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Image Glow? M51

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#1 Babard

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Posted 19 June 2017 - 05:30 PM

Hello CN

 

I'm having a particular issue with imaging that I'm hoping to get some feedback on. I'm experiencing some kind of light/lamp glow in the center of my images and I'm not sure as to the cause. I  have a Nikon D3300 (entry level) with an Orion ED80 on a Celestron AVX.

 

A few nights ago I took about an hour of M51  images and seem to be experiencing this issues on all my images, even in the original RAW image (have to up the exposure to see it).  

 

My question is this, how do I resolve the glow in the center of the frame, what could be causing the issue, and is there anything that can be done about it?

 

I'm not sure if this is an issue with my camera settings or with the camera itself (or maybe light pollution ?). Any suggestion would be most helpful.

 

I've attached some images via the link below to if you'd like to take a look.

 

https://drive.google...UmM?usp=sharing

 

Thanks in advance for any advise/help. 

 

Image M51

ISO 800
64 Lights @ 1min ea
15 Darks @ 1min ea
16 Flats @ 1min ea
16 Bias @ 1/4000 ea
Processing: Nebulosity / Photoshop
Nikon D3300

 

M51 Processed 2a

 

 



#2 leveye

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Posted 19 June 2017 - 06:08 PM

Really extreme vignetting. Flats and dark flats may help with it. I don't understand why your flats are a minute long. If you use AV mode they should be in fractions of a second.


Edited by leveye, 19 June 2017 - 06:10 PM.

  • RedLionNJ and PirateMike like this

#3 Imager

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Posted 19 June 2017 - 06:26 PM

Agree with above. It is vignetting. The brightness in the center is what you want to have extend all the way to the corners. Are you using an old 1.25" diameter adapter in a 42mm Nikon T-Ring mount? That would do it.

 

Harvey  Herman



#4 RedLionNJ

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Posted 19 June 2017 - 06:31 PM

The glow is skyglow, visible due to over-exposure. I would cut back on the exposure a bit. Then, as leveye suggests above, take more reasonable flats, which DSS should then be able to use to remove the remaining vignetting.  Where on the histogram is your flat peak coming, at a 60 second exposure time? I'd find it hard to believe it's not right against the extreme right edge.

 

Remember - flats are supposed to be of an even illumination, typically a fraction of a second, perhaps up to a second or so if your source of illumination is particularly dim. Depending on your sensor, try for somewhere between a 50% histogram and a 70% or so histogram.



#5 leveye

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Posted 19 June 2017 - 06:38 PM

I don't think that's skyglow from lots of LP. It's look like a good exposure under all that Vignetting. You want to use at the very least an M42 size t-ring and adapter when you image. M48 is even better. If you using a 1.25 fitting get rid of it.



#6 Babard

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Posted 19 June 2017 - 10:37 PM

Ah yes, okay!

 

I was under the impression that the Flats should match the Lights in time (arg, thump my head on the table). I will redo my Flats using AV mode as Leveye suggested. I'm using an M42 T-Ring now as well. Thanks and I'll re-post and let you know how it goes. 



#7 PhilHoyle

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Posted 20 June 2017 - 11:10 AM

How are you taking your flats?

 

Phil



#8 Babard

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Posted 21 June 2017 - 09:22 AM

Flats: Last night I worked on redoing my Flats but have run into a snag. I set everything back up to when I imaged my Lights a few nights ago. I then set my D3300 to AV mode while connected to my ED80 and pointed to a white screen. Unfortunately in AV mode I get the "Lens not attached" message. Question, does anyone know how to bypass this message? 

 

To continue I attached a 18-55mm Lens to my camera, set it to AV mode and pointed it at a white computer screen. I took the readings from the camera, reattached it to the ED80 and set the camera to manual mode and adjusted the settings to match what I had while in AV mode and took about 15 shots. Will this produce good enough Flats so I can reprocess the image, is this even an effective method  for acquiring Flats?

 

These are specific questions but I can't be the first one to ask. Thanks again! 



#9 leveye

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Posted 21 June 2017 - 09:34 AM

Remember that to take a correct flat don't change anything from when you took your lights. Especially the focus point and camera orientation Forget the messages. Your going to get those using a scope instead of a camera lens of course. The most important thing is does the light meter work and are the exposures even using AV mode? I have no trouble with my Canon cameras in this situation. Post an example of your flats using the telescope and AV mode.


Edited by leveye, 21 June 2017 - 09:42 AM.


#10 ChicagoBill

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Posted 21 June 2017 - 11:21 AM

Unfortunately in AV mode I get the "Lens not attached" message. Question, does anyone know how to bypass this message.

 

For my Nikon, switching to manual focusing (the switch on the cameras lens mount) fixes that.



#11 leveye

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Posted 21 June 2017 - 01:30 PM

Unfortunately in AV mode I get the "Lens not attached" message. Question, does anyone know how to bypass this message.

 

For my Nikon, switching to manual focusing (the switch on the cameras lens mount) fixes that.

The only problem with this is if your doing flats you must match each individual exposure exactly. This can be tedious in manual mode. AV mode works much better in these situations I have found but this is with a Canon.



#12 Babard

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Posted 21 June 2017 - 06:40 PM

Here is a copy of the most recent flat showing the levels. Below is a link to the actual flat (titled DSC_0122.NEF) 

 

https://drive.google...iew?usp=sharing

 

I tried a new stack with the attached flat (1/250 800 ISO) but unfortunately this stack resulted in a glow on the right edge of the frame, producing worst results than before. 

 

Due to the limitations of the camera I may have to do this without adding any Flats (?)

 

Flat


#13 leveye

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Posted 21 June 2017 - 06:45 PM

Here is a copy of the most recent flat showing the levels. Below is a link to the actual flat (titled DSC_0122.NEF) 

 

https://drive.google...iew?usp=sharing

 

I tried a new stack with the attached flat (1/250 800 ISO) but unfortunately this stack resulted in a glow on the right edge of the frame, producing worst results than before. 

 

Due to the limitations of the camera I may have to do this without adding any Flats (?)

 

Did you also use dark flats? You really want to. It's a tedious process I know but you must if you want great results. If you do not use flats at all your going to have results just like your first post and have  to crop the image most likely.


Edited by leveye, 21 June 2017 - 06:46 PM.



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