lets get this sorted!

[Rustang]

So its only really come to my attention today that I have been wrongly assuming in regards to my flats. I thought because my set up shows significant vignetting that when the flats are taken with each filter, they will have vignetting and so it wont be removed!! I just assumed it was down to my equipment being un compatible or something!. So anyway Olly has confirmed today that flats are supposed to get rid of vignetting so I'm here to work out whats gone wrong.

Equipment- QHY9 CCD mono, baader NB filters, SW 80 ED DS PRO with Altair 0.8 flattener/reducer., LED light panel and paper!

 I followed the advice Adam kindly told me in regards to taking flats, aim for somewhere between 27000 and 30000 ADU. I used the APT flats assistant to help me do this and got all of the filters into that range. I used my usual LED light panel as a light source with layers of paper over the top.

So I'm guessing for some reason the flats I took were never right as the vignetting has been in all of my stacked tiffs  making most images a right pain to process but Ive been getting by. I always just select approx 30 of each calibration set (flats, darkflats, and darks) each time i load my lights into DSS sas, i dont understand the master file side of things when it comes to calibration frames so I just load a quantity each time so could I / there be something going wrong in DSS?

 

I'm concerned this is going to get very technical and I'm afraid I probably wont understand your help/answers so go real easy on me!

 

P.S Olly recommended I download some free software to check the ADU range of my flats so if you know of any!?

 

 

Edited July 29, 2021 by Rustang

[The Lazy Astronomer]

Do you take flat darks as well?

The full image calibration process should be (flat - flat dark)/(light - dark)

[Rustang]

8 minutes ago, The Lazy Astronomer said:

Do you take flat darks as well?

The full image calibration process should be (flat - flat dark)/(light - dark)

Yes I use flats, dark flats and darks. When you say full image calibration process, I just select each in DSS then stack it all together with the lights like I've always done!? 

[The Lazy Astronomer]

3 hours ago, Rustang said:

Yes I use flats, dark flats and darks. When you say full image calibration process, I just select each in DSS then stack it all together with the lights like I've always done!? 

Yes DSS does all the background work for you (the main reason I like it - although it's far from the best stacker, it's much less faff than other software).

I doubt there's anything going wrong during the stacking process; due to it's automation, there's really very little you can do wrong in DSS. This leads me to believe it's the flats (or flat darks) themselves which aren't quite right - how do you take them? What does the histogram look like?

I had an issue with NB flats a month or so ago and the solution l found was to temperature match all subs, so I now take all lights and calibration frames at -10C. Seems to be working so far 🤞

[Rustang]

6 hours ago, The Lazy Astronomer said:

Yes DSS does all the background work for you (the main reason I like it - although it's far from the best stacker, it's much less faff than other software).

I doubt there's anything going wrong during the stacking process; due to it's automation, there's really very little you can do wrong in DSS. This leads me to believe it's the flats (or flat darks) themselves which aren't quite right - how do you take them? What does the histogram look like?

I had an issue with NB flats a month or so ago and the solution l found was to temperature match all subs, so I now take all lights and calibration frames at -10C. Seems to be working so far 🤞

I've been using an LED  drawing light panel as the light source with sheets of paper to dim it down. The camera was set to - 20 so the same temperature for everything. The hisgram to me in APT never seemed right, to far to the right (bright) but if I remember rightly I asked about this before and it was something to do with the hisgram not being able to show everything correctly! I think flats are the bane of many peoples lives in this game and when your barely scrapping by with all the technical aspects of this hobby it's frustrating when you follow step by step advice and for some reason it still doesn't work and that's where it leaves me with not alot of chance of figuring it out myself. 

You can see below an example of the histogram, it's reach the correct ADU but seems to far right to me. You can also see the vignetting in having to deal with. 

Edited July 30, 2021 by Rustang

[Budgie1]

Firstly, Masters - When DSS does the stacking for you with any calibration frames it creates a Master Flat, Master Dark, Master Bias or Master Dark-Flat. You can re-use these Master files if you restack the image or you stack another image with the same settings, focus and rotation (you didn't move anything or remove the camera from the scope  ). 

