ON THIS PAGE:

Intro
Setting the speed
Why use the shutter?
Stopping computer flicker

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PART 5: THE SHUTTER

by Christina Fox

There are four controls on the camera that affect exposure…

S     SHUTTER

I      IRIS

N    NEUTRAL DENSITY (ND)

G    GAIN

On this page we'll look at the shutter. On other pages we'll look at the Iris, ND Filters and gain.

INTRO

About 15 years ago, when CCD imaging chips were first launched they had a design fault. If the camera was pointed at a bright light, like a car head lamp, a red line (smear) would appear above and below the light source. To solve the problem the manufactuers introduced a mechanical shutter into the camera. Today the shutter speed is adjusted electronically by varying the amount of time the CCD (the part of the camera that forms an image) is allowed to form an image.

Today the red smear has been eliminated by redesigning the CCD chips but the shutter has remained as a gimmicky extra.

The shutter speeds available are: 1/3, 1/6, 1/12, 1/25, 1/50, 1/60, 1/100, 1/120, 1/150, 1/215, 1/300, 1/425, 1/600, 1/1000, 1/1250, 1/1750, 1/2500, 1/3500, 1/6000, 1/10,000 (of a second).

As the shutter speed increases, the amount of light entering the camera effectively decreases. In fact, a shutter speed of 1/120 reduces light levels by about a half. So, if you do want to use the shutter ensure you have sufficient light.

SETTING THE SHUTTER MANUALLY

1. Set the AUTO LOCK switch to the middle position
2. Press the SHUTTER SPEED button and the speed indicator will appear in the viewfinder/LCD screen.
3. Turn the SEL/PUSH EXEC dial to select the speed you want.

In manual you only have discrete shutter speeds to choose from as listed above. But in Auto the shutter seems to be infinitely variable and this can be exploited to stop computer screens from flickering (see below).

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WHY WOULD YOU USE THE SHUTTER?

With the shutter on high speed, the camera views the scene the way your eyes would, if it was lit by a stroboscopic light such as at a disco (remember those!). Fast moving objects take on a distinct look with very little motion blur. So, very fast shutter speeds are great for seeing fast moving subjects very clearly. Helicopter blades and tennis balls will seem clearer at high shutter speeds.

Lower speeds can be great for music videos. They are often used in documentaries to denote that the action on screen is a reconstruction. They can also give the actors eye view if they are portraying someone on drugs, drunk or very ill.

Leave the shutter speed at 50 for PAL cameras (60 for NTSC) if you want to see no shutter "effects".   50 (60) is close to how the eye and brain see the world

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SHOOTING COMPUTER SCREENS WITHOUT FLICKER

Many camera (Canon XL range, Sony DSR500 and Panasonix DVZ100) now have a clear scan feature for taking out the flicker from old computer screen. Unfortunately, Sony decided not to bother with this feature for the Z1. So, here is a very clever way of getting rid of computer screen flicker...

• Frame a shot of the computer screen
• Start with the camera set to manual gain (Low - 0dB) and auto shutter
• Use auto iris to get the exposure about right
• Then select manual iris and adjust up and down - you'll see black bars or white bars.
• Try and settle on an exposure that is somewhere around the transition from black into white bars.

  

• Slowly tilt the camera up and then down. You'll see black flickering bars and white flickering bars. Somewhere in between these two conditions is what you are after. So, keep tilting up and down until you see the flickering on the computer screen disappear.
• Once the screen has completely stopped flickering press the shutter button immediately.
• You are now in manual shutter mode – which holds the correct shutter speed.

  

Done!

© 2000 - 2010

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Move on to...

Part 6: WHITE BALANCE

Or back to...

Part 4: GAIN

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Christina Fox