CaK full-disk SHG images with a Canon 300mm lens

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thesmiths
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CaK full-disk SHG images with a Canon 300mm lens

Post by thesmiths »

Using essentially the same setup as we used for H-alpha, we today (9 Sept 2021) imaged Calcium K (not H). See viewtopic.php?p=306081#p306081. The only real difference was replacing the #29 Red + UV/IR filters on the Canon lens with a HOYA 72mm NDX4 neutral density filter (75% energy reduction). In front of the camera we put a 1.25 inch #47 violet filter. The results were not quite as sharp with the Canon lens as I have seen with my 107mm APO telescope. My suspicion is the Canon lens is not well corrected at 400nm. We tried using an aperture mask to reduce the f-ratio from about 4.5 to 9. This may have improved things a bit, but not significantly.

The mosaic below starts with the centre of the Calcium K line in the top left to -11 pixel shift in the bottom right. By this amount of wavelength shift, the images already look quite similar to a white light (continuum) image. I believe "+" means blue shifted and "-" means red shifted.

CaK images 0 to -11 pixel shift
CaK images 0 to -11 pixel shift
103457-small.jpg (344.2 KiB) Viewed 1029 times

The CaK images can be compared with the following post, which was taken a day earlier: download/file.php?id=58987. My guess is a CaK image taken with a Lunt filter is essentially an average of the SHG images from about -3 to +3 pixel shift (i.e. an average over a moderately wide bandwidth).

We assembled pixel shifted images from -20 to +20 in a short video that shows the transition from a continuum image, to the centre of the Calcium K line, back to a continuum image again. The frames in the video are actually horizontally (there was not a easy way to correct this in the video editor). The video actually has a higher resolution than the jpeg image above so when viewed full screen, more details are visible.



The acquisition parameters were: ASI 290MM camera; 6.0ms exposure; gain 98 (16%); 164 average FPS; ROI 1600x250; 1x1 binning; 1980 frames; Y/X ratio 0.946; 16x sidereal rate scan (HEQ5 Pro "3").


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Re: CaK full-disk SHG images with a Canon 300mm lens

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Here is another file processed more on an individual basis (the previous ones were done in a batch sort of way). This one was taken without the aperture mask. The acquisition parameters are the same as the file above, except the gain was lower, 47 (7%). For whatever reason, this file had less electronic noise (despite having slightly lower optical quality) so it looks better on a larger scale.

CaK without aperture mask, f4.5
CaK without aperture mask, f4.5
101452_shift=0.jpg (88.71 KiB) Viewed 1022 times


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Re: CaK full-disk SHG images with a Canon 300mm lens

Post by marktownley »

Very good indeed. What gamma setting do you use the 290 on when you are acquiring the data?


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Re: CaK full-disk SHG images with a Canon 300mm lens

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I have gamma deactivated in FireCapture. I guess the default is 50. I quite like the 290MM. Pixels are not the smallest and the sensor is not the largest; but I think the quantum efficiency is the highest.


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Re: CaK full-disk SHG images with a Canon 300mm lens

Post by marktownley »

Taking the last image as example what do it look like before post processing? Thanks.


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Re: CaK full-disk SHG images with a Canon 300mm lens

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marktownley wrote: Thu Sep 09, 2021 8:44 pm Taking the last image as example what do it look like before post processing? Thanks.
The original file size is 2030 x 1600:

as it comes from the SHG software
as it comes from the SHG software
101452_shift=0_clahe.jpg (87.84 KiB) Viewed 970 times


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Re: CaK full-disk SHG images with a Canon 300mm lens

Post by marktownley »

Excellent! You can easily see the proms in the unprocessed image, thought you should / would be able to.


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Re: CaK full-disk SHG images with a Canon 300mm lens

Post by thesmiths »

The original file is 2030x1600 16bit PNG. So there's a lot of depth in the original (vs the 8bit jpg above). File size 4.27MB vs 88kB.

Below is the output from the automated protuberance function of the software. Normally I would change the levels to darken the sky some more and do a little sharpening. I find you can quickly just put them on two layers and do a difference and it comes out quite well. You can give it a try.

protus image as it comes from SHG software
protus image as it comes from SHG software
101452_shift=0_protus.jpg (106.21 KiB) Viewed 961 times

To get the orientation right, you need to rotate by 90 degrees (since the image is acquired by scanning in DEC) and half the time you need to flip horizontally (it depends which direction the scan was).


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Re: CaK full-disk SHG images with a Canon 300mm lens

Post by Montana »

Absolutely amazing! even the unprocessed is a cracker, it is wonderful to see the proms :bow :hamster:

I wonder if you can pick up the massive filament at the moment as these only seem to be visible good SHG shots.

Alexandra


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