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Webcams and CCTV Cameras: Affordable Imaging Tools for the Amateur Astronomer Giles Hammond Institute for Gravitational Research University of Glasgow.

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Presentation on theme: "Webcams and CCTV Cameras: Affordable Imaging Tools for the Amateur Astronomer Giles Hammond Institute for Gravitational Research University of Glasgow."— Presentation transcript:

1 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 CCDs vs unmodified cameras How to modify a CCTV camera Astronomical CCDs 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 { "@context": "http://schema.org", "@type": "ImageObject", "contentUrl": "http://images.slideplayer.com/776512/3/slides/slide_2.jpg", "name": "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

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 2 16 =65536 levels from black-white (smoother image) 8 bits means 2 8 =256 levels from black-white (coarser image)

6 Astronomical CCDs vs unmodified webcams NoYesYes/NoColour ICX255 AL 1004X ICX098 ALICX055 ALCCD type Toucam 840Starlight Express MX5Camera

7 Astronomical CCDs vs unmodified webcams 9.8x6.35.6x5.69.8x6.3 Pixel size ( m) NoYesYes/NoColour 6.0x5.0 ICX255 AL 1004X 4.6x4.06.0x5.0CCD size (mm) ICX098 ALICX055 ALCCD type Toucam 840Starlight Express MX5Camera

8 Astronomical CCDs vs unmodified webcams 9.8x6.35.6x5.69.8x6.3 Pixel size ( m) 1/25s1/5sseveral hoursMax Exposure £40 £ Price NoYesYes/NoColour 8 Mono No 6.0x5.0 ICX255 AL 1004X 24 Colour (8 RGB)16 MonoBits NoYes (-30 o C ambient)Cooled 4.6x4.06.0x5.0CCD size (mm) ICX098 ALICX055 ALCCD type Toucam 840Starlight Express MX5Camera

9 How to modify a Camera 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 Front view Back view 32mm +12V Video out 0V Timing generator Power supply

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

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

13 Switch open (clocking disabled) Switch closed (clocking enabled) 1s 2s 4s 10s Clock Disable/Enable

14 Hot Pixels/Amplifier Glow When we take a long exposure (with lens cap on) we get this 10s 40s 60s 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 Unsolder pin 9 and attach a wire 10k Switch open: CCD voltage 9V and amplifier shuts down Charge containment remains active 10k Switch closed: CCD voltage = 15V Pin 9 (CCD voltage)

16 Astronomical CCDs vs modified webcams Up to 10 minsSeveral hoursMax Exposure NoYes/NoColour 8 (stacking can give 12) Can be!! 6.5x4.5 ICX255 AL 1004X Webcam 16Bits Yes (-30 o C)Cooled 6.5x4.5CCD size (mm) ICX055 ALCCD type Starlight ExpressCamera Astronomical

17 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 dont 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 Image Processing Signal=N*t Noise= (N*t)SNR= N*t / (N*t)= (N*t)

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

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

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 x140 0 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 AVIs 60s delay between images900s delay between images

25 1004X Images (Prime Focus) Barnard 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 M51 10 f4.8 Newtonian 30 mins total 200 1/30s stacked NGC mm f s 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 CCDs 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


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