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Still problems with flat field on ZWO 294 MC

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#1 Avenar

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Posted 24 January 2020 - 09:42 AM

Hello everyone!!

 

This is only a test image but I would like to show you my lights, flat balance VS unbalanced (only dark)...

as you can see without flat frames , the image can be processed, is better, but in the balanced version ,with flats, it becomes worse, very hard to remove the various gradients, vignetting, ecc

 

I Do the flat filed at -10C with a selfmade flatbox, (led lamps + several layers to reduce brightness)

- Use APT software to prepare the flats

 - duration of the flat 2'30'' second 25000 ADU,

 - this lights ith l-enhance filter on a newtonian 200/1000

- I have tried with longer exposures using multiple layers but without success. I also tried with the dark flat but no special improvements.

 - Same gain and offset as light frames (115 - 35)

- elaboration pixinsight: only Batchprocessing

 

with flats (batchprocessing + linearfit + stretch)
https://photos.app.g...WcqurhFEQznQ9k8

 

no flats (batchprocessing + linearfit + stretch)

https://photos.app.g...eiKkYYFW2mvvLA7

 

master Flat (debayer + linearfit + stretch)

https://photos.app.g...LVDLTFep7txiZj9

 

master flat (only stretch)

https://photos.app.g...L83NT93CBVduyAA

 

master flat (only debayer + stretch)

https://photos.app.g...3Hrtb1KPZGLybK9

 

Thanks



#2 andythilo

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Posted 24 January 2020 - 09:55 AM

You're not alone, I'm having issues with my 294 and flats. I get better results just integrating lights with darks only. My flats were at 27000 ADU and 4sec. Going to try some different exposure combinations and ADU values over the weekend.


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#3 dcollier

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Posted 24 January 2020 - 10:05 AM

https://astrobackyar...ke-flat-frames/


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#4 Eric Horton

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Posted 24 January 2020 - 12:34 PM

Same here. I have done 30,000 adu and 25k. I was going to try going down to 20 since going up doesnt seem to work
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#5 Avenar

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Posted 24 January 2020 - 04:26 PM

You're not alone, I'm having issues with my 294 and flats. I get better results just integrating lights with darks only. My flats were at 27000 ADU and 4sec. Going to try some different exposure combinations and ADU values over the weekend.

I know Andy... I have read a lot of post about flat issues on this camera... But I cant find the right one... I have tried 25000 adu 20000,10000 and also 5000 adu with different exposures but nothing good... Flat dark with longer exposure same result... Let me know if you get something good ok?

 

Thanks... I have read also this nice guide, and also his review of 294. For example he makes a lot of beautiful pictures with this camera, and explain his flat settings:  https://astrobackyar...4mc-pro-review/  "I use the CCD Flats Aid tool in Astro Photography Tool to find the correct exposure to hit my target ADU (25,000). In my experience the images are usually around an exposure of 0.03381 when using a gain setting of 120 (unity gain). This creates a flat field image with an ADU of approximately 25000.

I have heard that others have found success by using longer flat frame exposures, which can be accomplished by adding more layers of white t-shirts or with an adjustable flat panel"

 

So, why does he get good results and I don't with 25000 adu and a very short exposure?! lol.giflol.giflol.gif

 

Same here. I have done 30,000 adu and 25k. I was going to try going down to 20 since going up doesnt seem to work

At this point I will try to go up to 30,000 next time... frown.gif confused1.gif 

 



#6 andythilo

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Posted 25 January 2020 - 09:47 AM

Ok well either I'm doing something very wrong, or there's a problem with my flat field generator. So I created some new flats, all at gain 120, camera cooled to -20 and focus in same position as when I took the lights.I also created a fresh batch of BIAS files to use with the tests.

 

I took 30 subs each with the generator at full brightness (approx 12V), dimmed to 8V and dimmed to 5V. All at ADU values of 20000, 22000, 25000, 27000 & 30000. 

 

I then did some stacking in DSS and PI.

 

All processing in PI for comparison purposes was identical, ABE and SNCR. This was just to be able to get an idea on image quality.

 

In DSS I ran the same sequence with all 3 voltages @ ADU3000. All 3 resulting images looked virtually identical. So I then processed in PI. I then ran the same without flats.

 

In PI, I did a full manual integration as per the book Inside Pixinsight, and also used the BPP script. Again with and without flats.

 

6 images below show the following:

 

Top - DSS. Left with flats, right without flats

Middle - PI BPP. Left with flats, right without flats

Bottom - PI Full Manual Integration. Left with flats, right without flats

 

Again all 6 processed in PI with the Automatic Background Extractor and SNCR (green).

