Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Will this filter work with ASI120mc

Astrophotography Beginner Eclipse Equipment Filters Imaging Reflector Solar
  • Please log in to reply
9 replies to this topic

#1 MyPetCactus

MyPetCactus

    Sputnik

  • -----
  • topic starter
  • Posts: 25
  • Joined: 02 Feb 2021

Posted 17 October 2021 - 12:37 PM

I have a 6" dob (1200mm FL) and an ASI120mc. I got some pretty good shots of planets. I want to get into solar imaging, and am planning to get a baader solar film filter. My question is, will the Baader Solar Continuum Filter (540nm) help me? Someone said that I will need to also get a UVIR filter, and doesnt reccomend doing it with a colored camera.Should I just get the film and end there?



#2 MalVeauX

MalVeauX

    Cosmos

  • *****
  • Posts: 9,744
  • Joined: 25 Feb 2016
  • Loc: Florida

Posted 17 October 2021 - 01:01 PM

Hi,

 

So, it's the same as planetary imaging, except, there's no color to image (so RGB sensors won't do anything special except have lower resolution at any single wavelength in particular). Sampling is the same. Seeing requirements are the same, etc. Using a narrowband filter with a color sensor will still work, just lower resolution, it's not like there's a lack of light coming in for transmission purposes. Things to consider is that your angular resolution increases as the wavelength decreases; but the shorter wavelengths are more effected by atmospheric turbulence and so your seeing is poor during the day time, and using a shorter wavelength at critical sampling requires significantly better seeing to sample; so what I'm getting at is that sure 540nm Continuum filter can be great, for its angular resolution potential and contrast of the photosphere, but it may not be usable if your seeing is poor, since you're using a 6 inch F8 system and 3.75um pixels, which means your critical sampling range is going to be around F18 approximately, and that's a lot to ask of your day time seeing (ie, somewhere around 0.6~0.7 arc-seconds seeing to record that resolution, which you most probably do not have). I would start with a basic red filter first. Longer wavelengths are less effected by the seeing conditions, so red to IR is a better place to start just to get an idea of your seeing conditions and what's possible. Then, if your seeing is superb, around 1 arc-second, you could explore shorter wavelengths like green or continuum ranges, or if seeing is excellent, you could explore near UV wavelengths; but I don't suggest this unless you have proof of your seeing conditions supporting it, otherwise, throwing money away.

 

So yea, get the film and stop there. See if you can even get sharp focus on the limb, or if your seeing simply doesn't support 6" F8 at 3.75um pixel size for the resulting image scale at full spectrum; then limit things from there.

 

Very best,



#3 MyPetCactus

MyPetCactus

    Sputnik

  • -----
  • topic starter
  • Posts: 25
  • Joined: 02 Feb 2021

Posted 17 October 2021 - 01:29 PM

Hi,

 

So, it's the same as planetary imaging, except, there's no color to image (so RGB sensors won't do anything special except have lower resolution at any single wavelength in particular). Sampling is the same. Seeing requirements are the same, etc. Using a narrowband filter with a color sensor will still work, just lower resolution, it's not like there's a lack of light coming in for transmission purposes. Things to consider is that your angular resolution increases as the wavelength decreases; but the shorter wavelengths are more effected by atmospheric turbulence and so your seeing is poor during the day time, and using a shorter wavelength at critical sampling requires significantly better seeing to sample; so what I'm getting at is that sure 540nm Continuum filter can be great, for its angular resolution potential and contrast of the photosphere, but it may not be usable if your seeing is poor, since you're using a 6 inch F8 system and 3.75um pixels, which means your critical sampling range is going to be around F18 approximately, and that's a lot to ask of your day time seeing (ie, somewhere around 0.6~0.7 arc-seconds seeing to record that resolution, which you most probably do not have). I would start with a basic red filter first. Longer wavelengths are less effected by the seeing conditions, so red to IR is a better place to start just to get an idea of your seeing conditions and what's possible. Then, if your seeing is superb, around 1 arc-second, you could explore shorter wavelengths like green or continuum ranges, or if seeing is excellent, you could explore near UV wavelengths; but I don't suggest this unless you have proof of your seeing conditions supporting it, otherwise, throwing money away.

 

So yea, get the film and stop there. See if you can even get sharp focus on the limb, or if your seeing simply doesn't support 6" F8 at 3.75um pixel size for the resulting image scale at full spectrum; then limit things from there.

 

Very best,

Thanks for the detailed reply. Where I'm at, seeing is constantly changing. It can be horrible, or perfect. Ive done great and horrible moon shots before, just because of a change of seeing. So are you suggesting for me to start at a red filter? Would there be drawbacks to using a green filter even in poor seeing. And I didnt really catch it, but would I need a UVIR filter to go with it?



