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filter issues? Too small for focal ratio?

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#1 Ballyhoo

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Posted 11 February 2020 - 04:06 AM

I am getting these dark edges around the subs, and I am wondering of these could be because, the filters are 31mm and I am using a focal ratio of 5.25.

 

ASI 1600mm with ZWO LRGB 1.25."

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  • FRAME ISSUES.png


#2 Ballyhoo

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Posted 11 February 2020 - 04:10 AM

actually i think i am having flat calibration issues and i am having trouble getting to the bottom of it.


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#3 ManuelJ

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Posted 11 February 2020 - 06:30 AM

Light leak on the flats?



#4 Ballyhoo

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Posted 11 February 2020 - 12:45 PM

Light leak on the flats?

what does that mean? I have the light panel resting  on the dew shield.



#5 WadeH237

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Posted 11 February 2020 - 12:52 PM

It's not a focal ratio issue.  I used my ASI1600 with 1.25" mounted filters at F/4.8 and did not have this problem.

 

I think that a light leak may be a possible issue.  What that means is that, if light leaks between the rim of your OTA and the light panel, that will make an area of the flat field brighter than it should be.  Since flat frames work by using the flats to understand how to scale the brightness of the light at calibration time.  As such, an overly bright area in the flat will result in an overly dark area in the calibrated light frame.

 

Can you provide a single, raw flat frame?  We should see if the dark pattern in the calibrated light frame corresponds to a bright spot in the flat.


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#6 Madratter

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Posted 11 February 2020 - 01:00 PM

If this was a focal ratio issue, the dimming would be symmetric. It isn't, so it isn't. ;)


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#7 Ballyhoo

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Posted 11 February 2020 - 01:25 PM

here is the link for the flat and light:

 

https://1drv.ms/u/s!...7F7dAw?e=5cIwd6

 

https://1drv.ms/u/s!...Z15KMQ?e=x5LIkp

 

 

Another item I still need to find why is, when I run flat calibration I am getting a PI message 'dark not compatible with flat." I think it said "compatible." (message attached) I need to check the verbiage but I had posted it before. It is in the process console in purple letters. When I saw that i looked at the Fit attributes and I did not see what would be different since the gain and tec were same values. 

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  • warning.gif

Edited by Ballyhoo, 11 February 2020 - 01:25 PM.


#8 Ballyhoo

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Posted 11 February 2020 - 03:21 PM

also is light leak possible with a light panel that rests flush on a dew shield? 



#9 Alex McConahay

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Posted 11 February 2020 - 03:55 PM

Light can leak in other places besides the front of the tube. Maybe a fitting is not as tight as you think, or the camera itself has a gap, or there is something that reflects. 

 

But, I agree it has nothing to do with focal ratio.

 

Alex



#10 Ballyhoo

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Posted 11 February 2020 - 04:32 PM

I am not noticing calibration issues with NB frames.



#11 WadeH237

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Posted 11 February 2020 - 06:54 PM

here is the link for the flat and light:

 

https://1drv.ms/u/s!...7F7dAw?e=5cIwd6

 

https://1drv.ms/u/s!...Z15KMQ?e=x5LIkp

 

 

Another item I still need to find why is, when I run flat calibration I am getting a PI message 'dark not compatible with flat." I think it said "compatible." (message attached) I need to check the verbiage but I had posted it before. It is in the process console in purple letters. When I saw that i looked at the Fit attributes and I did not see what would be different since the gain and tec were same values. 

Let's start with the error.

 

PixInsight is doing some math to determine the level of noise in the light frame and in the flat frame.  It makes some assumptions about how the noise in the light and dark will compare to each other.  The error message indicates that it can't get the noise levels between the light and the dark to make sense.  As a result, it set the scaling factor to zero.  That is what the 0.000 means in the line directly above the purple one that you circled.  In other words, the affected light frame was not dark calibrated at all.

 

But here's the thing.  I think that it's only doing this because you have the "Optimize" box checked in the dark calibration section.  For the ASI1600 (and most, if not all, other CMOS cameras), you must disable the "Optimize" check box.  The reason is that CMOS cameras have characteristics that cause the amp glow to not accumulate in a linear fashion over time.  I have never had a single dark from my ASI1600 calibrate correctly with that box checked.