 

Conclusion, my flats are broke lol. My images are 100% cleaner with no flats and manual integration without flats the clear winner with DSS a close 2nd. For some reason BPP isn't removing my amp glow. No idea why, it used to! So I'm going to send this to the flat field generator supplier and manufacturer to advise. This is the generator I use:

 

https://www.astrosho...0mm-12v/p,46378

 

49439427497_7674bf759c_b.jpgPI_DSS_Flats_Noflats_Compare by Andy Thilo, on Flickr

 

 

 

 



#7 Avenar

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Posted 25 January 2020 - 05:04 PM

Thanks Andy,

 

Very nice comparison... I don't think the problem is the flat field generator. As you can see, in the astrobackyard test, he has a very bright flat panel, he needs a very fast explosure 0.03381 for 25000 ADU...  I think they probably use a different way of processing master flats, I don't think it depends on camera, scope, internal reflection, ecc

 

I tried DSS, Pixinsight batchprocessing but also manual calibration with different combination but I haven't t found significant differences between... So I'm still looking for a nice and easy solution.

 

It seems that with longer exposures flats field have more chance to calibrating correctly, maybe try to reduce brightness with some layers of paper. In my case I also reached 3 and a half seconds but nothing has changed lol.giflol.giflol.gif

 

 

 

 



#8 17.5Dob

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Posted 25 January 2020 - 10:31 PM

There are lot of well known problems involving the 294 and calibration frames. There seems to be few work- a- rounds, but a lot of people just get tired of dealing with it and end up just getting a better camera.

It's really a camera better suited for EAA, but somehow, people started pushing it for general usage...


Edited by 17.5Dob, 25 January 2020 - 10:33 PM.

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#9 andythilo

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Posted 25 January 2020 - 11:51 PM

Thanks Andy,

Very nice comparison... I don't think the problem is the flat field generator. As you can see, in the astrobackyard test, he has a very bright flat panel, he needs a very fast explosure 0.03381 for 25000 ADU... I think they probably use a different way of processing master flats, I don't think it depends on camera, scope, internal reflection, ecc

I tried DSS, Pixinsight batchprocessing but also manual calibration with different combination but I haven't t found significant differences between... So I'm still looking for a nice and easy solution.

It seems that with longer exposures flats field have more chance to calibrating correctly, maybe try to reduce brightness with some layers of paper. In my case I also reached 3 and a half seconds but nothing has changed lol.giflol.giflol.gif


I have to disagree, adding flats into my processing results in poor colour cast, blotches on the images and bad gradients. My previous flats processing was 4secs approx. Same result as with flats at 0.18 sec.

My conclusion is that as long as your darks are good to remove amp glow, and your optics are clean to avoid dust bunnies, the 294 doesn’t need flats. My processed images of M81/82 and Monkey Head are vastly superior without flats. Maybe this only works with more expensive optics, I don’t know, I’m just going by my limited experience.

I do need to retake my darks as I have some light leak and a sensor mark however. But they’re pretty good as they are, certainly they 100% remove the amp glow and a careful processing in PI with DBE removes any residual gradients.

Saying all that I might look at upgrading to a 071 . Any excuse haha.


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#10 Avenar

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Posted 26 January 2020 - 08:40 AM

No flats is the way lol.giflol.giflol.gif ....

I'm just trying here, to figure out who posts beautiful images of the 294 with flats calibration how he did it.

So, I think it's possible, but mode is unknown mad.gif



#11 andythilo

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Posted 26 January 2020 - 09:26 AM

I don’t think no flats is the way, but it’s certainly better without them for me at the moment. Might just try a T-shirt method and see what comes out. Or an iPad screen over a T-shirt.


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#12 nimitz69

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Posted 26 January 2020 - 11:48 AM

yes, your flats generator is broken ... :). people seem to just assume that if they just use a “white light” they will Be able to.  Get great flats and there is more to it than that. Don’t know what you are using but Many of the LED light panels people are using do not produce even RGB color channels.  Take a look at the individual channels in the historgram of one of your flats & see if the channels are producing the same output.  I had this same blotchy issue with the first panel i tried & it turned out the red channel was almost twice a strong as the others.   Finally just decided to buy a spike-a-flat, a light panel specifically designed for producing AP flats.  Fixed my “294 flats issue” over night ....dalek12.gif


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#13 andythilo

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Posted 26 January 2020 - 12:17 PM

yes, your flats generator is broken ... :). people seem to just assume that if they just use a “white light” they will Be able to. Get great flats and there is more to it than that. Don’t know what you are using but Many of the LED light panels people are using do not produce even RGB color channels. Take a look at the individual channels in the historgram of one of your flats & see if the channels are producing the same output. I had this same blotchy issue with the first panel i tried & it turned out the red channel was almost twice a strong as the others. Finally just decided to buy a spike-a-flat, a light panel specifically designed for producing AP flats. Fixed my “294 flats issue” over night ....dalek12.gif


Mine is the Gerd Newman Aurora. Heard good things about the spike-a-flat but it’s expensive.

