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#1 ParkerJohn

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Posted 08 March 2021 - 10:01 AM

I shot Bode's on three consecutive nights with an Optolong LPro, L-Extreme and then a ZWO UV/IR cut filter.  Is it better to stack them separately and merge later or stack them at the same time.  It may have been better choice to choose a single filter. I have tried doing both methods and did not see much difference.  Being new to this, it is at times hard to know what to do. 

 

I would appreciate any suggestions.

 

John



#2 sbharrat

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Posted 08 March 2021 - 10:50 AM

I shot Bode's on three consecutive nights with an Optolong LPro, L-Extreme and then a ZWO UV/IR cut filter.  Is it better to stack them separately and merge later or stack them at the same time.  It may have been better choice to choose a single filter. I have tried doing both methods and did not see much difference.  Being new to this, it is at times hard to know what to do. 

 

I would appreciate any suggestions.

 

John

Newbie here (joined after you) so take with some skepticism. 

#1. Most people will argue that for a a broadband target, you wouldn't want to use L-Extreme. Many will also argue against L-Pro as well on a galaxy. 

#2. I don't know definitively but the characteristics of subs with these filters are likely to be very different. Given that, I can see the rejection algorithms in stacking having errors in picking out outliers to discard/replace if they are all stacked together. Using straigh logic, I would stack separately. Of course, I have been coached multiple times that nothing in AP is intuitive so I would wait for additional opinions.

 

Cheers


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#3 sg6

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Posted 08 March 2021 - 10:59 AM

I would say the UV/IR cut is not supplying much, oddly and unfortunately it could be simply supplying the light pollution that the L-Pro removed, or should remove. The L-Pro cuts UV and IR much the same as a UV/IR cut does.

The L-Pro is the "useful" one, it is passing from Blue to Red and hopefully cutting out Na and Hg light pollution,

The L-Extreme is a fairly narrow 2 wavelength pass at the OIII and the Ha peaks.

 

So I would say:

The UV/IR cut is in effect doing or adding nothing other then adding the LP that the other 2 remove. In effect somewhat negative.

The L-Pro is the one collecting "most" of your color while managing to still remove the Na and Hg light pollution.

The L-Enhance is just collecting extra OIII and Ha to add to the final result/stack, if wanted.

 

I would remove the UV/IR component,

Stack the L-Pro, and for extra OIII and Ha add the L-Enhance to the stack.


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#4 Alex McConahay

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Posted 08 March 2021 - 11:16 AM

So, what we have are three OSC color pictures, each emphasizing a slightly different color. And because the colors are different, the details they bring out would be different.

 

I should think that which is the best would depend a lot on  the target.

 

The first thing I would do is register all the calibrated shots to the same master shot----whatever shot of the whole bunch regardless of filter was the sharpest, etc. You do not want to be re-registering over and over again. 

 

Then, I would first stack the groups separately by filter. And I would process them to the point of a good stretch and color correction. Then I would determine which is the nicest shot. Which has the best definition of the detail I wanted to see.

 

Then, I might go back and stack the whole pile together for noise control. And use the master from the filter I thought the nicest to provide the color and luminance to the other (whole) stack.

 

But really, you said you do not see much difference. I think that will still be true. But, you know, you have the data. Go run your experiment. 

Alex


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#5 BobE102330

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Posted 08 March 2021 - 11:18 AM

Shaun has it right, IMO.  Broadband targets need broadband signal capture.  Guessing that you have a OSC dedicated astro camera, given the filters you've collected.  IF the sensor window does not provide UV/IR cut, then use that filter, otherwise shoot unfiltered.  If an unmodified DSLR, no filter for broadband targets like galaxies.

 

Also guessing that since you are heavily invested in filters you're in a fairly light polluted area.  Shoot exposures as long as you can to without blowing out too many stars.  Just shoot lots of subs.  If you'd shot three nights unfiltered you could have around 18 hours and start to get a decent signal to noise ratio even from Bortle 7 or so.  Best for broadband targets to go someplace dark, though.  A single night in Bortle 3-4 will get better results than 3 in Bortle 7.  

 

As SG6 suggests, adding a bit of Ha to enhance star forming regions is helpful sometimes.  Take the red channel from your L-Enhance stack to add that in to your other data.  See if you can get anything decent out of the L-Enhance data on its own, if so, add in the broadband data.  Despite the horror stories about the learning curve, Pixinsight's pixel math makes adding the stacks together fairly easy.  Before I got it, I tried stacking various exposure types together and color balancing later.  Sometimes it worked, others not so much.  

 

Good luck 


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#6 ParkerJohn

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Posted 08 March 2021 - 05:04 PM

Thanks for all of the comments and suggestions.  I am in Bortle 6. I have a ZWO ASI294MC Pro.  I have the L-Extreme not the L-Enhance.  I may want to consider it.  I am just learning PixInsight so I will look into Pixel Math.

 

John


Edited by ParkerJohn, 08 March 2021 - 05:21 PM.


#7 jonnybravo0311

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Posted 08 March 2021 - 05:10 PM

OK... quick rule of thumb:

 

L-eXtreme / L-eNhance: emission nebulae ONLY. Not for use on broadband / reflection nebulae. Caveat: you can use them if you want to add Ha to an RGB broadband image (i.e. bringing out some of the Ha regions in Andromeda)

L-Pro / CLS / Whatever: sell them. Take more subs.



#8 ParkerJohn

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Posted 08 March 2021 - 06:01 PM

OK... quick rule of thumb:

 

L-eXtreme / L-eNhance: emission nebulae ONLY. Not for use on broadband / reflection nebulae. Caveat: you can use them if you want to add Ha to an RGB broadband image (i.e. bringing out some of the Ha regions in Andromeda)

L-Pro / CLS / Whatever: sell them. Take more subs.

Am I understand you to say sell the L-Pro? If that is the case then what do you suggest for Bode's or M31?



#9 sbharrat

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Posted 08 March 2021 - 06:09 PM

Am I understand you to say sell the L-Pro? If that is the case then what do you suggest for Bode's or M31?

The preponderance of answers for galaxies will be no filter. (Or just UV/IR if needed by your camera.)


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#10 jonnybravo0311

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Posted 08 March 2021 - 06:09 PM

That would be the second sentence: take more subs.

 

I'm not a fan of the light pollution filters - especially not on a broadband target like a galaxy. Light pollution filters by definition strip out swaths of the spectrum. They are NOT a magic bullet.

 

Think about it this way. If you were at a Bortle 1 site, would you use the L-Pro or CLS or anything like it?


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