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UV-IR Cut filter for Galaxies?

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#1 sdeming

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Posted 21 February 2021 - 07:00 PM

Hello Friends!

 

I purchased a UV-IR Cut filter specifically for imaging galaxies. I used it the other night and the amount of noise and grain in the sky was unreal. It was quite washed out. I kept the gain and offset exactly the same as when I'm shooting with just a LP filter. Did I misunderstand that these UV-IR cut filters are good for galaxies? I also have a CLS light pollution filter. Should I put that on with the cut filter? 

 

Thank you in advance for your help!

 

Scott



#2 RogerM

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Posted 21 February 2021 - 07:12 PM

What filter model/manufacturer?  A UV-IR has a bandpass spectrum that allows for good color transmission so yes, it's okay to use when imaging broadband targets like Galaxies.

 

However, just by the up front fact that you see 'noise and grain' could indicate poor signal to noise and that you need to increase your total integration time but that is only one possibility.

 

Please post specifics about your set-up (camera/telescope/lens as well as sub length & number of subs integrated) and an image so that we can see what you are seeing.  This will help immensely for you to receive a more detailed solution to your woes.



#3 hamers

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Posted 21 February 2021 - 07:13 PM

Hi-  More info on the specifics of the filter and wavelength response if known would be useful.  Do you have these available?



#4 sdeming

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Posted 21 February 2021 - 08:21 PM

What filter model/manufacturer?  A UV-IR has a bandpass spectrum that allows for good color transmission so yes, it's okay to use when imaging broadband targets like Galaxies.

 

However, just by the up front fact that you see 'noise and grain' could indicate poor signal to noise and that you need to increase your total integration time but that is only one possibility.

 

Please post specifics about your set-up (camera/telescope/lens as well as sub length & number of subs integrated) and an image so that we can see what you are seeing.  This will help immensely for you to receive a more detailed solution to your woes.

Thank you for your help. Here are my particulars.

 

Baader UV-IR Cut L filter

Orion 8" f3.9 Newtonian

QHY294C imaging camera

120 sixty second lights - 1600 gain, offset 10

40 darks

40 flats

40 dark flats

Attached Thumbnails

  • uv-ir-cut-filter-transmission_2.jpg


#5 sdeming

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Posted 21 February 2021 - 08:23 PM

Hi-  More info on the specifics of the filter and wavelength response if known would be useful.  Do you have these available?

Hi and thank you! I posted information above. 



#6 sdeming

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Posted 21 February 2021 - 08:32 PM

Here's another chart.

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  • uv-ir_cut_solar_spectrum_chart_2.jpg


#7 RogerM

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Posted 21 February 2021 - 08:47 PM

I am using that exact filter and haven't observed any increase in noise/grain due to using it.  Please post an image taken with your current set-up using this filter.



#8 rj144

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Posted 21 February 2021 - 08:50 PM

Well, I'm trying to post a typical galaxy spectrum and the site says I can't post a jpg for some reason.  (Have many times in the past.)

 

I made this mistake when imaging a galaxy at first too.  You're cutting out a lot of the spectrum.  I don't use a filter for galaxies now.



#9 sdeming

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Posted 21 February 2021 - 08:54 PM

I am using that exact filter and haven't observed any increase in noise/grain due to using it.  Please post an image taken with your current set-up using this filter.

Hi Roger. I am not at my office computer, but will post an image in the morning. Do you find it beneficial using this filter for galaxies, as opposed to no filter at all?

 

Thank you for your help!



#10 sdeming

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Posted 21 February 2021 - 08:56 PM

Well, I'm trying to post a typical galaxy spectrum and the site says I can't post a jpg for some reason.  (Have many times in the past.)

 

I made this mistake when imaging a galaxy at first too.  You're cutting out a lot of the spectrum.  I don't use a filter for galaxies now.

What are these filters for? I know you're not supposed to use them on nebulae. I use a narrowband filter for nebulae. 



