|
Betamovie is possible because the video drum was reduced to about half the size of the consumer Beta drum (See above). To record both scans necessary for frame of video a single dual azimuth video head is used. But did these two innovations alone make the Betamovie possible? No, the worlds first camcorder was much more clever and innovative than that. Check our the illustration above. It shows a see-through image of the first USA model of the Betamovie, the BMC-110K. Back then this was a revolutionary device and from a technical standpoint a mystery. Where did the tape go when it was loaded into the top of the camcorder? How could everything be so small, barely larger than the Beta cassette? With the Betamovie Sony engineers ushered in a new era of miniaturization and compact design. It closely matched Akio Morita's (Sonys head honcho) original vision of putting a simple, compact home movie recorder into the hands of the general public. This would eliminate the expensive and time consuming processing involved with taking 8mm (film) movies. So now there was the small Beta cassette using a small camera/recorder (that could be played back on a conventional Beta VCR). Click on the picture. To appreciate how the Betamovie was able to achieve this compact size and still remain compatible with regular Beta home units requires an overview of the tape path taken by both designs. Shown above is the path layout for the conventional Beta units. This is the last design, or the 711B chassis. Look at the video drum. Mounted inside this drum is a circular disk with two video heads mounted on it. They are directly across from each other exactly 180 degrees apart and they travel across the tape as the disks spins (called scanning). The heads stick out slightly from the drum and travel in a thin slot that allows them to just touch the video tape. (More on this scanning process can be found elsewhere in this "understanding Betamax" section.) The important thing we want to concentrate on here is that there are two single azimuth heads that record the information needed to make up the television picture.
Let me stop here for a second and let Sony explain the azimuth recording head design, click on the picture. The main thing to take away from their description here is that Beta requires two video heads with opposite angled gaps to record a single frame. Click on the picture again. This shows their revolutionary Betamovie Omega loading system designed to compress the Beta tape video envelope. The mechanical requirements remained basically the same as with original Beta (U-loading) and all the components are all present and in the right location for compatibility. These are the capstan, pinch roller, guides, FE (full erase) head, AC (audio and control) head and video drum are all there. The AC head is the audio and control head and it is located in precisely the right place to be compatible with full sized Beta. It takes the place of the ACE in conventional but since the Betamovie only records and is not capable of audio dubbing the audio erase component is omitted. The tape is still going into the path in the same manner. It only looks reverse because the cassette loads from the top, see the representation in the upper right in the picture. Look at the video drum size, which you know already is about half of Beta, and then notice the type of video head in the lower right. It is a compound head with two caps right next to each other. On each half the slant of the gaps (azimuth) is different by 7 degrees, same as big Beta. Everything is fully compatible.  Here comes the things that are unique to the Omega system. The whole top of drum turns with the compound head mounted in the bottom. It conventional Beta only the head disk spins. Full size Beta uses a stationary upper drum machined with tiny grooves to reduce friction during fast winding and special effects. Betamovies only records so the drum is smooth and runs flatter and closer to the tape. This makes for more stability and better head contact. In full size Beta the two heads stay recording all the time. The one on the opposite side of the one touching the tape is just sending magnetism into air. But not so with the Betamovie. The heads must be switched back and forth while it make the two revolutions needed for each frame of video. It goes A then B then A then B etc. Switching is accomplished electrically and is triggered by two tiny magnets mounted on the spinning drum that energize a coil. Now for some really interesting footwork. The drum has to spin twice as fast as with regular Beta, sixty rpms instead of 30 rpms. Another unique thing is the missing 60 degrees. Click the picture. Here's the conventional Beta again and now I want you to pay special attention to the video heads and their locations. Two spinning on a disk going 30 rpms makes the required 360 degrees necessary (2 x 180) for two heads to record two fields every second. Perfect for television because it matches the standard being broadcast. Check out the amount of scanning area being traced using a single head. Because you can't successfully wrap the tape around the entire drum the amount of area being touched against the tape is reduced. A full sixty degrees is lost with every scan. That is sixty degrees of the picture information, or roughly sixteen percent, that can't be recorded unless something is done. The next part is pretty neat. What Sony did was come up with a scheme that actually over traces the picture, thereby compressing it. The camera part of the unit doesn't care if the pickup beam is traveling 525 lines per frame or 630. So to make this work you take the information over traced by the electronics and pickup tube and just throw away the left over 105 lines. Your back to the 525 needed and the lost info is the sixteen per cent we know is not recordable anyway. The over tracing has an added benefit, it makes a better picture. The faster the traveling dot trace of the pick up tube (or later design, the image chip) the more information in picked up. Of course the picture has to converted into 525 NTSC standard. That is done using the same converting scheme as for original Beta but the clock rate (which the pickup uses for tracing and the electronics uses to make everything match the standard frame) is bumped up. The new rate is 18.881 Khz instead of 15.73426 Khz. Faster clock, faster traces. When the increased rate is played back at the regular Beta speed (which is slower) it automatically becomes correct. This is done with the color information too. Conventional Beta color (chroma) is 688 Khz, for Betamovie it 891 Khz. Correct when played back. How's that for overcoming a physical setback? Incidentally, these higher frequencies beg for the use of a high quality tape. Keep this in mind when you think about rate changes that tiny trace of magnetism going on to the tape. The scan is the same length as the one in conventional Beta but it is put down in a shorter distance as the tape travels through the machine. All Betamovies record at the  speed, the only with the exception is the BMC-1000, it is  .)To bring this all together here's the last part of the equation. The conventional Beta drum is 74.4mm in diameter. The Betamovie drum is 44.7mm or 29.8mm smaller. This is a reduction in size of approx. 40 per cent. If you do the math, and we won't mess with that, the reduced area for the tape to contact creates a writing speed that is 1.2 times faster than conventional Beta (840 cm/sec as opposed to 700 cm/sec). Think of it a playing a 45 rpm record at 33 1/3 rpm. Hows that for nostalgia? The magic comes in again when during playback when in a Beta machine everything plays at the most popular speed, BII. Pretty clever and Sony and others sold a ton of these crafty little camcorders. Listed below are several related subjects that you may want to check out. Each of the subjects gives you the option to return to this panel.
To go back to the beginning of "Understanding Betamax" click here. If you would you like to skip this section altogether and go forward on to the next subject panel "Innovative Betamax" click here. ©Misterßetamax go to homepage |