And lastly, stick to Lights, Flats, and Bias only with the 2600 cameras (and 268s). You don't need to do darks and dark flats, your flats problem will get worse (speaking from experience as I've seen it happen to my own images)
You may not even need flats/bias with the 2600, but it does depend on your image train. I have no material vignette so don't bother shooting flats. Flats would be useful for dust bunnies if you have them though.
I don't bother with any calibration frames on my 533 either (same silicon) albeit vignette is less of a concern on a small sensor.
Dithering and adaptive rejection algorithms in stacking do the job for me!
Thanks everyone for the help and advice with this, it is appreciated.
Yes i had a typo there when i said the lights were done at 22000ADU,
it was suppose to be Flats.
I have been playing around with different ADU vales, and the last one was 22000ADU.
It is sounding like ( as most of you are telling ) that the Flats are off, I am going to go back and have another look at APT as i am missing the main part of the instructions that everyone is telling me.
(Adjusting the brightness and achieving a “ADU range” on the histogram of roughly between 8500 and 35,000 ADU or up to half way)
I have just been selecting an ADU, say 22000, then letting APT do it Flats aid calculation.
So there is a way to actually measure the ADU of the flat panel first?
Then adjust the brightness to get the histogram to sit in the middle.
Then with this number, you then set the Flats aid to this number.
I will take a look into this.
I will have a look in the afternoon after i get some sleep, on a night shift leg this week.
I will then work through the rest of the advice given on here, most of it i have done correctly, just not the first part.
I don't think i am getting stray light in the imaging train, the bias frames all look black, might even just take it outside in the daylight and take some darks just to see if there is any light showing up in the frames also.
Peter,
What flat panel are you using for your Flats ?
Does it have adjustable brightness levels ?
Are you stretching a white T shirt over the end of the OTA wth a rubber band ?
I use a Huion led dimmable light panel and usually set t lowest brightness or just slightly above.
Photo my little 6” newt in Sydney taking Flats with APT
I set my panel brightness to lowest , Open CCD Flats Aid , Open the Histigram set it to Local , set APT Flats Aid to say 21000 target ADU , press Run then watch the Histogram move around until it stops. If it stops say between 8500 and 35000 ADU value where it says “Range” and the first peak ( RGB ) is located off the left hand side just away from blackpoint , 2nd peak in the middle and 3rd peak no further than halfway along the Histogram then I check Flats exposure value. For no filter used Flat are usually 0.2 sec to 0.5 sec , with L Extreme filter they can be 5 sec to 10 sec long
If the Histogram is not in the correct range then I adjust the light panel brightness ever so slightly or drop the ADU target range to 21,000 or even 20,000 sometimes
The Histogram Range is the key
Definitely check for light leaks as previously suggested by others. Bias frames will still be black due to their short exposure so if you do have light leaks, they won’t show up on the bias frames.
I had a light leak issue and found the sources by looping 1 second exposures and shining a torch around the OTA. For my Newtonian, the weak spots were the rear end and the focuser. Once I fixed these, I never got those weird patterns again and can stretch my images so much more with no trace of leaks.
Also for flats, is your camera orientation exactly the same? I learnt the hard way that it must be the same.
Yes as Stephane mentioned camera in same orientation and “Focus”
If camera moved or removed a new set of Flats should be taken eg: 2 nights imaging with camera removed and re installed 2nd night
I use a fresh set of Flats and Bias for each session even though you can reuse Bias
I’ve had issues with DSS and using Masters so I use a fresh set each session , haven’t had any issues to date
They don’t take long to capture anyway.
