SBIG STC-428-OEM CAMERA
USER’S MANUAL
42
(exposure length) and the temperature of the sensor. The longer the integration
time, the greater the dark current buildup. Conversely, the lower the operating
temperature, the lower the dark current. This is why the sensor is cooled for
long integration times. Dark Current is a mostly repeatable noise source,
therefore it can be subtracted from the image by taking a Dark Frame exposure
and subtracting it from the light image.
Dark Noise
- Dark Noise is Poisson shot noise from the Dark Current. It
results from exactly the same process and statics as photon shot noise, just
with thermal electrons instead of photo electrons. Hot pixels are noisier due to
higher Dark Noise, and that noise is not subtracted when you subtract a Dark
Frame.
Double-Correlated Sampling
–
Double-Correlated Sampling (DCS) is a
technique employed to lower the digitization errors due to residual charge in
the readout capacitors of the camera. This results in lower readout noise.
False Color
- False Color images are images that have had colors assigned to
different intensities instead of gray levels.
FITS Image File Format
–
The FITS image file format (which stands for
Flexible Image Transport System) is a common format supported by
astronomical image processing programs. MaxIm LT can save and read image
files in this format.
Flat Field
- A Flat Field is an image with a uniform distribution of light
entering the optical system. An image taken this way is called a flat field image
and is used to correct images for vignetting and minor obscurations caused by
dust particles on the sensor or camera window. It also corrects pixel-to-pixel
variations in light sensitivity within the sensor.
Focal Reducer
- A focal reducer reduces the effective focal length of an optical
system, and thereby provides a larger field of view to the camera sensor. While
this reduces image resolution, it also decreases exposure times since it
decreases the system’s effective focal ratio.
It consists of a lens mounted in a
cell and is usually placed in front of an eyepiece or camera. Focal reducers are
often used in electronic imaging.
Full Well Capacity
- Full Well Capacity refers to the maximum number of
electrons
that a sensor’s
pixel can hold. This number is usually directly
proportional to the area of the pixel.
Histogram
–
A histogram is a simple bar graph that shows the range of
brightness in an image. Each bar in the graph represents a range of
brightness. The leftmost bar represents the dimmest pixels, and the rightmost
bar is for the brightest pixels. The height of the bar is the total number of
pixels in that particular brightness range of the image. Every image has a
different histogram depending on how much of the image is bright or dark.
A typical histogram will have a peak that shows the most common brightness
in the image. For astronomical images this is often the sky background.
Light Frame
- A Light Frame is the image of an object or scene before a Dark
Frame has been subtracted.
