Correcting pixel vignetting with flat-fields is essential for the SVBONY SV105 camera

A SV105 camera was fitted with a double polarising filter which was tuned to give the correct exposure for the Moon. The camera was placed at the Newtonian focus of a Skywatcher Explorer 130 PDS 130mm, f/5 Newtonian mounted on a Celestron AVX EQ, GOTO mount.

Previously, using an overcast sky, a white styrene 1mm, Plasticard, plastic sheet was placed over the front of the telescope and AstroDMx Capture for Linux was used to capture flat fields and calculate a master flat field. The flat fields were captured with saturation turned off, giving an effective monochrome image.

Master unsaturated flatfield

Note the pixel vignetting gives the opposite effect to classical vignetting as has been reported here previously. With classical vignetting, the centre of the image would be lighter than the peripheral areas. Also note, that the vignetting is asymmetrical.

This master flat field could have been used to do real-time corrections to the video stream in AstroDMx Capture for Linux, but in this case real-time correction was not used as a comparison of flat field corrected and uncorrected results was intended.

Four overlapping, 1000 frame SER files were captured with AstroDMx Capture for Linux so that the whole of the 98.3% waxing Moon was covered by the four resulting panes.

The best 500 frames of each SER file were stacked in Autostakkert 3.1.0 running in Wine; firstly without flat field correction and then with flat field correction, producing four uncorrected and four flat field corrected panes.

The unprocessed data were stitched in Microsoft ICE running in Wine to produce an uncorrected image of the Moon and a flat field corrected image of the Moon. The two images were then made into a blink animation to show the effect of Flat field correction.

Uncorrected vs flat field corrected, unprocessed data animation

The benefit of flat field correction is evident from inspection of this animation.

The flat field corrected image was wavelet processed in Registax 5.1 running in Wine and post processed in the Gimp 2.10

Flat field corrected image

Closer view

Flat fields need only be captured once and can be used many times.
With the correct procedures, the SVBONY SV105 camera is a very capable, low cost, lunar and planetary camera.

58% waxing, gibbous Moon with AstroDMx Capture for Linux and a DMK 37AUX273 (USB3.0, 12 bit ADC) camera

A DMK 37AUX273 (USB3.0, 12 bit ADC) camera, fitted with an 850nm IR pass filter was placed at the prime focus of a Bresser Messier-AR-102-AS ED refractor, mounted on a Skywatcher Star Discovery AZ, GOTO mount, and AstroDMx Capture for Linux was used to capture 2 overlapping, 5,000 frame SER files of the 58% waxing, gibbous Moon at full resolution 1440 x 1080, in a twilight sky. The best 25% of the frames in the SER files were stacked in Autostakkert! 3.10 and wavelet processed in Registax 5.1 running in Wine. The two resulting images were combined in Microsoft ICE running in Wine and post processed in the Gimp 2.10.

58% waxing, gibbous Moon

Full Size

Screenshot of AstroDMx Capture for Linux capturing data from the 
DMK 37AUX273

The DMK 37AUX273 again proving that it is a very capable Lunar imager.

Comet 21P/Giacobini-Zinner

Comet 21P/Giacobini-Zinner was imaged using AstroDMx Capture for Linux with a ZWO ASI178MC camera at the prime focus of a Bresser Messier-AR-102-AS ED refractor, mounted on an iOptron Cube Pro AZ, GOTO mount. 10s, 16 bit TIFFs were collected with matching dark frames. The images were stacked and dark frame corrected in Deep Sky Stacker running in Wine. The image was post processed in the Gimp 2.10.

Comet 21P/Giacobini-Zinner

Alignment was difficult from the site chosen, and tracking was not perfect. However, about a third of the images captured were good enough to stack. The exposures were of limited duration due to tracking issues. Nevertheless, the comet tail and star colours showed up quite well. Focus was a little soft and is not as easy to achieve as with a dual speed focuser.


The ZWO ASI178MC camera

This camera has a 14 bit ADC so it is much less likely to saturate. AstroDMx Capture for Linux auto detects the ADC bit depth and so correctly places the data into either the bottom or the top bits (User defined) of a 16 bit container.

11.6% waxing, crescent Moon with a DMK 37AUX273 and AstroDMx Capture for Linux

The 11.6% waxing, crescent Moon was imaged in broad daylight with a DMK 37AUX273 camera fitted with a 850nm IR pass filter attached to a Skywatcher Explorer 130 PDS 130mm, f/5 Newtonian, mounted on a Celestron AVX EQ, GOTO mount. A 5,000 frame SER file was captured using AstroDMx Capture for Linux running on a Fedora machine. The SER file was stacked and wavelet processed in Registax 5.1 running in Wine and the final image was post processed in the Gimp 2.10.

At full resolution, the camera maintained a frame rate of 52 fps, which allows the acquisition of large numbers of frames in a short period of time.

A solar prominence in H-alpha light with a DMK 37AUX273 and AstroDMx Capture for Linux

A Solarmax ll, 60, BF15 H-alpha scope was mounted on a Celestron AVX mount. A DMK 37AUX273 camera was fitted with the lens from a 2x Barlow and was placed at the focus of the scope. AstroDMx Capture for Linux was used to capture a 10,000 frame SER file exposed for a prominence at 160 fps with a ROI of 640 x 480. A 3000 frame SER file was captured, exposed for the disk. Autostakkert! 3.1 running in Wine was used to stack the best 15% of the prominence frames and 50% of the disk frames. Registax 5.1, running in Wine was used to wavelet process the resulting images. The two images were combined and post processed in the Gimp 2.10.

Again, the DMK 37AUX273 proved its worth as a high speed capture device for H-alpha solar imaging with a ROI.

Protecting a Newtonian primary mirror from dew and extraneous light.

The telescope featured here is a Skywatcher Explorer 130 PDS 130mm, f/5 imaging Newtonian. The back end of the primary mirror is protected by a black, rubberised sheet.

The bottom of the Newtonian reflector 

A problem with Newtonian reflectors is that in very cold weather, the back of the primary mirror can cooled by being exposed almost directly to the cold, ambient air. This can result in the front of the primary mirror dewing up even though it is at the bottom of a long telescope tube.
One way to ameliorate this problem is to use foam packing material, cut to size and attached to the sheet at the back of the primary mirror. Two layers of this material can be used (depending on thickness) and they can be attached using double sided sticky tape.

The foam insulation in place

This insulating foam protects the back of the primary mirror from the cold, ambient air. However, if  any stray light should happen to fall on the bottom of the scope, the white, semi-translucent foam will direct some of it outwards towards the edge of the telescope tube. This presents the danger that some unwanted light might make its way from the back of the scope onto the edge of the primary mirror. Sources of such light could be street lights, light from windows, street light reflected off building walls etc.
What is required is to cut a disk of matt black, 1mm styrene Plasicard and attach at least one sheet to the foam insulation and with a slightly greater diameter than the foam insulation. This serves to prevent extraneous light from falling onto the foam insulation, as well as adding another thin layer between the ambient air and the back of the primary mirror.

The black styrene Plasticard on top of the insulation foam

A finishing touch could be to attach a black shower cap to the bottom of the scope. In addition to extra darkening, this would trap another layer of air at the bottom of the scope to act as extra insulation. 1mm black Plasticard, A4 styrene sheets can be obtained from Amazon.