 

As for your light and flat frames, the dark patterns in the images you've posted do not appear in the files that you gave me.  As a basic sanity check, I used PixelMath to partially calibrate the light frame manually.  Basically I created an expression that was "light_frame / flat_frame".  I then applied it to the light frame.  I've attached an autoSTF of the result.  It's not supposed to be perfect calibration, since the light and dark frames are uncalibrated and I don't have a bias (which means I can't make a calibrated flat).

 

Anyway, the result is pretty conclusive that if all of your lights and flats are like this one, then you are somehow introducing the problem in processing.  When I see something like this in my data, it often means that something happened during the run that introduced an actual shadow in some of the light frames.  I think that you should blink all of your dark frames, your bias frames, your flat frames and your light frames.  Make sure the the Blink process does an auto stretch, so that they should appear similar.  My guess is that you will have some frames somewhere with problems in the area that's dark in your result.

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#12 Ballyhoo

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Posted 11 February 2020 - 07:41 PM

Let's start with the error.

 

PixInsight is doing some math to determine the level of noise in the light frame and in the flat frame.  It makes some assumptions about how the noise in the light and dark will compare to each other.  The error message indicates that it can't get the noise levels between the light and the dark to make sense.  As a result, it set the scaling factor to zero.  That is what the 0.000 means in the line directly above the purple one that you circled.  In other words, the affected light frame was not dark calibrated at all.

 

But here's the thing.  I think that it's only doing this because you have the "Optimize" box checked in the dark calibration section.  For the ASI1600 (and most, if not all, other CMOS cameras), you must disable the "Optimize" check box.  The reason is that CMOS cameras have characteristics that cause the amp glow to not accumulate in a linear fashion over time.  I have never had a single dark from my ASI1600 calibrate correctly with that box checked.

 

As for your light and flat frames, the dark patterns in the images you've posted do not appear in the files that you gave me.  As a basic sanity check, I used PixelMath to partially calibrate the light frame manually.  Basically I created an expression that was "light_frame / flat_frame".  I then applied it to the light frame.  I've attached an autoSTF of the result.  It's not supposed to be perfect calibration, since the light and dark frames are uncalibrated and I don't have a bias (which means I can't make a calibrated flat).

 

Anyway, the result is pretty conclusive that if all of your lights and flats are like this one, then you are somehow introducing the problem in processing.  When I see something like this in my data, it often means that something happened during the run that introduced an actual shadow in some of the light frames.  I think that you should blink all of your dark frames, your bias frames, your flat frames and your light frames.  Make sure the the Blink process does an auto stretch, so that they should appear similar.  My guess is that you will have some frames somewhere with problems in the area that's dark in your result.

so helpful. only thing is I shared the wrong sub, not that I wasnt have the same issue, I was, except in the case of the seagull I did have the edge on artifact. nonetheless I will look to the pre proc process.



#13 Ballyhoo

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Posted 11 February 2020 - 11:05 PM

i am most doomed.   I tried everything. only checked calibrate. created new darks. Verified fits properties, gain, exp, tec.  No matter what I cannot get rid a the dust motes. My only hope is to raise the histogram, as it is only about  half way, to the half-way point, well, maybe 30%.  

 

I did not have this issue before I changed my configuration with the camera not attached to the flywheel direct. since I changed that per the ZWO website I have been most doomed.

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  • not flat calibrated.gif


#14 Ballyhoo

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Posted 12 February 2020 - 03:27 AM

now i am scouring the internet to find a solution.   There was another post way back when which discussed the need to sequence the darks /bias in a dark room  I do not do that. I just do the darks in my home-office. I dim the lights, but there is light about.  

 

I will try doing the darks in complete darkness. Though I have a tough time knowing whether some aberrant photons making there way into dark or bias frames could have such a dramatic affect.  Does not affect my ASI 294 PRo.   I am beginning to think OSC is calling me back. 