All you do is select the one Master file for that calibration set instead of all the darks/flat..... you selected before. So, for instance, say you took 50 Flats and added them to a stack in DSS. DSS will produce a Master Flat from those. Now, say you want to stack a second image using the same calibration frames, this time you don't need to add those 50 Flats to DSS, you just add the one Master Flat. DSS knows it's a Master file and it takes less time for DSS to process the stack because it's not building the Master for each calibration set.  

This works well for Darks because you can build a library of Master Darks for all the exposure, gain and temperature settings you use and then simply re-use the Master that matches the subs you're stacking. For my ASI294MC Pro I tend to stick with the same cooling temp (-10°C) and gain of 120. So I then used those settings and I have a Master Dark for exposures of 45s, 60s, 90s, 120s, 180s, 240s, 300s & 360s.  I built this library when I got the camera and used the same Masters from February through to June. This season I want to go to -15°, gain 120 and offset 20, so I'll have to build a new library. 

Flats - I used to use a blank MS Word document on the screen of my PC and a white T-shirt over the end of the scope to take the flats with my DSLR and it worked well. 

With the ASI294MC it didn't work very well at all and now I just point the end of the scope at a cloudy sky (during the day) with about 5 layers of white T-shirt over the scope and take flats that are still about 25000 ADU but are 2-3 seconds long. For my camera this does work and gives a nice flat image. It's a bit of a faff to get it right but I get there in the end. 

I guess what I'm trying to say is; try different options for taking the Flats, other light sources, exposure times and more paper/t-shirts!  

I was lucky, in a way, that the ASI294MC is renowned for being a bit of mare when it comes to flats, so searching for advice was quite easy. But have a search round for what others have done to get their QHY9 Flats.

I hope that sort of helps.  

[Rustang]

20 minutes ago, Budgie1 said:

Firstly, Masters - When DSS does the stacking for you with any calibration frames it creates a Master Flat, Master Dark, Master Bias or Master Dark-Flat. You can re-use these Master files if you restack the image or you stack another image with the same settings, focus and rotation (you didn't move anything or remove the camera from the scope  ). 

All you do is select the one Master file for that calibration set instead of all the darks/flat..... you selected before. So, for instance, say you took 50 Flats and added them to a stack in DSS. DSS will produce a Master Flat from those. Now, say you want to stack a second image using the same calibration frames, this time you don't need to add those 50 Flats to DSS, you just add the one Master Flat. DSS knows it's a Master file and it takes less time for DSS to process the stack because it's not building the Master for each calibration set.  

This works well for Darks because you can build a library of Master Darks for all the exposure, gain and temperature settings you use and then simply re-use the Master that matches the subs you're stacking. For my ASI294MC Pro I tend to stick with the same cooling temp (-10°C) and gain of 120. So I then used those settings and I have a Master Dark for exposures of 45s, 60s, 90s, 120s, 180s, 240s, 300s & 360s.  I built this library when I got the camera and used the same Masters from February through to June. This season I want to go to -15°, gain 120 and offset 20, so I'll have to build a new library. 

Flats - I used to use a blank MS Word document on the screen of my PC and a white T-shirt over the end of the scope to take the flats with my DSLR and it worked well. 

With the ASI294MC it didn't work very well at all and now I just point the end of the scope at a cloudy sky (during the day) with about 5 layers of white T-shirt over the scope and take flats that are still about 25000 ADU but are 2-3 seconds long. For my camera this does work and gives a nice flat image. It's a bit of a faff to get it right but I get there in the end. 

I guess what I'm trying to say is; try different options for taking the Flats, other light sources, exposure times and more paper/t-shirts!  

I was lucky, in a way, that the ASI294MC is renowned for being a bit of mare when it comes to flats, so searching for advice was quite easy. But have a search round for what others have done to get their QHY9 Flats.

I hope that sort of helps.  

Thanks for your advice/tips Martin, I will wait until my scope is sorted then look to re take the flats and go from there. Sadly I have to remove my camera from the scope after each session because i don't have anywhere for a permanent set up, so if I rotate the camera even slightly in the focus tube of my scope, even though the flattener, filterwheel and filters etc are all in the same position, I would need to re take flats for every single roation/ position of the camera? That would be a nightmare!