DSS loading Calibration Frames ( safest option )
1 nights imaging
Load Lights, Flats and Bias into Main group register and stack
2 nights imaging ( camera removed )
Load night 1 Lights , New Flats and New Bias into Main Group
Load night 2 Lights , New Flats and New Bias into Group 1
Register and stack
2 nights imaging ( camera not removed )
Load night 1 Lights, same Flats and same Bias into Main Group
Load night 2 Lights , same Flats and same Bias into Group 1
Register and Stack
NB: I’ve tried the reference frame method for multiple nights in DSS and it’s never worked for me
One important thing I do before loading Lights into DSS , I review the light frames in ASTAP and cull any lights with the following issues -
Bloated stars due to Ra or Dec excursions in PHD2 guiding
Tracking or guiding issues ( Star shape ) zoom in for inspection
Satellite trails
Aircraft trails
Cloud cover even high cloud ( Astap will pick it up )
Other anomalies
9/Stacking Parameters, Calibration Frames use Median
Martin
I am going to go back over and re do the stacking program again as there are a few things on there that i do need to change.
In regards to this one:
9/Stacking Parameters, Calibration Frames use Median
I can't see that option anywhere in DeepSky Stacker.
I even downloaded the latest version just to make sure.
Under the Stacking Parameters tab i re set the Lights, Flats, Bias to the suggested settings.
But i can't see the Calibration Frames tab,
The only thing that i found remotely close was in the Cosmetic tab.
If i click:
Detect and Clean remaining Hot Pixels,
Detect and Clean remaining Cold Pixels,
Then you get the option:
Replace pixel value with the median Test on first Frame
I selected this option and and let it do its Test on first image
It take a little while, but came back with:
Detected Hit Pixels 832023 (3.19%)
Detected Cold Pixels 1494800 (5.73%)
Also left the Alignment method as Automatic.
Sorry for dragging this out, but definitely learning some very valuable information here.
Last edited by bluesilver; 05-07-2022 at 02:36 PM.
Peter,
What flat panel are you using for your Flats ?
Does it have adjustable brightness levels ?
Are you stretching a white T shirt over the end of the OTA wth a rubber band ?
I use a Huion led dimmable light panel and usually set t lowest brightness or just slightly above.
Photo my little 6” newt in Sydney taking Flats with APT
I set my panel brightness to lowest , Open CCD Flats Aid , Open the Histigram set it to Local , set APT Flats Aid to say 21000 target ADU , press Run then watch the Histogram move around until it stops. If it stops say between 8500 and 35000 ADU value where it says “Range” and the first peak ( RGB ) is located off the left hand side just away from blackpoint , 2nd peak in the middle and 3rd peak no further than halfway along the Histogram then I check Flats exposure value. For no filter used Flat are usually 0.2 sec to 0.5 sec , with L Extreme filter they can be 5 sec to 10 sec long
If the Histogram is not in the correct range then I adjust the light panel brightness ever so slightly or drop the ADU target range to 21,000 or even 20,000 sometimes
The Histogram Range is the key
Hope the above helps
Martin
Hi Martin,
I am using a dimmable light box for a member on here that is making them and sealing them.
That are 12V dimmable LED light boxes that fit snugly over the top of my dew shield.
So i will definitely be re looking at those Flats again, I can see now where i messed them up.
Yes, i basically just finished the imaging session with my lights, left everything as it is, didn't touch a things and put the dimmable light box on and ran the Flats session, then then did the bias after that.
So that part at least i got correct, just the Flats setting are way off
I am going to go back over and re do the stacking program again as there are a few things on there that i do need to change.
In regards to this one:
9/Stacking Parameters, Calibration Frames use Median
I can't see that option anywhere in DeepSky Stacker.
I even downloaded the latest version just to make sure.
Under the Stacking Parameters tab i re set the Lights, Flats, Bias to the suggested settings.
But i can't see the Calibration Frames tab,
The only thing that i found remotely close was in the Cosmetic tab.
If i click:
Detect and Clean remaining Hot Pixels,
Detect and Clean remaining Cold Pixels,
Then you get the option:
Replace pixel value with the median Test on first Frame
I selected this option and and let it do its Test on first image
It take a little while, but came back with:
Detected Hit Pixels 832023 (3.19%)
Detected Cold Pixels 1494800 (5.73%)
Also left the Alignment method as Automatic.
