VIDEO CAMERA 1995

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FEATURE

 

HEAD

STABLE RELATIONSHIPS

 

INTRO

Image stabilisers on camcorders have been around for quite a while but no-one has ever really put them to the test, until now that is...

 

COPY

You can tell in a second when a video-movie has been shot by a professional. It’s got nothing to do with picture quality, texture or composition, it’s much simpler than that, professionally-shot movies don’t wobble! Camera shake is the instant give-away, it looks untidy and amateurish, but how can you avoid it?  The answer is simple, use a tripod or some other kind of rigid support, but how many of us are prepared to lug one around, let alone mess around setting it up for each shot.

 

The trouble is we all suffer from the shakes, even if your alcohol intake is moderate, or non-existent. Our arms and bodies are in a constant state of motion and we all experience involuntary muscle movements, the blood pumping through veins causes minute tremors. These tiny movements mostly go unnoticed but if you doubt they exist try holding a camcorder absolutely steady for more than a few moment. It can’t be done, even the tiniest movements show up on the recording, and they’re magnified at higher zoom settings. It’s not so bad with larger and heavier machines which have a damping effect, but as camcorders get smaller and lighter it can only get worse. Back in the late 1980’s one of the major manufacturers carried out detailed research into this problem and concluded that although it was technically feasible to build a camcorder weighing less than 500 grams camera shake would make it almost unusable.

 

Panasonic pioneered the concept of image stabilisation on camcorders and the NV-S1,  launched in the Spring of 1980, was the first domestic machine to feature an electronic image stabiliser (EIS). In fact image stabilisation systems of one kind or another have been around almost as long as there have been movie cameras, but the first serious attempt to fit one to a camcorder was in 1987, when Panasonic demonstrated a gyro-stabilised lens assembly, fitted to the front of one of their full-size VHS machine. It was a most impressive feat of miniaturisation, even so it was still quite bulky, and, we suspect mechanically fragile with a voracious appetite for power; as far we know it never went into production.

 

ELECTRONIC V OPTICAL

Nowadays image stabilisers fall into two very distinct categories. The first, and still the most common type uses electronic processing techniques to eliminate camera shake. The second type uses an opto-mechanical system, we’ll look at both of them in turn.

 

Several different electronic stabilisation systems have been developed, initially by Panasonic and later by Mitsubishi, Hitachi and Sony, but they all work on more or less the same principle. Light coming through the lens forms an image on the face of the CCD sensor chip. Any movement of the camcorder causes the image to shift across the face of the chip, when the stabiliser is switched on, motion detection systems inside the camcorder measure this movement and shift or ‘float’ the image area of the CCD on the face of the chip, to trace the path of the image, compensating for the movements. Until fairly recently electronic stabilisers suffered from one major problem, a significant reduction in picture quality. That was because the stabilised image area is smaller than the unstabilised one, so it is made up of fewer picture elements or ‘pixels’, making it look coarser. The difference in size is not usually apparent because the machine electronically enlarges the stabilised image to normal size. Both processes reduce the amount of detail in the picture, and in some cases give the picture a ‘blocky’ or pixellated texture. Within the last year or so we have seen stabilisers that do not impair picture quality;  they work by using higher density CCDs, so the number of pixels that make up the stabilised image are more or less the same as a normal, unstabilised picture.

 

Optical stabilisation was conceived by Canon and developed in collaboration with Sony. They work in an entirely different way to electronic systems, using a device called a vari-angle prism, positioned in front of the main lens assembly. It is made up of a sandwich of two flat glass plates, separated by a flexible sac filled with a transparent gel. The shape of the prism is altered by a set of servos, controlled by information from motion sensors inside the machine. The changing shape of the prism ensures the image is always squarely centred on the face of the CCD chip. This system has no effect on picture quality, but it is more expensive to manufacture, moreover it takes up more space and imposes a additional weight penalty, compared with electronic systems. It’s also fair to assume optical stabilisers consume more power though in practice the overhead is quite small.

 

As a matter of interest Canon have also developed an optically stabilised lens for the EX1/2 camcorder, though we were unable to obtain a sample in time for this feature -- we hope to be take a closer look at it in a future issue.

 

THE TESTS

So we come to the exclusive Video Camera image stabiliser tests, the first to compare older and more recent electronic systems with optical stabilisers. We’ve collected together an assortment of camcorders with stabilisers, almost all of the machines currently on the market in fact. Image stabilisers are still classed as a luxury feature, so the camcorders we’ve been testing are top-end models, costing from £1200 to £1500.  The main difficulty we had was that there are no set procedures for testing image stabilisation systems, so we built a test rig and devised our own units of measurement, which we’ve called Zimmers (Zims for short), in deference to the stability aid of the same name, (see How the Tests Work for more details). The tests replicate the kind of situations manufacturers claim their systems are designed to cope with. The two extremes are shooting whilst walking, and shooting from a moving vehicle. The first produces a lot of up, down and sideways movement, but at a fairly slow speed. The opposite happen in a moving car, there’s less movement, but it happens at a much faster rate. This is how they got on....

