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M 106 galaxy and friends from Bortle 7 and gradients from hell...

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#1 Campos

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Posted 13 May 2025 - 04:15 AM

Hi guys smile.gif

 

One more galaxy image captured from my backyard, this time is M 106 and it's friends, very happy with the details, not so happy with the gradients I'm getting lately on my images (circular semi arcs), this image could be strecehd a bit further but the background is a mess...I'm gessing it's because of the rampant light pollution on my already bad site...

 

I'm currently on the process of flocking the heck out of all my gear, tube walls, coma corrector, all adaptors, inside the filter wheel, focuser tube, back of the mirror etc etc...one particulat thing that is driving me nuts is the circular gradient I get when I mask the mirror, I had never noticed this untill now! 

 

With the full mirror apperture (200mm f/4 newtonian) I get a pretty good and even flat but if I mask the mirror...boom! I get this circular gradient (donut shaped) smack in the middle of the image, I can see it well on my flats! 

My mirror seems to have a slight turned down edge as I get way better pin point star shapes, that´s why I need a mask. 

 

With all the flocking I've been doing I got to a point where it seems minimized (still a lot more testing to do) but to me it seems that is some kind of light interference patern, something like newton rings interference when you place two filters together with no spacers for example tongue2.gif  

 

I''l post a few images of my finding soon, maybe they can be of good use to anyone else with this issue!

 

Well, here goes my M106 image, a bit cropped from full frame, taken with my 200mm f/4 newt (stopped down to 175mm), QHY 163M camera and EQ6 mount from Bortle 7 backyard:

 

54515316386_e1ed1a00c5_h.jpgM 106_final version 106x60_L by Luís Campos, no Flickr

 


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#2 VMan

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Posted 13 May 2025 - 05:42 AM

 

I'm currently on the process of flocking the heck out of all my gear, tube walls, coma corrector, all adaptors, inside the filter wheel, focuser tube, back of the mirror etc etc...one particulat thing that is driving me nuts is the circular gradient I get when I mask the mirror, I had never noticed this untill now! 

 

With the full mirror apperture (200mm f/4 newtonian) I get a pretty good and even flat but if I mask the mirror...boom! I get this circular gradient (donut shaped) smack in the middle of the image, I can see it well on my flats! 

 

Don't forget the insides of your filter holders. On some manufacturers these can be ridiculously shiny and you can indeed see it on your flats.

 

It's curious you are getting a gradient with a mirror mask and not without.... I assume the mask is on (very close to) the mirror right? (not on the opening aperture of the scope)... if adding that causes a gradient I can only imagine there is something reflective going on with it.... or the edge of it somehow


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#3 matt_astro_tx

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Posted 13 May 2025 - 06:51 AM

Have you considered adding baffles down the length of the tube? Effectively flocking should negate the need for this, but it popped in my head.


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#4 Campos

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Posted 13 May 2025 - 06:51 AM

Don't forget the insides of your filter holders. On some manufacturers these can be ridiculously shiny and you can indeed see it on your flats.

 

It's curious you are getting a gradient with a mirror mask and not without.... I assume the mask is on (very close to) the mirror right? (not on the opening aperture of the scope)... if adding that causes a gradient I can only imagine there is something reflective going on with it.... or the edge of it somehow

Thanks for your reply :)

 

Yep, my filters are all painted black on the edges also, on my "lum" filter the slot is empty as I use a Baader 2" threaded on the MPCC coma corrector, the empty slot is painted with mate black and I even made a square mask that seats on the sensor window itself to black any indirect reflexions, this is made out of thin soft black foan cut to size, it also covers the sides of the sensor chamber.

 

Yes, the mirror mask is made out of the same thin foam material and placed right on top of th emirror, hold in place by the mirror clips.

 

I think that masking the mirror causes some interference pattern because of the large secondary mirror size (70mm)...

 

I'm really going nut over this...but I'm a stubourn man! I hope I get to the bottom of it, one step at a time...

 

Cheers,


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#5 Campos

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Posted 13 May 2025 - 06:55 AM

Have you considered adding baffles down the length of the tube? Effectively flocking should negate the need for this, but it popped in my head.

Thanks for your reply Matt :)

 

Yes, the Altair astro imaging newt has full baffles on the tube, a lot of them!

 

I found that some of them are not so god because I can see the baffle edges shining under certain light conditions / angles...I was getting the same results with them in place, so I removed them all and I'm getting better results now, I've flocked the tube walls and everything I could with a mate black thin foam material.

