1. Institute for Gravitational Research
Webcams and CCTV Cameras: Affordable Imaging Tools for the Amateur Astronomer
Giles Hammond
Institute for Gravitational Research
University of Glasgow
Rugby Astronomical Society
22nd June 2008

2. Outline How a CCD works Astronomical CCD’s vs unmodified cameras
How to modify a CCTV camera
Astronomical CCD’s vs modified webcams!!!!
Basic Image Processing
Dark, Flat and Bias frames
Stacking
All Sky Camera at the University of Glasgow
Some results
Useful Links
Conclusions

3. How a CCD works
A CCD comprises an array of light sensitive silicon sites (pixels) of typical dimensions 6m x 6m
A photon of suitable energy hitting the pixel can produce an electron that is constrained within the pixel using electric fields
Typical energy response 0.5eV<E<3eV (440nm<<1000nm)
Typical well capacity is approximately 50k-150k electrons
Pixel Structure
H 656nm

4. At the end of the exposure the electric fields holding the charge are “clocked” at about 60Mhz to move the charge
Vertical/Horizontal clocks shift the charge down/across to the charge amplifier

5. The resulting voltage output from the charge amplifier is then digitised into a number of “bits” by the analogue-to-digital converter (ADC)
16 bits means 216=65536 levels from black-white (smoother image)
8 bits means 28=256 levels from black-white (coarser image)
256 16 5 3

6. Astronomical CCD’s vs unmodified webcams
Yes
Yes/No
Colour
ICX255 AL
1004X
ICX098 AL
ICX055 AL
CCD type
Toucam 840
Starlight Express MX5
Camera

7. Astronomical CCD’s vs unmodified webcams
9.8x6.3
5.6x5.6
Pixel size (m) No
Yes
Yes/No
Colour
6.0x5.0
ICX255 AL
1004X
4.6x4.0
CCD size (mm)
ICX098 AL
ICX055 AL
CCD type
Toucam 840
Starlight Express MX5
Camera

8. Astronomical CCD’s vs unmodified webcams
9.8x6.3
5.6x5.6
Pixel size (m)
1/25s
1/5s
several hours
Max Exposure
£40 £
Price No
Yes
Yes/No
Colour
8 Mono
6.0x5.0
ICX255 AL
1004X
24 Colour (8 RGB)
16 Mono
Bits
Yes (-30oC ambient)
Cooled
4.6x4.0
CCD size (mm)
ICX098 AL
ICX055 AL
CCD type
Toucam 840
Starlight Express MX5
Camera

9. How to modify a Camera http://www.qcuiag.co.uk
Webcams are limited to a maximum exposure of about 1/5s (okay for planets but not good for imaging nebulae/galaxies)
The CCD is continually clocked (5-25 frames/s) and a shutter operates in bright conditions
In order to take “long exposures” we need to disable the shutter/CCD clocks by applying suitable voltages/adding switches which can be opened/closed (Steve Chambers/Jon Grove etc. 1996)
We can control the switch with software which then picks the exposed frame when the switch is closed (ASTROVIDEO, K3CCD)
Lets look at the 1004X CCTV camera (the modification principle is similar for the Toucam 840 or SPC900NC)
Quick Cam and Unconventional
Imaging Astronomy Group

10. 1004X Board 32mm Video out Timing generator Power supply +12V 0V
Back view
Front view

11. Long Exposure Modification
Vertical clock
Point 2
+5V
Pin 20
Shutter control
Pin 5: Vertical
clock point 1
Track linking clock pulses

12. Shutter Disable +5V +5V Switch closed: shutter disabled (+5V)
Switch open: shutter operating
+5V
Switch closed: shutter disabled (+5V)

13. Clock Disable/Enable 1s 2s 4s Switch closed (clocking enabled)
Switch open (clocking disabled)

14. Hot Pixels/Amplifier Glow
When we take a long exposure (with lens cap on) we get this
10s s s
Hot pixels are due to an uncooled CCD
The bright corner is due to an on-chip amplifier that produces infra-red radiation (electroluminesence)
The amplifier can be disabled by reducing the voltage to the CCD chip during integration

15. Amp Off Modification 10k 10k Pin 9 (CCD voltage) Unsolder pin 9 and
Switch open: CCD voltage  9V and amplifier shuts down
Charge containment remains active
10k
Switch closed: CCD voltage = 15V
Pin 9 (CCD voltage)
Unsolder pin 9 and
attach a wire