Edited July 30, 2021 by Rustang

[Budgie1]

You may be able to get away with it if you leave the camera attached to the flattener & filter-wheel. The Flats are helping to remove the likes of dust motes and other stuff on the front of the sensor, on the lens of the flattener and on the filters. Dust etc on the lens of the scope is less of an issue, unless it's quite large, because of the distance. 

I have to break down after each session as well, but I can keep the camera attached to the scope. But I still take a new set of Flats & Dark-Flats if I change anything, like a filter (I don't have a filter-wheel so I have to take the camera off to change them at the moment) or from reducer/flattener to just the flattener.

Flat's & Dark-Flats don't take that long to do so I generally do them the next day and just cool the camera down to the same temp as the previous night. I don't go mad and normally only take 15-20 of each.  

[Rustang]

48 minutes ago, Budgie1 said:

You may be able to get away with it if you leave the camera attached to the flattener & filter-wheel. The Flats are helping to remove the likes of dust motes and other stuff on the front of the sensor, on the lens of the flattener and on the filters. Dust etc on the lens of the scope is less of an issue, unless it's quite large, because of the distance. 

I have to break down after each session as well, but I can keep the camera attached to the scope. But I still take a new set of Flats & Dark-Flats if I change anything, like a filter (I don't have a filter-wheel so I have to take the camera off to change them at the moment) or from reducer/flattener to just the flattener.

Flat's & Dark-Flats don't take that long to do so I generally do them the next day and just cool the camera down to the same temp as the previous night. I don't go mad and normally only take 15-20 of each.  

You say they dont take long to do! thats if you can get them right lol 😉 APT has a great Flats assistant which does help make them quicker to do, i just need to work out why it didnt work for me when I took them the first time!

[Budgie1]

2 hours ago, Rustang said:

You say they dont take long to do! thats if you can get them right lol 😉 APT has a great Flats assistant which does help make them quicker to do, i just need to work out why it didnt work for me when I took them the first time!

Well, I suppose I am only taking one set and not one set for each filter. 😳

Yep, I also use the APT Flats Assistant but I still have to take a few runs to get the historgram in the middle and at a suitable exposure to get a good flat. At least with flats, you can do some test runs during the day to see what works best and the Cat will be easier to see and kept away from the scope!

[teoria_del_big_bang]

I am no expert and although my flats seem to help my final results I am always doubting they are totally correct so taking interested in this thread.

Can you put one of your flats, and the corresponding master flat for the same filter so I can have a look ?

Steve

[Rustang]

36 minutes ago, teoria_del_big_bang said:

I am no expert and although my flats seem to help my final results I am always doubting they are totally correct so taking interested in this thread.

Can you put one of your flats, and the corresponding master flat for the same filter so I can have a look ?

Steve

Sure, il do so tomorrow sometime. 

[newbie alert]

On 30/07/2021 at 06:07, Rustang said:

I've been using an LED  drawing light panel as the light source with sheets of paper to dim it down. The camera was set to - 20 so the same temperature for everything. The hisgram to me in APT never seemed right, to far to the right (bright) but if I remember rightly I asked about this before and it was something to do with the hisgram not being able to show everything correctly! I think flats are the bane of many peoples lives in this game and when your barely scrapping by with all the technical aspects of this hobby it's frustrating when you follow step by step advice and for some reason it still doesn't work and that's where it leaves me with not alot of chance of figuring it out myself. 

You can see below an example of the histogram, it's reach the correct ADU but seems to far right to me. You can also see the vignetting in having to deal with. 

First of all flats aren't temperature related, so no need to cool your camera down to its imaging temp...and yes I'd agree that the histogram is too far to the right.. I'd suggest a third of your camera range for flats

I'd also suggest you take flats for each time you remove or rotate the camera and for each filter

[Rustang]

14 hours ago, teoria_del_big_bang said:

I am no expert and although my flats seem to help my final results I am always doubting they are totally correct so taking interested in this thread.

Can you put one of your flats, and the corresponding master flat for the same filter so I can have a look ?