#4 MalVeauX

MalVeauX

    Cosmos

  • *****
  • Posts: 9,744
  • Joined: 25 Feb 2016
  • Loc: Florida

Posted 17 October 2021 - 01:45 PM

Thanks for the detailed reply. Where I'm at, seeing is constantly changing. It can be horrible, or perfect. Ive done great and horrible moon shots before, just because of a change of seeing. So are you suggesting for me to start at a red filter? Would there be drawbacks to using a green filter even in poor seeing. And I didnt really catch it, but would I need a UVIR filter to go with it?

Hi,

 

I would start with red, especially if you already have one, and especially if seeing is not commonly good. If your night seeing is not superb all the time, you can surely expect your day time seeing to be awful all the time probably. Day time seeing is several magnitudes worse than night time even when its good. Red will handle bad seeing, better, than a shorter wavelength will. I would start there, with a polarizer filter (this helps with contrast on convection cells a lot). You can add UV/IR block if you want, but its not needed unless you want to ensure that it's extra-extra safe visually. For imaging, it may be useful to have if your imaging filter(s) do not have UV/IR blocking on them already. The drawback to using a green or continuum filter, in poor seeing, is that it will probably not even reach focus and will look like a boiling mushy mess, simply because the seeing is too poor at that image scale at that short of a wavelength. So again, longer wavelengths handle poor seeing better, they are less disturbed by turbulence. Shorter wavelengths are heavily effected by seeing conditions. So if seeing is bad, don't try to use short wavelength, it will be worse. When seeing is bad, use red or IR. When seeing is great, use shorter wavelength if you want more angular resolution and contrast (like green).

 

Very best,



#5 MyPetCactus

MyPetCactus

    Sputnik

  • -----
  • topic starter
  • Posts: 25
  • Joined: 02 Feb 2021

Posted 17 October 2021 - 02:29 PM

Hi,

 

I would start with red, especially if you already have one, and especially if seeing is not commonly good. If your night seeing is not superb all the time, you can surely expect your day time seeing to be awful all the time probably. Day time seeing is several magnitudes worse than night time even when its good. Red will handle bad seeing, better, than a shorter wavelength will. I would start there, with a polarizer filter (this helps with contrast on convection cells a lot). You can add UV/IR block if you want, but its not needed unless you want to ensure that it's extra-extra safe visually. For imaging, it may be useful to have if your imaging filter(s) do not have UV/IR blocking on them already. The drawback to using a green or continuum filter, in poor seeing, is that it will probably not even reach focus and will look like a boiling mushy mess, simply because the seeing is too poor at that image scale at that short of a wavelength. So again, longer wavelengths handle poor seeing better, they are less disturbed by turbulence. Shorter wavelengths are heavily effected by seeing conditions. So if seeing is bad, don't try to use short wavelength, it will be worse. When seeing is bad, use red or IR. When seeing is great, use shorter wavelength if you want more angular resolution and contrast (like green).

 

Very best,

Awesome, I see now. Will any cheap red filter do or do they have to be something legit? And if I get good seeing conditions, will the red help aswell or just do nothing? About polarizers, is there any example you can find/show compaing with it and without?



#6 MalVeauX

MalVeauX

    Cosmos

  • *****
  • Posts: 9,744
  • Joined: 25 Feb 2016
  • Loc: Florida

Posted 17 October 2021 - 02:40 PM

Awesome, I see now. Will any cheap red filter do or do they have to be something legit? And if I get good seeing conditions, will the red help aswell or just do nothing? About polarizers, is there any example you can find/show compaing with it and without?

Heya,

 

I wouldn't use any cheap filter, like a 20+ year old non-reflective coating based "visual" filter or something. I'm referring to imaging filters. They don't need to be super costly, but I would at least aim for a good quality filter that is good for visual and for imaging. An example for red would be the Baader 610nm long pass filter. It's technically a visual filter, but is a good imaging filter too (pair with a UV/IR block and its a complete red imaging filter and high quality, for cheap). Or any imaging based red filter (typically passes 600nm to 700nm and blocks the rest) from Baader, ZWO, Astronomik, etc, or anyone really. For the polarizer, a cheap GSO polarizer is totally fine.

 

Even if you think you might have good seeing conditions, it won't be good, it will just be less bad. The red filter will always help since you're using a large aperture (6 inches is a lot in solar). To even begin to come close to the angular resolution needs of red wavelengths around 650nm with that 150mm aperture, you would need around 0.8~0.9 arc-second seeing. You probably won't see this often, if ever, unless you live somewhere with excellent seeing conditions and even then probably only in the early morning as the sun is rising. You can always benefit having a red filter because you will always have poor seeing conditions. Having a green filter or shorter wavelength filter is great and all, if you have seeing to support it. Not many people are going to be able to show you images from a 150mm aperture with a green filter, critically sampled, with incredible convection cell clarity because most people simply do not have the seeing to support that image scale at that wavelength in poor seeing. A few can. But very few. That's high res territory and requires excellent seeing (0.8 arc-seconds or less to even start). I can't stress enough how critical seeing is to all of this and that day time seeing is really, really bad almost everywhere most of the day.

