Is it possible with 3.3 to dither without guiding and no live stack?

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Re: Is it possible with 3.3 to dither without guiding and no live stack?

#21

Post by admin »

Hi Rick,

the four values in the settings are just 'vaguely reasonable' default values - they may need to be changed, but I wouldn't try that unless you are having a problem. For instance depending on the focal length/pixel size of your guiding scope/camera you may want to change the size of the max dither step. If you are having problems with the frame after the dither being spoilt (perhaps because of the settle not quite finished), you could increase the minimum settle time or reduce the settle threshold.

The time in the live stack area (120s by default) is how long between dithers - You can obviously reduce this to dither more often, but every time you dither you maybe lose 30s of imaging time, so deciding just how often is a matter of balancing that against other considerations.

Robin
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Re: Is it possible with 3.3 to dither without guiding and no live stack?

#22

Post by RickBG »

Hi Robin,

When I looked at the log after each save when dithering, the exposure time will eventually drop to 1.0 second. A message on top would appear letting me know there is not enough light. This happened only when I dither. I checked the box for reduced exposure during dithering, might that be the cause for the anomaly?

Rick
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Re: Is it possible with 3.3 to dither without guiding and no live stack?

#23

Post by admin »

Hi Rick,

sorry to say that I'm a bit confused here - any chance you can share a screenshot of the message - that will hopefully put me on the right track again :)

cheers,

Robin
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Re: Is it possible with 3.3 to dither without guiding and no live stack?

#24

Post by RickBG »

Hi Robin,
Below are the two logs pertaining to the acquisitions taken on the March 15 when I first used dithering.
The 1st log after the first save shows Exposure=3.935s:
[ZWO ASI183MC Pro]
FrameType=Light
Debayer Preview=On
Pan=0
Tilt=0
Output Format=FITS files (*.fits)
Binning=1
Capture Area=5496x3672
Colour Space=RAW16
Hardware Binning=Off
High Speed Mode=On
Turbo USB=100(Auto)
Flip=Horiz
Frame Rate Limit=Maximum
Gain=0
Exposure=3.935s
Timestamp Frames=Off
White Bal (B)=53
White Bal (R)=82
Brightness=4
Temperature=-0.5
Cooler Power=42
Target Temperature=0
Cooler=On
Auto Exp Max Gain=326
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=158
Mono Bin=Off
Background Subtraction=Off
Planet/Disk Stabilization=Off
Banding Threshold=35
Banding Suppression=0
Apply Flat=None
Subtract Dark=None
Display Black Point=0
Display MidTone Point=0.5
Display White Point=1
Notes=
TimeStamp=2021-03-16T01:12:25.2587763Z
SharpCapVersion=4.0.7529.0
TotalExposure(s)=1530.649259
StackedFrames=389
LiveStack.SaveRawFrames=None
LiveStack.AlignFrames=True
LiveStack.Derotate=True
LiveStack.StarsForAlignment=15
LiveStack.MinStarSize=3
LiveStack.MaxStarWidth=16
LiveStack.AlignAutoDisabled=False
LiveStack.ReduceNoiseAmount=0.5
LiveStack.DigitalGain=Off
LiveStack.BlackThreshold=20
LiveStack.BrightnessLimit=81
LiveStack.FilterBrightness=True
LiveStack.AutoBrightnessLimit=False
LiveStack.FWHMLimit=9.810808
LiveStack.FilterFWHM=True
LiveStack.WarningThreshold=5
LiveStack.StackingMode=0
LiveStack.SigmaClipInitialCount=15
LiveSack.SigmaClipThreshold=3.492064
LiveStack.SigmaClipLowLimit=5.026454
LiveStack.AutoSaveReset=False
LiveStack.AutoSaveResetMinutes=30
LiveStack.LogarithmicHistogramHorizontalAxis=True
LiveStack.AutoSave=False
LiveStack.BlackLevel=0
LiveStack.WhiteLevel=100
LiveStack.MidLevel=25
LiveStack.WBB.db=0
LiveStack.WBG.db=0
LiveStack.WBR.db=0
LiveStack.Saturation=1.252567
AutoStretch.Strength=1.457286

