G band instead of Ca-k filter

[Stardust5858]

Hi all, would anyone know if this filter would work for G-Band imaging/observations. From Edmand Scientific 430nm CWL, 25mm Dia., Hard Coated OD 4.0 10nm Bandpass Filter. Obviously I'd use a pre filter probably baader solar film. Possibly on either my C11 f10 or 80ED f7. Appreciate any input.

[marktownley]

Yes it would work, you might find you need a UV/IR filter with it too. I'd cut your teeth with the 80mm first rather than the c11.

[Stardust5858]

Yes it would work, you might find you need a UV/IR filter with it too. I'd cut your teeth with the 80mm first rather than the c11.

Thanks Mark, appreciate your input. Not seen much about people going down this road but read a post on here. It's interesting as the cost isn't prohibited at around £177.

[Bob Yoesle]

An f10 achromatic refractor is your best bet for significantly better spherochromatic aberration at 430 nm:

https://www.telescope-optics.net/achromats.htm


A shorter f ratio APO or semi-APO (except Tak TAO 130/150 ;-) will generally not perform as well:

https://www.telescope-optics.net/semiap ... amples.htm


A SCT will be pretty poor at 430 nm, but with a suitable corrector lens, may be capable of much better results:

http://www.astrosurf.com/viladrich/astr ... C8Edge.htm

http://articles.adsabs.harvard.edu/cgi- ... etype=.pdf

[DeepSolar64]

Bob,

I always wondered what wavelength G band was. So it's 430 nm? That's in the blue-violet region of the spectrum. That would be quite a bit easier to see visually than CaH or CaK would be. What features would that concentrate on? PhotoSphere-Chromosphere transition region?

And I have an F10 achromatic refractor!

James

[Carbon60]

Hi,
I occasionally use the same filter on the output side of my Lacerta wedge with the brightness toned down with a suitably rotated polarising filter. I also have a UV/IR filter attached to the input side of the wedge for additional protection.

The ‘G-band’ at 10nm FWHM is not particularly tight, but it seems to enhance the granulation and faculae with a little more contrast than does my 540nm filter. I haven’t given it a full test drive in high res yet to see if it shows up any so called bright lanes between granules, so this is something to try in the spring with better conditions. A 2nm version may be better, if you can find one, but this filter works okay, as I say, for WL images with slightly improved contrast, but then that can also be achieved with processing.

Stu.

[Stardust5858]

Hi,
I occasionally use the same filter on the output side of my Lacerta wedge with the brightness toned down with a suitably rotated polarising filter. I also have a UV/IR filter attached to the input side of the wedge for additional protection.

The ‘G-band’ at 10nm FWHM is not particularly tight, but it seems to enhance the granulation and faculae with a little more contrast than does my 540nm filter. I haven’t given it a full test drive in high res yet to see if it shows up any so called bright lanes between granules, so this is something to try in the spring with better conditions. A 2nm version may be better, if you can find one, but this filter works okay, as I say, for WL images with slightly improved contrast, but then that can also be achieved with processing.

Stu.

Thanks Stu

[Stardust5858]

Another thought, would stacking up with a double stack430nm CWL, 25mm Dia., Hard Coated OD 4.0 10nm result in a narrower band of 5nm or am I being really stupid.

[marktownley]

Another thought, would stacking up with a double stack420nm CWL, 25mm Dia., Hard Coated OD 4.0 10nm result in a narrower band of 5nm or am I being really stupid.

Simple answer, no!

G-Band imaging to be 'true' G-band needs to be considerably narrower, like Ha or CaK - ultra narrowband. The 430nm filter is effectively only a narrow band filter, where it benefits is the shorter wavelength gives increased resolution over 540nm.

[rsfoto]

Another thought, would stacking up with a double stack420nm CWL, 25mm Dia., Hard Coated OD 4.0 10nm result in a narrower band of 5nm or am I being really stupid.

Simple answer, no!

G-Band imaging to be 'true' G-band needs to be considerably narrower, like Ha or CaK - ultra narrowband. The 430nm filter is effectively only a narrow band filter, where it benefits is the shorter wavelength gives increased resolution over 540nm.

