questions about this flat frame

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Florin Andrei
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questions about this flat frame

Post by Florin Andrei »

Here's a master flat I took today:
flat1.jpg
flat1.jpg (514.97 KiB) Viewed 418 times
And this is the system:
scope.jpg
scope.jpg (1.11 MiB) Viewed 418 times
The optical surfaces are:

- an UV/IR cut filter mounted in the focuser for energy rejection
- the Baader 3x telecentric
- Celestron 2" diagonal
- Quark filter
- 0.79x reducer
- ASI071MC camera

The solar disk barely fits in the central bright area of the flat, but if I'm careful with polar alignment and tracking then it seems fine.

The dust bunnies are probably not from the reducer + camera. I checked that assembly separately and I don't see anything wrong there. I'm starting to believe they have something to do with the Quark, but its surfaces look clean. They disappear after stacking with the master flat, but they are quite pronounced in the flat and I want to get rid of them.

OTOH, the dust bunnies do look kind of sharp, so maybe they are somewhere close to the sensor?

In the bottom-left quadrant - are those Newton rings? They move quite a bit in time, from one SER file to another. But they seem to disappear after stacking with the master flat.

Any suggestions for cleaning the system so the master flat looks better? The final image is fine, but it bothers me that the flat is so messy.


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Re: questions about this flat frame

Post by marktownley »

Post a picture with the sun in focus - no flat applied so can see where the dust bunnies are. Looking at them my money is on or somewhere very close to the chip.


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Re: questions about this flat frame

Post by Florin Andrei »

Here it is. It's really the same stuff like in the flat, except only a part is illuminated.

BTW, the flat really is a flat, it's not the Sun defocused. The sensor is pretty big (APS-C), looking through the keyhole in the Quark. :) But I got what I wanted - the whole disc in one shot (just barely).

The edge appears to be soft, which is not surprising.
1stframe.jpg
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Re: questions about this flat frame

Post by rigel123 »

I agree with Mark in that the dust is close to the chip, possibly on the window just above the sensor. Most can be removed with a blower or a soft lens brush. I like this one for my cameras but it is pricey.

https://www.bhphotovideo.com/c/product/ ... woQAvD_BwE


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Re: questions about this flat frame

Post by marktownley »

Those bunnies are either on the chip itself, the protective window over the chip (if it has one) or on the back face of the Quark.

If a dust blower doesn't work I found the sensor cleaning kits you can buy off the internet very effective, a cleaning solution and swabs, they work wonders!


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Re: questions about this flat frame

Post by minhlead »

Florin Andrei wrote: Mon Aug 02, 2021 3:28 am Here's a master flat I took today:

flat1.jpg

And this is the system:

scope.jpg

The optical surfaces are:

- an UV/IR cut filter mounted in the focuser for energy rejection
- the Baader 3x telecentric
- Celestron 2" diagonal
- Quark filter
- 0.79x reducer
- ASI071MC camera

The solar disk barely fits in the central bright area of the flat, but if I'm careful with polar alignment and tracking then it seems fine.

The dust bunnies are probably not from the reducer + camera. I checked that assembly separately and I don't see anything wrong there. I'm starting to believe they have something to do with the Quark, but its surfaces look clean. They disappear after stacking with the master flat, but they are quite pronounced in the flat and I want to get rid of them.

OTOH, the dust bunnies do look kind of sharp, so maybe they are somewhere close to the sensor?

In the bottom-left quadrant - are those Newton rings? They move quite a bit in time, from one SER file to another. But they seem to disappear after stacking with the master flat.

Any suggestions for cleaning the system so the master flat looks better? The final image is fine, but it bothers me that the flat is so messy.
Check the trimming filter (the red side filter of the Quark). The output beam of the Quark is nearly collimated (F/30 or so) so the dust motes in the red filter leave apparent shadow on sensor even though they are not very close to the sensor (and the shadows are diffused just like yours). Mine have some dust motes on the inside (the side that face the etalon chamber) so no cleaning for me. It's there from factory, obviously the guy who assembled mine was doing it in some dusty environment.
But my flats handle the dust okay and I rarely have any problem with them.


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Re: questions about this flat frame

Post by minhlead »

Florin Andrei wrote: Mon Aug 02, 2021 3:28 am Here's a master flat I took today:

flat1.jpg

And this is the system:

scope.jpg

The optical surfaces are:

- an UV/IR cut filter mounted in the focuser for energy rejection
- the Baader 3x telecentric
- Celestron 2" diagonal
- Quark filter
- 0.79x reducer
- ASI071MC camera

The solar disk barely fits in the central bright area of the flat, but if I'm careful with polar alignment and tracking then it seems fine.

