Page #1 - Main page with EXTA description

Page #2 - Measurements with analog video camera modul SK1004XC (this page)

Page #3 - Measurements with analog video camera WAT-902H2 Ultimate

Page #4 - Measurements with integrating analog video camera WAT-120N

Page #5 - Measurements with Astro CCD camera Atik 314L+

Page #6 - Measurements with IOTA-VTI device

Page #7 - Measurements with integrating analog video camera MINTRON 12V1C-EX

EXTA measurement setup for analog video camera modul SK1004XC

The source for the time stamps in the video images was the VTI KIWI-OSD which was synchronized to UTC with NMEA 0183 data sentences and 1 PPS signal of a Garmin GPS 18x LVC sensor. The digitizer used was a DFG/USB2-lt Videograbber device from The Imaging Source. The videograbber was connected via USB2.0 to a notebook running with a XP32 system. The capture software was VirtualDub. The CCIR video file was recorded uncompressed and lossless in Y800 format and in container format AVI direct to the harddisk.

Full frame video image from modul camera SK1004XC

CCIR video image with KIWI-OSD video time insertion

In this full frame CCIR video image above with video time insertion we can see on the right top seconds LED matrix that the exposure started in UTC second 24 and ended within the same 24th second. The same UTC second was inserted by the KIWI-OSD VTI in numbers on the bottom of the video frame. EXTA was set to mode 0 so every LED in the big LED matrix corresponds to 1ms. The exposure startet in the 672nd millisecond in this UTC second 24. The end of the exposure can be seen in the 712nd millisecond of this UTC second 24. If we count all the lit 1ms LEDs we get 41. But if we take a closer look at the LEDs we can see that the first and the last LED of the lit row are a little bit smaller than the others between them. So we can assume that both LEDs were not exposured for a full millisecond. And the over all exposure time may be a little bit over 40ms but surely not 41ms. This result matches with a full length exposured CCIR video frame.

Now if we compare the times measured by EXTA 24.672 - 24.712 and the times 24.671 - 24.711 inserted by the Video Time Inserter KIWI-OSD we can see a difference of about one millisecond. What is the reason for this difference? The answer is a time shifted output signal of the video camera. The start of the optical exposure is nearly one millisecond late to the output signal of the previous field with Vsync. And because this VTI and most others too are time stampimg the video fields triggered by the Vsync we get times shifted by nearly one millisecond. So this time shift is not caused by the VTI device and was also measured by me with my other measurement device VEXA some years ago. But this relative small time shift is absolutely no problem in normal occultation work.

One another detail which is remarkable in the measurement image above. The lit LED numbered with 692 does not shop stripes like the other do and so looks more brightful. The answer is given if we take a look on this video image with both fields separated as shown below.

The same video image split in both fields

Both fields of CCIR video image with video time insertion

Now both field exposure times are clear visible. The first field #15485 is exposured from 24.672 - 24.692 and the second field #15486 from 24.692 - 24.712. And we can see that the lit LED #692 is captured for a short time at the end/start in both fields. So this LED shows no stripes and looks brighter than all other.

The video camera modul SK1004XC is working only in automatic exposure mode. This means that the exposure duration is controlled by the image brightness. The camera shortens the exposure by shifting the exposure start in every video field to a later point of time if necessary. But due to the relative dark environment in this measurement images above the CCIR modul camera always made full length exposures of 20ms in every field.

Pages of the EXTA project

Page #1 - Main page with EXTA description

Page #2 - Measurements with analog video camera modul SK1004XC (this page)

Page #3 - Measurements with analog video camera WAT-902H2 Ultimate

Page #4 - Measurements with integrating analog video camera WAT-120N

Page #5 - Measurements with Astro CCD camera Atik 314L+

Page #6 - Measurements with IOTA-VTI device

Page #7 - Measurements with integrating analog video camera MINTRON 12V1C-EX

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