Hi Mark,

... where it benefits is the shorter wavelength gives increased resolution ...

Resolution or Contrast ?

[marktownley]

Simple answer, no!

G-Band imaging to be 'true' G-band needs to be considerably narrower, like Ha or CaK - ultra narrowband. The 430nm filter is effectively only a narrow band filter, where it benefits is the shorter wavelength gives increased resolution over 540nm.

Hi Mark,

... where it benefits is the shorter wavelength gives increased resolution ...

Resolution or Contrast ?
[/quote]

Hi Rainer.

Resolution certainly yes, if the seeing allows then for a given aperture a the shorter wavelength gives higher resolution compared to continuum - 1.25x in fact. So, using a 430nm filter on a 100mm scope would give the same resolution as using a 540nm filter on a 125mm scope.

In terms of contrast I have no first hand experience, however I do fancy trying to image at these shorter wavelengths. The other thing to think about is it is very likely the telescopes strehl ratio will be lower at 430nm than 540nm - most scopes are best corrected for the green where our eyes are most sensitive. This will impact i'm sure.

'True' G-band is centred on 430nm +/-1nm, so, a 10nm filter really isn't narrow enough by far and is only giving a 'blue' white light view really.

As this solar cycle picks up a bit, it is something I will likely explore more.

Mark

[marktownley]

Here's a good paper on G-Band http://articles.adsabs.harvard.edu//ful ... 3.000.html

[rsfoto]

Simple answer, no!

G-Band imaging to be 'true' G-band needs to be considerably narrower, like Ha or CaK - ultra narrowband. The 430nm filter is effectively only a narrow band filter, where it benefits is the shorter wavelength gives increased resolution over 540nm.

Hi Mark,

... where it benefits is the shorter wavelength gives increased resolution ...

Resolution or Contrast ?

Hi Rainer.

Resolution certainly yes, if the seeing allows then for a given aperture a the shorter wavelength gives higher resolution compared to continuum - 1.25x in fact. So, using a 430nm filter on a 100mm scope would give the same resolution as using a 540nm filter on a 125mm scope.

In terms of contrast I have no first hand experience, however I do fancy trying to image at these shorter wavelengths. The other thing to think about is it is very likely the telescopes strehl ratio will be lower at 430nm than 540nm - most scopes are best corrected for the green where our eyes are most sensitive. This will impact i'm sure.

'True' G-band is centred on 430nm +/-1nm, so, a 10nm filter really isn't narrow enough by far and is only giving a 'blue' white light view really.

As this solar cycle picks up a bit, it is something I will likely explore more.

Mark
[/quote]

Hi Mark,

So by just putting a 430 nm filter instead of 540 nm filter I resolve more details ? For me resolution is for example 1" arc second per pixel or 0.5" arc second per pixel and 0.5" arc second per pixel is more resolution then 1.0" ...

How does that work if I use the same scope, the same camera that I get finer details = more resolution ?

Sorry but still very confused ...

[Stardust5858]

Still interesting enough to put on the Santa list, lol. Thanks Mark.

[Bob Yoesle]

Resolution is wavelength dependent. So a shorter wavelength with the same aperture has the potential to have higher resolution if the optics and seeing conditions allow. For imaging of course you would need to match pixel size to the higher resolution to realize the benefit.

For example, the difference between H alpha and CaK is 656/394 nm = 1.66. Therefore imaging CaK with the same telescope will have 1.66 times the resolution of the H alpha. Equivalently you would need a 166 mm aperture telescope for H alpha to obtain the same resolution of CaK with 100 mm of aperture.

[MalVeauX]

Heya,

I have that filter (the E.O. 430nm 10nm OD4). Unfortunately it's not narrow enough to show Gband features. Andover used to have the filter that was narrow enough to be close to showing Gband features (it's $211, 2nm bandpass, but still basically too wide to show the Gband features, but it's never in stock for years now).

