31 december 22, sunspots white light and violet W47 ASI 174

[cte]

Yesterday, it was, as always, foggy with low clouds, but around noon, for about an hour,the sun was visible between milky mists . I took the chance to continue my testing of the asi 174 camera. This time I decided to try some higher resolution imaging with the 180 mm maksutov+astrosolar. Seeing was not good, nevertheless I wanted to try broad band imaging (full spectrum, only UV/IR cut in front of the camera) both at the native focal lenght of my scope (2700 mm) and with 2X barlow. I wanted to see whether the improved frame rate of the camera allows me to better combat unsteady seeing.

Later I tested some violet/uv imaging, by using a combination of W47 violet filter+IR cut at the native focal length, to see whether granulation and faculae become more obvious under these conditions.

With the full sensor I could shoot at around 60 fps, which increased to 120 under ROI (824x638). With violet/UV I could only reach 30 fps, but the sun was getting covered by clouds and mists, at times I was loosing the surface completely, so I had to increase the exposure a lot. I corrected with flats during video capture by using the defocusing technique. I stacked under the conditions suggested by Christian, with the 1 pixel blur in the "advanced" settings of autostakkert. Processing was with registax (wavelets) and with imppgg for deconvolution. Final touches with photoshop.

Overall I was pleased with the camera, I did not get any grid pattern (at least that I could notice) and details of the sunspot umbrae and in the granulation are quite evident. Seeing was not supporting the ca. 5.4 meter focal length under full spectrum, and I believe that with a green or red filter I could have improved significantly. Waiting for the next time

In the meantime, I wish an happy and fruitful 2023 to all solar astronomers here.

[DeepSolar64]

Very nice on all. That violet filter works well.

HNY

James

[MAURITS]

Thanks for sharing Stefano.

[Montana]

Great shots! interesting about the pixel blur, do you know what that is doing to the stack?



Alexandra

[cte]

Hi Alexandra,

I'm not sure about the effect of the pixel blur. Christian Viladrich adivsed to use it to see whether some fixed patter noise I was getting with my IMX 174 sensor could be removed. This time I corrected with flats, so either I removed it with flat correction, or, for some reasons it disappeared (cables, contacts and so on).
If you go under the "advanced" tab of ASIII you find "experimental features and parameter tuning" where you can select the gaussian blur in the pre-processing routine.
I tried the same processing without flagging the blur, I would say I've got comparable results for the case herein discussed. Attached you find AR 3176 with and without LR deconvolution, that you can compare with the one I uploaded yesterday. To me these are quite similar. I think this autostakkert feature is similar to the gaussian filter that is used in IRIS to denoise the imaging prior to wavelet sharpening, and if you don't have noise feature of the size of pixels (like thermal noise or some other of electronic spurious signal which should be also pixel sized) it will not make a large difference. Just guessing though, Christian could probably provide a more informed opinion, in the case he reads us.

[marktownley]

Good results, I wonder if the blur is just the seeing not supporting the aperture.

[DeepSolar64]

Good results, I wonder if the blur is just the seeing not supporting the aperture.

That is the single largest cause of blur for me. Second up is not being in precise focus.

[cte]

Yes, I believe that seeing that day was not supporting the focal length I was using, atmosphere was wobbling all around and it was hard to find a precise and consistent focus point. The picture obtained at 2700 mm, the violet one, seems better, even if is undersampled for this scope+camera combo

[ffellah]

You still have some very nice images there.

Franco

[arnedanielsen]

Very nice results!

Thanks for sharing,
Arne