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World's Ugliest Flat?

Astrophotography
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18 replies to this topic

#1 Destrehan Dave

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Posted 27 November 2021 - 01:06 PM

Hello

 

Under reasonably dark skies, I notice a dark globe in the right bottom quadrant of my images

.

SampleFitStretched3.JPG

 

SampleFitStretched.JPG

 

Purchased a Flat Fielding panel, and took the following image... it's horrible... don't know where to begin.

 

SampleFlatStretched.JPG

 

Is something wrong with my camera?  Where do I begin?  

 

Firstly, I was 'shocked' that the circle is not in the middle of the square... the Andromeda image is without a flattener; NGC1055 is with a flattener, as is the flat image.

 

Any and all comments greatly appreciated.

 

Thank you

 

David Diaz


Edited by Destrehan Dave, 27 November 2021 - 01:40 PM.


#2 Borodog

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Posted 27 November 2021 - 01:09 PM

Images not linked correctly.


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#3 Destrehan Dave

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Posted 27 November 2021 - 01:42 PM

Images not linked correctly.

Thanks!

 

Learned something valuable today...

 

Hopefully this community can help me figure out the troubleshooting steps I need to execute to get to the next level.

 

DD



#4 Tapio

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Posted 27 November 2021 - 02:08 PM

What is your imagin scope and camera ?

Could be useful to check collimation (if it's other than refractor).

 

But that doesn't look too alarming.

Everyone has more or less flats looking like that - and that's the reason we take & use them.



#5 Alex McConahay

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Posted 27 November 2021 - 02:08 PM

This is not a particularly horrible flat. I've seen worse. 

 

Just check your imaging train, particularly closer to the sensor. It is not crisp and sharp enough to be on the sensor itself (although it could be a blobby thing on the sensor). But more likely on the filter. 

 

Just clean it off and move on. 

 

It is so dense that the software would probably be hard pressed to make up for it. But it is worth a try. The lights do seem to have some data. 

 

Alex



#6 Destrehan Dave

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Posted 27 November 2021 - 02:25 PM

What is your imagin scope and camera ?

Could be useful to check collimation (if it's other than refractor).

 

But that doesn't look too alarming.

Everyone has more or less flats looking like that - and that's the reason we take & use them.

Thanks

 

I have a TAK TSA-120, a ZWO 2600mc camera, a ZWO Filter Wheel, and a TAK flattener.

 

Can you tell me why the 'circle' represented in the flat is not centered?  Is that common?

 

ZWO has a 'tip-tilt' mechanism, but I forfeited that so I could bolt the filterwheel directly, and they want you to buy their OAG to be able to connect it to the scope side of the wheel, which I find unconscionable, but these are the guys who won't let you use anything but their products on their ASI AIR products.

 

DD



#7 Psychlist1972

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Posted 27 November 2021 - 02:28 PM

You mostly just have a lot of dust to (gently) blow off various parts of your scope. The darker blobs may be closer to the sensor (on the filter or glass for the camera). Have to keep things clean smile.gif

 

Not sure why the vignetting is so bad, though. Filters or flattener or something in the imaging train too small for the camera you've picked? FWIW, they never appear to be centered, in my limited experience.

 

Given star shapes, I assume this is a refractor. Can you describe your setup from telescope to camera? That will help folks help you.

Edit: Including adapters (I see you described the main parts while I was typing this)

 

Pete


Edited by Psychlist1972, 27 November 2021 - 02:31 PM.


#8 Alex McConahay

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Posted 27 November 2021 - 02:45 PM

>>>>>Can you tell me why the 'circle' represented in the flat is not centered?  Is that common?

 

Why should it be centered? It is dependent on whatever speck is imaging train. It is on a filter or something. Just a big speck. Maybe a bug, although it looks too regular for that.

 

There is no reason for it to be centered. 

Alex


Edited by Alex McConahay, 27 November 2021 - 02:45 PM.


#9 Psychlist1972

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Posted 27 November 2021 - 02:59 PM

>>>>>Can you tell me why the 'circle' represented in the flat is not centered?  Is that common?

 

Why should it be centered? It is dependent on whatever speck is imaging train. It is on a filter or something. Just a big speck. Maybe a bug, although it looks too regular for that.

 

There is no reason for it to be centered. 

Alex

I think they were talking about the vignetting. I don't think I've ever seen that centered. 

 

Pete



#10 decep

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Posted 27 November 2021 - 03:07 PM

While the flat itself looks fairly normal, something does look odd to me.  Most of the dust motes have the same notch in the 12o clock position.

 

It is not necessarily a sign of a problem, just an interesting observation.  Maybe something in protruding into the light path.



#11 Destrehan Dave

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Posted 27 November 2021 - 03:07 PM

I think they were talking about the vignetting. I don't think I've ever seen that centered. 

 

Pete

Yes, the vignetting.

 

I would think the middle of the round large circle should be in the middle of the flat image.

 

Maybe it's a setting in SharpCap.  Love the Polar Alignment routine... best I've ever used.