#11 sdeming

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Posted 21 February 2021 - 08:56 PM

Well, I'm trying to post a typical galaxy spectrum and the site says I can't post a jpg for some reason.  (Have many times in the past.)

 

I made this mistake when imaging a galaxy at first too.  You're cutting out a lot of the spectrum.  I don't use a filter for galaxies now.

Try resizing your image. I've made that mistake many times.


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#12 jonnybravo0311

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Posted 21 February 2021 - 09:11 PM

OK... let's sort through this.

 

The 294MC sensor does not have any UV or IR filters in front of it. Therefore, it will be susceptible to those wavelengths, which will cause bloat / blooming. The reason you would use a UV/IR cut filter is to eliminate that.

 

A UV/IR cut filter does ABSOLUTELY NOTHING for your light pollution. The filter allows the entire spectrum (from ~400nm to ~700nm) through. This is a GOOD thing for galaxies and other broadband targets. You DON'T want to block any of the spectrum.

 

The LP filter strips out swaths of the spectrum in an effort to combat the artificial lights we humans developed to illuminate the night. Since the vast majority of these lights use sodium and mercury, the LP filters block those wavelengths.

 

The likely reason you're seeing "more noise and grain" now is because at the same gain/offsets more light is hitting the sensor using the UV/IR filter than was hitting it using the LP filter. Ultimately, the solution is to take more subs and have a lot more total integration time.

 

To answer your other question, no you don't stack the two filters... even if you could.


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#13 sdeming

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Posted 21 February 2021 - 09:19 PM

OK... let's sort through this.

 

The 294MC sensor does not have any UV or IR filters in front of it. Therefore, it will be susceptible to those wavelengths, which will cause bloat / blooming. The reason you would use a UV/IR cut filter is to eliminate that.

 

A UV/IR cut filter does ABSOLUTELY NOTHING for your light pollution. The filter allows the entire spectrum (from ~400nm to ~700nm) through. This is a GOOD thing for galaxies and other broadband targets. You DON'T want to block any of the spectrum.

 

The LP filter strips out swaths of the spectrum in an effort to combat the artificial lights we humans developed to illuminate the night. Since the vast majority of these lights use sodium and mercury, the LP filters block those wavelengths.

 

The likely reason you're seeing "more noise and grain" now is because at the same gain/offsets more light is hitting the sensor using the UV/IR filter than was hitting it using the LP filter. Ultimately, the solution is to take more subs and have a lot more total integration time.

 

To answer your other question, no you don't stack the two filters... even if you could.

Wow! Thank you for such a detailed answer. I just went to school! I did notice the stars were much less bloated using the filter, which is always a good thing when trying to stretch an image. I ran out of time the other night. Next time I will get more integration time in and see how things look after that. Again, thank you!



#14 imtl

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Posted 21 February 2021 - 09:56 PM

OK... let's sort through this.

 

The 294MC sensor does not have any UV or IR filters in front of it. Therefore, it will be susceptible to those wavelengths, which will cause bloat / blooming. The reason you would use a UV/IR cut filter is to eliminate that.

 

A UV/IR cut filter does ABSOLUTELY NOTHING for your light pollution. The filter allows the entire spectrum (from ~400nm to ~700nm) through. This is a GOOD thing for galaxies and other broadband targets. You DON'T want to block any of the spectrum.

 

The LP filter strips out swaths of the spectrum in an effort to combat the artificial lights we humans developed to illuminate the night. Since the vast majority of these lights use sodium and mercury, the LP filters block those wavelengths.

 

The likely reason you're seeing "more noise and grain" now is because at the same gain/offsets more light is hitting the sensor using the UV/IR filter than was hitting it using the LP filter. Ultimately, the solution is to take more subs and have a lot more total integration time.

 

To answer your other question, no you don't stack the two filters... even if you could.

