MallinCam Universe User Manual page 35

Using dark frames and flat fields
Dark frames are images that you take by capping your telescope to block all light coming into
the camera. The only data that will appear in your image is electronic noise generated by the
camera itself. This includes amplifier glow, dark current background noise, camera read noise,
and any hot pixels.
You can use dark frames to subtract this residual camera noise from your actual images.
The MallinCam Universe is remarkably quiet in terms of the noise it generates. You often don't
need to worry about dark frames to produce high-quality images. However, if you want to
produce the best possible imagery, consider learning more about dark frames and their usage.
Many sources of such information are available on the internet. Popular programs such as Adobe
Photoshop, Nebulosity, MaxIm DL and freeware programs such as Registax and DeepSky
Stacker all facilitate dark frame subtraction.
Flat fields are yet another aspect of image processing you may want to consider at some point.
These are images taken through your telescope of a featureless, uniform light source such as a
cloudless blue sky (best done after sunset or in the early morning), or using an artificial diffuse
white light source (commercial kits are available).
Flat fields record any unevenness in the illumination reaching your camera's CCD sensor. You
can use these to calibrate your actual images to remove such unevenness caused by factors like
vignetting, dust and other particles on optical surfaces, and various telescope artifacts.
Stacking your images
Stacking (also referred to as combining or integrating) your images is a technique used to
increase the signal-to-noise ratio of your final processed image. It involves capturing a number
of images of your target all at the same camera settings, and then layering these "sub-frames"
one on top of each other to mathematically combine them into one final version of the image.
Since the "noise" in each of the individual sub-frames is random, it will get averaged out and
therefore suppressed with respect to the signal – the object that you're trying to image. The
object's light data is constant from frame to frame, so stacking numerous images serves to build
that signal.
Popular programs such as Adobe Photoshop, Nebulosity, MaxIm DL and freeware programs
such as Registax and DeepSky Stacker all facilitate the stacking of images. This capability is also
included in the MallinCam image capture application. You can set up the application to capture a
sequence of images and automatically stack them for you. Refer to Procedure 5 in Section 6 to
learn how to perform this function. Note that if you stack your images using the capture
application, your telescope's mount must be accurately polar-aligned and preferably auto-
guided. This is required so that the image fields in each of the sub-frames will be identically
positioned, otherwise drift will be obvious in the final combined image. One advantage of doing
the stacking after your imaging session is that the other programs mentioned above allow you to
precisely shift the individual sub-frames with respect to one another to bring them into perfect
alignment. Another advantage is it allows you choose which images to use or discard. A few bad
captures (caused by tracking glitches, passing clouds, aircraft and satellite tracks, car headlights,
etc.) may spoil the final result if they are included in stack automatically.
MallinCam Universe - User's Guide v1.05 35