 

I'll try to dig up data that I have that shows what cells look like with zero processing with and without the polarizer. But it's rather significant for photosphere imaging, you want partially polarized light as it really does increase contrast significantly on the convection cells and spot structures, even visually, when I switch between them. A GSO polarizer filter is sufficient for this and they're dirt cheap. Use with any wavelength filter or full spectrum. Put it behind the other filters.

 

Very best,


Edited by MalVeauX, 17 October 2021 - 02:42 PM.


#7 MyPetCactus

MyPetCactus

    Sputnik

  • -----
  • topic starter
  • Posts: 25
  • Joined: 02 Feb 2021

Posted 17 October 2021 - 03:08 PM

Heya,

 

I wouldn't use any cheap filter, like a 20+ year old non-reflective coating based "visual" filter or something. I'm referring to imaging filters. They don't need to be super costly, but I would at least aim for a good quality filter that is good for visual and for imaging. An example for red would be the Baader 610nm long pass filter. It's technically a visual filter, but is a good imaging filter too (pair with a UV/IR block and its a complete red imaging filter and high quality, for cheap). Or any imaging based red filter (typically passes 600nm to 700nm and blocks the rest) from Baader, ZWO, Astronomik, etc, or anyone really. For the polarizer, a cheap GSO polarizer is totally fine.

 

Even if you think you might have good seeing conditions, it won't be good, it will just be less bad. The red filter will always help since you're using a large aperture (6 inches is a lot in solar). To even begin to come close to the angular resolution needs of red wavelengths around 650nm with that 150mm aperture, you would need around 0.8~0.9 arc-second seeing. You probably won't see this often, if ever, unless you live somewhere with excellent seeing conditions and even then probably only in the early morning as the sun is rising. You can always benefit having a red filter because you will always have poor seeing conditions. Having a green filter or shorter wavelength filter is great and all, if you have seeing to support it. Not many people are going to be able to show you images from a 150mm aperture with a green filter, critically sampled, with incredible convection cell clarity because most people simply do not have the seeing to support that image scale at that wavelength in poor seeing. A few can. But very few. That's high res territory and requires excellent seeing (0.8 arc-seconds or less to even start). I can't stress enough how critical seeing is to all of this and that day time seeing is really, really bad almost everywhere most of the day.

 

I'll try to dig up data that I have that shows what cells look like with zero processing with and without the polarizer. But it's rather significant for photosphere imaging, you want partially polarized light as it really does increase contrast significantly on the convection cells and spot structures, even visually, when I switch between them. A GSO polarizer filter is sufficient for this and they're dirt cheap. Use with any wavelength filter or full spectrum. Put it behind the other filters.

 

Very best,

Again, big thanks to these huge detailed answers. So does this "guideline" sound about right?

 

1. The solar film itself

2. Very preferably a red filter

3. Preferably a polarizer

 

And UV/IR filter is better to not have? Im not planning on doing visual, just imaging. 



#8 MalVeauX

MalVeauX

    Cosmos

  • *****
  • Posts: 9,744
  • Joined: 25 Feb 2016
  • Loc: Florida

Posted 17 October 2021 - 03:45 PM

Again, big thanks to these huge detailed answers. So does this "guideline" sound about right?

 

1. The solar film itself

2. Very preferably a red filter

3. Preferably a polarizer

 

And UV/IR filter is better to not have? Im not planning on doing visual, just imaging. 

Essentially yea,

 

I would suggest:

 

1 - Primary energy rejection filter assembly; inexpensive solar film to D-ERF range

2 - Wavelength selectivity filter; longer wavelength when seeing is poor, shorter wavelength when seeing is good to excellent

3 - Polarizer filter to partially polarize the light after the primary imaging filter (if the light is not already partially polarized)

 

Add UV/IR (or just IR) to any filter that you know to allow IR to pass (lots of filters already block this, some do not, simply refer to their transmission profile). Or add it when unsure and using something visually.

 

Very best,


Edited by MalVeauX, 17 October 2021 - 03:46 PM.


#9 hamers

hamers

    Viking 1

  • -----
  • Posts: 502
  • Joined: 16 Mar 2019
  • Loc: Madison, WI

Posted 17 October 2021 - 09:42 PM

I would definitely recommend the UV/IR cut filter.  Your camera has significant sensitivity all the way out to 1 micron, but your scope probably isn't well corrected out at such long wavelengths, so without an IR filter you might end up with defocused, long-wavelength light hitting your sensor.  As things go it's a moderate investment to up your changes of getting good results, and there's no down-side to it. In the 850 nm region the, R, G and B elements are *all* responding. 

https://astronomy-im...duct/asi120mc-s


Edited by hamers, 17 October 2021 - 09:43 PM.


#10 YossiZ

YossiZ

    Mariner 2

  • -----
  • Posts: 270
  • Joined: 21 Mar 2021

Posted 18 October 2021 - 06:20 AM

I'll try to dig up data that I have that shows what cells look like with zero processing with and without the polarizer.


That comparison would be very interesting to see. Thank you.
  • MalVeauX likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: Astrophotography, Beginner, Eclipse, Equipment, Filters, Imaging, Reflector, Solar



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics