MallinCam Universe User Manual page 20

Gain:
Used to set the camera's amplifier sensitivity. You should typically set the gain as low as
possible and adjust the exposure time, contrast, and gamma parameters to produce the image you
want. Set the gain higher if you need the additional boost in sensitivity, for instance, when you
need to keep your exposures as short as possible. This can be beneficial when your telescope
mount's tracking is not precise, or if you're imaging an event of short duration.
Select a value between 6.878 dB to 26.007 dB. The higher the value, the more sensitive the
camera will be. However, increasing the value of the Gain will also increase the relative
amount of noise in the image.
Long exposure:
Used to reduce amp glow and hot pixel intensities during long exposures at high gain settings.
If you take a long exposure with the gain set high, you may notice a slight glow in the upper left
corner of the image – that's amp glow. This results from the CCD chip's signal amplifier and is
normal. The Universe imager produces very little amp glow and so this is usually not apparent.
However, the amount of amp glow visible will actually depend on the particular combination of
exposure time, gain settings and histogram stretching that you choose:
Shorter exposure times produce less amp glow and fewer, less-intense hot pixels
Lower gain settings produce less amp glow and fewer, less-intense hot pixels
Histogram stretching increases amp glow and hot pixel visibility. If you leave the histogram
at its default (unstretched) setting, the amp glow will be at a minimum. However, this
decreases all the visible data in your image including your target, and so is usually not the
setting you want. Whenever you use the histogram's Auto function (or set it manually) to get
the best image, you may increase the visibility of amp glow, if it's there at all.
The Long Exposure control reduces (and in many cases, eliminates) the amount of amp glow
visible. It also reduces the visibility of any hot pixels. You enable this control by clicking in the
checkbox. Note that some of the faintest nebulosity in your image may also be reduced when you
use this setting.
If you want to see the effect of amp glow, try the following. Cap the Universe camera so that no
light reaches the sensor. The images you'll take here are called dark frames, with the only light
visible coming from the camera itself. Take three 5-minute images with Long Exposure not
selected: one with the gain set to minimum (6.878 dB), the next with gain around the mid-point
(~16 dB), and the last, at maximum (26.007 dB). Now repeat those exposures with Long
Exposure selected. Compare the images to see the effect of altering the gain, with and without
using Long Exposure. Try the same set of images, but this time, make them 10-minute long
exposures. Note the differences between the two sets. Particularly, notice how a 10-minute
exposure at mid-gain actually generates less amp glow than a 5-minute shot at maximum gain.
And again, the overall visible effect will increase on a real target, depending on how much you
stretch the histogram. You'll get the idea once you do a few of these comparisons.
TIP: You can also reduce or eliminate amp glow in an image by using dark frame subtraction
(refer to Section 10) or by simply cropping your final image in an image processing application.
MallinCam Universe - User's Guide v1.05 20