ASI294MC Flats help. I'm stumped!

[vlaiv]

12 minutes ago, Jamgood said:

@vlaiv Could the error with the Auto Flats Aid be anything to do with the use of the ASCOM driver as opposed to using the native ZWO driver?

@Budgie1 uses the same camera with APT and the Auto Flats Aid works well for him but he uses the Native Zwo driver at 120 gain, 8 offset.

I'm intrigued. It's going to be clear on Monday night so I can do some testing with manual flats. 

I advocate ASCOM drivers for two reasons:

1. I noticed long time ago that darks taken with ASCOM driver and ones taken with native driver are not compatible. I had issues with calibration of subs taken with native drivers and at the time - there was no way to set offset with native drivers. I was using SharpCap at the time.

2. ASCOM drivers are specifically designed with long exposure in mind and I concluded that it is the safest bet to use those

In any case - if you prefer native drivers or want to continue to use auto flats aid - by all means experiment with settings to find which ones work for you.

[Jamgood]

Well, I initially read that the ASCOM driver was better overall as it gives you more controls, which is why I went that way. I'll stick with it if I can. 

I'll update when I test with manual flats after Monday night.

[david_taurus83]

I ran the lot through PI and got the same results so nothing wrong with your DSS settings. I can remove it mostly with DBE but your left with noisy gradients after. Nothing more exposure can't help clear up. Your flat exposures look very low btw. I aim for around 2 or 3 seconds usually with any camera. Might help if you can diffuse the light a bit more and have a more even flat instead of the overly bright centre.

@vlaiv what is DC offset? Not a term I've heard?

[vlaiv]

32 minutes ago, david_taurus83 said:

 

@vlaiv what is DC offset? Not a term I've heard?

It's not term that is generally used for this purpose - but it is term from signal processing in general. It refers to voltage levels - and stands for direct current. If signal is encoded in voltage - say sound signal in analog circuits, then sound itself is not changed if we change reference point or we add direct current voltage to it (as long as it is not AC - or alternating current or some sort of varying voltage) - it does not matter. Sometimes it is used in FT of image - there is a single bright dot in the image and it represents infinite wavelength component - or DC component of FT.

For some reason I adopted that term to mean - offset but since offset has exact meaning of const value added to each pixel by sensor and I'm talking of any offset in the image - any const value added by say LP or in this case - unknown cause, I use term DC offset (that DC term in my head means - applied to each pixel in the image ).

If you want to try this in PI - after you create master flat (stack flats and subtract master flat dark) - use pixel math to add 25000ADU to each pixel in the image.

As for exposure length - I guess that depends on sensor? I happily use millisecond flat exposures on my ASI1600 and don't have issues with those (lum flats for example are just couple of milliseconds long due to my flat panel strength).

 

[Jamgood]

4 hours ago, david_taurus83 said:

I ran the lot through PI and got the same results so nothing wrong with your DSS settings. I can remove it mostly with DBE but your left with noisy gradients after. Nothing more exposure can't help clear up. Your flat exposures look very low btw. I aim for around 2 or 3 seconds usually with any camera. Might help if you can diffuse the light a bit more and have a more even flat instead of the overly bright centre.

@vlaiv what is DC offset? Not a term I've heard?

Cheers. Yeah, it's nice to know that it's not a problem with DSS. I wasn't sure what it was but I'll try doing manual flats as @vlaiv has suggested and go from there.

This was my first time taking flats with this camera so it's all new to me. (Bit different from point and click DSLR) I just went with what the Auto Flats Aid recommended as I assumed that would be sufficient.

There seems to be a lot of conflicting information around regards short vs longer flats. I guess I'll  have to try and find the best way with the camera and see what works for me. 👍

[david_taurus83]

12 minutes ago, Jamgood said:

Cheers. Yeah, it's nice to know that it's not a problem with DSS. I wasn't sure what it was but I'll try doing manual flats as @vlaiv has suggested and go from there.

This was my first time taking flats with this camera so it's all new to me. (Bit different from point and click DSLR) I just went with what the Auto Flats Aid recommended as I assumed that would be sufficient.