 

CANON UC7 Hi             £1200

The UC7 Hi is Canon’s third high-band palmcorder with optical image stabilisation. It’s a fairly routine design -- for Canon -- very similar in appearance to the unstabilised, low-band UC100. Features of note include stereo hi-fi sound, a 4-mode program AE system, built-in video light and wonder of wonders, a Control L/LANC editing terminal. Other exposure facilities are backlight compensation and a manual 7-speed shutter, but that’s about it, this machine is mostly aimed at discerning point and shoot users. Picture and sound quality are both reasonable but unexciting.

 

There is no loss of picture quality whatsoever. Some minor distortions are evident when the stabiliser is operating but this is only apparent on patterned or contrasty objects close to the lens. The stabiliser works best with slower movements, it operates over a fairly narrow range but it copes well with the motion of walking, even so there is always some slight movement giving the picture a not displeasing fluid quality. Loss of lock is progressive and occurred at around 5 degrees/8Hz on the test rig. One for walkers, rather than drivers.

 

Normal picture quality 8

Stabilised image quality            8

Stability factor                         4 Zims

 

HITACHI VM-H70                  £1200

The H70’s main claim to fame is that it is waterproof. Officially Hitachi will only say it’s ‘splashproof’ , but we’ve given it a thorough dunking with no ill effects. It’s also tough, with a resilient two-piece case that we’re told can withstand a lot of punishment. It has a fairly basic specification, as befits a no-nonsense ‘action-cam’ and apart from a fader it has no creative facilities to speak of. However, in good light both sound and unstabilised picture quality is up to the mark. Although it doesn’t have an editing terminal an optional 4-scene edit controller is available.

 

This machine has an older-style electronic image stabiliser and there is a perceptible reduction in resolution, and a change in image size, when the stabiliser is engaged. Moreover there is an increase in pixelation, most noticeable on normal 8mm recordings. The stabiliser works quite well at low speeds, and it can cancel out a moderate range of movements. Our sample lost  lock at 7degrees/12Hz on the test rig, our user tests confirmed that it was happiest walking or shooting from a car at slower speeds, though the drop in picture quality when the stabiliser is on puts it at a big disadvantage compared with the others.

 

Normal picture quality 9

Stabilised image quality            7

Stability factor                         3 Zims

 

 

PANASONIC NV-S90 £1200

Sony pipped Panasonic to the post by being the first to market a ‘no-loss’ electronic image stabiliser but Panasonic can justifiably claim to be the first to have one that works at full high-band resolution. By any reckoning the S90 is a damn fine machine, it’s designed to appeal to serious and semi-pro users; it has a full set of manual exposure controls, including iris and shutter, plus a 3-mode program AE and an eye-catching assortment of digital effects. In addition to an editing terminal (5-pin RMC) it also has an on-board timecode generator (VITC), for improved edit accuracy, and it’s one of only a handful of machines to have a timebase corrector, a useful editing aid when working with older or noisy recordings. Picture and sound quality are both excellent.

 

The CCD image sensor on this machine has a total of 680k pixels, of which 390k are used to create the stabilised image. That’s enough to give a resolution of 400-lines, though only just. There’s no change in image size with the stabiliser on, though we did notice some very slight changes when recording moving objects, caused by a switch in shutter speed to 1/250th sec when the stabiliser is on. On the test rig our sample had the widest range of any of the stabilisers we’ve tried, (previous samples had only been fairly average). Loss of lock is quite sudden and occurred at 10 degrees/7Hz, which backs up our findings that it works quite well in a moving vehicle. The picture can be quite jerky at times, when it looses lock, and this can be quite irritating, otherwise it works very well indeed and overall the machine is well worth considering if you’re looking for a high-performance palmcorder with better than average stabilisation.

 

Normal picture quality 9

Stabilised image quality            8.5

Stability factor             5 Zims            

 

SONY CCD-TR3                        £1500

This has been one of our favourite palmcorders since the day we first clapped eyes on it, but it’s a case of the heart ruling the head for at £1500 it’s somewhat expensive. We’ll look at the ‘Steady Shot’ electronic stabilisation system in a moment but first, the main features. They include a manual iris, 3-mode program AE, LCD colour viewfinder, RC time-coding, Control L/LANC editing terminal plus a couple of novelties, like an illuminated touch-sensitive control panel and a lithium ion re-chargeable battery. Above all it’s cute, fun, and easy to use. Picture quality is good, maybe not the best we’ve seen on a Hi8 machine, but images look clean and colours appear natural under most conditions.

 

The stabiliser has a 570k pixel CCD sensor chip with 350k pixels used to produce the image. Resolution on samples we’ve seen was a little down on the high-band benchmark of 400-lines, at around 380-lines, and there was some slight texturing on the picture with the stabiliser switched on; there was also a slight shift in position (though not in size). This proved to be the most responsive stabiliser in this roundup, able to deal with surprisingly rapid movement. On the test rig loss of lock occurred at 6 degrees/16Hz. Despite the slightly reduced resolution figure this stabiliser is the one we’d choose if shooting from a moving car, and small size were important factors.

