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st8300m

ST-8300M


Since 2011 I use this ST-8300M with a 5-position filterwheel. With the TEC I take luminance exposures binned 1x1 and RGB 2x2. With the Meade - with or without focal reducer - I always bin 2x2.

40d

Canon 40D


In december 2008 I bought a Canon 40D DSLR camera. The company Baader modified the camera for H-alpha astrophotography. This camera is better than the Canon 20Da. It has less noise. The blue corners at the right, which were always visible with the 20Da in exposures of several minutes, are not existant with the 40D. The Live View mode is even better then with the 20Da, because it is no longer necessary that the star is in the middle of the field. Focussing on a bright star with the 25cm Meade with 40D live view and a Bahtinovmask is done in a few seconds.
In the summer of 2009 I constructed a box with a peltier element to cool the camera. It takes one and a half hour to cool the camera, but then the the temperature is 12° C cooler then the ambient temperature.
When the sky is clear and there is no or little light polution, I take images of 10 minutes and no pause between the exposures.
20da

Canon 20Da


In 2005 Canon came with a DSLR camera optimized for astrophotography, the 20Da. The two most important features of the camera were on that moment:
  • Live view mode. To ensure a sharp focus, the central portion of the image can be magnified on the LCD by 5x (4% of the picture area) or 10x (1% of the picture area). I think this real time focussing mode is the most important feature. For fine focussing take a star witch is not to bright. While focussing in the 10x mode (FC2) you see the star appearing and disappearing.
  • The low-pass filter positioned in front of the sensor has been modified to increases the transmission of light at the - for astrophotographers important - wavelength of 656nm, the Hydrogen Alpha line, by a factor of 2.5x compared to the standard EOS 20D digital SLR.
    The standard 20D digital SLR transmits 20% of this 656nm wavelength, the 20Da transmits 69%. The company Hutech modifies camera's witch transmit even 95%, but then it is not longer possible to use the camera for "normal" use.

Imaging Strategy for the Canon 20Da


Noise reduction is one of the most important struggles for the astrophotographer. In this struggle there are several weapens available:
  • Start with a cold camera. Put your camera in crisper compartment of your refrigerator (not in the freezer).
  • Keep the camera cold with a cold pack. When the ambient temperature is 20°C, and the camera is also 20°C, it takes about 30 minutes before the "cold" reaches the chip.
  • Take the exposures in RAW format on 1600 ISO.
  • Take more exposures of the object and pause between the exposures to cool down the chip. Under a real dark sky my strategy is:
    Temperature ISO Exposure Pause
    3° C 1600 9 minutes 4 minutes
    8° C 1600 8 minutes 4 minutes
    12,5° C 1600 7 minutes 4 minutes
    17° C 1600 6 minutes 5 minutes
    22° C 1600 5 minutes 5 minutes

    This strategy was adopted from Philippe Vercoutter, a Belgian astrophotographer who wrote a brochure about deep sky photography with a digital camera (see www.astrolab.be). With the 40D I dropped the cool down time to one minute.
  • Dithering: Move the picture a few pixels after 3 or 4 exposures in order to shift the noise pattern.