Should I get a narrow band filter?

[Bc0428]

Hello there, I’m new to this hobby.
 
since I’m living under bortle 8 skies, and I would love to do some DSo photography, can it be done with a narrow band filter regardless the severe light pollution? It would be perfect if I could see the comparison that shows how effective the filter is. 
I saw some filter from STC is duo narrowband or multi spectra, is it better to buy them instead of filters with one wavelength only if I’m on low budget? Do they perform in the same way of single wavelength filter?
 
Besides, I bought an astronomik cls filter recently, it allows me to take longer shots but the colour becomes bluish, what should be done in photoshop to correct the colour tone? I searched online but seems quite confusing.
 
thanks a lot!
 

Edited June 14, 2020 by Bc0428

[Graham Darke]

Hello, welcome. 

Yes it can be done and a narrower band pass filter will help to cut through the light pollution for certain targets, basically emission nebulae and give you increased contrast. I live in Bortle 9 zone and have used an Astronomik UHC with a DSLR camera to much better effect than broadband filters. Your CLS filter with its wider band pass will be useful still for star clusters and galaxies. I assume that you are using a colour camera rather than mono? If mono then individual line filters (hydrogen alpha, oxygen III and sulphur II) work better.  

The STC Duo filter is just one option, there are also the Optolong L-eNhance, Altair Astro’s trio band and quad band filters and the  Astronomik UHC. Optolong have a new even narrower band filter called the L-eXtreme due out soon. What you are looking for is something that passes the light of hydrogen alpha and oxygen III and not much else. Many of these filters transmit the light from hydrogen beta and sulphur II too (hence tri and quad band designations) but with a colour camera the sulphur signal is lost in the red channel a bit.

To correct your colour balance in Photoshop, Have a look at the talk that Nik Szymanek gave recently on the Stargazine channel on YouTube.  There’s a link below. At 18 minutes in Nik explains the selective colour tool with the sliders. Have a play with those to see if it helps. 

 

[Bc0428]

2 minutes ago, Graham Darke said:

Hello, welcome. 

Yes it can be done and a narrower band pass filter will help to cut through the light pollution for certain targets, basically emission nebulae and give you increased contrast. I live in Bortle 9 zone and have used an Astronomik UHC with a DSLR camera to much better effect than broadband filters. Your CLS filter with its wider band pass will be useful still for star clusters and galaxies. I assume that you are using a colour camera rather than mono? If mono then individual line filters (hydrogen alpha, oxygen III and sulphur II) work better.  

The STC Duo filter is just one option, there are also the Optolong L-eNhance, Altair Astro’s trio band and quad band filters and the  Astronomik UHC. Optolong have a new even narrower band filter called the L-eXtreme due out soon. What you are looking for is something that passes the light of hydrogen alpha and oxygen III and not much else. Many of these filters transmit the light from hydrogen beta and sulphur II too (hence tri and quad band designations) but with a colour camera the sulphur signal is lost in the red channel a bit.

To correct your colour balance in Photoshop, Have a look at the talk that Nik Szymanek gave recently on the Stargazine channel on YouTube.  There’s a link below. At 18 minutes in Nik explains the selective colour tool with the sliders. Have a play with those to see if it helps. 

 

Thank you so much!

do separate filters perform better than those allow multiple wavelength? I am struggling which to buy...

[ollypenrice]

NB filters are staggeringly effective at beating LP. They work best with monochrome cameras because there is no colour matrix blocking the light on some pixels. They will only produce good standalone images on emission nebulae, though. Galaxies shot in HA only really show blobs of signal from HII regions. OIII and SII show little. Still, there are lots of emission nebulae out there.

Balancing the colour in Ps: once you've stretched the image, open up the histogram in All Channels View so you have separate histograms for each channel. As a rule of thumb try to get the top left hand side of the histo peaks aligned - ie the same distance from the left hand edge. You can only move them one way, ie to the left, and you do this by moving the black point slider for that channel to the right.

Since you can only move the peaks to the left it is vital during the stretch in Levels or Levels and Curves, to leave plenty of flat line to the left of the histo peaks.  The background will look pretty light but don't worry about that. It can be darkened later. For now you must have plenty of flat line to the left to allow you to clip it and move the peaks into alignment.

