47 replies to this topic

[RoscoeD]

I recently completed my first imaging session (M101). Took 89 Subs, and 30ea darks, flats, and dark flats.  The flats were taken at 3s (per other discussions about the 294 not liking short exposures), all at the same gain as the lights, using an iPad as the light source with several sheets of paper to control the brightness.

 

Problem was my flats showed the unfortunately common characteristic of red splotches (no filters except UV-IR L2).  I used a trial version of APP to preprocess them and the final result was awful.  I emailed ZWO and was told by TJ Connelly that this type of flat was "normal" and would calibrate out.  Since I failed, I dropbox'ed my files to him and he took a crack at them...and he also failed.  He suggested that using an iPad was a likely cause of the goofy flats, claiming he had similar struggles until he switched to a Spike-a-flat.  In subsequent testing, I moved the iPad around, tried a T-shirt instead of paper, and adjusted brightness on the iPad itself, all gave me the same results (proving to me that uneven lighting was NOT the problem).

 

I would greatly appreciate if somebody could take a crack at my images and hope for better luck pre-processing them (I can share them from my dropbox)

 

(That said, how do other 294MC users do their flats?  If I'm going to live stack on my AA+, I'll need to shoot them first which could mean after dusk, meaning an illumination source could be required)

 

At this point I'm trying to convince ZWO the sensor is bad and wanting to return it.  Since the debit card account I use to purchase the camera is closed (and that bank is no longer open) a straight refund is not going to be easy (or possible?), so I'm seeking credit toward a different sensor (and maybe additional hardware if the replacement sensor is cheaper than the 294MC).

 

What sensor would folks recommend I switch to?  I want to stay OSC for now (newb, not ready for filters and the associated processing complexities). I was considering the ASI533MC but it wouldn't cover the credit (I am looking to get their EAF so...).  It's my impression that the 533 is virtually identical (14 bit ADC, low read noise) as the 294 except a smaller, and square, sensor.  I really don't want to drop another $1000 to bump up to the 2600MC.

 

Thoughts?

 

Sample light:

 

Master Flat:

 

Final stacked image:

 

[Mike7Mak]

Try taking tee shirt flats just pointing at the daylight sky. It may not be uneven light from the ipad but possibly the spectral bandwidth of the screen. At any rate sky flats should identify or rule out the ipad as the culprit.

[jdupton]

Roscoe,

 

I would greatly appreciate if somebody could take a crack at my images and hope for better luck pre-processing them (I can share them from my dropbox)

   I don't seem to be able to find the link to your DropBox with the files. Can you help me find the right location? I can take a look to see if I can see anything out of the ordinary.

 

   I also agree with Mike in Post #2. I can see a way in which the Flat light source could trigger some of the spectral effects on the IMX294 sensor. It would be best if you could try some "Wall Flats" where you illuminate a white wall in the house and point the telescope at it for a few Flat frames.

 

 

John

[RoscoeD]

I need your email address and I can share them with you.  I don't know any other way.  You can message me.

 

(Thanks)

 

edit: See if this works https://www.dropbox....4SmmICwjPa?dl=0

Edited by RoscoeD, 23 June 2022 - 10:13 PM.

[DirtyRod]

I spent a month trying to make my 294 work. Flats from 1s to 10s, various WB settings including auto and 50/50, up to 5 t-shirt layers, ADU from 20k up to 35k, different times of the morning,  various wizards, etc. If I used an offset of 0, I could get flats to work with all filters. If I went to an offset of 10 or higher my IR cut filter worked but my L-Extreme gave me that splotchy red flat and ruined my images. I didn’t have a chance to test other filters.

 

Perhaps I’m just spoiled with my 533, which is a breeze to calibrate, but I gave up and sent my 294 back for a refund in favor of the 071 while I still could. Seems like every other day I see a post about calibrating the 294 on one of the forums. The 071 seems to be much less picky like the 533 from the conversations I’ve had with owners.

Edited by DirtyRod, 24 June 2022 - 12:47 AM.

[RoscoeD]

I just tried a wall flat with T-shirt in the basement.  I don't have any rubber bands so I had to hold the t-shirt tight with one hand and manipulate my iPhone AA+ app with the other.  That said, the shots didn't look that different.  I'm recovering from a surgical procedure so I won't be hauling it outside anytime soon for a sky flat.

 

Edited by RoscoeD, 23 June 2022 - 10:11 PM.

[bobzeq25]

Thoughts, per your request. 

 

We do this to have fun.  You don't seem to be having much.

 

A 533 is really easy to use.  A 2600 is a better camera in every way, the ease of use of a 533, a bigger chip, a more modern sensor.

 

Some people are perfectly happy with their 294.  Others have problems.  I'm sure any number of factors contribute to that.

 

It costs money to change course.  How much of a problem is that for you?  Is it real, or esthetic?

Edited by bobzeq25, 23 June 2022 - 11:19 PM.

[RoscoeD]

If this sensor can’t be calibrated, I’ll just have to figure something out. Knowing me I’ll probably go up (2600) rather than down (533) but the option will probably come down to availability.  Other option is to have them send a replacement 294 and see of it works any better…but I really don’t subscribe to “hope as a strategy”

What’s really frustrating is that I researched and thought I had the right camera…then after I take delivery I discover all these issues.

#sigh

[Craigar]

I don't think any camera is "perfect" and the 294 is a really good value although it may have a slightly steeper learning curve then some much more expensive cameras. I have a (less expensive) passive cooled version (Mallincam Dsc10)  that was running at 74 degrees last night so I took darks at the end of the session (as is generally suggested) cause I could see way more hot pixels than when it was 10 degrees cooler - here's a rendering from about 40 minutes of (hand picked) subs using my C8 with a UV/IR filter and the (Mallincam Dsc10) - on an ES EXOS2 pmc8 mount. About 15 minutes of the subs are 10 second exposure, the rest are 15 seconds.

 

I cropped it all the way down to 1600px cause that is the max Cloudy nights will display.  Stacked with DSS using raw 16 bit per chanel .FITS files and the "Bayer drizzle Algorithm" = very important for great results. ThenGIMP for star reduction and shrinking and color balance.

 

 

 This is where I've posted images only taken with this camera and over time my imaging techniques are improving - and many were taken with bortle 9 light pollution.

 

Album: MC DS10c OSC camera + C8

30 images

0 comments

 

I've never tried "calibrating" my camera and maybe I should, although the mfgr. says it a "hand picked class 1" sensor whatever that means?

 

Thank You

 

Edited by Craigar, 24 June 2022 - 03:20 AM.

[Craigar]

I've been making my flats by putting on the dew shield and holding it up against a middle of the road LCD flat screen with a white screen at low brightness and making sure a live histogram shows the RGB colors output within 20 % of the middle range. It seems to give me better results than a tshirt and the sky - my "dust bunnys" seem clearer also.

[jdupton]

Roscoe,

 

I recently completed my first imaging session (M101). Took 89 Subs, and 30ea darks, flats, and dark flats.  The flats were taken at 3s (per other discussions about the 294 not liking short exposures), all at the same gain as the lights, using an iPad as the light source with several sheets of paper to control the brightness.

 

Problem was my flats showed the unfortunately common characteristic of red splotches (no filters except UV-IR L2).  I used a trial version of APP to preprocess them and the final result was awful.  I emailed ZWO and was told by TJ Connelly that this type of flat was "normal" and would calibrate out.  Since I failed, I dropbox'ed my files to him and he took a crack at them...and he also failed.  He suggested that using an iPad was a likely cause of the goofy flats, claiming he had similar struggles until he switched to a Spike-a-flat.  In subsequent testing, I moved the iPad around, tried a T-shirt instead of paper, and adjusted brightness on the iPad itself, all gave me the same results (proving to me that uneven lighting was NOT the problem).