Sorry for dragging this out, but definitely learning some very valuable information here.
Sorry Peter,
Forget item 9 Calibration frames tab ( I corrected that in item 10 and 11 ) and forgot to delete item 9
Do not touch anything in Cosmetics tab
Only check or tick Use all available processors
Stacking Parameters, Alignment tab set should be set to “Automatic”
Finally in Stacking Parameters under Light tab , with Per Background Channel , when you click on this it opens a menu with Options….. click Options and select Linear ( Calibration Method ) and None ( RGB Background Calibration Method )
That’s about it
I tested some data today and used Per Channel Background Calibration as well as No Background Calibration in DSS and the resultant processed image was the same in Startools using identical settings and procedures. But I’m still going to use Per Channel Background Calibration as I’ve always used this even though Ivo from Startools recommendation is use No Background Calibration to keep the DSS stacked image purely Linear.
I’m sure even when you use No Background Calibration your background across a whole session can be fairly uniform under dark skies.
I really hope you achieve some better processed images in Startools
It just takes some time as long as your data has good calibration, registering stacking is done correctly in DSS and the initial processing procedures are followed in Startools
Thanks again for all this great information.
Just running it all through the stacking process aging now for those two images.
Might try and upload them to the One Drive that was generously offered to be by AdamJL
Cheers,
Peter
Peter,
Just so you get an understanding of the File Groups in DSS
There are 2 Groups
1/ Main Group
2/ Group 1 and onwards
Light frames in the Main Group are only associated with the Flats and Bias frames in the Main Group
Flats and / or Bias frames in the Main Group are only associated with Light frames in Group 1 onwards
Flats and / or Bias frames from Group 1 and onwards are only associated with Light frames from same group
So in other words, Flats and or Bias placed in Main Group will calibrate with Light frames placed in Main Group or Group 1 or Group 2 and so on …,
You can’t place Light frames in Main Group and Flats or Bias in Group 1 or Group 2 and so on …. and expect them to calibrate, they won’t
That’s why the safest way to load your files is -
Night 1 only, load Lights , Flats and Bias into Main Group
Nights 1 and 2 ( camera removed ) load Lights , Flats and Bias night 1 into Main Group and load Lights , Flats and Bias night 2 into Group 1
Nights 1 and 2 ( camera not touched ) load night 1 Flats and Bias into Main Group , load Lights night 1 into Group 1 and Lights night 2 to Group 2 ( no need for night 2 Flats or Bias as Main Group night 1 Flats and Bias are common to Groups 1 and 2 Lights )
Thanks Martin,
Yes that makes perfect sense,
I have printed out all these instructions and making up a word document so that i can print out and refer back to in the future.
Things are now starting to make sense.
Just a slow learner i guess.
Cheers,
Peter.
check this video out (there are actually 3 i think) - it isn't necessarily just about the ADU with the modern cmos, they alter their read out if they are captured quickly (so adu and length of time to capture the adu). Perhaps try and dim the flat source and take a longer flat to get to the required adu. worth a try.
Peter,
What flat panel are you using for your Flats ?
Does it have adjustable brightness levels ?
Are you stretching a white T shirt over the end of the OTA wth a rubber band ?
I use a Huion led dimmable light panel and usually set t lowest brightness or just slightly above.
Photo my little 6” newt in Sydney taking Flats with APT
I set my panel brightness to lowest , Open CCD Flats Aid , Open the Histigram set it to Local , set APT Flats Aid to say 21000 target ADU , press Run then watch the Histogram move around until it stops. If it stops say between 8500 and 35000 ADU value where it says “Range” and the first peak ( RGB ) is located off the left hand side just away from blackpoint , 2nd peak in the middle and 3rd peak no further than halfway along the Histogram then I check Flats exposure value. For no filter used Flat are usually 0.2 sec to 0.5 sec , with L Extreme filter they can be 5 sec to 10 sec long
If the Histogram is not in the correct range then I adjust the light panel brightness ever so slightly or drop the ADU target range to 21,000 or even 20,000 sometimes
The Histogram Range is the key
Hope the above helps
Martin
Sorry to bother you again with yet more questions,
Got everything back up and running again, just got to test it all out when we get clear skies.
