12 replies to this topic

[Toufikk94]

Hi all,

 

I have a Lunt LS40 B600 and Im trying to take images with it. 

 

What Ive noticed is when processing the image there is some sort of glowing noticeable around the solar limbs.

 

See the example below:

 

 

 

Im not talking about the glow close to the limbs, because thats the results of the tone curve stretch in imppg and Im fine with that. Im talking about the darker orange/reddish glow in the background. You can clearly see it. And it differs per image. Here is another image:

 

 

 

 

Its really annoying when making timelapse because you see that glow jumping around and it distracts the audience from the main target. 

FYI: the glow is already there in the raw black and white footage. The stretching in imppg and Photoshop only made them more obvious.

 

How do people work around these kind solar backgrounds? Ive seen plenty of timelapses where this doesnt occur that much.

Edited by Toufikk94, 22 June 2025 - 09:07 AM.

[Phil Perry]

Could you possibly be capturing the inner solar corona? If it's changing from image to image, it could be, rather than some scattering effect from your optical train or the atmosphere. BTW, nice images!

[Toufikk94]

Could you possibly be capturing the inner solar corona? If it's changing from image to image, it could be, rather than some scattering effect from your optical train or the atmosphere. BTW, nice images!

Im not sure. How would one determine that? It could also be the result of high clouds passing by now and then.

 

Btw: these extreme glows only appear in the first 5-10 images. Ive captures 120 shots and the further it goes in time, the less I experience that glow.

[auroraTDunn]

Its not impossible to do this in PS, or others, using luminosity masking. Just be careful with areas on the limb or interior to proms, flares, ect and do NOT forget to feather the mask. Plus ideally you will use opacity to minimize but not completely replace or heck maybe even blur a bit to even things our as well.

Its only a gentle hand that can make it improve the image as often the result looks worse.

[BYoesle]

It's not the corona, it's background scattered light enhanced by your prominence image processing. It will be less noticeable with better transparency, and greatly improved if not eliminated with double stacking a second etalon. 

 

I follow the KISS principle and usually get rid of this noise via adjustment to the histogram or curves where it shows up as a spike in the low brightness values.

 

 

If you try to completely eliminate it you will lose some of your fainter prominence details.

Edited by BYoesle, 22 June 2025 - 10:55 AM.

[Toufikk94]

Its not impossible to do this in PS, or others, using luminosity masking. Just be careful with areas on the limb or interior to proms, flares, ect and do NOT forget to feather the mask. Plus ideally you will use opacity to minimize but not completely replace or heck maybe even blur a bit to even things our as well.

Its only a gentle hand that can make it improve the image as often the result looks worse.

But the thing is: there isnt really 1 setting that rules them all. This might work fine for 1 picture, but not for all 120 shots.

 

How can I manage that? This would be a very tough task to do for 120 individual frames 1 by 1.

[Toufikk94]

It's not the corona, it's background scattered light enhanced by your prominence image processing. It will be less noticeable with better transparency, and greatly improved if not eliminated with double stacking a second etalon. 

 

I follow the KISS principle and usually get rid of this noise via adjustment to the histogram or curves where it shows up as a spike in the low brightness values.

 

Processed background glow.jpg

 

If you try to completely eliminate it you will lose some of your fainter prominence details.

Nice! What program did you use? 

 

Same question: how manageable is this when you have 120 images to process? Like...the histogram of all those images arent the same so you cant apply the same process for every frame in a batch.

 

Also: how does this light scattering happen? How can I prevent it?

[steveward53]

You could start by not over-exposing when capturing the original data.

 

You can see this is evident by the 'blown out' centre of the disc , under-exposing gives you much more control in post processing as it's easy to adjust levels up from dark , once you've over-exposed and saturated the white end you cannot retrieve it retrospectively.

[NuovaApe]

The scatter can be caused by the atmosphere itself - dust/smoke/moisture high up.

It can be caused by OTA reflections, camera reflections etc. There's not much to flock in a Lunt40 though.

 

As Bob showed, you can use curves (or levels) to say "I want anything this brightness or less to be black".

 

You could try setting "offset" in the camera settings to zero.

Offset adds a fixed bias to all pixels, to prevent "black crush" in the darker fainter areas of DSO images.

By setting offset=0 any faint glow won't get bumped up as much.

 

That faint glow in your image is "Red=40 to 50" out of 255. That's 5 to 6 bits (presumably dimmer in the originals).

Even your "black" area is Red=32 (5 bits).

 

You could try recording 16-bit. Assuming you have a 12-bit camera then the glow will be in the bottom few bits and the main image in the top 8 bits. When you convert to 8-bit the "glow bits" get deleted. It's seems pointless to record 12-bit then immediately convert to 8, but sometimes it helps.

 

Given that the minimum level (black) is 32, it looks like a constant offset. I'd play with this first.

 

Regards, Ed.

[vincentv]

 

Btw: these extreme glows only appear in the first 5-10 images. Ive captures 120 shots and the further it goes in time, the less I experience that glow.

Are you sure all telescopes components are dry at the start of the session? This lunts have a heft to them and if stored in slightly humid environments can have a thin layer of condensation on some surfaces.

Second idea is to check the red filter. You will need to shine light through it to see any damage. It's unlikely given how new it is but you never know.

[rigel123]

I typically see this type of effect when there are high, thin clouds that pass in front of the sun and you may not even know it.  Since you say only the first ones were like this I would say this is your issue and the clouds/haze burned off as your animation captures went on.  In some cases it actually helps to make the background sky a bit brighter, which is what I will do when there are very faint proms involved.  Then the change in brightness is less apparent.

[stargazer julie]

You don’t adjust pictures individually. After stacking is when you adjust. You can try imppg (free program) to adjust the curves. Photoshop will do it too. 

[BYoesle]

Nice! What program did you use?

First, like Steve Ward noted, do not overexpose. Double stacking will help tremendously by removing photosphere disc continuum and better equalizing the disc and prominence brightness.

 

I use Paint Shop Pro, but most photo editing programs have the necessary tools:

 

Histogram:

 

 

Curves:

 

 

Make multiple copies and adjusting brightness and contrast make several copies to do a HDR image:

 

 

Result of HDR:

 

 

A lot of imagers over-process and exaggerate contrast for my taste. I prefer greyscale images and pretty much dislike inverted disc images, and if doing inversion prefer inverted prominences as the detail of the prominences is more easy to perceive when presnted as dark on a lighter background.

 

 

These are relatively simple tools to use and for me produce fewer artifacts compared to layers and masks, etc. But then again I'm not a photo editing expert, and generally would rather observe and do outreach than spending a lot of time on image processing.