Dark webbed lines across images

Hello! I had recently got a new Sony a6100 and the Sigma 56mm f1.4 lens to do astphotography. Although the lens has been doing excellent so far, with great sharpness and very minimal aberrations, I have come across something very weird that kind of spoils the Images. These images are a stack of about a 100 frames each, taken at, ISO:800 Shutter speed: 4 seconds F-stop: F1.4 These aren't the final pictures of course but stretching the data even by a little bit shows these dark lines orginating from the corners towards the center. Also I tried removing it during post-processing in the second image, but it was extremely difficult, and I don't to spend all day trying to remove it. I have Individually checked all the frames and it seems that this isn't a stacking issue since this was there in all of them. At first I thought maybe it was a vignetting issue, so I tried using flat frames to remove it but that didn't make It any better. I have also observed that the Sony cameras produce lossless compressed RAW, so it results in weird circular artifacts if the images are underexposed, but I had taken all the subs 'exposed to the right' without them clipping. Could it be because I was using it wide-open? Any help would he appreciated! Attached are the images showing a webbed sort of structure. [epzimg]332906_1598951298.jpg[/epzimg] [epzimg]332906_1598951344.jpg[/epzimg] Thanks! Regards

Hello!

I had recently got a new Sony a6100 and the Sigma 56mm f1.4 lens to do astphotography.
Although the lens has been doing excellent so far, with great sharpness and very minimal aberrations, I have come across something very weird that kind of spoils the Images.

These images are a stack of about a 100 frames each, taken at,
ISO:800
Shutter speed: 4 seconds
F-stop: F1.4

These aren't the final pictures of course but stretching the data even by a little bit shows these dark lines orginating from the corners towards the center. Also I tried removing it during post-processing in the second image, but it was extremely difficult, and I don't to spend all day trying to remove it.

I have Individually checked all the frames and it seems that this isn't a stacking issue since this was there in all of them.
At first I thought maybe it was a vignetting issue, so I tried using flat frames to remove it but that didn't make It any better.

I have also observed that the Sony cameras produce lossless compressed RAW, so it results in weird circular artifacts if the images are underexposed, but I had taken all the subs 'exposed to the right' without them clipping.

Could it be because I was using it wide-open?
Any help would he appreciated!

Attached are the images showing a webbed sort of structure.





Thanks!
Regards

Are you using a filter?

Are you using a filter?

I'm not into Astro photography, but here's my thoughts The lines look more like they originate from the centre off the image and extend to the edges, might be caused by the poss highlight close to the centre of image 1. Did you use a lens hood ? if you have a skylight filter on the lens as protection, try removing it, ensure the lens is spotlessly clean and when your shooting try and be as far away from any light source i.e streetlight or similar as possible, pick a night when the moon isn't at its brightest and poss shoot away form the moon as well.

I'm not into Astro photography, but here's my thoughts

The lines look more like they originate from the centre off the image and extend to the edges, might be caused by the poss highlight close to the centre of image 1.

Did you use a lens hood ? if you have a skylight filter on the lens as protection, try removing it, ensure the lens is spotlessly clean and when your shooting try and be as far away from any light source i.e streetlight or similar as possible, pick a night when the moon isn't at its brightest and poss shoot away form the moon as well.

I think a little more information about when and where you took the images would be helpful. Do you get it no matter whether you shoot N, E, S or W? I ask as I think this could be the moon interfering - you didn't say when you took them - the moon has been very bright here (Dorset) in the last few days. I agree with Chrism8 above - remove all filters and use a hood.

I think a little more information about when and where you took the images would be helpful. Do you get it no matter whether you shoot N, E, S or W? I ask as I think this could be the moon interfering - you didn't say when you took them - the moon has been very bright here (Dorset) in the last few days. I agree with Chrism8 above - remove all filters and use a hood.

You may also be interested in this https://www.vox.com/science-and-health/2020/1/7/21003272/space-x-starlink-astronomy-light-pollution not saying this was the cause of your 'dark web' but it is something to be aware of.

You may also be interested in this

https://www.vox.com/science-and-health/2020/1/7/21003272/space-x-starlink-astronomy-light-pollution

not saying this was the cause of your 'dark web' but it is something to be aware of.

Thanks for all the replies! To sherlob: No, I wasn't using any filters. To Chrism8: Yes I was using the lens hood provided by Sigma to avoid any of the lights nearby interfering. But I wasn't using any filter, so I don't know how that would affect the image. To Tianshi_angie: I took this image after 8pm in the northern hemisphere. Usually twilight starts dying here around that time. It was towards the South. Yes the moon was nearby 94% illuminated and I live in a Bortle class 7 sky, but I hadn't seen anything like this before when I used to image with my old camera and lens under similar conditions. Maybe I am missing something here. Thanks! Regards

Thanks for all the replies!

To sherlob: No, I wasn't using any filters.

To Chrism8: Yes I was using the lens hood provided by Sigma to avoid any of the lights nearby interfering. But I wasn't using any filter, so I don't know how that would affect the image.