The 2nd log after the second save shows Exposure=1.000s:
[ZWO ASI183MC Pro]
FrameType=Light
Debayer Preview=On
Pan=0
Tilt=0
Output Format=FITS files (*.fits)
Binning=1
Capture Area=5496x3672
Colour Space=RAW16
Hardware Binning=Off
High Speed Mode=On
Turbo USB=100(Auto)
Flip=Horiz
Frame Rate Limit=Maximum
Gain=0
Exposure=1.000s
Timestamp Frames=Off
White Bal (B)=53
White Bal (R)=82
Brightness=4
Temperature=-0.5
Cooler Power=37
Target Temperature=0
Cooler=On
Auto Exp Max Gain=326
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=158
Mono Bin=Off
Background Subtraction=Off
Planet/Disk Stabilization=Off
Banding Threshold=35
Banding Suppression=0
Apply Flat=None
Subtract Dark=None
Display Black Point=0
Display MidTone Point=0.5
Display White Point=1
Notes=
TimeStamp=2021-03-16T01:21:52.7151618Z
SharpCapVersion=4.0.7529.0
TotalExposure(s)=1621.150372
StackedFrames=412
LiveStack.SaveRawFrames=None
LiveStack.AlignFrames=True
LiveStack.Derotate=True
LiveStack.StarsForAlignment=15
LiveStack.MinStarSize=3
LiveStack.MaxStarWidth=16
LiveStack.AlignAutoDisabled=False
LiveStack.ReduceNoiseAmount=0.5
LiveStack.DigitalGain=Off
LiveStack.BlackThreshold=20
LiveStack.BrightnessLimit=81
LiveStack.FilterBrightness=True
LiveStack.AutoBrightnessLimit=False
LiveStack.FWHMLimit=9.810808
LiveStack.FilterFWHM=True
LiveStack.WarningThreshold=5
LiveStack.StackingMode=0
LiveStack.SigmaClipInitialCount=15
LiveSack.SigmaClipThreshold=3.492064
LiveStack.SigmaClipLowLimit=5.026454
LiveStack.AutoSaveReset=False
LiveStack.AutoSaveResetMinutes=30
LiveStack.LogarithmicHistogramHorizontalAxis=True
LiveStack.AutoSave=False
LiveStack.BlackLevel=0
LiveStack.WhiteLevel=100
LiveStack.MidLevel=25
LiveStack.WBB.db=0
LiveStack.WBG.db=0
LiveStack.WBR.db=0
LiveStack.Saturation=1.252567
AutoStretch.Strength=1.457286

Please note the exposure time was automatically changed from 3.935s (1st log) to 1.000s (2nd log). My question is how is this possible? This happened again when dithering on March 17th but this time it occurred after the 6th save and also showing up on the 7th save as well. Obviously, the time should remain as 3.935s in the second log and continue no matter how often you save your live stacked images.

Rick
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Re: Is it possible with 3.3 to dither without guiding and no live stack?

#25

Post by admin »

Hi Rick,

the key fields in those files are actually these

Code: Select all

TotalExposure(s)=1530.649259
StackedFrames=389
and

Code: Select all

TotalExposure(s)=1621.150372
StackedFrames=412
These show the number of frames that have gone into the stack and the total exposure of all those frames - divide the total exposure by the stacked frames and you get 3.93ish in both cases.

The exposure field is obviously a bug, but I don't think it is causing any problems - it's just the wrong number getting into the settings file under some circumstances - I don't think it is causing a problem with the saved images or indicating that 1s frames are being used for stacking.

I will try to work out how it could be happening and stop it if possibly though.

cheers,

Robin
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Re: Is it possible with 3.3 to dither without guiding and no live stack?

#26

Post by RickBG »

Thanks Robin! It appears to be a random anomaly that occurs only when dithering since I don't see it when not dithering.
Rick
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Re: Is it possible with 3.3 to dither without guiding and no live stack?

#27

Post by Menno555 »

Two questions in preparation of first time ASCOM dithering:
  1. With Live Stacking, when I choose to save each raw capture to stack it in DSS, does that mean it will not save the visual settings made in the Live Stack part but it will save the captures as set with the main settings (gain, brightness/offset, white balance)?
  2. I do know there is a correlation between telescope/camera combi and dither step. This can be set in the Settings-Guiding-Dithering part. My setup gives a resolution of around 0.486 arcsec/px with a FOV of around 40' 4.5" x 26' 37.2" and planning on RA dither only because the DEC on my mount is slow to react. What would be good/logical dither settings to start with? Max Dither Step now has the default value of 20.
Menno
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Re: Is it possible with 3.3 to dither without guiding and no live stack?

#28

Post by admin »

Hi Menno,

If you save the RAW frames then the following adjustments will not affect them :

* Anything in the 'preprocessing' section of the camera controls
* Any changes to the display histogram stretch in the camera controls
* Anything at all done in the live stacking panel

All the other controls in the camera control panel will affect the raw frames (since everything else on there is sent to the camera and affects the data before SharpCap sees it).

That means that the frames can be processed later in some other application like DSS.

If you have ~0.5 arcsec/px then the default dither value of 20 will generate random dithers of up to 20 arc seconds, or up to 10 pixels. That sounds reasonable to me. Of course, over time the frame will drift as a result of multiple dither operations (drunkards walk). I wonder if I should try to limit this?

cheers,

Robin
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Re: Is it possible with 3.3 to dither without guiding and no live stack?

#29

Post by Menno555 »

Thanks Robin, totally clear.

Menno
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Re: Is it possible with 3.3 to dither without guiding and no live stack?

#30

Post by RickBG »

Hi Robin,

In my case, it is 1.0 arcsec/pixel and with a default of 20 would make it a 20 pixel movement. Maybe I should change the default to 10. What do you think? What other parameters do you recommend changing?

Rick
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