there are plenty of video cameras that shoot interlaced footage, every DSLR I can think of shoots progressive footage.

10. Shutter Speed

Shutter speed refers to the length of time an image is exposed. For film SLRs, this would be measured by the amount of time the camera’s mechanical shutter is open, but for shooting video on DSLRs, this is simulated electronically. Shutter speed affects the amount of light that reaches the camera and also affects the motion rendering of the moving image. Lower shutter speeds yield a brighter and smoother image (up to and including water and light blurring tricks), whereas higher shutter speeds result in a darker and more stroboscopic image. Motion picture film cameras typically shoot with a 180-degree shutter, which means that the shutter is open 50% of the time (180 out of 360 degrees). This means the amount of time your shutter is open is half of the shooting frame rate; thus, at 24 frames per second, a 180-degree shutter is best emulated on a DSLR by choosing a shutter speed of 1/48.

This may not be possible depending on your DSLR, so the closest reading will do — 1/50 or 1/60, for example. This gives the most “filmic” rendering of motion, but can be varied greatly depending on your intention. Higher shutter speeds create “jerkier” images, as most famously seen in action films like Saving Private Ryan and Gladiator. Conversely, lower shutter speeds create “smoother” images due to increased motion blur. There is no hard and fast rule when it comes to shutter speed, but if you’re not sure of what shutter speed to select, go with the setting that’s closest to half that of your current frame rate.

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1 Comment

  • shubhkaran | July 13, 2013 9:13 AMReply

    thank you.It was very helpful.