16. Astronomical CCD’s vs modified webcams
Up to 10 mins
Several hours
Max Exposure No
Yes/No
Colour
8 (stacking can give 12)
Can be!!
6.5x4.5
ICX255 AL
1004X
Webcam 16
Bits
Yes (-30oC)
Cooled
CCD size (mm)
ICX055 AL
CCD type
Starlight Express
Camera
Astronomical

17. Image Processing Typically we need 3-4 types of exposure per object
The image frame
Dark frame (hot pixels)=D
Flat frame (non-uniform pixels, vignetting)=F
Bias frame (0s exposure for readout noise)=B
Typically I don’t worry about bias frames
Final image = (I-D-B)/(F-D-B)  (I-D)/(F-D) for webcams
Noise is random but signal is coherent. Therefore the image quality improves with increased number of exposures or exposure time
If we obtain N photons/s during an exposure time, t, then
Signal-Noise-Ratio (SNR) improves with increased exposure
With webcams you typically take may short exposures (t<60s) and stack them together to reduce noise
Signal=N*t Noise=(N*t) SNR= N*t / (N*t)= (N*t)

18. Image Correction 1 Raw image Dark corrected image (I-D) Raw flat
Dark corrected flat (F-D)

19. Image Correction 2 Flat corrected image (I-D)/(F-D)
Dark corrected image
Single exposure
Sum of 44

20. All Sky Camera at Glasgow
Developed from a project run for two 3rd year students studying Physics at the University of Glasgow
Aim is to develop an all sky camera based on the 1004X modification capable of taking images throughout the day/night
The camera uses a 1.6mm fisheye lens attached to the front of the 1004X board to produce a 1800x1400 field of view

21. All Sky Camera at Glasgow

22. Control Software
Camera control is based on MATLAB (a powerful mathematics software which also includes image acquisition tools)
The control program has been turned into a standalone executable (quite large) which can run on any Windows PC
Begin loop
Take an image of 0.1s
Sum up the intensity in the image
Determine whether the sun is out (saturated pixels)
Adjust exposure length
Take 10 images
Remove hot pixels using a pixel map
Sum up images
Save as a JPEG
End loop
Combine images into an AVI after 90 frames (and start again)

23. The cameras can be used as weather monitors, satellite trackers, meteor detectors and will show plenty of interesting astronomical/meteorological events
The hardware is now at a fairly stable design but the software needs some work (a windows executable would be much better than the MATLAB executable)
The plan is to apply for research council funding to produce some cameras in kit form and distribute them to schools etc…
The next stage is to install one on the western coast of Scotland on Islay
100 miles

24. Example AVI’s
60s delay between images
900s delay between images

25. 1004X Images (Prime Focus) Barnard 33 10” f4.8 Newtonian
44x16s (H filter) M1
10” f4.8 Newtonian
32x16s (H filter) M1
10” f4.8 Newtonian
40x16s (Meade UHC filter)
M81
10” f4.8 Newtonian
40x16s (Meade UHC filter)
M82
10” f4.8 Newtonian
50x16s (Meade UHC filter)
M81
135mm lens f2.4
40x8s (Meade UHC filter)

26. Barnard 33 mosaic
10” f4.8 Newtonian
58 mins total (H filter)
Barnards loop
50mm f2.4
35x8s (H filter)
B33+flame
200 1/30s stacked
M51
10” f4.8 Newtonian
30 mins total
NGC 1499
50mm f2.4
300s total (H filter)

27. Useful Links 1004X distributor
1004X modifications
Philips SPC900NC distributors
Philips SPC900NC modifications

28. Useful Links
Useful source of Electronic Components (can buy over the counter))
Maplin Electronics:
Software
AstroVideo:
K3CCD Tools:
Registax:
Yahoo Group for modified cameras
QCUIAG:

29. Conclusions
Webcams and surveillance cameras offer a cheap alternative to astronomical CCD’s
The results can be comparable
The only limitation is bit depth which can be partially overcome by stacking/mosaicing
The exposures are usually short which makes guiding/accurate polar alignment less critical
Narrow band imaging can offer a method of imaging under light polluted skies (H, SII and OIII)
Faint nebula are still within reach under suburban skies
Galaxies are harder targets due to their broad emission