 

Cheers,


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#6 Dan_I

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Posted 13 May 2025 - 07:17 AM

Great image Luis with perfect framing, despite the gradient issues.

 

 

It's strange that these issues occur only with the mask... did you add some flocking on the top of the aperture mask ?

 

 

Clear skies,

 

Dan


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#7 Campos

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Posted 13 May 2025 - 08:42 AM

Great image Luis with perfect framing, despite the gradient issues.

 

 

It's strange that these issues occur only with the mask... did you add some flocking on the top of the aperture mask ?

 

 

Clear skies,

 

Dan

Thank you Dan :)

 

The mask is made out of mate black thin foam materail, so it's well dull and flat, I even painted the mirror clips with mate black paint just to give you an idea of the level of "paranoia" this is giving me...:p

 

More testing to be done...

 

Cheers,



#8 VMan

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Posted 13 May 2025 - 10:39 AM

I still can't wrap my head around a matte black mask on a mirror causing gradients.... I'm becoming stubbornly obsessed on your behalf now...

 

Just an idea... but you appear to have definitely determined it's the mask... so perhaps I would start messing around with different mask shapes and sizes and materials... to really convince myself of this....  rather than flocking everything else.

 

A crazier idea... maybe your scopes natural gradient was somehow being hidden by the light scatter caused from the up turned edge??

 

How much of a gradient are we talking about here? ...auto stretching algo's will make something out of nothing...

 

Please solve this before tonight: I don't want to start losing sleep over it
 


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#9 Campos

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Posted 14 May 2025 - 03:05 AM

I still can't wrap my head around a matte black mask on a mirror causing gradients.... I'm becoming stubbornly obsessed on your behalf now...

 

Just an idea... but you appear to have definitely determined it's the mask... so perhaps I would start messing around with different mask shapes and sizes and materials... to really convince myself of this....  rather than flocking everything else.

 

A crazier idea... maybe your scopes natural gradient was somehow being hidden by the light scatter caused from the up turned edge??

 

How much of a gradient are we talking about here? ...auto stretching algo's will make something out of nothing...

 

Please solve this before tonight: I don't want to start losing sleep over it
 

Let's see if I can get some clear sky these next few days and make a few more tests now that I've flocked the bejesus of everything I could with mate foam and mate chalk black paint too:)

 

My best guess is that these circular gardients are not beeing corrected because they are simply put, light pollution coming from multiple sources and bouncing all over the tube walls, dew shield, etc...I know for sure my neigboors like to turn the ligths on and off a million times every night on their tasks, and these polluted sub frames are thrown in the mix on the finalç stack...not much I can do here, ecept mannually selecting them one by one...let's see if I can get to a conclusion.

 

Unfortunately I think you have to wait a few more days hahahaha laugh.gif

 

Cheers,


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#10 Campos

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Posted 14 May 2025 - 03:24 AM

Here's what I've been up to in regards to flocking the inside of my OTA and everything I could think of...

 

One interesting aspect to prevent the light entering the base of the focuser and to reenforce this, is to place this type of material glues with doubled sided tape inside the OTA and cut a circle to fit the focuser tip, this way it seals any possible light that could creep in from there smile.gif

 

I'm attaching a few images of this, it's not pretty but looks to be effective, time will tell...

 

Cheers,

 

IMG_20250513_204059 (Medium).jpg IMG_20250513_204044 (Medium).jpg IMG_20250513_204123 (Medium).jpg IMG_20250513_204216 (Medium).jpg

 

 


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#11 Campos

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Posted 14 May 2025 - 03:26 AM

...And a few more:

 

IMG_20250513_204224 (Medium).jpg IMG_20250513_204252 (Medium).jpg IMG_20250513_204602 (Medium).jpg


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#12 VMan

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Posted 14 May 2025 - 09:06 AM

what about the edge of your secondary? 


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#13 Campos

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Posted 14 May 2025 - 09:48 AM

what about the edge of your secondary? 

Painted flat too :)

 

I also thought about that and could swear it was the culprit, this one is mounted on a plastic cell with quite shinny edges...no difference at all :(

 

Sun is shining over here and maybe we have some clear nights ahead, time to test this flockmania! :D


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#14 VMan

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Posted 14 May 2025 - 11:49 AM

But you said you could get the gradient with the flats right? And they disappear if you remove the primary mask, also with flats right? So can't you solve the problem without everyone having to wait for your weather to clear? (asking for a friend)

It's how I found the 'gradient'... more like glow... caused by one particular optolong filter.. saw it in the pictures, saw it in the flats, went away in the flats when I removed the filter etc...




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