Thursday, 6 August 2015

A camera needs a lens. I this case, a 150mm f/5 Newtonian

I have obtained an ideal portable system for use with deep sky astrovideography in the field. The new Skywatcher Star Discovery mount with Synscan 4 and Freedom find (allowing manual movement of the scope without losing alignment. The scope with the mount is the 150P f/5 Newtonian. The mount is a more robust version of the AZ Synscan mount that carries the 130mm Newtonian or the 127mm Maksutov. The quick release knob allows for easy movement of the scope in altitude:

The collimation screws are hidden behind a cap so it is hard to accidentally change collimation. The scope arrived in perfect collimation as checked by two laser collimator systems working on different principles.

The spider is thick and will most likely produce prominent diffraction spikes on the brighter stars.

This is the portable system that I shall be using with a frame integrating video camera to image deep sky objects in the field. Being an altazimuth mount is not a problem as each frame integrated exposure will be short enough for there to be no image rotation within an exposure, and between exposure image rotation can be dealt with by Deep Sky Stacker during the stacking process.

First light was achieved by putting a DMK camera at the Newtonian focus. Images of the Ring nebula and the Swan nebula were obtained:

Ring nebula with a DMK

Swan nebula with a DMK

The next day, a Mintron 22S85HC-EX Mintron monochrome frame-integrating video camera with a 1/2" sensor was placed at the Newtonian focus and DVD was recorded at high quality of M17, the Swan nebula and M27, the Dumbbell nebula and M20, the Trifid nebula. The individual BMP frames were extracted from the DVD VOB (Video object) files using Ian Davies's Vob Frame Extractor set to extract a unique frame every 256th frame from the VOB and save the BMPs. The BMPs were stacked in Deep Sky Stacker which derotates the image before stacking them. The resulting 16 bitTiff file was post processed in Photoshop and then the aspect ratio was corrected using Nicola Mackin's Aspect Ratio Corrector software:
M17 with a Mintron

The larger sensor of the Mintron produces a wider field of view

M27 with a Mintron

Images of M27 stacked in Registax with no derotation, clearly show image rotation. This is why it is important to stack with Deep Sky Stacker when using an AZ mount.

M20, the Trifid nebula

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