Steve

Flat files as promised!

F_HA_2021-02-28_14-24-52_Bin1x1_4.8125s__-20C.fit MasterFlat_ISO0.tif

[Rustang]

21 minutes ago, newbie alert said:

First of all flats aren't temperature related, so no need to cool your camera down to its imaging temp...and yes I'd agree that the histogram is too far to the right.. I'd suggest a third of your camera range for flats

I'd also suggest you take flats for each time you remove or rotate the camera and for each filter

what i dont get then is i used APT's flats assistant to gain the correct ADU so the corresponding exposure is whats determining the histogram so if I try and move the histogram, wont the ADU then be wrong!? There's no way I'm taking new flats every time I remove the camera, its just to practical because it comes off after every session.

[tooth_dr]

@Rustang that histogram looks ok. The scale is 1-34k not 0-65k.

You could try 25000 for your ADU, see if that helps. 

[Rustang]

2 minutes ago, tooth_dr said:

@Rustang that histogram looks ok. The scale is 1-34k not 0-65k.

You could try 25000 for your ADU, see if that helps. 

Thanks Adam, by scale do you mean what the histogram is showing as i think that was mentioned before, possibly by yourself? I tend to easily forget these things! if so is there a way of changing the scale in APT to show the full range of the histogram!?

[teoria_del_big_bang]

Take this with a pinch of salt as I am in no way expert but to me generally if I auto stretch the flats they look just as I expect with the exception of the black areas on the corners.

If it were vignetting I would expect these corners not to have such a defined circular edge but to gradually merge from grey to darker grey to blackish, If that make sense.
On the RH side the corners are a bit like that but on the left there is a very defined hard edge where it goes almost black from light grey as if the  sensor is too big for the optical disc.

I know I may be talking rubbish here as this is my very naive way I see it.
And one reason I have taken great interest in this thread is that since going to the bigger sensor on the QHY268M mine are very similar, just with far more crap and dust bunnies than yours and I have had the same concerns as you.
Not all my filters show the same though some look worse than others. Here is my  Red filter, okay the edge is not so defined but it soon goes from light grey to black.

 

But this is the LUM, a lot of dust bunnies or dirt but much more what I would expect.

I know this is not a real test as you have to be careful when auto stretching as you need to see how much it has been stretched and all these images will have different amounts so difficult to directly compare them.

I probably have not helped whatsoever here because of my lack of knowledge and understanding, so sorry if this just confuses things more, but I asked very similar questions sometime ago to whether my flats looks correct and never really got a definitive answer so still worry I am not doing things right, or something in my optics is not quite right.

Steve

Edited July 31, 2021 by teoria_del_big_bang

[tooth_dr]

28 minutes ago, Rustang said:

Thanks Adam, by scale do you mean what the histogram is showing as i think that was mentioned before, possibly by yourself? I tend to easily forget these things! if so is there a way of changing the scale in APT to show the full range of the histogram!?

Yes I don’t like the way it displays part of the range. I think you can click the buttons below the graph - log, auto str L auto str R and clear - to change the range. 

[teoria_del_big_bang]

55 minutes ago, Rustang said:

There's no way I'm taking new flats every time I remove the camera, its just to practical because it comes off after every session.

I thought is was essential to take flats just after, or just before every session and that the camera rotation with respect to the optics must not move.
I have heard of people not taking them for every filter, which is not ideal, but not using flats taken with a possible different camera rotation.

Steve

[Rustang]

8 minutes ago, teoria_del_big_bang said:

Take this with a pinch of salt as I am in no way expert but to me generally if I auto stretch the flats they look just as I expect with the exception of the black areas on the corners.

If it were vignetting I would expect these corners not to have such a defined circular edge but to gradually merge from grey to darker grey to blackish, If that make sense.
On the RH side the corners are a bit like that but on the left there is a very defined hard edge where it goes almost black from light grey as if the  sensor is too big for the optical disc.

I know I may be talking rubbish here as this is my very naive way I see it.
And one reason I have taken great interest in this thread is that since going to the bigger sensor on the QHY268M mine are very similar, just with far more crap and dust bunnies than yours and I have had the same concerns as you.
Not all my filters show the same though some look worse than others. Here is my  Red filter, okay the edge is not so defined but it soon goes from light grey to black.

