How Did Film Crews Back in the Day Film Footage of CRT Screens Without the Screens Flickering?

Filming CRT (Cathode Ray Tube) screens without capturing flicker was a common challenge for filmmakers back in the day. However, several techniques were developed and employed to overcome this issue and ensure smooth and professional-looking footage. Join us as we explore the methods used by filmmakers to achieve flicker-free CRT footage.

Frame Rate Matching

One effective technique utilized by filmmakers was matching the frame rate of the camera to the refresh rate of the CRT. CRTs typically refresh at specific rates, 60 Hz in the U.S. and 50 Hz in Europe. For instance, using a camera that operated at 24 frames per second (fps) allowed for capturing footage without flicker as the shutter speed could be adjusted to avoid capturing the refresh cycles. This synchronization effectively eliminated the flicker effect, making the CRT footage appear smooth and visually appealing.

Shutter Speed Adjustment

Another technique involved adjusting the shutter speed of the camera to synchronize with the refresh rate of the CRT. By carefully calibrating the shutter speed, filmmakers could minimize the risk of capturing flicker. This method required a fundamental understanding of both the camera and the CRT's refresh cycle to ensure that the two were in sync.

Interlacing Techniques

Some filmmakers employed interlacing techniques to reduce the perception of flicker. This involved filming the CRT in a way that captured alternating lines of the screen. By doing so, the flicker effect was less noticeable, creating a more stable and smoother visual experience.

Post-Production Techniques

In certain cases, post-production techniques were used to stabilize and reduce flicker in the footage. Although less common in earlier filmmaking practices, modern post-production tools have significantly improved the ability to further refine the footage. These techniques often involved frame interpolation and other stabilizing algorithms to enhance the smoothness of the final output.

Lighting Conditions

Filming in well-lit environments also played a crucial role in reducing flicker. The ambient light helped to mask some of the flickering effects, contributing to a more stable and clear image. Filmmakers often aimed to achieve a balance between lighting and exposure to ensure that the CRT footage remained free from distracting flicker.

Modern Solutions: Sony XDCAM Camcorders

Modern technology has introduced advancements such as the electronic shutter mode (ECS) found in Sony XDCAM camcorders. These camcorders can counteract flickering at various frequencies, making them highly effective for filming CRT screens, old CCFL-backlit LCDs, videowalls, and even some older oscilloscopes and radars. The ECS mode works well with fluorescent lamps, RGB triad LED lights, and other sources of flickering light.

Setting Shutter Speed for CRTs

For CRTs, it is essential to know the actual refresh rate and set the shutter speed accordingly. If possible, the shutter speed can be set to full, double, or quadruple the rate of the CRT's refresh cycle. For NTSC CRTs and 60 Hz LCDs, a shutter speed of 1/30 is recommended, while for PAL CRTs, 1/25 should be used. For 75-85 Hz CRTs, 1/30 or 1/40 should suffice.

It is important to note that while Sony XDCAM camcorders can counteract most flickering, sometimes there is still a minor residual flicker, but it is much less noticeable. In most cases, scan lines on CRTs are also minimized, resulting in a cleaner and more professional appearance.