         |
|
|
Video Archiving - Restoration - Remastering - Duplication - Transfer - Vintage - Antique - Conversion
Sony introduced the CV-2000 VTR in
1964 and was released in the US in 1965. It was the first reel to reel b/w only
VTR introduced for home use, though most found their way into industrial service.
This format only recorded the luminance information. There was no electronics to
process or record color information, thus color programming would be recorded
only in black and white monochrome.
In the skip field format, video is recorded by only one of the two video heads, resulting in only one field being recorded. On playback, the second rotating head sweeps the same track as the first, effectively repeating the same field. Since the tape has advanced by the time the second head was coming into position for the second sweep, the "B" head was placed slightly behind and below the "A" head as opposed to 180 degrees apart and on the same horizontal plane as in other schemes. The positioning of the "B" head was critical and set by the factory and thus no provision for field adjustment is possible.
Since there were very few video recorders in the marketplace at the time, there was never the consideration of tape/machine interchangeability. You would be lucky to locate another CV machine anywhere in the entire county ! Video recorded on your CV machine was meant to be played back only on that machine and would probably not play back reliably on another. There was no tracking control on the CV series of machines for this reason.
Since there is usually little change from field to field, picture quality losses employing this technique were negligible and the resulting quality surprisingly good. Employing this technique allowed efficient use of the tape - effectively, a 2 to1 compression !
The CV-2000 as depicted to the right, used 1/2" reel to reel tape on 7" 2400 ft reels. The unit weighs approximately 70 lbs and originally sold for $695 when it was first introduced..... Though $695 doesn't sound too bad a price today, consider that $695 in 1964 equates to about $4775 in 2008 deflated dollars ! Only several hundred CV-2000 models were ever sold in the US, though later CV models such as the CV-2100 and CV-2200 were sold in far greater numbers. Though the machines used the same tape stock as the later to come EIAJ machines and were similar in appearance, the format was not compatible with EIAJ.
Video Rover - Sony DV-2400
The Sony Video Rover was released in 1967 as a record only machine that recorded in the Skip Field Format. Every effort was made to keep the machine as light as possible for the sole purpose of recording video, and as such, any feature not absolutely required to record video was left out. That even included a motorized rewind function ! Instead, it came with a hand crank for manually rewinding the tape !
To better understand what a skip field format is, requires a basic understanding of video fields and frames and just why we have interlaced video in the first place. The following will simply explain the concepts....
In the NTSC system, 30 separate images (called Frames) are displayed at a rate of 30 frames/second (actually 29.97 fps in color) and consisting of 525 lines.
Instead of drawing each of the 525 lines in sequence - called progressive scanning) (ie: drawing lines 1,2,3,4,5,6,7 . . . . . 525) then going back & repeating the process 30 times/second), the NTSC specification calls for each frame to be divided into 2 Fields.
Field 1 draws only the odd lines (ie 1,3,5,7,9 . . . . . . 525) while the second field draws & fills in the even lines (2,4,6,8,10 . . . . . 524). Drawing or scanning first the odd lines then coming back to fill in the even lines is called interlaced scanning.
For Video to appear "smooth" and without flicker, images should be refreshed 60 times each second. So why not just draw lines 1 to 525 sequentially & repeat the process 60 times each second ??? Seems simple enough..... yet for the limited technology of the day it had one serious limitation.......
In the early days of TV, there was a severe limit as to how many pixels or lines of resolution could be transmitted each millisecond compared with today. Only so much information could be crammed down the "narrow electronic pipe". Today, we define that as having a limited bandwidth. Vacume tubes and the large capacitor - resistor discreet circuitry of the day, was very slow and was incapable of passing high frequency information... It simply was incapable of passing such a huge amount of information in such a short time.....
The NTSC standard however, specified 30 frames per second refresh rate. In order that moving objects not look smeared, the phosphors on the picture tube had to fade between "visits" by the electron beam. At the agreed on resolution for NTSC for example, the entire picture could be redrawn (repainted; refreshed) a maximum of 30 times a second. However 30 fps was too slow.... At that rate, the top of the picture began to fade before the bottom was completely drawn - resulting in a "fading flicker", for lack of a better way of describing it. Using a longer persistence phosphor to eliminate the fading flicker would result in smearing of any motion - the "cure" now being worse than the original ill. It was clear that a 30 frames/second refresh rate was simply not going to be fast enough.....
The obvious solution was to simply double the refresh rate to say 60 frames/sec. Only problem back then, was that the technology for achieving such a high bandwidth was not yet available with the vacuum tube technology of the day. No way could 525 lines of information be repeated 60 times each second.... Then someone came up with the idea of drawing all the odd scan lines first in 1/60th of a second, then coming back and filling in the even scan lines in the second 1/60th of a second, which virtually eliminated that rolling fading flicker and obtained a much better looking and smoother picture for the same amount of transmitted information.
Effectively, it doubled the refresh rate without any increase in bandwidth, by refreshing only 1/2 the information but twice as fast.
Pretty clever !
Even although there is only half the vertical detail in the skip field format, unless compared side to side with EIAJ for example, most people would be hard pressed to tell the difference
Today the Skip Field (also known as the CV format) is considered rare... Each year, spare parts are getting harder to locate. Though not in immediate danger of extinction, one can count the number of working machines still existing on both hands and still have plenty of fingers left over !
Since 1978 - Copyright © 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Video Interchange
Video Interchange
92 George Luce Rd
Waldoboro, ME - Maine 04572
207-832-5064 - mail@videointerchange.com
Northeast Region - New England
