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Planetary Imaging Filters

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#1 MountainAir

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Posted 14 October 2021 - 11:51 AM

I am getting back to some planetary imaging after a hiatus, and want to understand the most optimal workflow and equipment.

 

Current gear:

EdgeHD 9.25

Luminos 2.5 barlow (hope to get a 2x PowerMate soon)

ZWEO Atmospheric Dispersion Corrector

ASI290MC -- for RGB OSC using a UV/IR cut filter

FireCapture via USB3

 

Gear to add:

ASI462MC -- for IR with an IR-pass filter

 

Capture Workflow:

  1. Find target
  2. Focus using ASI290MC for RGB
  3. Capture ~3 1.5 minute runs at roughly 75 fps (~13ms) with whatever gain gets me to an 80% histogram
  4. Quickly switch to ASI462 for IR (or I could always use the ASI462, but switch filters -- they're fairly similar)
  5. Quickly focus the ASI462
  6. Capture ~3 1.5 minute runs at 75 fps like above

My problem is that to either switch filters or switch cameras requires time -- then more time to focus.  With the multiple video runs per filter, Jupiter will rotate a fair amount and the IR images will see rotation compared to the RGB images.  So how do people do this with multiple filters?

 

I Googled around a bit, but couldn't find a UV-CUT/IR-PASS filter (or, I guess just a UV-Cut filter would be the same thing).  Such a thing would be awesome -- I don't want that skewed, bloated UV light but do want IR for the banding in the gas giants.  Is there some reason why capturing both RGB and IR in the same images would be bad?  I understand you can't really process them differently in that scenario, but wouldn't this be better than the 3-5 minutes it might take to switch cameras and refocus?


Edited by MountainAir, 14 October 2021 - 11:55 AM.


#2 Tapio

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Posted 14 October 2021 - 12:02 PM

I think most just use one camera and change filters (using filter wheel).

 

IR-pass filter just lets IR light through (for example Astronomik Planet IR Pro 742 passes above 742nm), so no visible and no UV light.



#3 MountainAir

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Posted 14 October 2021 - 12:57 PM

I think most just use one camera and change filters (using filter wheel).

 

IR-pass filter just lets IR light through (for example Astronomik Planet IR Pro 742 passes above 742nm), so no visible and no UV light.

Yes, but my filter wheels are set up for DSOs, plus all the 1.25" filters I have for planetary won't fit the 36mm filter wheels.

 

Yep, understood on the IR pass.  It just seems convenient to me to be able to capture RGB and IR in one pass, but wasn't sure if there was a processing reason not to do it that way.



#4 Tulloch

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Posted 14 October 2021 - 05:06 PM

I am getting back to some planetary imaging after a hiatus, and want to understand the most optimal workflow and equipment.

 

Current gear:

EdgeHD 9.25

Luminos 2.5 barlow (hope to get a 2x PowerMate soon)

ZWEO Atmospheric Dispersion Corrector

ASI290MC -- for RGB OSC using a UV/IR cut filter

FireCapture via USB3

 

Gear to add:

ASI462MC -- for IR with an IR-pass filter

 

My problem is that to either switch filters or switch cameras requires time -- then more time to focus.  With the multiple video runs per filter, Jupiter will rotate a fair amount and the IR images will see rotation compared to the RGB images.  So how do people do this with multiple filters?

 

I Googled around a bit, but couldn't find a UV-CUT/IR-PASS filter (or, I guess just a UV-Cut filter would be the same thing).  Such a thing would be awesome -- I don't want that skewed, bloated UV light but do want IR for the banding in the gas giants.  Is there some reason why capturing both RGB and IR in the same images would be bad?  I understand you can't really process them differently in that scenario, but wouldn't this be better than the 3-5 minutes it might take to switch cameras and refocus?

This is why you don't want to capture RGB and IR at the same time, the IR gets into all the colour channels and you cannot remove it.

https://www.planetar...ilter-asi224mc/

 

If you look at the spectral response of the ASI462MC, you can see that the RGB channels are more or less equally sensitive to IR - so not removing the IR will affect all the channels.

https://astronomy-im...t/asi462mccolor

 

I'm not sure why you think that an IR pass filter will still let UV through - they are usually high pass filters.

https://astronomy-im...b-specefication

 

If you don't have a filter wheel that takes an IR pass filter, you will need to pull the camera out, apply the filter, refocus etc. However, I'm not sure what you are trying to achieve...