 

I would greatly appreciate if somebody could take a crack at my images and hope for better luck pre-processing them (I can share them from my dropbox)

 

(That said, how do other 294MC users do their flats?  If I'm going to live stack on my AA+, I'll need to shoot them first which could mean after dusk, meaning an illumination source could be required)

 

At this point I'm trying to convince ZWO the sensor is bad and wanting to return it.  

   Thanks a bunch for posting the link to your files. I did not download all of them and instead grabbed 5 of each type to run some experiments. This was very, very interesting to me as I have worked with others on IMX294 red pattern issues before but have rarely had any such issues with my own copy of this camera.

 

   I will outline my experiments below but the net is that I think your Flats are at fault in this case.

 

   The IMX294 sensor appears to have an issue with narrow-band light at longer (red) wavelengths. This has been documented here on CloudyNights in many threads. The most obvious such cases of fixed red channel patterns are seen when using longer wavelength narrow-band filters such as Ha, L-eNhance, L-eXtreme, and Radian Triad tri-band and quad-band filters. The issue is thought to be caused via a process called "etaloning" -- an interference effect of light. It shows up as light and dark patterns where the light is interfering with itself at the surface of the sensor at some wavelengths.

 

   There have been some reports from users who have seen the effect to some extent or other even when not using a narrow-band filter of any sort. This is the case you are seeing. I have not had the opportunity to closely examine a set of files such as you supplied. It has sort of strengthened one of my suspicions I have had about the effect but was never able to reproduce. 

 

   The seed of the idea (or suspicion) I have had is that the nature of the light source used for taking Flat frames might cause the effect to show up. My thoughts were that if the Flat light source contained either narrow-band light at longer wavelengths or possibly had some specific polarization characteristics, it might cause the etalon effect to appear in the Flats even though the Lights used no filters. 

 

   Your use of an iPad might be behind the issue you are seeing. LCD screens, in general, are very polarized light sources. (Put on a pair of polarized sunglasses and look at your iPad while turning it 90° and you will see the polarization at work.) I know lots of others use LCD screens without issues but I have always had this nagging suspicion, nonetheless.

 

   Here is what I did as an experiment in PixInsight:
      Part #1:

1. I integrated 5 of your Dark frames to make a Master_Dark
2. I integrated 5 of your Flat-Darks to make a Master_Flat-Dark
3. I calibrated 5 of your Flat frames using the Master_Flat-Dark
4. I integrated the 5 calibrated Flat frames into a Master_Flat
5. I calibrated 5 Lights with the Master_Dark and Master_Flat
6. I deBayered the 5 calibrated Lights
7. I aligned the 5 deBayered Lights
8. I integrated the 5 aligned Lights
    
9. I ran ABE to remove a linear gradient (only) from the integrated result
10. I ran DBE to remove any residual vignetting (only) from the result
     
11. The following shows a very stretched view of the result of this processing.
    It shows the same fixed Red pattern you are seeing in your processing.
    

     Part #2:

1. Pick up the Master_Dark from Step #1 of Part #1
2. I calibrated 5 Lights with the Master_Dark only -- No Flats
3. I deBayered the 5 calibrated NoFlat Lights
4. I aligned the 5 deBayered NoFlat Lights
5. I integrated the 5 aligned NoFlat Lights
    
6. I ran ABE to remove a linear gradient (only) from the integrated result
7. I ran DBE to remove the significant vignetting (only) (from not using Flats) from the result
    
8. The following shows a very stretched view of the result of this processing.
   I used a similar strength of stretch to match that done in Part #1 of the experiment.
   This version without the Flats shows none of fixed Red patterns seen before.
   There are still remnants of dust motes and residual vignetting that DBE did not fully remove. (And DBE cannot remove Dust Mote shadows.)
   

   From this experiment, I would conclude that the Flats are the source of the fixed red pattern in your image. Even though this fixed pattern red issue usually comes from the use of narrow-band filters, it appears to have originated in your Flats and then been imparted onto the Lights during image calibration. (It was seen even in the single calibrated Lights when I used your Flats.)