The dust bunnies are probably not from the reducer + camera. I checked that assembly separately and I don't see anything wrong there. I'm starting to believe they have something to do with the Quark, but its surfaces look clean. They disappear after stacking with the master flat, but they are quite pronounced in the flat and I want to get rid of them.

OTOH, the dust bunnies do look kind of sharp, so maybe they are somewhere close to the sensor?

In the bottom-left quadrant - are those Newton rings? They move quite a bit in time, from one SER file to another. But they seem to disappear after stacking with the master flat.

Any suggestions for cleaning the system so the master flat looks better? The final image is fine, but it bothers me that the flat is so messy.
Oh and the strippy things on the flats, they're not Newton's Ring but rather quantitization error (dynamic range banding) especially if you are shooting that flat in 8 bits mode and it's not stacked (1 shot).
Don't worry, it'll go away with stacking since stacking get rid of quantitization error by increasing bit depth.
I can see that you are using a color camera in mono mode (binning 2x2 perhasp?) I am doing so too. How is your frame rate doing full res binning? Perhasp cropping the ROI would increase the frame rate and reduce file size a bit?


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Loves from Viet Nam <3
My gear:
Scope: SkyRover (Kunming Optics) 152mm F/6 Doublets
Mount: JTW Tridents GTR
Camera:
PlayerOne Apollo M-Max
Quark Chromosphere Doublestacked with PST etalon
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Re: questions about this flat frame

Post by Florin Andrei »

Minh,

I will go over all surfaces involved, again, this time more carefully, and I'll remove all dust that I can remove. I was actually thinking of the fact that f/30 is a really long focal ratio, so the culprits might be anywhere after the telecentric.

The banding artifacts do disappear after stacking.

The camera is actually used in full-bit-depth mode - 14 bit for this camera. I would never do this for planetary imaging with a small ROI (would be pointless with thousands of frames), but here I'm doing experiments since all I do now is learning a new hobby.

No binning. I shrink the image 2x after all processing.

I capture in full color mode, full frame, and then in SER Player I drop the G and B channels and save the SER file as mono. I have a fast laptop, seems like it can handle all that deluge of data. I get about 10 fps this way, the limit is at the camera (it's in the camera specs).


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Re: questions about this flat frame

Post by minhlead »

Florin Andrei wrote: Wed Aug 04, 2021 2:40 am Minh,

I will go over all surfaces involved, again, this time more carefully, and I'll remove all dust that I can remove. I was actually thinking of the fact that f/30 is a really long focal ratio, so the culprits might be anywhere after the telecentric.

The banding artifacts do disappear after stacking.

The camera is actually used in full-bit-depth mode - 14 bit for this camera. I would never do this for planetary imaging with a small ROI (would be pointless with thousands of frames), but here I'm doing experiments since all I do now is learning a new hobby.

No binning. I shrink the image 2x after all processing.

I capture in full color mode, full frame, and then in SER Player I drop the G and B channels and save the SER file as mono. I have a fast laptop, seems like it can handle all that deluge of data. I get about 10 fps this way, the limit is at the camera (it's in the camera specs).
Try this work flow:
There's a mono mode on your 071MC (I am not sure what it's called on the specific driver/capture software. But I know it's there, my friend's 071MC has it) but on sharpcap and my QHY294C I simply turn on binning 2x2 and turn off debayering it will throw out the color information, bin 4 color pixel into 1 mono pixel, double the light gathered (and halves the exposure time). This way you got several benefits:
1. You dont have to do any post process on your data to get mono, you get mono picture ready for stacking. Also you still retain some signal from G and B pixels instead of throwing them out completely. You dont have to watch the exposure for each layer instead everything is now combine to 1 , you only have to watch 1 histogram and not having to worry some layer over or under exposed.
2. Since 4 pixel bin into 1, you save 3/4 disk space. (The frame rate still as before binning because you still have to do all pixel read out).
3. You got 2x bigger pixel. This is actually a good thing for a Quark since the barlow is 4.3x. You can get a 12um pixel and still oversampled by a good margin. Less oversampled mean sharper detail and higher contrast.
4. Less noise and higher resistance to newtons ring due to binning.
5. Flats/ dark all work the same.
6. Also, you do not need 14 bits. 8 bits is enough as long as you stack enough frame, the bit depth will expand to 10-12 bits which is plenty.
I am using a mono camera with upper mentioned data acquiring method to very good result. I think you 071MC will do just fine as long as you can live with the frame rate. Here's one timelapse that I took with my 294C


Minh.
Loves from Viet Nam <3
My gear:
Scope: SkyRover (Kunming Optics) 152mm F/6 Doublets
Mount: JTW Tridents GTR
Camera:
PlayerOne Apollo M-Max
Quark Chromosphere Doublestacked with PST etalon
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