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My second H-alpha Sun

JamesF

By JamesF
in Imaging - Solar

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JamesF

JamesF

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Working through breaks in the cloud and still rather more hurried than I'd like to be, this is my second attempt at an H-alpha image with my modded PST. I'm rather happier with this one though I really still want a few hours of clear sky to work on getting the tuning right. I don't think I'm too far off now.

All advice on improving the image gratefully received.

ha-sun-2013-06-28-01-small.png

1800 frames of 0.4ms stacked with AS!2 and sharpened in Registax v6 and minor tweaks for levels and curves (plus the colours) in PS.

I think what I'd like to do is to darken the filaments at little to make them stand out better, and darken the "glow" around the disc possibly brightening the proms at the same time. When it comes to Photoshop however, "I am only an egg".

Then use a camera that has a large enough sensor to fit the entire image in :) That might actually get rid of the slight banding I think I can detect, too.

James

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JamesF

JamesF

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Thoughts on the accuracy of focus would also be welcome. I'm not sure I have it nailed, but I don't have the cues I'm used to with white light or planetary images :)

James

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DrRobin

DrRobin

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Nice one James,

Focus looks okay, but you could probably sharpen the image a little more. I use Sharpen+, High Pass sharpen and Local Contrast in Paint.net rather than Registax to sharpen my solar pictures now, Photoshop has similar features. You could try posting a stacked, but un-sharpened image if you would like me to give it a try?

There is just a slight hint of 'Newton Rings' coming through, I might be wrong though but there looks to be some banding running North East, South West.

Robin

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JamesF

JamesF

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Thank you Robin. I'll drag the stacked TIFF from the laptop and post it shortly. I agree on the banding. That's the way it appears to be running to me too, so I think we can be sure it's there :)

James

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allcart

allcart

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Thats quite good james. I don't really see any banding and the focus is almost there. Unfortunately there are very few distinct features to focus on today so you haven't had the best day for it. A tiny bit more sharpening might help, or it may just ruin the image. The Sun is a big ball of flaming plasma with several layers at the surface. It should not look like a ball of concrete.

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JamesF

JamesF

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Fabulous James :)

Ditch the Registax wavelets and use only Photoshop Smart sharpen or Unsharp mask. Mark Townley has a great video tutorial for darkening the disk features and bringing out the proms.

Thank you Alexandra. Is there a technical reason for not using Registax, or is it just that people have come to a consensus that PS just works better?

James

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Polar Bear

Polar Bear

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Then use a camera that has a large enough sensor to fit the entire image in :) That might actually get rid of the slight banding I think I can detect, too.

James

or do a mosaic? :wink:

Great image by the way, and I will add my thanks for your excellent tutorial on imaging.

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DrRobin

DrRobin

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Hi James,

I had a play with your image, but I couldn't improve on your picture. The tiff you posted seems quite dark and there doesn't seem to be too much contrast. You mentioned that it was 1800 frames at 0.4ms, that is 1/2500th second, by the way which camera did you use and did you have a histogram when setting the exposure?R

Robin

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JamesF

JamesF

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I was using the ASI120MM. The exposure time was really quite hit and miss. I had very little time that wasn't cloud-affected (tens of seconds at a time at most) and trying to balance between that and having the image blow out was quite tricky. It's entirely possible I overdid it.

James

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allcart

allcart

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Yes James, overcooked. The bright patch is more than likely a tuning issue.

I had a fiddle with your pic. Robin was correct that it lacked contrast. I do see what looks like a very mild case of newton rings now though. Anyway, here it is.

post-25425-0-96160800-1372450257_thumb.j

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DrRobin

DrRobin

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James,

The bright patch is a tuning issue, it is referred to as the sweetspot, the area where the Etalon correctly tunes to the Ha band. It is quite difficult to get a full disc on band with a PST, or for that matter any solar scopes. You could take a flat field, but for a full disc that isn't easy either.

I think you have a great image there, something to build on, focus looks okay, just pop up the histogram next time and try to get the exposure correct and you will be there.

Robin

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allcart

allcart

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it would be very hard to explain Robin. It is basically sharpened a level adjusted, but when adjusting the levels in several itterations, I used layer masks with a circular gradient to even out the exposure across the disc. That way I could brighten the outside of the disc until it matched the centre hotspot. Once the disc was even I sharpened and coloured as normal. It was fiddly, but only took ten minutes.

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JamesF

JamesF

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Have to agree that Allan's looks far better than either of mine :)I'm really not very good at using Photoshop, I have to admit. Much of it is a black art to me. Still, got to learn some time...

James

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JamesF

JamesF

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James,

The bright patch is a tuning issue, it is referred to as the sweetspot, the area where the Etalon correctly tunes to the Ha band. It is quite difficult to get a full disc on band with a PST, or for that matter any solar scopes. You could take a flat field, but for a full disc that isn't easy either.

I think you have a great image there, something to build on, focus looks okay, just pop up the histogram next time and try to get the exposure correct and you will be there.

Ok, so seeing the sweet spot is a good thing because it means you have the etalon correctly tuned. Or at least, it is correctly tuned across part of its aperture?

Getting out when the sky is relatively clear would be helpful. At least then I won't have to try to guesstimate where I should be for exposure because the histogram won't stabilise. That's just a matter of waiting, I guess. I can manage that bit :) The PST is coming to France with us next week so if things don't improve before then hopefully I should get a good opportunity then.

James

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