Advanced techniques for imaging with MaxIm DL include imaging sequences for easily taking multiple images, more advanced color imaging methods such as LRGB imaging, and taking calibration images such as flat fields to improve image quality.

Imaging Sequences

Multiple exposures are the ticket for CCD imaging.  More exposures mean less noise and more detail in the final image.  MaxIm DL makes taking multiple exposures simple by allowing the user to take sequences of images which are automatically saved.

Begin by selecting the Sequence tab in the MaxIm CCD window.

This will bring up the Sequence window.

Above:  The Sequence window set for a sequence of 6 images of the Whirlpool Galaxy, M51.

Select a name for the files and enter it into the Autosave Filename box.  Select 1 for Start At.  If you have already taken a sequence of images, say on a previous night, and wish to add to that total, change the Start At number to the next number in the sequence.  (For example, if you have taken 6 images and wish to add 6 more, select Start At 7.)

Next, click Options > Setup Sequence to open the Setup Sequence window.

Above:  The Setup Sequence window set for a simple black-and-white sequence.

For a simple black-and-white sequence, highlight the Enable checkbox next to only the Clear filter.  Be sure the Type is set to Light.  The suffix may be left blank or set to L.  The L stands for Luminance and is used in LRGB imaging.  Color imaging sequences are described below.  Set the Exposure to the appropriate time (in seconds).  Binning is typically left at 1.  At the bottom of the window are Delay settings.  These are usually left at 0 for black-and-white imaging.  Click OK.

Click Options > Set Destination Path and choose a folder in which to save the images.

Click OK to return to the Sequence window.  Everything is now set and you can begin the exposures.  Simply click Start and the images will be taken and automatically saved.

Color Imaging

While RGB imaging is capable of producing good color images, there is a lack of sensitivity associated with shooting through color filters.  Many imagers use a popular technique known as LRGB imaging.  By combining a detailed, high-resolution black-and-white image (the Luminance image) with an RGB image, a much better image can be obtained.  Also, since the detail in an LRGB image comes entirely from the L image and not the RGB, the color frames can be binned for greater sensitivity (and shorter exposures) and then combined with a more detailed unbinned L image.

Taking an LRGB image can be as simple as taking four images, one each through clear, red, green, and blue filters.  Typically you will want to combine multiple exposures as described previously.  This will minimize the noise in the image.  The most common procedure for LRGB imaging involves binning the color images either 2x2 or 3x3.  This increases the sensitivity of the CCD and shortens the necessary exposure time.  This is ideal since a longer exposure is required for color-filtered images.  A 1x1-binned luminance image is then combined to create a high-resolution color image.

LRGB Sequences

MaxIm DL makes capturing LRGB images simple with the Sequence feature.  Begin as above to set a filename for the images, then open the Setup Sequence window.

Above:  The Setup Sequence window set for LRGB imaging.

For LRGB imaging, four filters are set to Enable.  You may select any order you like, but the default is Red, Green, Blue, then Clear.  The suffixes L, R, G, and B are added to each filename to distinguish the images later.  Exposures can be set independently.  Note that above the red, green, and blue exposures are binned 3x3 and the Sequence is set to take 3 images in each color.  More than 3 exposures in each color is usually unnecessary for LRGB images.  The luminance image (clear filter) is set to 1x1 binning with a total of 6 exposures being taken.  Since the color images are being binned, the sensitivity is increased and therefore a shorter exposure will yield an equivalent exposure to the longer unbinned L exposure.

Be sure to visit the Image Processing with MaxIm DL section to see how LRGB images are created once the images have been captured.

Flat Fields

Note:  This section describes how to take a flat field image with MaxIm DL.  For information on methods for obtaining flat fields and on how to determine exposure times, see the Calibration Images page of the Advanced Imaging section.

Flat field images are used to remove uneven illumination from a CCD chip.  This uneven illumination generally has two sources:  dust in the optical path, and vignetting.  Keeping the CCD and all optical accessories capped when not is use and only uncapping them briefly before installing them will keep much of the dust out of the optical path.  However, a few specks will inevitably appear, especially in dusty regions such as the desert southwest.  Vignetting is inherent in all optical systems, but some more so than others.  Vignetting is a darkening of the corners of an image due to light dropping off toward the edges of the field.  Typically, fast systems have more vignetting than slow ones, and large CCDs will show more than small ones.

Taking a flat field is similar to capturing a dark frame.  As with dark frames it is recommended that you take 3 or more flat fields and median combine them to reduce noise variations from image to image.

Tip:  Remember that the orientation of the camera affects the flat field.  Be sure to take flat fields in the same orientation as the light exposures.

Select the Expose tab in the MaxIm CCD window.  Be sure the temperature is set equal to that at which the light frames were taken (or will be taken).  Select an appropriate exposure time (see the Calibration Images page of the Advanced Imaging section).  Under Type, select Flat.  Click Expose to begin taking the image.

Above:  Expose tab set to take a flat field image.  The exposure time is dependant on the type of CCD used.

Above:  A flat field for an ST-10XME camera on an 11" SCT with f/6.3 focal reducer.  The dark donuts are caused by dust specks in the optical path.

Next, Self-Guided CCDs....

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