Cocoon

[vlaiv]

Not overly happy with this one - there is some blue bloat around bright stars. Don't know why, it's APO scope and I haven't seen much of that. Maybe it's due to focusing?  I aim for best HFR but I'm not sure if I can tell Ekos to look at blue channel for that. Maybe tightest focus in green leaves blue a bit out of focus?

4h, 80mm Apo, ASI178mcc, 4 minute exposures ...

[TiffsAndAstro]

Still very nice.

[AstroMuni]

16 hours ago, vlaiv said:

Not overly happy with this one - there is some blue bloat around bright stars.

Thats a nice image. On screen it appears to have a pinkish tinge to the halos but that could just be due to the uploaded version here or my screen.

[vlaiv]

1 minute ago, AstroMuni said:

Thats a nice image. On screen it appears to have a pinkish tinge to the halos but that could just be due to the uploaded version here or my screen.

It's not due to upload - it actually has pinkish / violet halo.

Not sure why. I'm guessing it has something to do with focusing - I probably missed focus a bit and it was enough to throw blue part of spectrum slightly off focus. Add atmosphere to the mix and we end up with less than perfect correction in blue, although scope is APO.

[AstroMuni]

4 hours ago, vlaiv said:

I'm guessing it has something to do with focusing

Could measuring the focus using FWHM or other measures available in Ekos solve your problem? Not sure if John the author of the Ekos Focus routine is in this forum

[vlaiv]

55 minutes ago, AstroMuni said:

Could measuring the focus using FWHM or other measures available in Ekos solve your problem? Not sure if John the author of the Ekos Focus routine is in this forum

I used HFR and in that image I had the lowest HFR so far (in just a couple of sessions). It was about 1.3 (whichever units it uses - I'm guessing pixels), while other times it ranged from 1.5 to 1.8.

Last night I did a session on Crescent but I'm yet to process the data. HFR hovered around 1.6 for that one.

I thought of another possible reason for slight CA visible. I have FF/FR in optical train and I've might put it a bit too far at 62mm. Looking at the specs it's supposed to sit at 61mm away from the sensor.

Since it is small sensor - I don't see any sort of distortion and I believe that it won't show significant distortion even if I miss by a mm or two either side of ideal spacing, but I wonder if less then ideal spacing can introduce a bit of CA?

I need to try imaging without it - again, with such a small sensor - I might not even see any field curvature - I was primarily using it as FR as this camera has 2.4um pixel size - which is a bit on the smallish side.

[wimvb]

Nice cocoon. My guess is that the Ekos focus routine doesn't deBayer, so you won't be able to focus on blue with an OSC camera. I would test what you already suggested, and take the FR/FF out of the equation. Does your camera have a UV/IR block window? Otherwise the bloat may actually be UV.

[vlaiv]

12 minutes ago, wimvb said:

oes your camera have a UV/IR block window?

Yes, it does come with UV/IR window installed.

Mono has AR only window.

I was able to do very nice color calibration on it so I think it shows fairly accurate color. Most times we talk about "blue" fringing - but shortest wavelengths are in fact violet and above image matches well ...

(spectrum taken from wiki page on visible spectrum ...).

 

[ONIKKINEN]

Same setup as the Stephan/NGC7331 image?

Isnt it a bit weird that the issue was only seen here if the kit is the same. Maybe these are just bluer stars and thats mostly it but could it be some kind of atmosphere thing? Some high cloud or smoke shenanigans, although not sure why it would specifically hit the blues.

[vlaiv]

15 minutes ago, ONIKKINEN said:

Same setup as the Stephan/NGC7331 image?

Yep, same setup but different focus point and different processing.

There was also just a tad of violet bloat in that image as well - but it was piece of cake to take out with Gimp's selective desaturation.

[vlaiv]

@ONIKKINEN

Here is quick stretch of NGC7331 data without violet desaturation to show what level of it is there in that image:

It is there - but barely noticeable and can be easily removed.

[symmetal]

Without using star removal techniques, you're going to have a hard time with the cocoon as the area is jam packed with stars and stretching to reveal the nebula leads to an image like this

Using star removal I achieved this

I think you've overdone the saturation a little which hasn't helped, but using Photoshop's Defringe tool in its Camera Raw Filter on your image gives this result which has neutralized the purple bloat. 🙂

Alan

 

[vlaiv]

7 minutes ago, symmetal said:

I think you've overdone the saturation

I actually never touched the saturation (tried desaturation on violet stars - but it did not look nice so I gave it up).