 

   To further investigate, I would suggest a next step where you try a new method of taking Flats with a different light source. You indicated that you had taken Wall Flats and they looked the same as your iPad Flats but I wasn't able to understand if you only compared iPad Flats to Wall Flats or if you ran through the full imaging calibration process with both and compared the end results.

 

   As I mentioned, I have not really seen this issue with with own ASI294MC-Pro but then I always used a Flat light source which used indirect reflected LED light inside the flat field device. I have also used Wall Flats without this sort of fixed red patterning.

 

 

John

[unimatrix0]

Have someone tested or have some information about the light emitted by an LCD screen vs light emitted from another defused artificial light source, like a real flat panel or a cheap tracing board? 

 

Also natural light from the sky, diffused via t-shirt or diffused material like a semi-transparent vinyl vs.  electronic devices listed above? 

 

To me, this sounds like a good educational youtube episode (all you, youtubers out there) , who have experience and have devices measuring how various wavelengths and whatnot effects on various camera sensors etc? 

With everyone carrying a camera in their smart phones plus all the hobbyst and pro-photographers, I would assume there would be some scientific method of evaluation and recommendation has already made in this, since even daytime landscape/sport/art photographers take flats time to time to correct their low-light photos. 

Edited by unimatrix0, 24 June 2022 - 12:45 PM.

[RoscoeD]

Roscoe,

 

   Thanks a bunch for posting the link to your files. I did not download all of them and instead grabbed 5 of each type to run some experiments. This was very, very interesting to me as I have worked with others on IMX294 red pattern issues before but have rarely had any such issues with my own copy of this camera.

 

John

Thanks so very much John...having read many of your posts in regards to this sensor and its issues, I was hoping you'd take a shot at these.

 

   To further investigate, I would suggest a next step where you try a new method of taking Flats with a different light source. You indicated that you had taken Wall Flats and they looked the same as your iPad Flats but I wasn't able to understand if you only compared iPad Flats to Wall Flats or if you ran through the full imaging calibration process with both and compared the end results.

My wall flats were just a few individuals shots to compare to the iPad flats that I shared.  I understand your conclusion and why you reached it, but the few wall flats I took did not change significantly.  Given that the room is illuminated by LED tubes (fluorescent replacements) it could be that the light contains the same red content that the iPad does, although I'd have to think polarization isn't a factor in this case.  When I recover from the surgical procedure I had a couple of days ago I'll haul my scope back outdoors and take some sky flats and see if that changes anything.

 

Also still looking for tracing tablets or other light sources that folks have used successfully on this sensor.  Given that some tablets dim through pulsing I was always second guessing that technique, but since 294 flats need to be a few seconds long I'd think all that would be lost in the wash.  I really don't want to drop $300 on a Spike-a-Flat without knowing it will fix the problem...

[jdupton]

Frank (unimatrix0),

 

Have someone tested or have some information about the light emitted by an LCD screen vs light emitted from another defused artificial light source, like a real flat panel or a cheap tracing board? 

 

Also natural light from the sky, diffused via t-shirt or diffused material like a semi-transparent vinyl vs.  electronic devices listed above? 

   That sounds like something that could be very useful. For this particular issue, which is specific to the IMX294 and possibly the IMX492 sensors, it would be great to see such a study. (I'll note that the issue is usually seen on the IMX294 sensor in the red light portion of the spectrum but has also possibly been seen on the IMX492 sensor in the green portion of the spectrum.)

 

   In a more general sense, the light source used for Flats is supposed to be very even in illumination intensity and also Lambertian in nature. A Lambertian source will emit light identically in all directions. This may not be true of all LCD types of sources. For many to most sensors, it may not matter enough to be detectable. The IMX294 sensor might just be an exception in that regard because of the potential for interference effects at the sensor's surface.

 

 

John

[unimatrix0]

I examined the flats and the lights.  The lights have none of the discoloration around the borders.  The problem is the flats. The flats are adding the mis-coloration into it.  Whether it's a combination of whatever filter used and the light source as well as the method. 

