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DMK or WebCam - digital output/digital signal recording
Since December 2002 I used a webcam for planet recordings. In January 2010 I additional purchased a more sensitiv DMK 21AU04.AS-USB camera. In this cameras the output signal is transmitted via USB in the notebook for direct harddisk recording. In this process the transmitted signal is only digital from the camera output to the harddisk. So using this cameras there is no need of a video grabber for signal conversion analog/digital.
|The digital camera signal is recorded direct on a harddisk|
Video camera - analog output/digital signal recording
After my visual occultation observation work since August 2003 I continued this work after January 2006 only with video cameras. I had choosen the technical better and over all more simple way of direct harddisk recording on my notebbok.
Only in this way the later evaluation, postprocessing and optionally conversion of video data could be done lossless and very efficiently. Even an expensive tape machine could not act in all the features like a cheap notebook can do.
Because of the analog output signal of a normal video camera the signal must be converted to digital. Therefor a plug in video card can be used in a normal PC and an external USB video grabber on a mobile notebook.
|Direct video recording on a harddisk|
In January 2006, I bought a relative cheap external video grabber from Kworld with a price of 48,- Euro. With this device I gained my first experiences in direct video recording.
|The cheaper external video grabber - Kworld|
After two years of work with a cheap video grabber in January 2008 a second and higher priced video grabber was bought. The price of this second video grabber was 190,- Euro and about four times the price of the first one. But he should have a better image quality. However there was no audio input.
|The higher priced external video grabber - The Imaging Source|
In October 2008 I bought a third and very cheap external video grabber Vivanco for only 25,- Euro. The device works without problems on my PC systems. In format 720x576 it deliveres in contrary to the Kworld real 720 individual horizontal pixel.
|My cheap but good video grabber - Vivanco|
A list of as functioning known video grabbers (USB and Firewire). With this types also single fields are recorded.
USB2.0 Video Grabber Firewire (1394) ==================== =============== ADS Video Express Imagesource 1394 video converter Dick Smith USB2.0 Avermedia DVD EZMaker USB2.0 EasyCAP USB 2.0 KWORLD DVD Maker USB 2.0 The Imaging Source DFG/USB2-lt Vivanco
See also my special video grabber page about:
Digitizing analog video signals
Guiding and recording with one video camera
Because of several video grabbers I have a backup device and the opportunity to split the output signal of one video camera over a video amplifier and transmit two signals over two video grabbers in the notebook. Thus two software applications can use the same camera signal. For instance a guiding and a recording software.
This combination makes it possible to record and guide with only one video camera. A practical application would be the recording of relative fast moving objects like near Earth asteroids. So this objects can be hold in the field of view for hours and the stars in the background would move.
|Two external video grabbers simultaneous used for guiding and recording|
Video amplifier for signal splitting (#15)
If the signal of a video camera should be splitted to two video inputs there could occur problems with video levels. Inputs and outputs of video devices use an impedance of 75 Ohms. If two inputs are connected to one output a maladjustment happens and signal amplitude gets smaller.
But signal amplitude has also an impact on black and white levels. So it could become possible that an automatic gain control or the synchronisation impulse detection of a simple input circuit fails. Mostly the failing depends of image contents. In this way we suddenly can get jumping images in bright video sequences.
But this problem can be solved easy with a small and cheap video amplifier. With this device the camera signal can be distributed to several inputs without signal worsening or without a compromise of synchronisation.
|The video amplifier prevents level problems|
To be able to use the device also mobil I bought a video amplifier with external 12V DC power supply for 30 Euro. Because I am using only a 5.5/2.1mm connector system on all of my astronomical equipment an additional DC socket was assembled in the video amplifier.
|The video amplifier with second DC socket 5.5/2.1mm|
With this amplifier the signal of a video camera can be used on two external video grabbers or a video time inserter as a second input without problems. Thus video recording with simultaneous guiding on a object of the video image is possible.
Video amplifier with controllable outputs (#15)
Because I want to set video signal level to optimum I bought a video amplifier with controllable outputs. For this amplifier I had to pay only 20 Euro. So this device was cheaper than the first device.
|The video amplifier has only one video input beside the DC connector.|
Because I am using only a 5.5/2.1mm connector system on all of my astronomical equipment on this device too a DC socket was assembled in the video amplifier.
|Overall six controllable video outputs could be used|
Also with this amplifier the signal of a video camera can be used on two external video grabbers or a video time inserter as a second input without problems. Thus video recording with simultaneous guiding on a object of the video image is possible.
June 13, 2010
Questions and suggestions to => Gerhard Dangl