Does it also work with CLS or duo band pass filters?


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#14 andythilo

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Posted 26 January 2020 - 12:18 PM

This is my one


https://www.gerdneum...v-inverter.html


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#15 andythilo

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Posted 26 January 2020 - 05:37 PM

Seems my darks were a big problem. They had a bad light leak. Old left, new right. Still no flats though.

76727b4e9de2a498194a9bd6eb5dacba.jpg


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#16 Biggen

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Posted 26 January 2020 - 05:48 PM

I’m not having any issues with flats with my 294. Just using a led tracing panel and using a tshirt. I use the CCD flats aid in APT and set the ADU to 30000.

 

Flats take about 2 seconds.

 

Here is about 3.5 hours on Rosette the other night using that camera: https://www.cloudyni...-294mc-pro-osc/


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#17 nimitz69

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Posted 26 January 2020 - 06:10 PM

Mine is the Gerd Newman Aurora. Heard good things about the spike-a-flat but it’s expensive.

Does it also work with CLS or duo band pass filters?


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Expensive?  how’s that ‘cheaper’ one working out for you ... dalek12.gif

didn’t mean to make fun of your problems but I rarely find that the more expensive AP stuff doesn’t o exactly what its supposed to.  While ill probably never buy a Mach 2 i understand why people do ...

I don’t use any filters since I have a 1600 but I don’t know why it wouldn’t?  Contact them and ask, I’m sure they will be happy to give you the details ...


Edited by nimitz69, 26 January 2020 - 06:13 PM.


#18 andythilo

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Posted 27 January 2020 - 03:47 AM

Expensive?  how’s that ‘cheaper’ one working out for you ... dalek12.gif

 

Affordability is relative :).



#19 andythilo

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Posted 27 January 2020 - 03:52 AM

Ok, SOLVED!!

 

It was darks all along for myself. Flats are working perfectly. Once I took some new darks (stuck the camera in the fridge with it's cap on and halfway inserted into it's bag) it all calibrated out fine. 

 

Worst case - Old darks and Flats/Dark Flats

 

Old Darks with Flats and Dark Flats.jpg

 

New Darks with Flats and Dark Flats

 

New Darks with Flats and Dark Flats.jpg

 

 

CONCLUSION - Check your darks, if they don't look like my new one posted earlier, you'll have massive problems. Light leaks in the darks are not good!!!


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#20 Biggen

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Posted 27 January 2020 - 06:30 AM

Excellent! Good advise!

I put my telescope in a bathroom with no windows and close the door to take darks. Insures no light leak issues.

#21 Avenar

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Posted 28 January 2020 - 07:53 AM

yes, your flats generator is broken ... smile.gif. people seem to just assume that if they just use a “white light” they will Be able to.  Get great flats and there is more to it than that. Don’t know what you are using but Many of the LED light panels people are using do not produce even RGB color channels.  Take a look at the individual channels in the historgram of one of your flats & see if the channels are producing the same output.  I had this same blotchy issue with the first panel i tried & it turned out the red channel was almost twice a strong as the others.   Finally just decided to buy a spike-a-flat, a light panel specifically designed for producing AP flats.  Fixed my “294 flats issue” over night ....dalek12.gif

Thanks for you advice! I want to test my flats with pixinsight. I Know how to split masterflat in 3 channels (RGB) but I don't know how and what look in the historgram... I have to check it with Hinstogram trasformation or any other pixinsight's tool? thanks

 

I believe at this point a lot of issues with flats are with selfmade flatboxes, as you say. My Flatbox is built with a 6000K led strip...



#22 Avenar

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Posted 28 January 2020 - 08:00 AM

Seems my darks were a big problem. They had a bad light leak. Old left, new right. Still no flats though.

76727b4e9de2a498194a9bd6eb5dacba.jpg


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My master Dark are the same of yours, (up - right picture), with heavy amp glow in the righ corner and a smaller one in the lef...


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