 

I noticed that the exposure settings has the curve moved quite high for midpoint, I think this is too much if you ask me. I always try to shoot so the ADU average is around 28,000-30,000. This one has 39,000. 

 

I would try to take new flats with shorter exposures and "darker" ones, meaning whatever method used, referring to NINA, I would use 40% or 30% mean ADU in the options menu. 

 

 

I use asifitview to check on this stuff. Obviously the flats highlight the filter, creating the colored banding, and that would be all cool if the lights would have it, but they don't.   I guess the 294 is very sensitive in this regard, so while many goes with going longer flats, maybe try shorter flats with less illumination. 

Attached Thumbnails

• 

Edited by unimatrix0, 24 June 2022 - 03:02 PM.

[johrich]

I have both the ASI294MC pro and ASI 294MM pro. I found I have the best luck with flats using 4 layers of t-shirt material and an LED tracing pad from Amazon, (~$15). Using my tablet with a white screen app worked well with my ASI183MC but not with the ASI 294 series. I have to use sky flats with my red filter on the ASI294mm pro, but the SII, OIII, Ha, green and blue filters seem to work fine the tracing pad.

John

[Craigar]

Before I started using any filter I remember getting some of the red puffy banding trying do flats using daytime sky with T-shirt. I've only been using "SkyRaider Series MALLINCAMSKY" to run/capture the camera data. By my 5th session with this (Mallincam Dsc10) IMX294 and C8 SCT scope, I inserted an inexpensive Svbony UV/IR cut filter and it has been my only filter in use since - before that I tried to use a Hutech LPS-D2 filter on emissions nebula under bortle 9 skies and was not happy with the colors.

 

Since I've had the UV/IR cut filter in I haven't seen this red puffy banding in any of the different flat methods I've tried.  I get good consistent results using my PC's 22" ( BenQ Gw2280 "VA Backlight Technology LED backlight") which I have on very low (10%) brightness with just a white screen and very fast exposure time around 80ms through my C8, here's a flat sub viewed with ZWO's ASIFitsView free software.

 

 

 

pertinent data from .FITS header

 

 

EXPTIME =                 0.05 / Exposure time in seconds                       EXPOSURE=                 0.05 / Exposure time in seconds
GAIN    =                 1545 / Analog Gain                                    XPIXSZ  =                 4.63 / Pixel Width in microns
YPIXSZ  =                 4.63 / Pixel Height in microns                        XBINNING=                    1 / Binning level along the X-axis
YBINNING=                    1 / Binning level along the Y-axis                 INSTRUME= 'SkyRaiderDS10C'     / Camera Model
OBJECT  = 'NA      '           / name of observed object                        CCD-TEMP=                 27.6 / actual measured sensor temperature in degrees
CIMAGETYP= 'Light Frame'        / type of image                                  CREATOR = 'MALLINCAMSKY V4.11.19627.20210925' / the name of the software task
thPROGRAM = 'MALLINCAMSKY V4.11.19627.20210925' / the name of the software task thSWCREATE= 'MALLINCAMSKY V4.11.19627.20210925' / string indicating the software
COLORTYP= 'GBRG    '           / Bayer mosaic                                   BAYERPAT= 'GBRG    '           / Bayer pattern
BAYOFFX =                    0 / Bayer offset X                                 BAYOFFY =                    1 / Bayer offset Y
END

 

 

 

header information from DSS when creating a master from many flat subs.

 

 

Bitmap.BitPerChannels=16
Bitmap.FileName=E:\VIDEO_E_HPZ2\raw\2021\Astronomy\_MC\_FlatHighGain\Flat-f10-22062\MasterFlat_Gain1545.tif[6/23/2022 7:15:46 AM]
Bitmap.Height=2778
Bitmap.NrChannels=1
Bitmap.Width=3704
Fits.BayerPattern=3
Fits.BlueScale=1.2000
Fits.Brighness=1.0000
Fits.DSLR=Generic GBRG
Fits.FITSisRAW=1
Fits.ForceUnsigned=0
Fits.RedScale=1.1000
Flat_Iteration=5
Flat_Kappa=2.0000
Flat_Method=1

For DSO's I use high conversion gain mode usually set at 15 (on a scale that goes up to 200)

Edited by Craigar, 25 June 2022 - 02:44 AM.