You can also put four colour sampler points on different parts of the background sky. The tool is in the Eyedropper menu. A good background sky, in my view, should be 23/23/23 per channel or a tad lower, but not lower than 20/20/20.

While this will balance your colours it will not get rid of colour gradients, unfortunately. Since you have Ps you might consider Russ Croman's Gradient Xterminator plug-in. It's not free but it's effective. The best gradient tool is Pixinsight's Dynamic Background Extraction but GradX is also good. Do not fight gradients by clipping the black point.

Olly

Edited June 14, 2020 by ollypenrice

[Graham Darke]

The very best quality images will always be obtained with a mono camera and individual line filters. If you are using a colour camera, however, then the filters I mentioned above will be your best bet. 

[Bc0428]

7 minutes ago, Graham Darke said:

The very best quality images will always be obtained with a mono camera and individual line filters. If you are using a colour camera, however, then the filters I mentioned above will be your best bet. 

I’m using eos r full frame

just curious, I read other threads saying that multi band is less flexible, so why it’s still recommended instead of individual line filter on colour camera ?

[Graham Darke]

There is nothing stopping you from using line filters with a colour camera but it’s not the most efficient method. For most people the whole point of colour cameras is capturing your shot in one go, without  swapping filters and that is what these multi band filters are for. They let you collect light for important emission bands at the same time. With a colour camera there is a Bayer matrix over the chip so some pixels collect red light, some  blue and some green. Every pixel on a colour camera is not sensitive to all wavelengths of light.

With a mono camera all pixels are sensitive to all wavelengths so by putting different filters in front of it and collecting different bands one at a time you are using all of the cameras pixels for each exposure. With your camera only one in every four pixels is sensitive to hydrogen alpha because of the Bayer matrix. 

As I said at the beginning there is nothing to stop you from using individual line filters with your colour camera and combining them later but you will be collecting light for twice or three times as long. You’d effectively be using a mono camera technique with a colour camera but you won’t replicate a mono cameras performance.  

[Bc0428]

47 minutes ago, Graham Darke said:

There is nothing stopping you from using line filters with a colour camera but it’s not the most efficient method. For most people the whole point of colour cameras is capturing your shot in one go, without  swapping filters and that is what these multi band filters are for. They let you collect light for important emission bands at the same time. With a colour camera there is a Bayer matrix over the chip so some pixels collect red light, some  blue and some green. Every pixel on a colour camera is not sensitive to all wavelengths of light.

With a mono camera all pixels are sensitive to all wavelengths so by putting different filters in front of it and collecting different bands one at a time you are using all of the cameras pixels for each exposure. With your camera only one in every four pixels is sensitive to hydrogen alpha because of the Bayer matrix. 

As I said at the beginning there is nothing to stop you from using individual line filters with your colour camera and combining them later but you will be collecting light for twice or three times as long. You’d effectively be using a mono camera technique with a colour camera but you won’t replicate a mono cameras performance.  

I see, thanks a lot!

[Graham Darke]

I only use colour cameras and I’m highly anticipating the arrival of Optolong’s new L-eXtreme filter which will have two very narrow bandpass windows  of just 7nm each centred on H alpha and O III. The other filters currently on offer are wider than this so I’m hoping this one will have an even more dramatic effect for emission nebulae from light polluted areas. 

[johnoelliott]

I live in Toronto Canada at a lovely Bortel 9.

I just picked up the Altair Tri-Band and am completely impressed!

Here is a single unprocessed 40 second unguided  sub of NGC7000 from my balcony  this past Friday just before the clouds started rolling in.

Please ignore the framing, was my first ever attempt at this target and I really didn't think I'd get anything from my location 

Have a field flattener , guide cam and scope on order and am looking forward to seeing just what this little setup can accomplish from my balcony... Celestron AVX, ES ED80 f/6 Air-Spaced Triplet, ASI224MC Pro, Altair Tri-Band

The SharpCap polar alignment process is incredible!  The way my balcony is situated, when I have my scope pointed at Polaris, I can just barely see it in the scope next to the edge of the balcony above me and I can't see it at all in my finder but SharpCap finds it and in just a minute or two, I have an excellent alignment ! 

NGC7000_00173 01_19_05_.fits