#15 happylimpet

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Posted 12 February 2020 - 03:47 AM

 My only hope is to raise the histogram, as it is only about  half way, to the half-way point, well, maybe 30%.  

 

I am making it my mission to correct this myth wherever possible. Flat exposure, provided not saturated, doesnt matter. Underexposed just means you need more to get a decent noise level in your master flat. Obviously you need to calibrate your flat with flat darks, or biases if you've lax standards.


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#16 Biggen

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Posted 12 February 2020 - 07:52 AM

Definitely try to take darks in a dark room. I move my scope into an interior bathroom, turn off the lights, and close the door when I update/create my dark library.

 



#17 WadeH237

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Posted 12 February 2020 - 09:23 AM

so helpful. only thing is I shared the wrong sub, not that I wasnt have the same issue, I was, except in the case of the seagull I did have the edge on artifact. nonetheless I will look to the pre proc process.

I also looked at the Seagull image.  I got similar results as M101.  I just didn't attach an image.

 

I will say that the Seagull looked pretty over exposed to me.  The unstretched pixel values for the background were 0.3+ (normalized in 0-1 range).



#18 WadeH237

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Posted 12 February 2020 - 10:26 AM

No matter what I cannot get rid a the dust motes.

This indicates that something is wrong in how you are calibrating.

 

In order to get correct flat calibration, you need to be able to extract just the signal* from the light frames and just the signal from the flat frames before the flat calibration happens.  If you don't get that right, then either under or over correction is pretty much guaranteed.

 

In looking at your data, I find some stuff that's unusual.  For example, looking at the FITS headers, it looks like you are using gain 128.  For the ASI1600, this is an unusual setting.  My suggestion is (for the time being) to just use unity gain.  That is 139.  And I would recommend an offset of 40.  There are valid reasons to use other settings, but until you get your calibration working like clockwork, I strongly suggest using only the following camera settings, which should get you solid and repeatable performance:

 

Gain: 139

Offset: 40

Temperature: -10C

 

I can also see that you are using 90 second exposures.  That should be fine.  In fact, for the time being, go ahead and always use 90 seconds, regardless of target.  Again, there are valid reasons for different length exposures, but until you get your calibration working like clockwork, 90 second exposures should work for any target with the above gain/offset/temp.

 

Ok, so now that the settings and exposure times are locked down, here is how I would recommend that you do your calibration (Check, double check, and triple check that you are using gain 139, offset 40 and temp -10C.  Do not proceed until that's true):

 

1) Set the exposure time to 0.1 seconds, cap the camera and put it in a dark place.  Take 100 exposures.

 

2) Open the ImageIntegration process and click the reset icon (the rightmost icon at the bottom right corner).  Add the 100 image files that you just made and use the following options:

  • Combination: Average
  • Normalization: No normalization.
  • Weights: Don't care (all weights = 1)
  • Scale estimator: Iterative k-sigma / biweight midvariance
  • Just leave the others at the default settings
  • Under Pixel Rejection (1) use the following options:
  • Rejection algorithm: Winsorized Sigma Clipping
  • Normalization: No normalization
  • Ensure that "Clip low pixels" and "Clip high pixels" are both checked.
  • Leave the other settings at the defaults

Under Pixel Rejection (2) use the following options:

  • Sigma low: 4.000
  • Sigma high: 2.400
  • Winsorization cutoff: 5.000
  • Leave the other settings at defaults

Leave Pixel Rejection (3) and Large-Scale Pixel Rejection at defaults

Run the process and save the resulting file with the name "Master_bias_gain139_offset40_minus10C.xisf"

 

3) Using the same camera settings (check, double check and triple check), set the exposure time to 90 seconds, cap the camera and put it in a dark place.  Take 15 exposures.

 

4) Open the ImageIntegration process and use all the same settings as step 2).

Run the process and save the resulting file with the name "Uncalibrated_master_dark_gain139_offset40_minus10C_90seconds.xisf"

 

5) This step should be repeated for each of your filters

Take flats using your normal procedure

Open the Blink process and examine each flat to ensure that they are look about the same.  Delete any that look significantly different.