[RoscoeD]

As I mentioned, I have not really seen this issue with with own ASI294MC-Pro but then I always used a Flat light source which used indirect reflected LED light inside the flat field device. I have also used Wall Flats without this sort of fixed red patterning.

What light source do you use?

[Fegato]

I have the ASI294MC Pro and use it with my 8 Edge HD. My flats were OK using a tracing panel, but I upgraded to a Gerd Neumann Aurora flat panel when I got my RASA 11 *, and this certainly works perfectly. I use it with both my combinations - the RASA 11 / ASI2400MC Pro and with the 8 Edge / ASI294MC Pro.

 

The ASI294MC Pro is a bit more finicky than the more recent CMOS cameras, but it does work fine, and I'm quite happy using it. You have to use darks to remove the amp glow. You have to find a way to take optimum flats as per this discussion, and as you say, flat darks have to be used rather than bias.

 

* - the Aurora panel is a lot more expensive, but once I had to cover 11 inches, the tracing panel wasn't big enough, and a larger one would have been horribly unwieldy. GN also provides "filters" that you can fit inside the Aurora panels, which allow you to dim the light and more easily find the right exposure length without fiddling about with T shirts and goodness knows what.

[jdupton]

Roscoe,

 

What light source do you use?

   My light panel is one I designed and built myself. I was using Sloan science filters with a monochrome sensor at the time and had to custom build a panel that provided UV and IR light in order to keep my Flat exposure times reasonable (under 15 seconds). The design is hard to describe and I don't have any inside photos of the "works".

 

   Imagine a tube 12" diameter (for my 11" SCT) and 18" long. About 3" from the bottom of the tube (nearest the telescope) there is a ring of LEDs around the inside periphery about 1/2" wide with LEDs pointing upwards away from the telescope's aperture. There are 18 sets of White (broadband) LEDs, 385 nM (soft UV) LEDs, 650 nM (for Ha) LEDs, and 910 nM (IR) LEDs alternating in groups around the ring and separately controllable.

 

   The light from these shines upward towards the sky inside the closed tube. At the top end, a silvery white reflector is illuminated and reflects the light back down toward the telescope aperture and the source LEDs. At the bottom of the tube below the level of the LED ring is a white translucent panel that further diffuses the light just before it exits the tube and enters the telescope.

 

   Because of the reflection and diffusing inside the tube, the light is pretty uniform and well mixed without any of the polarization that you get from LCD screens. While complex and overkill for most other uses, this Flat light source has served me well for about 10 years. When not using the Sloan filters, the controlled multi-spectral nature allows me to tune the mix of light so that each color channel is well balanced in the Flat's histogram.

 

   Since I have not used the Sloan filters much in recent years, I am building a new light source that is much more compact and easier to use. It will also be 12" in diameter but only about 2" tall making it much easier to pack in with my other gear when travelling to a dark site.

 

   I am sure that is much more that you really wanted to know...

 

 

John

[Borodog]

I have a suggestion.

1) Create a calibrated master flat.

2) Debayer it.

3) Extract the green channel only, and use this as the master flat to calibrate the lights.

Edited by Borodog, 25 June 2022 - 11:33 AM.

[RoscoeD]

Not a clue how to do that, but it sounds clever

Edited by RoscoeD, 25 June 2022 - 01:22 PM.

[jdupton]

Borodog,

 

I have a suggestion.

1) Create a calibrated master flat.

2) Debayer it.

3) Extract the green channel only, and use this as the master flat to calibrate the lights.

   That is an excellent idea for working around the red pattern issue with the IMX294 OSC camera when a narrow-band filter is not being used! I had not considered doing that but it makes perfect sense.