To Tianshi_angie: I took this image after 8pm in the northern hemisphere. Usually twilight starts dying here around that time. It was towards the South. Yes the moon was nearby 94% illuminated and I live in a Bortle class 7 sky, but I hadn't seen anything like this before when I used to image with my old camera and lens under similar conditions. Maybe I am missing something here.

Thanks!
Regards

Tianshi_angie Thanks for the sharing the link, will definitely look into it :)

Tianshi_angie Thanks for the sharing the link, will definitely look into it

Although I do think you all may be right because a week earlier, I captured the Andromeda Galaxy and the Triangulum Galaxy and didn't face any issues there, since they were on the opposite side of the moon (towards hight north). But it doesn't make sense why the moon should create those webbed patterns... [epzimg]332906_1598957609.jpg[/epzimg]

Although I do think you all may be right because a week earlier, I captured the Andromeda Galaxy and the Triangulum Galaxy and didn't face any issues there, since they were on the opposite side of the moon (towards hight north). But it doesn't make sense why the moon should create those webbed patterns...

A brightish light source ( moon ) bouncing light within the lens, similar to flare in the daytime perhaps ?

A brightish light source ( moon ) bouncing light within the lens, similar to flare in the daytime perhaps ?

Oh! But it was all covered on the side by my apartment, so technically from my perspective, the moon wasn't visible. It was behind the apartment and only affecting the light pollution in the sky, although you may be on to something. I will go check today to see if there was any other light source that I wasn't able to block off, maybe another streetlight from the same spot and hopefully be back with some news later. Thanks! Regards

Oh! But it was all covered on the side by my apartment, so technically from my perspective, the moon wasn't visible. It was behind the apartment and only affecting the light pollution in the sky, although you may be on to something. I will go check today to see if there was any other light source that I wasn't able to block off, maybe another streetlight from the same spot and hopefully be back with some news later.

Thanks!
Regards

The moon may not have been visible to you nor shining on your camera and actually behind you but it was affecting the light in the sky and may have been reflecting on nearby buildings and creating light which you weren't able to see. I think that you can only really get good star photos if you are in a truly dark area - the sky in my neighbourhood actually only looks dark blue when there is a bright moon, the rest of the time it is black and in all of your images the sky is dark blue. Can you not take your stuff off into the countryside to achieve what you want? To really understand the true brightness of the moon perhaps try taking some photos of the moon so that you can see the shadows caused by the edges of the craters.

The moon may not have been visible to you nor shining on your camera and actually behind you but it was affecting the light in the sky and may have been reflecting on nearby buildings and creating light which you weren't able to see. I think that you can only really get good star photos if you are in a truly dark area - the sky in my neighbourhood actually only looks dark blue when there is a bright moon, the rest of the time it is black and in all of your images the sky is dark blue. Can you not take your stuff off into the countryside to achieve what you want? To really understand the true brightness of the moon perhaps try taking some photos of the moon so that you can see the shadows caused by the edges of the craters.

I hate to signpost to a none Epz resource, but it might be worth asking the same question on the nightscaper or any of the astro photography groups on FB.

I hate to signpost to a none Epz resource, but it might be worth asking the same question on the nightscaper or any of the astro photography groups on FB.

Its worth adding that this could be condensation. For astro work I tend to always use a lens warmer attached to a rechargeable battery bank (usb). The cloudiness is characteristic with condensation, but I'm not sure why it would be patterned.

Its worth adding that this could be condensation. For astro work I tend to always use a lens warmer attached to a rechargeable battery bank (usb). The cloudiness is characteristic with condensation, but I'm not sure why it would be patterned.

I tried capturing right now, and I am almost certain that the moon is definitely not the issue, it seems that this pattern is there across all my images including the Andromeda-Triangulum galaxy photo that I shared earlier. It's just that it's not very apparent in them until I stretch the image aggresively. I would love to go out and find a dark sky location, but with the current situation in the world, it doesn't seem very ideal :( True, maybe I will get more exposure to understanding the sky once I get the time to go out. The temperature in my location is actually quite warm (25-30C) even post midnight. Usually I have to deal with a lot of noise in my images because of that, stacking and dark frames help a lot. So I am not sure about condensation being the problem. Anyways thank you all so much for your help, it really means a lot! I will try troubleshooting a little more and maybe go for a second opinion online. I am also very new to the forums community, and I am glad to be able to discuss in it. I will be back once I find the solution :) Once again, thank you all! Regards

I tried capturing right now, and I am almost certain that the moon is definitely not the issue, it seems that this pattern is there across all my images including the Andromeda-Triangulum galaxy photo that I shared earlier. It's just that it's not very apparent in them until I stretch the image aggresively.

I would love to go out and find a dark sky location, but with the current situation in the world, it doesn't seem very ideal
True, maybe I will get more exposure to understanding the sky once I get the time to go out.

The temperature in my location is actually quite warm (25-30C) even post midnight. Usually I have to deal with a lot of noise in my images because of that, stacking and dark frames help a lot. So I am not sure about condensation being the problem.

Anyways thank you all so much for your help, it really means a lot! I will try troubleshooting a little more and maybe go for a second opinion online. I am also very new to the forums community, and I am glad to be able to discuss in it.
I will be back once I find the solution

Once again, thank you all!
Regards