Small B/W CCTV board cameras with the number "1043" in their designation contain Sony HAD CCD chip and the whole camera system on one small circuit board. Some of them ( usually labelled "X" ) have a sensitive ExView HAD CCD. Unfortunately a good low-light performance is limited by the slowest shutter speed 1/50 sec. Long exposures may be enabled forcing the timing chip to omit some CCD readout control pulses. It means a rough interference in the camera electronics but it works. Video frames produced during the long exposure are blank; after the exposure end one accumulated frame is sent. If the video output is captured by some computer device the proper frames can be selected and saved using a video editing software.
Some time ago Jon Grove published his 1004X camera modification detailed description. I have to send many thanks to Jon for his investigative work and I recommend to read his pages at first. The "1043" camera is slightly different from the "1004" - it has 760 pixel columns instead of 510, almost square pixel cells ( 6.50 x 6.25 um ) and different PCB layout. But the timing control chip is the same in both cameras so the base idea of the "1043" long exposure adaptation comes from Jon's "1004" conversion design. Major differences are in the control circuit ( daughterboard ) :
If you are interested in this adaptation first take into account that any mistake may damage your camera. The design described here is provided "as is" with no guaranty of being correct and I accept no responsibility for any injury or damage caused by the implementation.
Deterrent : look at that clutter of wires - this is my prototype camera uncovered. It works but as you can see it is probably a miracle that it works.
If you are still interested in the "1043" camera long exposure adaptation then you are probably skilful and/or courageous enough so you may read the instructions below.
Some signals from the camera board must be led through the switching circuit on the daughterboard. It requires PCB tracks cutting and wires soldering between small-sized components. Look at the description of the camera board modification, check everything twice and test the modified board.
Next, the daughterboard with the switching and control circuit is needed. Take my description and schematic of the daughterboard as the initial working design and try to build something like that ( or anything better ).
During a long exposure the MCU code should switch signals in the following sequence :
Updated 02/15/2004 20:00 :
I modified the switching algorithm and MCU code. It is now "optimized for darkness". All strips and interlacing artefacts caused by AGC at the capture card are eliminated if the image is dark ( e.g. night sky ). If you have already downloaded the code please take a new version - it's really better for night time images.
I discovered the way how AGC works at my Bt878 based TV card. It detects bright peaks in the field and if they are too bright it immediately decreases both contrast and brightness for the next field. If the peaks are too low the contrast and brightness are slowly increased. It may be easily messed up by switching pulses when CCD and VH voltages are switched on just before the first field is read. CCD supply voltage rising causes an intensive white line, then a dark strip ( voltage too low for amplifier ) and then a white strip gradually fading into a normal ( dark ) signal. VH supply restoration causes a bright strip first and then a black strip. The whole transient process takes approx. 100 horizontal lines. AGC reduces the brightness and contrast for the first captured field in accordance with that bright strips in the last "blank" field so the first field is too dark. Then the brightness and contrast are increased for the second field so the fields are different and there are visible interlaced lines, more noise in the second field etc.
I modified the code to keep the last "blank" field as dark as possible. CCD +15V power is restored before that field scan during the vertical sync. pulse and next VH power is switched on at the end of the sync. pulse. The transient state is mostly hidden by the blanking pulse and the white strip from CCD amplifier is partially covered by the black strip produced by VH switch. Most of the following field is not affected by the strips and normal dark signal is given. AGC then sets the brightness and contrast for the first captured field to maximum values.
This algorithm works correctly when the captured image is dark. If the first captured field is too bright then lower brightness and contrast will be set for the second field and there will be a difference between interlaced lines. If the code is to be optimized for some "normal" average brightness then my previous algorithm would be better. It was based on optimal selection of the moment when CCD +15V power is restored during the last "blank" field readout. AGC sets some "average" values for the first field if the CCD power is restored approx. at horizontal line n. 200 when VH power is already on.
You can take my latest version of the MCU code here. Both HEX file and assembler source are included so you may modify it as you want ( without any warranty from me; of course ) or use it as a basis for your own experiments.
The code provides following functions :
The prototype was tested with 8" Newtonian reflector, f/4. This was a test only - no astrophotography ( some collimation and better focus would be nice ). You can see a part of the Beehive cluster ( M44 ). It is a single frame without any adjustment scaled to 1/2 size. It was captured in "normal" mode with 1/50 sec. shutter and a lower gain was set to keep a low noise. Clicking on the image you can see a full frame with SAO numbers and magnitudes.
Long exposure effect can be seen at the images below. It is a sector marked at the first image containing two 11 magnitude stars ( not visible with 1/50 sec. and low gain ). Images are cutted out from single frames captured with various exposure times.
|0.08 sec. 2 frames||0.5 sec. 12 frames||1 sec. 24 frames||3.8 sec. 96 frames|
Here you can see M51 galaxy