[Rallemikken]

On 12/08/2024 at 20:31, vlaiv said:

some blue bloat around bright stars

This is what I get when I overdo the "Asinh" function in Siril. Always start with that. Got my own way. Incremental. Start with i.e. 6, then 5 and so on down to 2.

[symmetal]

On your NGC7331 none of the stars appear severely clipped, as is the case on the cocoon image, and it's really only the heavily clipped stars showing purple bloat.

37 minutes ago, vlaiv said:

I actually never touched the saturation (tried desaturation on violet stars - but it did not look nice so I gave it up).

Ah. The nebula looked oversaturated to me, but it's probably the reluctance to stretch it any more due to the stars, that made it look that way.

If you want to post your raw stack I'll see what I can do with it. 🙂

Alan

Edited August 13 by symmetal

[vlaiv]

9 minutes ago, symmetal said:

If you want to post your raw stack I'll see what I can do with it. 🙂

Sure, here it is for anyone interested:

NStack0002.fitsNStack0001.fitsNStack0000.fits

0 - red

1 - green

2 - blue channel

[symmetal]

Here's my processing vlaiv using PI and PS with all the Xterminator tools which you're not fond of. 😁

The green channel is sharp with the red slightly soft and the blue very soft in comparison. BlurXterminator reduced the blue bloat by about 50% and using StarXterminator and processing the stars separately enabled a much smaller stretch on the stars, and PS Defringe took care of the rest.

The background has some large scale mottling remaining beyond the dust which may be real, or perhaps NoiseXterminator didn't react to noise of such low frequencies. Less background stretching may be preferable but I wanted to see if the dust was resolved. Not too bad a result though. 🙂

Alan

Edited August 13 by symmetal

[JonHigh]

Definitely agree regarding star removal before stretching. II ran into these exact same problems before with my refractor.  Certainly in the UK, seeing has been awful especially where I am so it’s been a real struggle just to get good subs. Are the stars like that on the subs or after stretching the stack?
Good to see your images again!
 

Edited August 14 by JonHigh

[vlaiv]

39 minutes ago, symmetal said:

Here's my processing vlaiv using PI and PS with all the Xterminator tools which you're not fond of. 😁

Very nice processing. You have a good point about processing stars separately, although, I'd be much happier with tight stars "out of the box" so to speak.

40 minutes ago, symmetal said:

The green channel is sharp with the red slightly soft and the blue very soft in comparison.

That is sort of expected for less than perfect color correcting. In other image green has probably been a bit out of focus and other two a bit more in focus - so the effect was minimal.

I'm just wondering if it is the primary lens of the scope or maybe FF/FR and it's position that is to blame in this case.

I wonder how much of it will be seen with mono + LRGB setup? That is my next "move" - to fit filter wheel and ASI1600 to this scope. There are some larger targets to aim for in autumn (I would surely like to do proper mosaic of M31 - need just two tiles to cover it properly).

In any case - there is Astronomik L3 to the rescue if problem persists (just need to get one).

[wimvb]

34 minutes ago, vlaiv said:

I wonder how much of it will be seen with mono + LRGB setup? That is my next "move" - to fit filter wheel and ASI1600 to this scope

That will allow you to first investigate if there is chromatic aberration and how much, and then correct it with focus offsets. If the blue bloat varies between nights, the earth's atmosphere may contribute to it. Generally when there are high clouds, Ekos will report a higher median value for subexposures. You can have this shown in the statistics tab in Ekos. I find it a reliable cloud warning system.

[symmetal]

4 hours ago, JonHigh said:

Are the star like that on the subs or after stretching the stack?

Here are the RGB stacks given the same degree of stretching for comparison.

4 hours ago, vlaiv said:

I wonder how much of it will be seen with mono + LRGB setup? That is my next "move" - to fit filter wheel and ASI1600 to this scope. There are some larger targets to aim for in autumn (I would surely like to do proper mosaic of M31 - need just two tiles to cover it properly).

In any case - there is Astronomik L3 to the rescue if problem persists (just need to get one).

As Wim says using focus offsets for each colour should help a lot if it is the scope. I have the L3 luminance in my RASA which I had originally bought for my FLT98 as the FLT had slight blue bloating before, and it helped there. I don't think the RASA needs it but it saved buying another filter. 🙂

Alan

[AstroMuni]

9 hours ago, wimvb said:

Generally when there are high clouds, Ekos will report a higher median value for subexposures. You can have this shown in the statistics tab in Ekos. I find it a reliable cloud warning system.

Thats a good tip. Whereabouts would I find this in the Analyse tab?

EDIT: Pls ignore. Found it !

Edited August 14 by AstroMuni