Open the ImageCalibration process, click the reset icon in the lower right, and use the following settings:

  • Under Output Files, pick an output directory and keep the rest at default
  • Check the Master Bias option and provide a path to the "Master_bias_gain139_offset40_minus10C.xisf" file
  • Ensure that the Calibrate box under Master Bias is unchecked
  • Ensure that Master Dark and Master Flat are unchecked

Run the ImageIntegration process

Open the ImageIntegrationProcess, click the reset icon in the lower right, and use the following settings:

Under Image Integration:

  • Combination: Average
  • Normalization: Multiplicative with scaling
  • Weights: Don't care (all weights = 1)
  • Scale Estimator: Iterative k-sigma / biweight midvariance
  • Leave the rest at defaults

Under Pixel Rejection (1):

  • Rejection algorithm: Sigma Clipping (if you have more than 15 flats per filter, go ahead and use Winsorized Sigma Clipping)
  • Normalization: Equalize fluxes
  • Ensure that "Clip low pixels" and "Clip high pixels" are set

Under Pixel Rejection (2):

  • Sigma low: 4.000
  • Sigma high: 2.400
  • Leave the rest at defaults

Leave Pixel Rejection (3) and Large-Scale Pixel Rejection at defaults

Add the calibrated files that were produced by ImageCalibration

Run the process and save the resulting file with the name "Calibrated_master_flat_<filtername>.xisf"

Repeat for each filter

 

You now have the calibration masters that you'll need.  They will work with light images taken at gain 139, offset 40, temperature -10C and 90 second exposures. Do not use any other settings.  So go image something using those settings.

 

Before calibrating the light files, it's a good idea to blink them and remove any that are obviously bad.

 

To calibrate the light files, open the ImageCalibration process, click the reset button in the lower right and use the following settings:

  • Under Output Files, add your light frames.  Use default settings, except for Output Pedestal (DN).  Set that to 1000 (which I find helps greatly with the ASI1600).
  • Ensure that Master Bias is unchecked
  • Check Master Dark and set the path to "Uncalibrated_master_dark_gain139_offset40_minus10C_90seconds.xisf"
  • Ensure that both Calibrate and Optimize are unchecked
  • Check Master Flat and set the path to "Calibrated_master_flat_<filtername>.xisf"
  • Ensure that Calibrate is unchecked
  • Run the process

Ok, so now you have what should be properly calibrated light files.  Blink through them.  You should not see any remains of dust motes.  You may or may not see some residual vignetting or gradients.  That's fine.

 

I'm going to stop here, since the topic here is to get properly calibrated files.  From here, you can integrate them and start to process them.


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#19 Ballyhoo

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Posted 12 February 2020 - 12:21 PM

This indicates that something is wrong in how you are calibrating.

 

In order to get correct flat calibration, you need to be able to extract just the signal* from the light frames and just the signal from the flat frames before the flat calibration happens.  If you don't get that right, then either under or over correction is pretty much guaranteed.

 

In looking at your data, I find some stuff that's unusual.  For example, looking at the FITS headers, it looks like you are using gain 128.  For the ASI1600, this is an unusual setting.  My suggestion is (for the time being) to just use unity gain.  That is 139.  And I would recommend an offset of 40.  There are valid reasons to use other settings, but until you get your calibration working like clockwork, I strongly suggest using only the following camera settings, which should get you solid and repeatable performance:

 

Gain: 139

Offset: 40

Temperature: -10C

 

I can also see that you are using 90 second exposures.  That should be fine.  In fact, for the time being, go ahead and always use 90 seconds, regardless of target.  Again, there are valid reasons for different length exposures, but until you get your calibration working like clockwork, 90 second exposures should work for any target with the above gain/offset/temp.

 

Ok, so now that the settings and exposure times are locked down, here is how I would recommend that you do your calibration (Check, double check, and triple check that you are using gain 139, offset 40 and temp -10C.  Do not proceed until that's true):

 

1) Set the exposure time to 0.1 seconds, cap the camera and put it in a dark place.  Take 100 exposures.

