The super large filaments on the Sun's surface now, very visible in H-alpha, have led Ken to notice how much better the very narrow bandwidth of the spectroheliograph (SHG) is to see these features in Calcium K. See viewtopic.php?f=4&t=34008 and viewtopic.php?f=4&t=34024. We had actually deliberately lowered the spectral resolution of our 300mm Canon lens SHG in order to see if the wider bandwidth better matched the normal Calcium filter images. But we got distracted by the search for filaments, after seeing Ken's results.
The grating in this case was 1800 l/mm (intermediate between the 1200 l/mm and 2400 l/mm gratings that we also have tried) and the slit width was 20 microns (vs 10 and 30 micron that we have also experimented with). The SHG image was taken using an ASI 290MM, with a #47 violet filter in front to block out stray light. The collimator lens was 100mm and the camera lens was 135mm.
The optics in this setup did not seem ideal for focusing at 400nm and the experimental conditions were not ideal (imaging through the bedroom window, Sun very low in the sky). I believe there are some signs of the filaments in the bottom portion but the contrast is not as high as with Ken's setup, which uses a 2400 l/mm grating and a narrower slit, so has a significantly narrower bandwidth.
I just managed a quick CaK PST image before the Sun dipped below the trees:
This image, taken with exactly the same camera (including the #47 violet filter), is of quite reasonable quality, all things considered, but there are no signs of the filaments in the bottom portion of the image.
While the big filaments last, I will attempt a narrower bandwidth experiment using better optics.
Another comparison of CaK SHG and PST -- looking for filaments
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Re: Another comparison of CaK SHG and PST -- looking for filaments
Good comparison Douglas!
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Re: Another comparison of CaK SHG and PST -- looking for filaments
Doug,
Very good presentation. The comparison helps understand to issue/ problem with CaK filaments.
I've tried to summarise what I've found:
viewtopic.php?f=4&t=34040
Very good presentation. The comparison helps understand to issue/ problem with CaK filaments.
I've tried to summarise what I've found:
viewtopic.php?f=4&t=34040
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
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"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer
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"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer
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Re: Another comparison of CaK SHG and PST -- looking for filaments
I can definitely see the filament in your SHG image
I love the SHG images which are coming out at the moment
Alexandra
I love the SHG images which are coming out at the moment
Alexandra