 

I will bite the bullet and force myself to use SGP, which I abandoned for the simplicity of SharpCap.

 

But I have obviously tweaked many 'wrong' parameters in the software.. I have lots of other small issues with it.

 

DD


Edited by Destrehan Dave, 27 November 2021 - 03:08 PM.


#12 Psychlist1972

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Posted 27 November 2021 - 03:18 PM

Yes, the vignetting.

 

I would think the middle of the round large circle should be in the middle of the flat image.

 

Maybe it's a setting in SharpCap.  Love the Polar Alignment routine... best I've ever used.

 

I will bite the bullet and force myself to use SGP, which I abandoned for the simplicity of SharpCap.

 

But I have obviously tweaked many 'wrong' parameters in the software.. I have lots of other small issues with it.

 

DD

This isn't software, it's the optics.

Clean your optics first, and then you can debug issues from there. Right now, though, you have a ton of dust and some shmoo to deal with. While you have it apart, make sure the 2600mc doesn't have any silicone grease on the sensor (a common problem if you search here). Your images are all black & white, so do you actually have the MC or is it the MM?

 

Also, you didn't mention which adapters (diameter and legnth) and whatnot you have between the camera and the scope. Is the filter 2 inch or is it 36 or something else?

 

Pete



#13 Alex McConahay

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Posted 27 November 2021 - 03:19 PM

I think they were talking about the vignetting. I don't think I've ever seen that centered.

Pete


Okay. Yeah, it usually is. Sorry, I was thinking of the blob.


Alex

#14 Astrolamb

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Posted 27 November 2021 - 04:04 PM

I can't say I'm all that familiar with refractors but I would guess that you've got some tilt or sag in the imaging train..  

 

For me with a reflector if my secondary mirror isn't aligned well I will see that sort of thing. I didn't think there was much that ever needed alignment in the optics for refractors though. 

 

That's why I'm leaning towards tilt of the imaging train or sag of the focuser...



#15 decep

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Posted 27 November 2021 - 04:18 PM

If you are talking about the vignetting circle not being centered, this is actually not that uncommon, even with refractors.

 

It could be focuser sag, perhaps the focuser tube is not perfectly centered, maybe the image sensor is slightly offset in housing.


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#16 Destrehan Dave

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Posted 27 November 2021 - 08:50 PM

This isn't software, it's the optics.

Clean your optics first, and then you can debug issues from there. Right now, though, you have a ton of dust and some shmoo to deal with. While you have it apart, make sure the 2600mc doesn't have any silicone grease on the sensor (a common problem if you search here). Your images are all black & white, so do you actually have the MC or is it the MM?

 

Also, you didn't mention which adapters (diameter and legnth) and whatnot you have between the camera and the scope. Is the filter 2 inch or is it 36 or something else?

 

Pete

Pete

 

I have the TAK TOA-35 flattener, the CA-35 adaptor, the T2 adaptor, and just enough spacers to mate with The ZWO EFW and the 2600mc.  I am using 2” filters.

 

I havent debayerd yet, but it is a color cam.

 

I believe I may have some dust on the inside of my objective lens… will require some courage, but I do believe it is removable.

 

How the heck do you find a spot that has a minimal amount of dust to clean? I mean, my house is neat, but dust is unbiquitous!

 

I will do a thorough cleaning and try again… Thanks!

 

DD


Edited by Destrehan Dave, 27 November 2021 - 08:57 PM.


#17 TxStars

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Posted 27 November 2021 - 10:21 PM

It looks like you have dust and perhaps dried moisture spots on multiple surfaces.

I would go though and clean everything and then shoot new flats.

 

Charles



#18 Psychlist1972

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Posted 27 November 2021 - 11:02 PM

Pete

 

I have the TAK TOA-35 flattener, the CA-35 adaptor, the T2 adaptor, and just enough spacers to mate with The ZWO EFW and the 2600mc.  I am using 2” filters.

 

I havent debayerd yet, but it is a color cam.

 

I believe I may have some dust on the inside of my objective lens… will require some courage, but I do believe it is removable.

 

How the heck do you find a spot that has a minimal amount of dust to clean? I mean, my house is neat, but dust is unbiquitous!

 

I will do a thorough cleaning and try again… Thanks!

 

DD

I wouldn't take out the objective here. Clean up other surfaces first. It would be more common to have dust and crud on the flattener, camera, filter, etc.

 

You don't need a perfect spot to clean. I've done it here in my basement which has a fair bit of dust, and managed to mostly clean mine (I have two stubborn spots, one of which must be on the sensor, but it's otherwise good. 

Then, after cleaning, always use dust/lens caps.

I keep my scope and imaging train fully assembled all the time so I can minimize backfocus creep and also dust.

 

Pete



#19 Alex McConahay

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Posted 28 November 2021 - 02:48 AM

>>>>>dust on the inside of my objective lens

 

Dust on a far away objective lens will rarely have any real effect on the image. It is just too far away. Nearly every dust mote you see in a flat is on the sensor, filter, or at worst on one of the late correcting lenses. 

 

Alex




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