 

2) Open the ImageIntegration process and click the reset icon (the rightmost icon at the bottom right corner).  Add the 100 image files that you just made and use the following options:

  • Combination: Average
  • Normalization: No normalization.
  • Weights: Don't care (all weights = 1)
  • Scale estimator: Iterative k-sigma / biweight midvariance
  • Just leave the others at the default settings
  • Under Pixel Rejection (1) use the following options:
  • Rejection algorithm: Winsorized Sigma Clipping
  • Normalization: No normalization
  • Ensure that "Clip low pixels" and "Clip high pixels" are both checked.
  • Leave the other settings at the defaults

Under Pixel Rejection (2) use the following options:

  • Sigma low: 4.000
  • Sigma high: 2.400
  • Winsorization cutoff: 5.000
  • Leave the other settings at defaults

Leave Pixel Rejection (3) and Large-Scale Pixel Rejection at defaults

Run the process and save the resulting file with the name "Master_bias_gain139_offset40_minus10C.xisf"

 

3) Using the same camera settings (check, double check and triple check), set the exposure time to 90 seconds, cap the camera and put it in a dark place.  Take 15 exposures.

 

4) Open the ImageIntegration process and use all the same settings as step 2).

Run the process and save the resulting file with the name "Uncalibrated_master_dark_gain139_offset40_minus10C_90seconds.xisf"

 

5) This step should be repeated for each of your filters

Take flats using your normal procedure

Open the Blink process and examine each flat to ensure that they are look about the same.  Delete any that look significantly different.

Open the ImageCalibration process, click the reset icon in the lower right, and use the following settings:

  • Under Output Files, pick an output directory and keep the rest at default
  • Check the Master Bias option and provide a path to the "Master_bias_gain139_offset40_minus10C.xisf" file
  • Ensure that the Calibrate box under Master Bias is unchecked
  • Ensure that Master Dark and Master Flat are unchecked

Run the ImageIntegration process

Open the ImageIntegrationProcess, click the reset icon in the lower right, and use the following settings:

Under Image Integration:

  • Combination: Average
  • Normalization: Multiplicative with scaling
  • Weights: Don't care (all weights = 1)
  • Scale Estimator: Iterative k-sigma / biweight midvariance
  • Leave the rest at defaults

Under Pixel Rejection (1):

  • Rejection algorithm: Sigma Clipping (if you have more than 15 flats per filter, go ahead and use Winsorized Sigma Clipping)
  • Normalization: Equalize fluxes
  • Ensure that "Clip low pixels" and "Clip high pixels" are set

Under Pixel Rejection (2):

  • Sigma low: 4.000
  • Sigma high: 2.400
  • Leave the rest at defaults

Leave Pixel Rejection (3) and Large-Scale Pixel Rejection at defaults

Add the calibrated files that were produced by ImageCalibration

Run the process and save the resulting file with the name "Calibrated_master_flat_<filtername>.xisf"

Repeat for each filter

 

You now have the calibration masters that you'll need.  They will work with light images taken at gain 139, offset 40, temperature -10C and 90 second exposures. Do not use any other settings.  So go image something using those settings.

 

Before calibrating the light files, it's a good idea to blink them and remove any that are obviously bad.

 

To calibrate the light files, open the ImageCalibration process, click the reset button in the lower right and use the following settings:

  • Under Output Files, add your light frames.  Use default settings, except for Output Pedestal (DN).  Set that to 1000 (which I find helps greatly with the ASI1600).
  • Ensure that Master Bias is unchecked
  • Check Master Dark and set the path to "Uncalibrated_master_dark_gain139_offset40_minus10C_90seconds.xisf"
  • Ensure that both Calibrate and Optimize are unchecked
  • Check Master Flat and set the path to "Calibrated_master_flat_<filtername>.xisf"
  • Ensure that Calibrate is unchecked
  • Run the process

Ok, so now you have what should be properly calibrated light files.  Blink through them.  You should not see any remains of dust motes.  You may or may not see some residual vignetting or gradients.  That's fine.

 

I'm going to stop here, since the topic here is to get properly calibrated files.  From here, you can integrate them and start to process them.

Thank you so much Wade

 

is there an importance of -10C v -13C that I have been using?