Also, the unique feature of Gband is very tiny and requires extraordinary seeing conditions and a very large aperture at critical sampling to achieve, the iron bits between convection cells, bright spots basically, are what are unique to the 430nm wavelength in the photosphere. It takes about a 10" aperture at critical sampling and it takes way more narrow bandpass, more like 1A~2A to even begin to to see the bright spots. So if you're not using a very narrow filter like that, and you're not resolving with a huge aperture, you're really not going to see anything special in 430nm photosphere imaging that you wouldn't already see with 540nm continuum or any other wavelength of photosphere. That means you need sub-arc-second seeing conditions (so basically go to a mountain top or an island with no jetstream, etc, you have to go to unique places on Earth to get that kind of seeing routinely and steady for this purpose).

The only benefit outside of that is that it's 430nm and thus higher angular resolution, so you could critically sample it and do higher resolution than 540nm continuum or similar common wavelengths. But if you're just going for angular resolution, then 430nm isn't what I would get, instead, look to a 395nm near UV (conintuum A) filter that is as narrow as possible, but be prepared to only use long focal-ratio refractors or newtonians (avoid SCT/Mak with fast mirrors, huge SA in these short wavelengths, not worth it).

So I use the E.O. 430nm filter basically for its angular resolution, with a long achromatic doublet refractor and a longer focal-ratio newtonian mirror (F6 or longer, Quartz) because these short wavelengths are not friendly with other optics that are fast focal-ratio and not figured for near UV and short wavelength like Calcium, Continuum A and Gband (ie, don't' use an SCT/Mak; the SA is too much and its useless basically, compared to just using a long focal-ratio refractor and/or newtonian mirror).

I use the Baader Blue CCD-IR block filter (2") as my sub-aperture D-ERF for 430nm when I'm using a refractor, no need for any special front mounted D-ERF for this. I then use a Baader 10 stop ND filter to cut transmission as the transmission is saturating even at 0.03ms exposure time with this. The 10 stop makes it reasonable and still very short (less than 1ms). Then the E.O. 430nm filter. I use a 290MM for this, for 2.9um pixels; 430nm critically samples at F16 on 2.9um pixels. For my 200mm F6 newtonian, I just use Baader Photo Grade Solar Film and the same 10 stop ND filter and the E.O. 430nm filter for the same effect, but it needs the film filter since its a mirror design.

Anyhow, here's results with this E.O. filter, under moderately high resolution with sub-arc-second seeing conditions. But 10nm bandpass simply won't show the unique Gbrand bright spots between the convection cells, and not at 8" aperture either. You'd need bigger aperture, better seeing, and a more narrow bandpass filter.

200mm F6 Quartz Newt with ND3.8 Baader Solar Film & E.O. 430nm 10nm Filter:

baader_solarfilm_ND38_200mmF6Newt_03112020.jpg (228.85 KiB) Viewed 610 times

And here's from a 150mm F8 achromatic doublet with the Baader Blue CCD-IR Block filter as an internal D-ERF with the E.O. 430nm filter:



My advice: don't buy this filter for Gband. If you want higher angular resolution, get 395nm and really good seeing and use a big refractor or long focal-ratio newtonian. Otherwise, stick to 540nm or longer wavelength on any instrument type.

Very best,

[Stardust5858]

Heya,

I have that filter (the E.O. 430nm 10nm OD4). Unfortunately it's not narrow enough to show Gband features. Andover used to have the filter that was narrow enough to be close to showing Gband features (it's $211, 2nm bandpass, but still basically too wide to show the Gband features, but it's never in stock for years now).

Also, the unique feature of Gband is very tiny and requires extraordinary seeing conditions and a very large aperture at critical sampling to achieve, the iron bits between convection cells, bright spots basically, are what are unique to the 430nm wavelength in the photosphere. It takes about a 10" aperture at critical sampling and it takes way more narrow bandpass, more like 1A~2A to even begin to to see the bright spots. So if you're not using a very narrow filter like that, and you're not resolving with a huge aperture, you're really not going to see anything special in 430nm photosphere imaging that you wouldn't already see with 540nm continuum or any other wavelength of photosphere. That means you need sub-arc-second seeing conditions (so basically go to a mountain top or an island with no jetstream, etc, you have to go to unique places on Earth to get that kind of seeing routinely and steady for this purpose).

