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False colors on ASI MC cameras

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#1 matt_astro_tx

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Posted 22 April 2021 - 09:48 AM

I’ve been using a new ASI183MC for about 3 weeks now, only shooting Astro targets with it and am really impressed.

Yesterday though I fired it up during the day to adjust back focus after adding a flattener and noticed my neighbors green bushes are red. My green field is brown.

I’m shooting in fire capture with debayer RGGB nearest neighbor.

What gives?

#2 Professor2112

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Posted 22 April 2021 - 09:56 AM

If I had to guess, it would probably have something to do with the increased sensitivity to Ha that these cameras are designed for vs something like a DSLR.  It sounds a lot like how a DSLR takes pics after it is modded. 


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#3 Pelayo

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Posted 22 April 2021 - 10:03 AM

Have you used an IR/UV filter? If not that's probably the answer.


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#4 happylimpet

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Posted 22 April 2021 - 10:18 AM

Have you used an IR/UV filter? If not that's probably the answer.

Yup, thats my bet too. Colours are way off without, except for the blue sky and white clouds as thats consistent into the IR.



#5 sharkmelley

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Posted 22 April 2021 - 10:48 AM

You need to use a IR/UV blocking filter and you also need to use the appropriate white balance.

 

Mark


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#6 matt_astro_tx

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Posted 22 April 2021 - 11:06 AM

Thanks everyone!  I didn't realize that.  I have a UV/IR cut filter on its way already.  I'll give it a shot this weekend and see how it differs.  Interesting experiment.

 

Ok so here's my next question:  I was told I must shoot with an IR/UV Cut filter on this camera for the above stated reasons.  But, wouldn't I want that sensitivity when shooting astro?



#7 jonnybravo0311

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Posted 22 April 2021 - 11:44 AM

Thanks everyone!  I didn't realize that.  I have a UV/IR cut filter on its way already.  I'll give it a shot this weekend and see how it differs.  Interesting experiment.

 

Ok so here's my next question:  I was told I must shoot with an IR/UV Cut filter on this camera for the above stated reasons.  But, wouldn't I want that sensitivity when shooting astro?

Must? That's a strong word... you _should_ use a UV/IR cut filter. You don't want the UV/IR wavelengths as they aren't visible, and only cause star bloat.


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#8 matt_astro_tx

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Posted 22 April 2021 - 11:50 AM

Must? That's a strong word... you _should_ use a UV/IR cut filter. You don't want the UV/IR wavelengths as they aren't visible, and only cause star bloat.

Roger that.  Makes sense



#9 Stelios

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Posted 22 April 2021 - 03:46 PM

Must? That's a strong word... you _should_ use a UV/IR cut filter. You don't want the UV/IR wavelengths as they aren't visible, and only cause star bloat.

Sometimes strong words convey the correct meaning. "Should" is weaker than "must" and one could draw the conclusion that it's probably OK to not use the filter.



#10 TelescopeGreg

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Posted 22 April 2021 - 05:21 PM

Must? That's a strong word... you _should_ use a UV/IR cut filter. You don't want the UV/IR wavelengths as they aren't visible, and only cause star bloat.

+1.

 

Adding an explanation...  The reason for star bloat is that many telescopes, even "fully corrected" "APO" refractors, focus light very well in the visible spectrum, but that ability breaks down when you get into the UV and IR parts of the spectrum.  The reason is that light refracts differently depending on its color - that's how prisms work - but lens designers can correct for it only so well.  So, without the filter, that out-of-focus light will land on your camera sensor, making the stars a bit blurry.  A telescope with a solely mirror-based system won't have that problem, but they often have others (e.g. coma), which often require glass lenses to correct, and that re-introduces the problem.


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#11 jdupton

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Posted 22 April 2021 - 07:18 PM

Matt,

 

I’ve been using a new ASI183MC for about 3 weeks now, only shooting Astro targets with it and am really impressed.

Yesterday though I fired it up during the day to adjust back focus after adding a flattener and noticed my neighbors green bushes are red. My green field is brown.

I’m shooting in fire capture with debayer RGGB nearest neighbor.

What gives?

   It is also possible that the color balance of the new camera needs to be adjusted. ZWO/ASI cameras default to an odd color balance setting when using the native (non-ASCOM) drivers.

 

   When you connect to the camera, try to find the white balance settings in one of the camera control settings dialogs. If you cannot find it in FireCapture, you might try running the camera with ASICap (part of ASI_Studio). Once connected to the camera, the while balance can be found in the detailed settings for the camera. There are two settings and they usually default to the values of 52 and 95 (I think). Change them to 50 and 50 and then exit / save the dialog. The camera and driver will remember them from then on. See if that changes the daytime colors you are seeing.

 

 

John



#12 matt_astro_tx

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Posted 22 April 2021 - 07:51 PM

Matt,

 

   It is also possible that the color balance of the new camera needs to be adjusted. ZWO/ASI cameras default to an odd color balance setting when using the native (non-ASCOM) drivers.

 

   When you connect to the camera, try to find the white balance settings in one of the camera control settings dialogs. If you cannot find it in FireCapture, you might try running the camera with ASICap (part of ASI_Studio). Once connected to the camera, the while balance can be found in the detailed settings for the camera. There are two settings and they usually default to the values of 52 and 95 (I think). Change them to 50 and 50 and then exit / save the dialog. The camera and driver will remember them from then on. See if that changes the daytime colors you are seeing.

 

 

John

Thanks for the advice!  I hadn't considered that.  Once I get the filter (on Saturday) I'll install it and try this process out to get a true to life color.  Shooting in RAW, WB is somewhat irrelevant until post processing, but I would like it to be "correct" out of the gate.