 

I have only shot lumen at 90 seconds. everything else has been at 180 seconds.

 

Do you normally shoot lumen at same exp time as RGB?



#20 WadeH237

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Posted 12 February 2020 - 12:35 PM

is there an importance of -10C v -13C that I have been using?

There is nothing technically important about it, except that you can probably reach that temperature on any imaging night, without running the cooler at 100% power. Also, I tend to like round numbers, except where the precision is important for some reason. In this case, I don't expect that -13 will make your images any better than -10.

 

I suppose that I would think this is a better question:  How did you arrive at -13 as the temperature to use?  Does it do anything for you that -10 or -15 does not?  Any time that I see an "unround" number, this question comes to mind.
 

I have only shot lumen at 90 seconds. everything else has been at 180 seconds.
 
Do you normally shoot lumen at same exp time as RGB?

The noise on this camera is low enough, that 90 seconds should work fine for anything right now.  Doing different filters at different exposure times, means building a bigger calibration library.  And since calibration is currently the area where there are things to fix, there is no sense making it any more complicated than it needs to be.

 

As for me, I can't remember the last time I shot luminance.  I tend to do either narrow band or RGB and build an artificial luminance to meet whatever my need-of-the-day is.  Luminance is valuable in the case where imaging time is limited, and that doesn't describe my typical work flow.


Edited by WadeH237, 12 February 2020 - 12:41 PM.

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#21 Ballyhoo

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Posted 12 February 2020 - 12:44 PM

just to be safe I thought I better have you check to make certain I have the correct save settings:

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#22 Stelios

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Posted 12 February 2020 - 01:19 PM

I think we should start a thread "Legends of the ASI1600." Certainly there are a lot of different ways I've seen proposed to calibrate both flats and lights--for me, the original by Warren Keller in his book, works great. 

 

The one thing I got out of this thread is the need to be careful about external light when taking flats. I've noticed extra edge brightness in some of mine, and it may well be due to my taking flats about an hour before sunset. I'll make sure I take them when it's dark--wasting 20 minutes of so of imaging, but so be it. One more of the little astrophotography gotchas.



#23 WadeH237

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Posted 12 February 2020 - 02:39 PM

just to be safe I thought I better have you check to make certain I have the correct save settings:

That's fine.

 

The important part about that dialog is to have 32 bit IEEE 754 floating point selected.  Personally, I never use the thumbnail, so I uncheck that.



#24 WadeH237

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Posted 12 February 2020 - 02:49 PM

Certainly there are a lot of different ways I've seen proposed to calibrate both flats and lights--for me, the original by Warren Keller in his book, works great. 

I have some commentary about "Legends of the ASI1600", but I will refrain from making them until and unless someone creates that thread.

 

Regarding the steps that I use for all of my processing, I use the published works of a number of people (including Warren Keller, Adam Block, Kayron Mercieca of Light Vortex Astronomy, and countless others).  But I use them as a starting place; a jump off point for me to learn more.

 

The steps that I listed above are not in any way meant to be applicable for every situation (and not even necessarily the way that do it all the time, even with this camera).  They are specifically meant to help ballyhoo find some solid ground and get past some of the calibration problems that he's having.  Anyone else who's not getting satisfactory results with this camera, is welcome to try them.



#25 Ballyhoo

Ballyhoo

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Posted 12 February 2020 - 03:06 PM

 Wade:

well I have not yet changed my exp time and gain settings, since that requires another session under a dark sky. but using your flow chart, (g 128, per current, not future settings) I get the following in the 180 red channel.

 

Also I am wondering, is there any chance that my focal reducer could be incompatible? It is the branded FR for the refactor. just had to ask.

 

anyways tonight I am going to change things up with the suggested gain, offset and exp time. Wondering whether I might even just lower my exp time to 60 seconds. 

 

The lumen (bottom) looked a little better and I wonder if that is be it is 90 seconds. 

 

edit

still open to the possibility of light leakage in the flat exposures, though it is not apparent from where. 

Attached Thumbnails

  • red m101.gif
  • lumen.jpg

Edited by Ballyhoo, 12 February 2020 - 03:08 PM.



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