The only benefit outside of that is that it's 430nm and thus higher angular resolution, so you could critically sample it and do higher resolution than 540nm continuum or similar common wavelengths. But if you're just going for angular resolution, then 430nm isn't what I would get, instead, look to a 395nm near UV (conintuum A) filter that is as narrow as possible, but be prepared to only use long focal-ratio refractors or newtonians (avoid SCT/Mak with fast mirrors, huge SA in these short wavelengths, not worth it).

So I use the E.O. 430nm filter basically for its angular resolution, with a long achromatic doublet refractor and a longer focal-ratio newtonian mirror (F6 or longer, Quartz) because these short wavelengths are not friendly with other optics that are fast focal-ratio and not figured for near UV and short wavelength like Calcium, Continuum A and Gband (ie, don't' use an SCT/Mak; the SA is too much and its useless basically, compared to just using a long focal-ratio refractor and/or newtonian mirror).

I use the Baader Blue CCD-IR block filter (2") as my sub-aperture D-ERF for 430nm when I'm using a refractor, no need for any special front mounted D-ERF for this. I then use a Baader 10 stop ND filter to cut transmission as the transmission is saturating even at 0.03ms exposure time with this. The 10 stop makes it reasonable and still very short (less than 1ms). Then the E.O. 430nm filter. I use a 290MM for this, for 2.9um pixels; 430nm critically samples at F16 on 2.9um pixels. For my 200mm F6 newtonian, I just use Baader Photo Grade Solar Film and the same 10 stop ND filter and the E.O. 430nm filter for the same effect, but it needs the film filter since its a mirror design.

Anyhow, here's results with this E.O. filter, under moderately high resolution with sub-arc-second seeing conditions. But 10nm bandpass simply won't show the unique Gbrand bright spots between the convection cells, and not at 8" aperture either. You'd need bigger aperture, better seeing, and a more narrow bandpass filter.

200mm F6 Quartz Newt with ND3.8 Baader Solar Film & E.O. 430nm 10nm Filter:

baader_solarfilm_ND38_200mmF6Newt_03112020.jpg



And here's from a 150mm F8 achromatic doublet with the Baader Blue CCD-IR Block filter as an internal D-ERF with the E.O. 430nm filter:



My advice: don't buy this filter for Gband. If you want higher angular resolution, get 395nm and really good seeing and use a big refractor or long focal-ratio newtonian. Otherwise, stick to 540nm or longer wavelength on any instrument type.

Very best,

Many thanks for this, very informative. Will have to have a rethink.

[MalVeauX]

Many thanks for this, very informative. Will have to have a rethink.

What kind of seeing conditions are you commonly seeing? Not your best ever. But your more likely seeing conditions? Short wavelength is very much effected by atmospheric seeing, unlike long wavelength which is less effected so it appears more steady at the loss of angular resolution. The increase in contrast using 430nm or any other shorter wavelength is relative to its resolution, higher resolution (if sampled appropriately and not limited by seeing), less blur, more contrast on transitions. But you have to have sub-arc-second seeing for this with a large aperture (even 6 inches is pushing it with 393~430nm near UV and into blue wavelengths). To attempt it with a C11, you'd have to follow Christian up into a mountain top to get that good 0.3" seeing to attempt 430nm or 395nm at critical sampling with an aperture like that.

If you've already exhausted and tapped out red and near IR wavelengths with your C11 for photosphere imaging, then by all means, go where you're next challenge is. But if you've not gotten some critically sampled red/IR wavelength convection cell/spot images with your C11, then start there first. You still need sub-arc-second seeing but your odds of lucky imaging are significantly higher than attempting it with 395~430nm.