 

But this is the LUM, a lot of dust bunnies or dirt but much more what I would expect.

I know this is not a real test as you have to be careful when auto stretching as you need to see how much it has been stretched and all these images will have different amounts so difficult to directly compare them.

I probably have not helped whatsoever here because of my lack of knowledge and understanding, so sorry if this just confuses things more, but I asked very similar questions sometime ago to whether my flats looks correct and never really got a definitive answer so still worry I am not doing things right, or something in my optics is not quite right.

Steve

So if i do understand you correctly, it could be that my scope and camera are not quite compatible then and that's whats causing the dark corners? but my flats in general seem ok?

 

[Rustang]

4 minutes ago, teoria_del_big_bang said:

I thought is was essential to take flats just after, or just before every session and that the camera rotation with respect to the optics must not move.
I have heard of people not taking them for every filter, which is not ideal, but not using flats taken with a possible different camera rotation.

Steve

Your probably right but what a complete pain in the back side that would be, I really could do with a more permanent setup but there's no chance of that yet. As i say I always take the camera off and rotate each session to find the best orientation for each target.

[teoria_del_big_bang]

28 minutes ago, Rustang said:

So if i do understand you correctly, it could be that my scope and camera are not quite compatible then and that's whats causing the dark corners? but my flats in general seem ok?

 

Pass, I think that is my worry same as my setup but I am not sure.
Also even if that is the case then so long as you are aware of them and they get cropped from final image then does it matter ?

Again, these are questions I am also asking myself. and my lack of knowledge is not helping me. 
I think that because this larger chip size on my new camera is fairly new and I did not see this before it just worried me, but then again I do worry about a lot of things hat I probably shouldn't 🙂 

 

And yes to me at least the rest of the flats look as I would expect but you can see the issue that if the camera rotates, even slightly, all those dark spots where dust is on your optics will be in a different place and so the flats will not remove them from the final image and also will add some lighter spots that correspond to the dark spots.

Steve

Edited July 31, 2021 by teoria_del_big_bang

[Rustang]

6 minutes ago, teoria_del_big_bang said:

Pass, I think that is my worry same as my setup but I am not sure.
Also even if that is the case then so long as you are aware of them and they get cropped from final image then does it matter ?

Again, these are questions I am also asking myself. and my lack of knowledge is not helping me. 
I think that because this larger chip size on my new camera is fairly new and I did not see this before it just worried me, but then again I do worry about a lot of things hat I probably shouldn't 🙂 

 

And yes to me at least the rest of the flats look as I would expect but you can see the issue that if the camera rotates, even slightly, all those dark spots where dust is on your optics will be in a different place and so the flats will not remove them from the final image and also will add some lighter spots that correspond to the dark spots.

Steve

I'm still very much learning a lot of things so in the same boat as you and that's well into my 3rd year of doing this. The dark corners have been a bit of an issue especially with details and nebulosity that I would like to keep in the corners but it is what it is. In regards to compatability, i.e camera sensor size to scope apature/fl what would it need to be to gain the correct compatibility if that makes sense? Bigger apature? Smaller focal length!? 

Edited July 31, 2021 by Rustang

[teoria_del_big_bang]

28 minutes ago, Rustang said:

Your probably right but what a complete pain in the back side that would be, I really could do with a more permanent setup but there's no chance of that yet. As i say I always take the camera off and rotate each session to find the best orientation for each target.

I do not have a permanent setup either - on my wish list as it has been last few years. But I do keep all my imaging train, including FW and camera set up permantly. I have a sturdy handle on top of the rig and take the whole rig off that is sat on the dovetail and store it in a cupboard.
I am a bit of a fussy sod so I still take flats after each session, with a flat field panel really does not take long, for each filter I have used after each session. There has been a few instances this did not happen for what ever reasons but so long as the camera and image train has not moved I can pretty safely use the last set of flats. Yes a few more bits of dust may have settled or moved but generally it is better to use the last flats than not use any I have found.

Steve