There seems to be a lot of conflicting information around regards short vs longer flats. I guess I'll  have to try and find the best way with the camera and see what works for me. 👍

How do you take flats BTW? I struggled with a 200P when I had it. I was putting the flat panel on top of the OTA but in hindsight, this was probably putting stray light into the focuser. Might be better to point a newt at a light source so only light from the primary is reflected into the focuser.

[Jamgood]

18 minutes ago, david_taurus83 said:

How do you take flats BTW? I struggled with a 200P when I had it. I was putting the flat panel on top of the OTA but in hindsight, this was probably putting stray light into the focuser. Might be better to point a newt at a light source so only light from the primary is reflected into the focuser.

I've got a big ipad/tablet thing that covers the 130PDS nicely. I just used a white image, stretched full screen. Never had a problem using this method with a DSLR. 

I did this lots of times until recently when my 60Da died. Flats came out great and always worked really well so I figured I'd be able to carry on using this method with the 294MC pro. 

The only thing I wasn't sure about was if the the new CC and L-Enhance filter would make a huge difference but I think @vlaiv has proven that they don't as there is an issue with the flat files themselves.

I'll investigate further on Monday night when it's clear. I'll grab some data and spend some time on flats and see what happens.

[Budgie1]

11 hours ago, Jamgood said:

@vlaiv Could the error with the Auto Flats Aid be anything to do with the use of the ASCOM driver as opposed to using the native ZWO driver?

@Budgie1 uses the same camera with APT and the Auto Flats Aid works well for him but he uses the Native Zwo driver at 120 gain, 8 offset.

Just to add to this; I've only ever used the native driver because that's what I downloaded went I got the camera and stuck with it. I also use a refractor scope with my ASI294MC Pro (an Evostar 100ED DS Pro) so I don't know if that would make any difference?

On the back on this thread and @Jamgood issues + some research this evening, I've downloaded the ASCOM driver for the ZWO ASI and set it to Unity Gain (120 gain and 30 offset) and will run that to see what the difference is.

Using the native drivers, the offset is fixed at 8 and there is nowhere to change it. I did think it was a little on the low side, seeing others reporting they were using an offset of 30, but as I couldn't change it then I stuck with it.

Anyway, I currently have the camera off the scope and it's creating a new set of Darks at Unity Gain and -10°C with the ASCOM drivers. The forecast for here is 50-100mm of rain over the next couple of days, so I may as well use the time to start building the library with the new settings ready for when the skies next clear.

It'll be interesting to see if author of APT comes up with anything on the back fo your findings, Vlaiv. In the meantime, I won't tell APT when I'm doing flats or dark-flats. 🤫

[Jamgood]

1 hour ago, Budgie1 said:

Just to add to this; I've only ever used the native driver because that's what I downloaded went I got the camera and stuck with it. I also use a refractor scope with my ASI294MC Pro (an Evostar 100ED DS Pro) so I don't know if that would make any difference?

On the back on this thread and @Jamgood issues + some research this evening, I've downloaded the ASCOM driver for the ZWO ASI and set it to Unity Gain (120 gain and 30 offset) and will run that to see what the difference is.

Using the native drivers, the offset is fixed at 8 and there is nowhere to change it. I did think it was a little on the low side, seeing others reporting they were using an offset of 30, but as I couldn't change it then I stuck with it.

Anyway, I currently have the camera off the scope and it's creating a new set of Darks at Unity Gain and -10°C with the ASCOM drivers. The forecast for here is 50-100mm of rain over the next couple of days, so I may as well use the time to start building the library with the new settings ready for when the skies next clear.

It'll be interesting to see if author of APT comes up with anything on the back fo your findings, Vlaiv. In the meantime, I won't tell APT when I'm doing flats or dark-flats. 🤫

It'll be interesting to see if you have any difference between the 2 drivers. Especially if you try using the Auto Flats Aid. Might help to narrow down the source of the issue if you see something similar to me.