Here's an example of the kind of seeing I need to even begin to attempt 430nm or 393nm with 6" or 8" apertures, critically sampled. This isn't my every day seeing, my every day seeing is around 1" in the mornings give/take a bit. In the spring and summer it's sub-arc in the morning, but in the late fall and into winter, it goes up into the 1.5~2" fast. But I can reliably image sub-arc second in the late spring and summer when its warm with the least amount of temp swing from night to morning. This is the reason I can attempt 8" aperture solar at critical sampling.

SeeingConditions_08022020.gif (60.06 KiB) Viewed 591 times

Very best,

[Stardust5858]

Thanks Martin. My seeing can be very variable living by the seaside. Also the jet stream can be turbulent over the South West of the UK. However in saying that I've had very good seeing usually early morning in spring and autumn. I'll probably go down the Lunt Cak route instead for now to compliment the HA I'm currently doing.

[MalVeauX]

Thanks Martin. My seeing can be very variable living by the seaside. Also the jet stream can be turbulent over the South West of the UK. However in saying that I've had very good seeing usually early morning in spring and autumn. I'll probably go down the Lunt Cak route instead for now to compliment the HA I'm currently doing.

Sounds good

Honestly, while there are some less popular options like Gband, SodiumD, etc, ultimately the top ones for showing the major features really comes down to CaK, HA and any form of photosphere continuum (be it 540nm or even just red 656nm, whatever has the best seeing conditions to sample). This shows the upper chromosphere, lower chromosphere and photosphere. Pretty much the best trio to focus on.

If you're super interested in many wavelengths, and you're ok losing resolution, look into building a digital spectroheliograph and image any wavelength that fancies you. I'm wanting to build one of these just for fun to explore the less popular frequencies.

Very best,

[Stardust5858]

Thanks Martin. My seeing can be very variable living by the seaside. Also the jet stream can be turbulent over the South West of the UK. However in saying that I've had very good seeing usually early morning in spring and autumn. I'll probably go down the Lunt Cak route instead for now to compliment the HA I'm currently doing.

Sounds good

Honestly, while there are some less popular options like Gband, SodiumD, etc, ultimately the top ones for showing the major features really comes down to CaK, HA and any form of photosphere continuum (be it 540nm or even just red 656nm, whatever has the best seeing conditions to sample). This shows the upper chromosphere, lower chromosphere and photosphere. Pretty much the best trio to focus on.

If you're super interested in many wavelengths, and you're ok losing resolution, look into building a digital spectroheliograph and image any wavelength that fancies you. I'm wanting to build one of these just for fun to explore the less popular frequencies.

Very best,

Thanks, appreciate your help and advice.

[DeepSolar64]

Where would I find a 430nm filter and would it be of any real use visually? Would it benefit me in a similar way as a 540nm filter does? Obviously a true ultra-narrowband Gband filter would be better but I bet they are pricier too.

[Stardust5858]

Where would I find a 430nm filter and would it be of any real use visually? Would it benefit me in a similar way as a 540nm filter does? Obviously a true ultra-narrowband Gband filter would be better but I bet they are pricier too.

I found this one at:-
Edmund Scientific.
430nm CWL, 25mm Dia., Hard Coated OD 4.0 10nm Bandpass Filter

[DeepSolar64]

Where would I find a 430nm filter and would it be of any real use visually? Would it benefit me in a similar way as a 540nm filter does? Obviously a true ultra-narrowband Gband filter would be better but I bet they are pricier too.

I found this one at:-
Edmund Scientific.
430nm CWL, 25mm Dia., Hard Coated OD 4.0 10nm Bandpass Filter

Do they make a 1.25" size? One that will screw into an eyepiece?

[marktownley]

Where would I find a 430nm filter and would it be of any real use visually? Would it benefit me in a similar way as a 540nm filter does? Obviously a true ultra-narrowband Gband filter would be better but I bet they are pricier too.

I found this one at:-
Edmund Scientific.
430nm CWL, 25mm Dia., Hard Coated OD 4.0 10nm Bandpass Filter

Do they make a 1.25" size? One that will screw into an eyepiece?

No, these are filters for laser system optics, their sizes are not natively designed to go in 'scope sizes', however they will fit with a suitable sized cell to hold them.