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Webcams and CCTV Cameras: Affordable Imaging Tools for the Amateur Astronomer

Giles Hammond Institute for Gravitational Research University of Glasgow. Webcams and CCTV Cameras: Affordable Imaging Tools for the Amateur Astronomer. Glasgow Astronomical Society 18 th September 2008. Outline. How a CCD works Astronomical CCD’s vs unmodified cameras

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Webcams and CCTV Cameras: Affordable Imaging Tools for the Amateur Astronomer

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  1. Giles Hammond Institute for Gravitational Research University of Glasgow Webcams and CCTV Cameras: Affordable Imaging Tools for the Amateur Astronomer Glasgow Astronomical Society 18th September 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. H 656nm Pixel Structure 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 http://www.microscopyu.com/articles/digitalimaging/ccdintro.html

  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 http://www.microscopyu.com/articles/digitalimaging/ccdintro.html

  5. 256 bits 16 from CCD (e-) voltage charge amplifier ADC 3 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)

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

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

  8. Camera Starlight Express MX5 Toucam 840 1004X Colour Yes/No Yes No CCD type ICX055 AL ICX098 AL ICX255 AL CCD size (mm) 6.0x5.0 4.6x4.0 6.0x5.0 Pixel size (m) 9.8x6.3 5.6x5.6 9.8x6.3 Max Exposure >1 hour 1/25s 1/25s Cooled Yes (-30oC ambient) No No Bits 16 Mono 24 Colour (8 RGB) 8 Mono Price £400-650 £40 £40 Astronomical CCD’s vs unmodified webcams

  9. How to modify a Camera • Webcams are limited to a maximum exposure ≈1/25s (okay for planets but not good for imaging nebulae/galaxies) • The CCD is continually clocked 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) http://www.qcuiag.co.uk Quick Cam and Unconventional Imaging Astronomy Group

  10. 1004X Board 32mm Power supply Video out Timing generator +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. +5V +5V Switch open: shutter operating Switch closed: shutter disabled (+5V) Shutter Disable

  13. 1s 2s 4s Switch closed (clocking enabled) Switch open (clocking disabled) 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. 10k 10k Pin 9 (CCD voltage) Pin 9 (CCD voltage) Switch open: CCD voltage  9V and amplifier shuts down Charge containment remains active Switch closed: CCD voltage = 15V Amp Off Modification Unsolder pin 9 and attach a wire

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

  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

  18. Image Processing • 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) • 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

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

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

  21. 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

  22. All Sky Camera at Glasgow

  23. 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)

  24. 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

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

  26. M1 10” f4.8 Newtonian 32x16s (H filter) M1 10” f4.8 Newtonian 40x16s (Meade UHC filter) Barnard 33 10” f4.8 Newtonian 44x16s (H 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) 1004X Images (Prime Focus)

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

  28. Useful Links 1004X distributor http://www.rfconcepts.co.uk/board_camera.htm 1004X modifications http://www.geocities.com/jgroveuk/ExViewMod.html http://www.leadbeaterhome.fsnet.co.uk/1004xcam.htm http://www.saao.ac.za/~wpk/1004x/index.html Philips SPC900NC distributors http://www.amazon.co.uk/gp/product/B000BEY4DE?ie=UTF8&tag=km_10000-21&gclid=CIK-84eZipQCFQ8gQgodGBYgXA http://www.kikatek.com/product_info.php?products_id=19218&source=froogle http://www.pcworld.co.uk/martprd/store/pcw_page.jsp?BV_SessionID=@@@@1823582525.1214211267@@@@&BV_EngineID=ccffadeegkihhffcflgceggdhhmdgmh.0&page=Product&fm=null&sm=null&tm=null&sku=638873&category_oid= Philips SPC900NC modifications http://home.zonnet.nl/m.m.j.meijer/D_I_Y/spc900nc.htm

  29. Useful Links Useful source of Electronic Components (can buy over the counter)) Maplin Electronics: http://www.maplin.co.uk/ Software AstroVideo: http://www.coaa.co.uk/astrovideo.htm K3CCD Tools: http://www.pk3.org/Astro/ Registax: http://www.astronomie.be/registax/ Yahoo Group for modified cameras QCUIAG: http://www.megastronomy.150m.com/New-QCUIAG/ Webcam adaptor: http://www.telescopehouse.com/cgi-bin/sh000001.pl?REFPAGE=http%3a%2f%2fwww%2etelescopehouse%2ecom%2facatalog%2fOnline_Catalogue_Camera_Adaptors_15%2ehtml&WD=webcam&PN=Webcam_Adaptor_1_25__%2ehtml%23aAC378#aAC378 http://www.moggadapters.com/astro/adapter.asp

  30. 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

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