 

Andrew



#5 PiotrM

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Posted 14 October 2021 - 05:06 PM

I am getting back to some planetary imaging after a hiatus, and want to understand the most optimal workflow and equipment.

 

 

I Googled around a bit, but couldn't find a UV-CUT/IR-PASS filter (or, I guess just a UV-Cut filter would be the same thing).  Such a thing would be awesome -- I don't want that skewed, bloated UV light but do want IR for the banding in the gas giants.  Is there some reason why capturing both RGB and IR in the same images would be bad?  I understand you can't really process them differently in that scenario, but wouldn't this be better than the 3-5 minutes it might take to switch cameras and refocus?

Visible spectrum would use IR/UV cut filter (L in LRGB filter ser) - and for planetary to work you have to use that ADC. UV-cut only would be longpass filter and would work only with excellent dispersion correction but for SCT I would use something similar and better - yellow and orange visual (Wratten) filters. Yellow passes IR + visible light except blue. Orange similar but cuts bit of green. SCT design causes them to have spherochromatism and spherical aberration at short wavelengths so cutting blue is quite handy at getting sharper "wide spectrum" images (ADC required as well). This would work best with mono cameras, less so with the color ones but you can try it. RGB with IR/UV cut and then false-L with Yellow Wratten filter to then compose a LRGB image.

 

Here is my old Jupiter: RGB, LRGB, Yellow-RGB, RedWratten-RGB. Colors change but you can also gain some sharpness. If L filter works then you are good with colors but if not then yellow could salvage things a bit:

 

2013-12-23-2300_0-RGB.jpg2013-12-23-2256_0-LRGB.jpg2013-12-23-2303_0-yellow-LRGB.jpg2013-12-23-2306_0-redlum-LRGB.jpg



#6 RedLionNJ

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Posted 15 October 2021 - 06:43 PM

Most glass attenuates UV pretty effectively.  Add to that the relative insensitivity of most common sensors to UV wavelengths and I wouldn't be too concerned about UV.

 

As far as the IR goes, block it out when capturing in OSC.  If you want to add it to your final image, you can have up to a few minutes to switch filters and refocus, then use Winjupos to align the IR with the RGB to form a final image.



#7 MountainAir

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Posted 15 October 2021 - 09:12 PM

This is why you don't want to capture RGB and IR at the same time, the IR gets into all the colour channels and you cannot remove it.

https://www.planetar...ilter-asi224mc/

 

If you look at the spectral response of the ASI462MC, you can see that the RGB channels are more or less equally sensitive to IR - so not removing the IR will affect all the channels.

https://astronomy-im...t/asi462mccolor

 

I'm not sure why you think that an IR pass filter will still let UV through - they are usually high pass filters.

https://astronomy-im...b-specefication

 

If you don't have a filter wheel that takes an IR pass filter, you will need to pull the camera out, apply the filter, refocus etc. However, I'm not sure what you are trying to achieve...

 

Andrew

This is very helpful thanks.  Not having imaged in IR before, I didn't realize how badly IR would affect the RGB frames.  Makes sense now-- RGB + IR need to be two stacks.

 

I didn't think that IR-PASS would let UV through, but I was looking for a filter that cut UV, but let through the visible spectrum and IR.  But as you stated above, that's a bad idea.

 

I do already have UV-IR Cut filters from ZWO and Baader, and an IR-PASS filter is on the way with the ASI462MC.  So I should be all set to image RGB without UV and IR, and IR without anything else.

 

Visible spectrum would use IR/UV cut filter (L in LRGB filter ser) - and for planetary to work you have to use that ADC. UV-cut only would be longpass filter and would work only with excellent dispersion correction but for SCT I would use something similar and better - yellow and orange visual (Wratten) filters. Yellow passes IR + visible light except blue. Orange similar but cuts bit of green. SCT design causes them to have spherochromatism and spherical aberration at short wavelengths so cutting blue is quite handy at getting sharper "wide spectrum" images (ADC required as well). This would work best with mono cameras, less so with the color ones but you can try it. RGB with IR/UV cut and then false-L with Yellow Wratten filter to then compose a LRGB image.

 

Here is my old Jupiter: RGB, LRGB, Yellow-RGB, RedWratten-RGB. Colors change but you can also gain some sharpness. If L filter works then you are good with colors but if not then yellow could salvage things a bit:

Thanks, also very useful.  I've probably bitten off as much as I can chew this season (I want to get my Edge back to DSOs), but I do have an ASI290MM I can use for color filters.  I just ran across this complex table with its 13 filter recommendations -- yikes, I'll need until next season to read up on 'em!




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