History of Long-Range Photography in Astronomy

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If an image is to be sharpened, you will get the best results with images that are well sampled.

Slide 16

Pixel Binning

Most CCDs have the ability to clock multiple pixel charges in both the horizontal and vertical direction into a single larger charge or “super pixel”.

The super pixel represents that area of all individual pixels contributing to the charge.

2x2 binning increase the sensitivity by a factor of 4, but the resolution of the image is cut in half.

Slide 17

Bloomimg vs. Anti-Blooming

Slide 18

Bloomimg vs. Anti-Blooming

Slide 19

Readout Noise

Readout noise is specified both for the CCD sensor and the total system.

First, there is not perfect repeatability each time charge is dumped out of the CCD and digitize.

Conversions of the same pixel with the same charge will not always yield the same result from the A/D.

The second aspect of noise is the injection of unwanted random signals by the sensor and electronics which ends up getting digitized along with the pixel charge.

Read-out noise is often expressed in the unit known as an electron.

Cameras geared towards amateur astronomy have read noise between 10 and 100 electrons per pixel.

Slide 20

Thermal Noise

Thermal Noise

The most common term used when describing thermal noise is dark current

Thermal noise charges, again expressed as electrons, are generated in a CCD camera regardless as to whether it is exposed to light or complete darkness

Thermal noise is temperature dependent

The higher the temperature of the CCD the higher the thermal noise

The lower the temperature of the CCD the lower the thermal noise

Thermal noise is lowered by decreasing temperature of the CCD. The read out noise stays the same

Slide 21

Thermal Noise

Slide 22

System Gain

System gain is a way of expressing how many electrons of charge are represented by each count (ADU). A gain of 2.5 electrons/ADU indicates that each count or gray level represents 2.5 electrons.

Kodak KAF-0400=85000/2.5=34000 counts.

As long as the total well depth of a sensor can be represented, a lower gain is better to minimize the noise contribution from the electronics and give better resolution.

Gains which are unnecessarily high can result in more digitization noise, while gains which are too low will minimize noise at the expense of well depth.