 

   I tried the idea but changed one thing. If you look at Flats that show this red interference issue, the green channel of the Flat always has some artifacts also due to the overlap and red and green response in the sensor at longer wavelengths. However, the blue channel is usually not affected at all, so I used the blue channel rather than the green. 

 

   Here is a highly stretched view of what I got:

 

   This looks just about as clean (color pattern wise) as the NoFlats example I posted in Post #11 above. However, since a flat was actually used, the dust mote and vignetting are fully corrected. Some experimentation may be required but this looks like something others should try if they have issues with the fixed red patterns in images from the IMX294 sensor= due to using an LCD Flat light source.

 

 

Roscoe,

 

   What this means is that you should be able to use your existing data to process your images. I can outline the general extra steps required but it may depend on the specific software you use and what tools are available to you.

1. Stack your Dark frames into a Master_Dark
2. Stack your Flat-Dark frames into a Master_FlatDark
3. Calibrate your Flat frames with the Master_FlatDark
4. Stack the calibrated Flat frames into a Master_Flat
    
5. Debayer the Master_Flat
6. Extract (or split the color channels) to get the Blue channel only of the Master_Flat (Blue_Master_Flat)
    
7. Calibrate your Light frame using the Master_Dark and Blue_Master_Flat
    
8. Proceed with your normal calibrated Light processing -- DeBayer, Align, Stack, etc.

   The steps in bold above are the added steps to a normal pre-processing workflow.

 

   I may go back to another user's data I still have and try this again but the method seems to hold great promise for folks having this issue when it is present in the Flats but not the Lights. I don't think it will help the more general case where a narrow-band filter is used in the image train for Lights.

 

 

John

Edited by jdupton, 25 June 2022 - 02:13 PM.

[RoscoeD]

That's amazing...Ive been using APP but a total n00b so if someone could step me through this process I'd like to try it.

 

(I tried taking T-shirt sky flats today but I couldn't get any consistency between shots and suffered from horrible vignetting [most likely from the t-shirt] )

[Borodog]

Borodog,

 

   That is an excellent idea for working around the red pattern issue with the IMX294 OSC camera when a narrow-band filter is not being used! I had not considered doing that but it makes perfect sense.

 

   I tried the idea but changed one thing. If you look at Flats that show this red interference issue, the green channel of the Flat always has some artifacts also due to the overlap and red and green response in the sensor at longer wavelengths. However, the blue channel is usually not affected at all, so I used the blue channel rather than the green. 

 

   Here is a highly stretched view of what I got:

Roscoe_M101_wBlueFlats.jpg

 

   This looks just about as clean (color pattern wise) as the NoFlats example I posted in Post #11 above. However, since a flat was actually used, the dust mote and vignetting are fully corrected. Some experimentation may be required but this looks like something others should try if they have issues with the fixed red patterns in images from the IMX294 sensor= due to using an LCD Flat light source.

 

 

Roscoe,

 

   What this means is that you should be able to use your existing data to process your images. I can outline the general extra steps required but it may depend on the specific software you use and what tools are available to you.

1. Stack your Dark frames into a Master_Dark
2. Stack your Flat-Dark frames into a Master_FlatDark
3. Calibrate your Flat frames with the Master_FlatDark
4. Stack the calibrated Flat frames into a Master_Flat
    
5. Debayer the Master_Flat
6. Extract (or split the color channels) to get the Blue channel only of the Master_Flat (Blue_Master_Flat)
    
7. Calibrate your Light frame using the Master_Dark and Blue_Master_Flat
    
8. Proceed with your normal calibrated Light processing -- DeBayer, Align, Stack, etc.

   The steps in bold above are the added steps to a normal pre-processing workflow.

 

   I may go back to another user's data I still have and try this again but the method seems to hold great promise for folks having this issue when it is present in the Flats but not the Lights. I don't think it will help the more general case where a narrow-band filter is used in the image train for Lights.

 

 

John

There you go.