I have ben working on the Flats Aid in APT, It appears that adjusting the light level, ( in my case it is a dimmable light box ) it is like a fine tuning of the histogram, while changing the ADU vales is a more course adjustment, at least that is what i am finding.
Si i have sort of ended up with an ADU value of 22000 for the asi2600mc,
This puts the 3rd peak of the histogram about half way along.
I the images below, the first one is with an ADU vale of 22000 and the range comes back at 12338 - 31587, i think this is look ok.
The second image is with an ADU of 30000 and the range is 16494 - 41419 and the 3rd peak is a little over half way along, but i think this is way over exposed.
I use the astronomy.tools to work out the arc seconds per pixel which comes back very simular to what you have said, 0.73 or 0.74 using astronomy.tools site
I do get wildly different histogram results depending on what you select on the histogram, ,like Log, Auto St-L, Auto Str-R, Local ( the range results remain results unaffected of course)
So just interested to know if i am on the right track here, to me it looks good, but still learning about this.
Cheers,
Peter.
Sorry to bother you again with yet more questions,
Got everything back up and running again, just got to test it all out when we get clear skies.
I have ben working on the Flats Aid in APT, It appears that adjusting the light level, ( in my case it is a dimmable light box ) it is like a fine tuning of the histogram, while changing the ADU vales is a more course adjustment, at least that is what i am finding.
Si i have sort of ended up with an ADU value of 22000 for the asi2600mc,
This puts the 3rd peak of the histogram about half way along.
I the images below, the first one is with an ADU vale of 22000 and the range comes back at 12338 - 31587, i think this is look ok.
The second image is with an ADU of 30000 and the range is 16494 - 41419 and the 3rd peak is a little over half way along, but i think this is way over exposed.
I use the astronomy.tools to work out the arc seconds per pixel which comes back very simular to what you have said, 0.73 or 0.74 using astronomy.tools site
I do get wildly different histogram results depending on what you select on the histogram, ,like Log, Auto St-L, Auto Str-R, Local ( the range results remain results unaffected of course)
So just interested to know if i am on the right track here, to me it looks good, but still learning about this.
Cheers,
Peter.
Peter,
Yes you are on the right track !!!!
I’m using APT v3.90 whereas your using v4.10 which has a few more features like showing the Gain value in Flats Aid but generally both do the same thing
Yes your key to good Flats is your “ADU range on the Histogram” with Local button , you just have to juggle the ADU target value and the brightness of your light source to achieve the best range ( definitely a Range no higher than 35,000 or halfway. 31,000 to 33,000 max on your ADU histogram Range is excellent)
The ADU range of 12,100 to 31,000 approx and your Histogram looks OK to me
Another thing to check is on the left side of the Histogram you just want to make sure your not black clipping but your 1st peak or left hand peak is around 12,100 which is fine , my 1st peak or left hand peak is usually around 8,500 to 9,000 which is also ok
Do you use a white T shirt stretched over the end of the scope ? I find a nice white T shirt works well, it gives you some flexibility with your light source and ADU Range.
I usually take 40 Flats and 60 Bias
A lot of folk say just take 15 to 20 Flats and 20 Bias but I still had some Vignetting with small amounts of calibration frames
To me the more the better as the calibration will result in less noise due to the Stacking algorithms
I revised the DSS settings again checklist for Stacking and using Startools, so here it is ( only minor changes and an addition)
DSS Latest Settings for both RGB and Narrowband data ( Prerequisites for Startools )
1/ Tick “No White Balanced Processing” in Raw Files Digital Development
2/ Leave “Set the Blackpoint to 0” unticked in Bayer Matrix Transformation
3/ Select “Per Channel Background Calibration” in Stacking Parameters even though when using Startools it should be “No Calibration”. I found Per Channel Calibration no issue when using Startools.
