Imaging and Processing

Focusing is the first critical step for any imaging session. To avoid focus shifting caused by the main mirror of SCTs, the mirror should be locked. First I calibrate my go-to mount and use a bright star to focus the D-SLR. Visual focusing is easier when using the 2.5x angle viewer. A Hartmann mask or two parallel tapes across the lens improve the judging of the best focus. After determining the best focus it is essential to prove the focus by taking a test image of say 30 seconds and then checking it on the PC. At the optimum focus, sharp spikes and interference patterns on bright stars can be seen from the tapes. The freeware DSLRFOCUS helps with this procedure. Then the scope can be slewed to the desired object and the imaging can begin. Fast lenses should be stopped down one or two steps after focusing. During the night, as the temperature is typically dropping, a refocusing should be considered every one to two hours.

The quality of a deep-sky image proportionally increases with the S/N ratio. Doubling the exposure time improves the S/N by V2 = 1.4 and so on. Taking many raw images is the key to deep and high-quality images. Find out what maximum exposure time your mount is capable of. My setup with separate guide scope achieves 5- to 10-minute subexposures. If combining say 16 raw images, you should also collect 10 to 16 dark frames under the same conditions. They can be taken automatically with the telescope or lens closed.

For processing large raw files, ImagesPlus image processing software is very capable and reliable, able to perform all the necessary steps. First, average the darks and make a master dark of them. Then load the master dark as reference in the calibration setup and calibrate your raw images. If you have vignetting in your optical system, you should also include a flat for calibration. Next step is aligning the calibrated images, easily performed by "Image File Operations/ Align File/ Translate, Scale, Rotate" by marking reference stars. When using Canon raw files, convert them to 16-bit tiff files first, then align and average them in 16 bit. When using 8-bit jpg files, you should use the "extended add" for combining.

SCT focuser USß to PC

* p screws for mirror lock

Lumicon^iant reducer 0,6x

Heltcc! fine focuser

SCT focuser USß to PC

^AP 2x barlow 2"

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