Actually just to add a bit to this. It's better to get a UV-IR filter with a cutoff at 420nm since most refractors start to suffer quite a bit below that.


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#15 RogerM

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Posted 21 February 2021 - 11:58 PM

Eyal, that is exactly why I chose the Baader filter, most other filter manufacturer’s UV-IR (Luminosity for those shooting mono) have a range typically at 400nm to around 700nm.  On my rig being just a doublet, the difference in moving the upper cutoff down to about 680nm made a significant improvement in star profiles.



#16 RogerM

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Posted 22 February 2021 - 12:05 AM

Hi Roger. I am not at my office computer, but will post an image in the morning. Do you find it beneficial using this filter for galaxies, as opposed to no filter at all?

 

Thank you for your help!

Instead of retyping, here is a post I made in reply to another CN’er with about the same concern as yours.  In it I also talked about the use of another filter (prior to my using the Baader) in my search for a solution to LP.



#17 sdeming

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Posted 22 February 2021 - 08:03 AM

Instead of retyping, here is a post I made in reply to another CN’er with about the same concern as yours.  In it I also talked about the use of another filter (prior to my using the Baader) in my search for a solution to LP.

THank you. I read the entire thread. Much of it seems to focus on refractors and I am using a Newtonian. Someone mentioned more integration to improve SNR. Should I lower my exposure time and double the number of subs, or keep my exposure time the same and just add as many subs as time will allow? For M51 I took 60 second subs.



#18 unimatrix0

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Posted 22 February 2021 - 08:13 AM

Is it possible, that it was rather your sky was hazy , although clear? 
Happens to me all the time. First, I blame my camera, then I check the lens what's going on, then I see the humidity report. 

I can barely can get any good shots, and that makes me pack up for the night. 



#19 sdeming

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Posted 22 February 2021 - 08:27 AM

Is it possible, that it was rather your sky was hazy , although clear? 
Happens to me all the time. First, I blame my camera, then I check the lens what's going on, then I see the humidity report. 

I can barely can get any good shots, and that makes me pack up for the night. 

It was mid 30s and very dewy. 



#20 sdeming

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Posted 22 February 2021 - 10:54 AM

What filter model/manufacturer?  A UV-IR has a bandpass spectrum that allows for good color transmission so yes, it's okay to use when imaging broadband targets like Galaxies.

 

However, just by the up front fact that you see 'noise and grain' could indicate poor signal to noise and that you need to increase your total integration time but that is only one possibility.

 

Please post specifics about your set-up (camera/telescope/lens as well as sub length & number of subs integrated) and an image so that we can see what you are seeing.  This will help immensely for you to receive a more detailed solution to your woes.

Here is an auto stretched image from PixInsight straight from the stack. No processing.

Attached Thumbnails

  • M51 Stacked TIFF to JPEG resized.jpg

Edited by sdeming, 22 February 2021 - 10:59 AM.


#21 TxStars

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Posted 22 February 2021 - 05:28 PM

Part of the reason for the filter in a refractor other than reducing blue halo's is to maintain proper spacing when using a mono camera ,flattener/coma corrector  & filter wheel combo..

With a reflector you could just use a clear filter..


Edited by TxStars, 22 February 2021 - 07:03 PM.


#22 RogerM

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Posted 01 March 2021 - 10:46 PM

Here is an auto stretched image from PixInsight straight from the stack. No processing.

 

Need to know how many subs and exposure time/sub were used for your posted image.

 

 

Can only take a 'wild guess' just looking at an undocumented image as to what's going on.

 

FWIW, taken at face value your posted image has a significant gradient and the washed out appearance could be either that you overstretched it or even that your individual sub exposure times are too long allowing background levels to swamp out your target signal.

 

Hard to work with a posted jpg image and I'm no wizard but this is after I extracted wavelet layers to isolate and reduce as much gradient as possible, further masking and adjusting curves.  There's more that can be done... you have data to work with.

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  • sdeming.jpg



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