4/ In Stacking Parameters, Lights , Channel Background, under “Options” select Linear and None
5/ Select either “Standard Mode”or “Intersection Mode” in Stacking Parameters (Intersection helps reduce stacking artefacts)
6/ Tick “Align RGB Channels in final image” in Stacking Parameters
7/ Digital Development Process Fits setting and Raw settings select Bilinear Interpolation
8/ In Digital Development Process Settings ensure you tick “Monochrome 16bit Fits files created by a DSLR or a colour CCD camera” when using a DSLR or OSC camera.
9/ Stacking Parameters, Lights use Kappa Sigma Clipping
10/ Stacking Parameters, Flats use Median Kappa Sigma Clipping
11/ Stacking Parameters, Bias use Median Kappa Sigma Clipping
12/ In Stacking Parameters under relevant Tabs , only tick box at bottom that reads “Use all available processors”
13/ Ensure you save your stacked file as a “32 bit channel integer Fits files with no adjustments applied”
No problem if you any further questions or queries
I’m still learning as well after 5 years at it , you never stop learning in this hobby
Thanks Martin, very much appreciated.
Good to know i am heading in the right direction now.
I didn't use the white T-Shirt method, mainly because my light box sits down over the dew shield, so the dew shield is sort of half way inside the box.
A tad tight to get a T-Shirt stretched over in there, but i might give that a try next time as well to see if that makes any difference even though the box has a dimmer on it.
Just looking at your attached images there and noted you are using gain 100, I never use that for flats as I found it produced flats which corrected quite poorly. At gain 100, each electron is about 5 ADU and I found the result to look quite posterised when applied to lights and integrated.
I always do my flats at gain 0 with my 2600 cams (Both mono and OSC) and I don't aim for a specific AUD, just somewhere in the 20,000-30,000 range, so long as nothing is down near zero and nothing near saturated.
Just looking at your attached images there and noted you are using gain 100, I never use that for flats as I found it produced flats which corrected quite poorly. At gain 100, each electron is about 5 ADU and I found the result to look quite posterised when applied to lights and integrated.
I always do my flats at gain 0 with my 2600 cams (Both mono and OSC) and I don't aim for a specific AUD, just somewhere in the 20,000-30,000 range, so long as nothing is down near zero and nothing near saturated.
Paul,
Thanks for your experiences
I found not matching light frame Gain to Flat frame Gain doesn’t quite correct dust donuts other similar spots etc
I use both Gain 0 and Gain 100 to capture my lights in two different locations and corresponding Gain for my Flats and Bias and found no major issues.
Although in saying that my Gain 0 calibrated images are always so much better in regard to SNR due to the Bortle 3 skies
Just looking at your attached images there and noted you are using gain 100, I never use that for flats as I found it produced flats which corrected quite poorly. At gain 100, each electron is about 5 ADU and I found the result to look quite posterised when applied to lights and integrated.
I always do my flats at gain 0 with my 2600 cams (Both mono and OSC) and I don't aim for a specific AUD, just somewhere in the 20,000-30,000 range, so long as nothing is down near zero and nothing near saturated.
Appreciate the advice there,
Might be worth while next time i get some clear skies to do a run of Flats at Gain 0 and a run at Gain 100 then do two separate stacks to see what the difference is there.
Might also try taking some Lights at Gain 0 to see how they perform as we have around Bortle 2-3 skies here.
I have not been using my MC a lot lately (Too little clear sky and I have been too busy to manage two scopes at once) but I normally shot everything at gain 0 with the MC, with my MM, I typically shoot lum at gain 0 and RGB and Narrowband at gain 100.
