Flats problem - Forums

Renaat Vandewiele

Topic starter

Feb 27, 2023 · Edited: Feb 27, 2023

I have an issue with my flat frames.
for example : to me everything looks normal in the preview ...

now if I go stacking I get ...

without flats I get

I stack in PI

does anyone have an Idea what could be wrong here? Using an Altair hypercam 294c PROTEC. I have managed to get a decent looking image with using only the blue channel from the master flat but that does not seem an option for me to do this every time

note : i DID clean my rig in the mean time

Joon Ren

Feb 27, 2023

Were you using local normalisation by any chance? If the reference image has flaws, it will cause an uneven discoloured background. Another possibility is if the flats or lights were not calibrated properly, the flat corrections will be inaccurate.

Well Written Helpful Concise

Michael E.

Perfect post

Feb 27, 2023

How do you acquire your flats? Are you perhaps using a DIY flat-panel with the led-lighting not being uniformly enough?
Because your first image looks pretty uneven to me, displaying a similar pattern as in your stacked and corrected image.
If you're not already doing so, it might help to produce the flats by pointing the telescope to the sky at dusk, with or without a t-shirt.

Well Written Helpful Insightful Respectful Concise Engaging Supportive Perfect post

Renaat Vandewiele

Topic starter

Feb 27, 2023

Michael:
How do you acquire your flats? Are you perhaps using a DIY flat-panel with the led-lighting not being uniformly enough?
Because your first image looks pretty uneven to me, displaying a similar pattern as in your stacked and corrected image.
If you're not already doing so, it might help to produce the flats by pointing the telescope to the sky at dusk, with or without a t-shirt.

Hi Michael, I'm using an ipad with a double layer of white tshirt. I'm using the ekos flat wizard that will automatically look foor 3200 ADU and determine the exposure time

Renaat Vandewiele

Topic starter

Feb 27, 2023

Were you using local normalisation by any chance? If the reference image has flaws, it will cause an uneven discoloured background. Another possibility is if the flats or lights were not calibrated properly, the flat corrections will be inaccurate.

is that a setting in weightedbatchprocessing in PI?

thank you for the reply

Michael E.

Perfect post

Feb 27, 2023

Hi Renaat
I still think the uneven screen illumination of your iPad might be the cause. Try the "sky-method" occasionally, at least you can rule this out as an error if it won't help.
clear & even skies :-)

Renaat Vandewiele

Topic starter

Feb 27, 2023

Michael:
Hi Renaat
I still think the uneven screen illumination of your iPad might be the cause. Try the "sky-method" occasionally, at least you can rule this out as an error if it won't help.
clear & even skies :-)

Will do thx

Renaat Vandewiele

Topic starter

Feb 27, 2023 · Edited: Feb 27, 2023

ok so here I am pointing at the sky with 4 layers

Jonny Bravo

Feb 27, 2023

Renaat Vandewiele:
I have an issue with my flat frames.
for example : to me everything looks normal in the preview ...

now if I go stacking I get ...

without flats I get

I stack in PI

does anyone have an Idea what could be wrong here? Using an Altair hypercam 294c PROTEC. I have managed to get a decent looking image with using only the blue channel from the master flat but that does not seem an option for me to do this every time

note : i DID clean my rig in the mean time

294... you're going to need a different light source. When I first got my 294 (mono) I was using an iPad as my light source. My red filter looked exactly like what you're presenting here. I stopped using the iPad... no more problem with the red calibration.

Helpful Concise

andrea tasselli

Frequent contributor

Feb 27, 2023

Apart from the issue with using an IPad as flat panel (bad idea unless you put a lot of diffuser screens in between) your master flat looks wrong. it shouldn't be de-bayered at all. Just remove the master dark-flat from each of the frames and stack in PI using multiplicative normalization, no weights and equalize flux.

Concise

Joon Ren

Feb 27, 2023 · Edited: Feb 27, 2023

Renaat Vandewiele:
Were you using local normalisation by any chance? If the reference image has flaws, it will cause an uneven discoloured background. Another possibility is if the flats or lights were not calibrated properly, the flat corrections will be inaccurate.

is that a setting in weightedbatchprocessing in PI?

thank you for the reply

@Renaatit is turned on by default in certain versions of Pixinsight. More info here https://www.cloudynights.com/topic/826992-turn-off-local-normalization-in-pixinsight-weightedbatchpreprocessing/

Also, +1 to what Andrea said above. Don’t debayer the flats when calibrating. If you’re using WBPP it should do exactly that but won’t hurt to check.

Tom Boyd

Feb 27, 2023

Maybe way off base here, but curious. Are you concerned by the red circular streaks in the stacked image? If so, these look to me like ABE artifacts. Could you repost simply using an unlinked screen stretch? Simply take your raw image, and before you screen stretch it, de-select the little chain link icon on the upper left of the ScreenTransferFunction. This will stretch each of your color channels independently. If the unlinked screen stretch images looks ok, get rid of the background gradient using DBE instead ABE.

Just a thought…

Helpful Insightful Respectful

Jonny Bravo

Feb 27, 2023

Tom Boyd:
Maybe way off base here, but curious. Are you concerned by the red circular streaks in the stacked image? If so, these look to me like ABE artifacts. Could you repost simply using an unlinked screen stretch? Simply take your raw image, and before you screen stretch it, de-select the little chain link icon on the upper left of the ScreenTransferFunction. This will stretch each of your color channels independently. If the unlinked screen stretch images looks ok, get rid of the background gradient using DBE instead ABE.

Just a thought...