#13 CCD-Freak

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Posted 22 April 2021 - 08:24 PM

Use a UV-IR filter.  I did not use one for my first outing with my ASI-533MCP and IR leakage messed with the color. 

The star at the right edge should be red instead of pink and the micro-lens artifacts would be much less obvious.

 

NGC2244-Sigma-crop-GR-CB-Sat-Curves-3x3-3.jpg


Edited by CCD-Freak, 22 April 2021 - 08:25 PM.


#14 jdupton

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Posted 22 April 2021 - 08:36 PM

Matt,

 

Thanks for the advice!  I hadn't considered that.  Once I get the filter (on Saturday) I'll install it and try this process out to get a true to life color.  Shooting in RAW, WB is somewhat irrelevant until post processing, but I would like it to be "correct" out of the gate.

   Actually, the white balance settings are important even though the image is being captured in raw format. The ugliness of this setting in the driver is that it modifies the data read from the sensor before sending it to the capture software. What the capture software sees and writes to the disk for you is not the data the sensor had seen. The data itself has been permanently modified and normal processing will have trouble reversing what was done to the data.

 

   There are a number of threads on the subject here on CN. You really need to change the camera / driver settings before trying anything else. Please look at the following post and scan the two linked threads in the post for details on why this is an issue.

 

https://www.cloudynights.com/topic/709866-asi533mc-pro-dark-frame-white-pixels/?hl=%2Bwhite+%2Bbalance+%2Bbernd#entry10225548

 

 

John


Edited by jdupton, 22 April 2021 - 08:39 PM.

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#15 matt_astro_tx

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Posted 23 April 2021 - 08:40 AM

Matt,

 

   Actually, the white balance settings are important even though the image is being captured in raw format. The ugliness of this setting in the driver is that it modifies the data read from the sensor before sending it to the capture software. What the capture software sees and writes to the disk for you is not the data the sensor had seen. The data itself has been permanently modified and normal processing will have trouble reversing what was done to the data.

 

   There are a number of threads on the subject here on CN. You really need to change the camera / driver settings before trying anything else. Please look at the following post and scan the two linked threads in the post for details on why this is an issue.

 

https://www.cloudynights.com/topic/709866-asi533mc-pro-dark-frame-white-pixels/?hl=%2Bwhite+%2Bbalance+%2Bbernd#entry10225548

 

 

John

Wow, thanks.  Ok, so the path ahead:

 

1. Download the ASCOM driver from ZWO (Better than the windows driver and doesn't modify the FITS data)

 

2. Download ASIStudio from ZWO and adjust color balance to 50 for all channels.  Save.

 

3. Recheck histogram in FireCapture for a single peak when shooting a dark frame.

 

4. Reshoot some color landscape frames to see if color balance is true to life.  For S&G, attach the UV/IR cut filter and try again.


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#16 matt_astro_tx

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Posted 23 April 2021 - 08:41 AM

Use a UV-IR filter.  I did not use one for my first outing with my ASI-533MCP and IR leakage messed with the color. 

The star at the right edge should be red instead of pink and the micro-lens artifacts would be much less obvious.

 

attachicon.gifNGC2244-Sigma-crop-GR-CB-Sat-Curves-3x3-3.jpg

Thanks for this visual example!  I can see it clearly now.



#17 happylimpet

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Posted 29 April 2021 - 03:46 AM

+1.

 

Adding an explanation...  The reason for star bloat is that many telescopes, even "fully corrected" "APO" refractors, focus light very well in the visible spectrum, but that ability breaks down when you get into the UV and IR parts of the spectrum.  The reason is that light refracts differently depending on its color - that's how prisms work - but lens designers can correct for it only so well.  So, without the filter, that out-of-focus light will land on your camera sensor, making the stars a bit blurry.  A telescope with a solely mirror-based system won't have that problem, but they often have others (e.g. coma), which often require glass lenses to correct, and that re-introduces the problem.

Not so. I use an f4 16" newtonian with a coma corrector and often image unfiltered. My stars remain just as sharp.



#18 matt_astro_tx

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Posted 29 April 2021 - 09:53 AM

Update:  I received a 1.25" Baader UV/IR cut filter last weekend.  I went with a 1.25" because I will use it when imaging planetary through my newtonian with the 1.25" nosepiece attached, but was at first perplexed how to install a filter into my imaging train when using my AT60ED refractor with field flattener installed.  After some digging I realized ZWO includes an adapter for this purpose.  See picture.

 

I've also downloaded the ASCOM drivers and calibrated the white balance using the above procedure and all I can say is wow.  I was impressed with this camera before, but now with the proper filter (terrestrial viewing at least) looks phenomenal!  It's springtime in Texas so clouds and rain galore.  Praying for a clear night soon.

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#19 Professor2112

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Posted 29 April 2021 - 09:42 PM

Update:  I received a 1.25" Baader UV/IR cut filter last weekend.  I went with a 1.25" because I will use it when imaging planetary through my newtonian with the 1.25" nosepiece attached, but was at first perplexed how to install a filter into my imaging train when using my AT60ED refractor with field flattener installed.  After some digging I realized ZWO includes an adapter for this purpose.  See picture.

 

I've also downloaded the ASCOM drivers and calibrated the white balance using the above procedure and all I can say is wow.  I was impressed with this camera before, but now with the proper filter (terrestrial viewing at least) looks phenomenal!  It's springtime in Texas so clouds and rain galore.  Praying for a clear night soon.

That’s awesome! Glad you got it figured out, let us know how the real test under the stars goes... after the clouds clear out that is.  Dealing with a massive batch of rain that’ll be streaming over southern New England for the next several days myself.  Nothing but clouds in every forecast as far as they can “see”. 




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