 

Normal picture quality 8

Stabilised image quality            7.5

Stability factor                         6 Zims

 

 

SONY CCD-TR2000             £1300

It’s debatable whether this chunky and deceptively heavy (1.3kg all up) camcorder actually needs an image stabiliser in the first place; the optical stabiliser (also confusingly called Steady Shot), clearly adds significantly to the weight and bulk. Nevertheless, there’s plenty else to interest serious movie-makers, it has a manual iris, 4-mode program AE, LANC editing terminal and the facility to read and write RC time-codes, for accurate editing. Picture performance is average to good, there have been reports of colour smearing on some samples, but in general it is capable of impressive AV performance.

 

Test results were very similar to the Canon model, with no reduction in picture quality when the stabiliser is engaged. The stabilisation range is also about the same, compared with the electronic systems it responds to a narrower range of movements, though it is less liable to loose lock at slower speeds. Generally a fine machine, well suited to demanding applications, the stabilisation feature just seems a little out of place amid the other high end editing facilities. 

 

Normal picture quality 8

Stabilised image quality            8

Stability factor                         4 Zims

 

SIDEBAR 1

STABILISING INFLUENCES

1987 -- Summer, Panasonic show prototype VHS camcorder with gyro-stabilised lens

1990 -- September Panasonic NV-S1 first palmcorder with digital image stabiliser (DIS)

1991 -- Steadicam JR gimballed, counterbalanced hand grip, eliminates camera shake

1991 -- September, Panasonic NV-S5, second generation palmcorder with DIS

1992 -- February, Panasonic NV-S7, first high-band palmcorder with image stabilisation

1992 -- June, Mitsubishi CX4/6, VHS-C palmcorder ‘twin-gyro’ electronic image stabiliser

1992 -- June, Mitsubishi CX7 S-VHS-C palmcorder with twin gyro electronic stabiliser

1992 -- August, Panasonic NV-S6, stereo upgrade of  S5, with DIS

1992 -- October, Sony TR-805, first camcorder with ‘Steady Shot’ optical image stabiliser

1992 -- August, Panasonic NV-R50, first slimline machine with colour viewfinder and DIS

1993 -- October, Canon UC5 Hi their first with optical image stabilisation

1993 -- November, Canon E700 and Sony TR606, both with optical stabilisers

1993 -- Canon announce stabilised lens for EX1/2, we’re still waiting...

1994 --  March, Sony TR2000, high-end palmcorder with optical stabiliser

1994 -- April, Sony CCD-TR3, first ‘no-loss’ electronic stabiliser

1994 -- May, Hitachi H70 Weathercam, first waterproof machine with stabiliser

1994 -- July, Sony TR550, cheapest palmcorder with ‘no-loss’ electronic stabiliser

1994 -- July, Panasonic NV-S90, first electronic no-loss stabiliser that actually works

1994 -- August, Sony TR750, their third palmcorder with a no-loss electronic stabiliser 

1994 -- September, Canon UC-X1 Hi, miniaturised optical stabiliser

1994 -- October, Canon UC7 Hi, mid-range palmcorder with optical stabilisation

to be continued....

 

SIDEBAR 2

HOW THE TESTS WORK

The main difficulty was to create a standardised and repeatable test routine that simulate the effects of different kinds of movement. These have to range in speed and intensity from a slow undulation, to a rapid, jerking motion. The solution was to design and build a test rig that could recreate this variety of movements. It consists of a motor, connected through a set of levers, to a modified pan tilt head, that rocks the machine in two planes (up and down and side to side), the amount of movement and the speed can be continuously varied, whilst the machine is focus on a fixed target a set distance from the lens. We experimented with a variety of subjects, at various distances but this didn’t appear to make any significant difference on the operation of the stabilisers.

 

 The amount of motion, and the speed of the test rig were increased until the stabiliser began to lose lock. The results from the rig test are combined with information gleaned from field trials and the data obtained from our usual AV performance test routines. As far as we’re aware there are no standardised units of measurement for image stability, so we invented the ‘Zimmer’. The Zimmer scale runs from zero to ten, where zero is no stabilisation at all and 10 Zims represents a stable picture, with the machine rocking through an angle of 20 degrees, 20 times a second (20 Hz); that’s an extremely violent motion that would shake some machines apart and in any case is beyond the capability of most tape transport mechanisms, let alone stabilisers, to cope with. Five Zims is a good average score, indicating a machine will give a stable picture whilst walking, and iron out all but the most intense vibrations when shooting from a moving car. Picture quality also comes into the final equation, and where’s there’s a loss of resolution, or any significant texturing we knock off a Zim or two, depending how severe it is.

 

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Ó R. Maybury 1994 2711

 

 

 

 

 

 

 

 

 

 


 

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