It's not a background extraction artifact. It is an issue with the 294 sensor and using an iPad as the light source for flats.

Well Written

Renaat Vandewiele

Topic starter

Feb 27, 2023

restacking with sky as lightsource now … we'll see..
I have tried dbe and abe for extraction method. stacking almost done .. :-) we'll see

Renaat Vandewiele

Topic starter

Feb 27, 2023

ok it looks different (not talking about the object I had the same problem with this one. So i redid the flats with the sky as a lightsource with shirt 2 layers. I did not change the parameters of the preprocessing yet.

and after a quick hist transfo

Renaat Vandewiele

Topic starter

Feb 27, 2023

Thank you all for the responses!!

Roger Nichol

Feb 27, 2023

Can you confirm what your flats exposure duration is? You need at least 3s for that camera.

Well Written

andrea tasselli

Frequent contributor

Feb 27, 2023

Roger Nichol:
Can you confirm what your flats exposure duration is? You need at least 3s for that camera.

Absolutely NOT.

Renaat Vandewiele

Topic starter

Feb 27, 2023

0.19s is automatically set

Roger Nichol

Feb 27, 2023 · Edited: Feb 28, 2023

The ASI294MC, which uses the same IMX294 sensor has a recommendation of 5s due to a characteristic of the sensor - from what I've read it switches to settings optimised for video below 3s which introduces some non-linearity (?) (I can't find a reference for that apart from numerous reports on cloudy nights, FB, etc.)

"2. I’ve heard there might be strange patterns on some ASI294MC Pro stretched images, does this mean the camera is defective?:

NO, it is not a defect, and it is just a characteristic of the sensor. The pattern calibrates out of the light image with proper flat frames. A proper flat frame is a capture using an evenly illuminated light source, dimmed down to achieve an average ADU value of 24,000 (this is up to the user and their setup – recommended the histogram peak at 1/3 to 1/2 from the left, as shown in the figure below), a 5-second exposure, captured with the same gain and focus point as the light frames." (https://astronomy-imaging-camera.com/product/asi294mc-pro-color/comment-page-6#comments)

There is a good guide to using the ZWO version of this camera at https://www.indilib.org/forum/ccds-dslrs/7402-starters-guide-to-asi294mc-pro.html which describes this issue.

Some other threads and guides:

https://www.youtube.com/watch?v=z_koNt5J1I0

https://forums.sharpcap.co.uk/viewtopic.php?t=5561

The Sensor datasheet at IMX294.zip may be useful.

Give it a try and see if it help. If so, please report that back here.

Helpful

andrea tasselli

Frequent contributor

Feb 27, 2023

Roger Nichol:
The ASI294MC, which uses the same IMX294 sensor has a recommendation of 5s due to a characteristic of the sensor

There is no such recommendation anywhere in the user manual. Do you actually own it?

Well Written

Tom Boyd

Feb 27, 2023

andrea tasselli:
Roger Nichol:
The ASI294MC, which uses the same IMX294 sensor has a recommendation of 5s due to a characteristic of the sensor

There is no such recommendation anywhere in the user manual. Do you actually own it?

I own the 294MC and collect flats via a flat panel. I routinely collect flats with exposure times of less than a second and observe no issues with the flats produced.

Well Written Concise

Greisy Valdes

Feb 28, 2023 · Edited: Feb 28, 2023

Hi! I had posted about this same issue before, I use the zwo294mc pro, and what worked for me was taking flats at around 4-5 seconds. I no longer deal with this issue. If you use NINA to take your flats, my settings are here. These settings got rid of the gradients completely, at least for me. (I use a cheap tracing light pad from amazon to take my flats)

Renaat Vandewiele

Topic starter

Feb 28, 2023

getting somewhere :-)

Roger Nichol

Feb 28, 2023

getting somewhere :-)

What have you changed?

Related discussions

What's wrong with my filters?

Hi! I'm getting some immense gradients in my final stacked images, which "should not happen" since I have proper Flats. The filters are in an EFW and they look clean (basically placed directly in the EFW straight from purchase). They do...

Gradients in stacked images despite proper flats; similar calibration issue.

Nov 19, 2024

Spikes problem

Hi everybody, I have shot IC63 some days ago (here) and i wonder why is Navi looking like that? I mean, i saw other photos with 4 long spikes on it and mine seems to have a lot of intermediate spikes to the center of the photo (and small ones to the ...

Flat frames can cause diffraction spikes and artifacts in stacked images.

Oct 10, 2021

Pixinsight not using flats when stacking with WBPP - not sure why

Hi everyone. It seems I have a new problem… I have been using PixInsight for quite a while now and I finally got the hang of it. Over the last few days I've noticed that some of my images especially the ones with Ha are not incorporating th...

PixInsight not applying flats during stacking; directly addresses author's problem.

Oct 14, 2024

PixInsight WBPP and calibration frames

I wanted to keep this on the PI forums but my account still waiting for admin approval so here it goes. I use PI and WBPP. as for calibration frames I use masters created from the ASAIR plus. Is this okay to do? might not be ideal I know, but is ther...

PixInsight WBPP calibration frames; relevant to author's stacking and flat issues.

Aug 21, 2024

Trouble with Deep Sky Stacker applying flats correctly

I'm having trouble with stacking photos lately and not sure what changed. I'm seeing dust mote artifacts in stacked & calibrated images that shouldn't be there. Below is an image straight out of DSS. No further editing, STF applied. Y...

Deep Sky Stacker not applying flats correctly; similar flat calibration problem.

Dec 9, 2024