I'm looking forward to getting back out and trying again. Bloody weather though. It's a shame we can't test and troubleshoot things like this in the day time.

[Jamgood]

@vlaiv @Budgie1 @david_taurus83

Vlaiv was absolutely spot on. Manual flats at 0.35031 work perfectly. I must have a bug somewhere between camera and APT.  6x300 on the Monkey Nebula with 10 Darks and 10 Flats and a very quick stretch looks like this. Now I can crack on with some imaging!

Thanks again guys.

[Stuf1978]

Thread hijak

I've also just bought a 294MC Pro and last night was the first chance I have had to use it and I'm also having issues with calibration. I had read this thread prior to using it (some great advice here) and took a lot of it into consideration. So I shot the Leo Triplet and I gathered 39 x 180 second light frames, 20 x 180 second dark frames, 20 flats x 7 seconds and 20 dark flats x 7 seconds. All were shot at 120 (unity) gain and with an offset of 30, the flats were taken using APT flat aid with a target ADU of 25000 with a double layer white t-shirt and white screen from an ipad. The ipad screen brightness was turned down pretty low to ensure that the flat exposures were greater than 3-4 seconds as is recommended for this camera. I stacked/debayered everything in DSS and processed in photoshop. On first impressions it all looked good, however once I started to stretch the image there is a dark band along the top of the image attached (aggressively stretched to highlight). I also tried manual flats but the result was exactly the same. 

Does this look like a flats issue or something else?

The equipment was as follows:

ZWO ASI 294MC Pro > Spacers for required 55mm back focus > OVL Field Flattener with 2" UV/IR cut filter > Evostar 72ED

Thanks,

Stu

 

[Jamgood]

2 minutes ago, Stuf1978 said:

Thread hijak

I've also just bought a 294MC Pro and last night was the first chance I have had to use it and I'm also having issues with calibration. I had read this thread prior to using it (some great advice here) and took a lot of it into consideration. So I shot the Leo Triplet and I gathered 39 x 180 second light frames, 20 x 180 second dark frames, 20 flats x 7 seconds and 20 dark flats x 7 seconds. All were shot at 120 (unity) gain and with an offset of 30, the flats were taken using APT flat aid with a target ADU of 25000 with a double layer white t-shirt and white screen from an ipad. The ipad screen brightness was turned down pretty low to ensure that the flat exposures were greater than 3-4 seconds as is recommended for this camera. I stacked/debayered everything in DSS and processed in photoshop. On first impressions it all looked good, however once I started to stretch the image there is a dark band along the top of the image attached (aggressively stretched to highlight). I also tried manual flats but the result was exactly the same. 

Does this look like a flats issue or something else?

The equipment was as follows:

ZWO ASI 294MC Pro > Spacers for required 55mm back focus > OVL Field Flattener with 2" UV/IR cut filter > Evostar 72ED

Thanks,

Stu

 

 

It does look like it could be Flat related. Did you have the tshirt stretched tight? Maybe try without the tshirt or try with plain paper.

I don't use a tshirt or paper as I've never found the need to with my tablet. (Although I tried everything to fix my issue) A white screen seems to do the job just nicely. My flats with the 294MC are between 0.1 and 0.3 seconds depending on the filter I use.

[Stuf1978]

2 minutes ago, Jamgood said:

It does look like it could be Flat related. Did you have the tshirt stretched tight? Maybe try without the tshirt or try with plain paper.

I don't use a tshirt or paper as I've never found the need to with my tablet. (Although I tried everything to fix my issue) A white screen seems to do the job just nicely. My flats with the 294MC are between 0.1 and 0.3 seconds depending on the filter I use.

Thanks, yeah T shirt was stretched tight and held in place by an elastic band. I just wasn't sure whether this was flat related with it just being that dark band across the top of the image with the rest of image looking fine. I'll hopefully be gathering more data on this tonight so I'll try shooting various combinations of flats and see what happens. 

