12 replies to this topic

[meansrt]

Shot M81 the last couple nights with my ASI294MM, LRGBSHO filter wheel, and AT60.

 

I've noticed on my Lum, Green, and Red frames I have these weird image artifacts. Can anyone Identify these? I assume they must be dust but was surprised my flat frames didnt remove them. could it be that my flat light is too bright?

 

The stretched image is attached for your viewing pleasure

 

Also... Can anyone tell me how to edit them out?

Attached Thumbnails

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Edited by meansrt, 25 January 2021 - 12:58 PM.

[imtl]

A horde of space seagulls attacked M81?

 

It looks like smudges all over your sensor. Maybe also some clouds?

Are you sure you applied flats properly?

Can you show a raw light and calibrate one? Not stacked.

[pedxing]

Is this an individual frame or a stack?

[Tapio]

a) flats not taken same optic configuration as lights (same focus, rotation)

b) light leak

c) flats not in the correct brightness region - about half of full well capacity

 

So how did you take your flats ?

[Sky King]

Definitely space seagulls.

 

+1 for checking individuals frames. 

[meansrt]

I'll attach some photos of my light frames when I get home but I can tell you now individual lights on L, R, and G had these artifacts and so did the calibrated images. Interestingly, I cant see any of these smudges in my flat frames. The focus was not exactly the same as the lights for each filter when I did the flats but I am very sure that it was very close from the EAF readings. The blue filter and the Ha filter has none of these artifacts on them so it makes me thing it's dirty filters but I havent seen these patterns on them since the last time I used them and havent touched them in the meantime. 

 

As far as light leaks go, there is an apartment front porch light nearby that could've leaked light into the OTA lens but it's never been a problem before

 

 

The flats were taken with an illuminated drawing pad stacked on top of the scope and made to have a mean value of 30k out of a full well of ~65k so I dont know if that's the problem either.

[Tapio]

If you are not seeing smudges in flat frames then something is wrong with them OR it's a light leak.

Dust motes don't typically look like that.

[meansrt]

Ok as promised here is a single uncalibrated light from my red channel and the same light with calibration applied. What do you guys make of it? 

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[Midnight Dan]

Judging by how small and sharply defined they are, it looks like dust on the sensor itself. Look into the camera window with a strong flashlight held at an angle.

 

-Dan

[meansrt]

Judging by how small and sharply defined they are, it looks like dust on the sensor itself. Look into the camera window with a strong flashlight held at an angle.

 

-Dan

Good suggestion I definitely found a little bit of dust on there and removed it. I don't think that can account for a lot of it though. If you look below, I've attached an uncalibrated and a calibrated single stack from the green channel. The dust pattern is different here than the red channel which makes me think that theres dust on the filter (obviously) but I don't know why my flat frames wouldnt have caught this? The distance from the filter to the camera should be independant of the focus so they shouldve been picked up right? 

Attached Thumbnails

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Edited by meansrt, 25 January 2021 - 04:47 PM.

[Midnight Dan]

Good suggestion I definitely found a little bit of dust on there and removed it.

 

...

 

The distance from the filter to the camera should be independant of the focus so they shouldve been picked up right? 

You wouldn't have been able to remove it without disassembling the camera.  I'm talking about dust on the sensor, not on the window in front of the camera.  You might want to look again.

 

The distance from the sensor to the dust definitely has an effect on the "focus" and size of the artifacts on the image.  Dust motes on the sensor itself will be small, relatively sharply defined, and variable in shape and size.  If the dust is even a few mm in front of the sensor, such as on the camera window, it will be larger, softer, and uniformly round.  There is a calculator you can use to determine the distance of the dust from the sensor surface:

 

https://www.ccdware.com/resources/

 

-Dan

[Sky King]

Try one of your other cameras, same setup. If the seagulls go back to Capistrano, you know what did it.  

[meansrt]

You wouldn't have been able to remove it without disassembling the camera.  I'm talking about dust on the sensor, not on the window in front of the camera.  You might want to look again.

 

The distance from the sensor to the dust definitely has an effect on the "focus" and size of the artifacts on the image.  Dust motes on the sensor itself will be small, relatively sharply defined, and variable in shape and size.  If the dust is even a few mm in front of the sensor, such as on the camera window, it will be larger, softer, and uniformly round.  There is a calculator you can use to determine the distance of the dust from the sensor surface:

 

https://www.ccdware.com/resources/

 

-Dan

Ah I see I did misinterpret that. Unfortunately that calculator doesnt seen to work anymore. I just tried rotating my camera and taking flats and the dust/seagull pattern changes so that rules out the sensor dust right?

 

What I was trying to say in my previous comment was that the small more defined motes (not the seagulls but the ones that look like the floaters you get in your eyes sometimes) vary from the red filter to the green filter so I think that's definitely dust on those filters. And then since the distance from the camera sensor to the filter does not change regardless moving the focuser they should have showed up no matter what the focus position was. Any idea why my flat frames would not have picked that up?

Edited by meansrt, 25 January 2021 - 06:21 PM.