That's good to know you can get away with shorter flat exposures 👍

[Stuf1978]

Edit to my post above..... the issue isn't the flats. I've stacked just the light and dark frames and the band is still there 🤷‍♂️

The flats appear to be doing their job in the original stack as without them there is much more pronounced vignetting etc. 

Edited April 6, 2021 by Stuf1978

[david_taurus83]

Is the band in the flats?

[Stuf1978]

9 minutes ago, david_taurus83 said:

Is the band in the flats?

Nope.

Although I said the issue isn't the flats I'm guessing it could still be a flat issue in that they should be calibrating this out. 

Edited April 6, 2021 by Stuf1978

[david_taurus83]

If its not in the flats then it's not anything in the light path from front of scope to sensor. So could be reflection or light leak during capture. What does a stretched dark look like?

[Stuf1978]

4 minutes ago, david_taurus83 said:

If its not in the flats then it's not anything in the light path from front of scope to sensor. So could be reflection or light leak during capture. What does a stretched dark look like?

Here is a stretched dark, nothing but amp glow. I've also tried just stacking the lights frames and it's also apparent in these so could be something that's happened during capture. 

 

[david_taurus83]

I get a similar effect with my 6D but I know its to do with the mirror! I would say it's a reflection of something during capture but when I get those (glare off a streetlamp lighting up one side of the dew sheild) it tends to move as the mount tracks away from the source. 

[Stuf1978]

10 minutes ago, david_taurus83 said:

I get a similar effect with my 6D but I know its to do with the mirror! I would say it's a reflection of something during capture but when I get those (glare off a streetlamp lighting up one side of the dew sheild) it tends to move as the mount tracks away from the source. 

It's annoying as you can't see it in the individual subs, only the stack. I guess I'll just have to gather more data and stretch it less aggressively in order to get something from the image and hopefully try and minimise it in post processing.

Edited April 6, 2021 by Stuf1978

[The Admiral]

18 minutes ago, Stuf1978 said:

It's annoying as you can't see it in the individual subs, only the stack.

So, it's not visible in the darks, it's not visible in the flats, and it's not visible in the subs! In which case, could it be something in the way that DSS is doing the calibration, registration, and stacking? What else could it be? What software did you use to capture the files? At what temperature(s) did you take the files? All the same? I don't suppose you have an alternative means of stacking to test it do you? Otherwise, I wonder if you are able to upload all the files so that others could have a tinker?

Ian

Edited April 6, 2021 by The Admiral

[Stuf1978]

14 minutes ago, The Admiral said:

So, it's not visible in the darks, it's not visible in the flats, and it's not visible in the subs! In which case, could it be something in the way that DSS is doing the calibration, registration, and stacking? What else could it be? What software did you use to capture the files? At what temperature(s) did you take the files? All the same? I don't suppose you have an alternative means of stacking to test it do you? Otherwise, I wonder if you are able to upload all the files so that others could have a tinker?

Ian

It's the first time I've stacked data from a dedicated astro camera so it could be all or none of the above  All frames were taken at -10 degrees and at the same gain and offset value and the images were captured in APT. I will have a go at stacking the images in Siril and see if I get the same results and I'll try and share the files on here for others to have a play.

[Jamgood]

4 minutes ago, Stuf1978 said:

It's the first time I've stacked data from a dedicated astro camera so it could be all or none of the above  All frames were taken at -10 degrees and at the same gain and offset value and the images were captured in APT. I will have a go at stacking the images in Siril and see if I get the same results and I'll try and share the files on here for others to have a play.

Have you got Dark Optimization ticked in DSS Settings? If so, turn it off.

[Stuf1978]

5 minutes ago, Jamgood said:

Have you got Dark Optimization ticked in DSS Settings? If so, turn it off.

no, it's unchecked

[The Admiral]

It's not the first time I've read about issues with this camera, nothing very consistent though. In this thread a particular issue is raised.

 

Now the effects are quite different to what you are finding, but Vlaiv raised an issue with APT in his post on 26 March where he thought that APT wasn't working properly. So clutching at straws, it might be worth checking it out. Sorry if this is a red herring.

Ian