G band instead of Ca-k filter

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G band instead of Ca-k filter

Post by 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.


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Re: G band instead of Ca-k filter

Post by 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.


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Re: G band instead of Ca-k filter

Post by Stardust5858 »

marktownley wrote: Mon Nov 23, 2020 10:29 pm 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.


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Re: G band instead of Ca-k filter

Post by 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


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Re: G band instead of Ca-k filter

Post by 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


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Re: G band instead of Ca-k filter

Post by 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.

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Re: G band instead of Ca-k filter

Post by Stardust5858 »

Carbon60 wrote: Tue Nov 24, 2020 8:06 am 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


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Re: G band instead of Ca-k filter

Post by 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.


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Re: G band instead of Ca-k filter

Post by marktownley »

Stardust5858 wrote: Tue Nov 24, 2020 3:50 pm 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.


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Re: G band instead of Ca-k filter

Post by rsfoto »

marktownley wrote: Tue Nov 24, 2020 3:58 pm
Stardust5858 wrote: Tue Nov 24, 2020 3:50 pm 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 ?


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Re: G band instead of Ca-k filter

Post by marktownley »

rsfoto wrote: Tue Nov 24, 2020 4:37 pm
marktownley wrote: Tue Nov 24, 2020 3:58 pm
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


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Re: G band instead of Ca-k filter

Post by marktownley »



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Re: G band instead of Ca-k filter

Post by rsfoto »

marktownley wrote: Tue Nov 24, 2020 4:50 pm
rsfoto wrote: Tue Nov 24, 2020 4:37 pm
marktownley wrote: Tue Nov 24, 2020 3:58 pm
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 ...


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Re: G band instead of Ca-k filter

Post by Stardust5858 »

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


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Re: G band instead of Ca-k filter

Post by 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.


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Re: G band instead of Ca-k filter

Post by 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
baader_solarfilm_ND38_200mmF6Newt_03112020.jpg (228.85 KiB) Viewed 10109 times
Image

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:

Image

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,


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Re: G band instead of Ca-k filter

Post by Stardust5858 »

MalVeauX wrote: Wed Nov 25, 2020 12:17 am 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

Image

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:

Image

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.


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Re: G band instead of Ca-k filter

Post by MalVeauX »

Stardust5858 wrote: Wed Nov 25, 2020 11:39 am 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
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Very best,


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Re: G band instead of Ca-k filter

Post by 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.


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Re: G band instead of Ca-k filter

Post by MalVeauX »

Stardust5858 wrote: Wed Nov 25, 2020 4:20 pm 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,


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Re: G band instead of Ca-k filter

Post by Stardust5858 »

MalVeauX wrote: Wed Nov 25, 2020 5:21 pm
Stardust5858 wrote: Wed Nov 25, 2020 4:20 pm 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.


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Re: G band instead of Ca-k filter

Post by 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.


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Re: G band instead of Ca-k filter

Post by Stardust5858 »

DeepSolar64 wrote: Thu Nov 26, 2020 3:29 am 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


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Re: G band instead of Ca-k filter

Post by DeepSolar64 »

Stardust5858 wrote: Thu Nov 26, 2020 2:52 pm
DeepSolar64 wrote: Thu Nov 26, 2020 3:29 am 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?


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Re: G band instead of Ca-k filter

Post by marktownley »

DeepSolar64 wrote: Thu Nov 26, 2020 4:03 pm
Stardust5858 wrote: Thu Nov 26, 2020 2:52 pm
DeepSolar64 wrote: Thu Nov 26, 2020 3:29 am 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.


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Re: G band instead of Ca-k filter

Post by DeepSolar64 »

Does anyone make one to mount in an eyepiece, already mounted in a 1.25" cell? I am surprised Baader does not have one.


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Re: G band instead of Ca-k filter

Post by marktownley »

DeepSolar64 wrote: Thu Nov 26, 2020 4:27 pm Does anyone make one to mount in an eyepiece, already mounted in a 1.25" cell? I am surprised Baader does not have one.
Nope, just us nerds on here aware of them.


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Re: G band instead of Ca-k filter

Post by MalVeauX »

DeepSolar64 wrote: Thu Nov 26, 2020 4:03 pm
Stardust5858 wrote: Thu Nov 26, 2020 2:52 pm
DeepSolar64 wrote: Thu Nov 26, 2020 3:29 am 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?
I have that filter, I mounted it into a 28mm holding cell (standard 1.25") which then threads to anything like a typical 1.25" filter.

That said, this is not a useful filter for visual, and frankly not that useful for imaging either. See above notes.

Stick to 540nm, or longer, for photosphere visual. Going any shorter wavelength, visually to see something meaningfully different than just the photosphere would be 396nm and even then only at around 5~6A or less. CaH basically. Shorter than that and you likely won't see anything due to yellowing of your cornea.

Very best,


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Re: G band instead of Ca-k filter

Post by DeepSolar64 »

Thanks Marty,
I do already have a 540nm filter. I would like to have one of those Sodium Quarks to use with my Astro-Tech AT72EDII refractor.

James


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Re: G band instead of Ca-k filter

Post by DeepSolar64 »

marktownley wrote: Thu Nov 26, 2020 4:32 pm
DeepSolar64 wrote: Thu Nov 26, 2020 4:27 pm Does anyone make one to mount in an eyepiece, already mounted in a 1.25" cell? I am surprised Baader does not have one.
Nope, just us nerds on here aware of them.
:beanie: :lol:


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Re: G band instead of Ca-k filter

Post by christian viladrich »

Hello,
Here is a comparison of a G-band 430-10 nm filter (Edmund Optics) and a 430-2nm filter (Andover Optics). The 2 nm FWHM filter provides more contrast on intergranular bright points.
Image

Image

The intergranular bright points (also called G-band bright spots) are also visible with a 395-5 nm filter or with Baader K-line filter :
Image

The minimum diameter required to observe the G-band bright spots is 200 mm (in best condition and only for the larger points) but this is definitely better with a 300 mm telescope (and excellent seeing).

The G-band filter is also my favourite for visual observation of granulation and sunspot with my Taka TOA 150. The contrast and resolution is increased compared to a continuum green filter.

You have to check Andover "surplus" for the 430-2 nm or a 396-5 nm filter.


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Re: G band instead of Ca-k filter

Post by Stardust5858 »

Hi,
Would this be a good filter. 433.9nm 1.0nm 25mm

Andover Custom BP filter CWL 433.9nm/HBW 1.0nm/25.0mm dia.
433.9 / 1.0 - 59622
$154.05
Center Wavelength 433.9+0.2/-0 nm
Bandwidth 1.0+0.2/-0.2 nm
Transmission 40%





Blocking 1x10-4 avg. X-Ray to FIR
Size +0/-0.25mm
Thickness 7.0 +0/-nom mm
Effective refractive index (n*) -
Filter Type 2 (Click for profile)
CSV File (typical) N/A


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Re: G band instead of Ca-k filter

Post by christian viladrich »

Unfortunately not. It should be 430.5 nm. The 433.9-1 nm is off G-band.


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Re: G band instead of Ca-k filter

Post by christian viladrich »

This is the right filter :
Custom BP filter CWL 430.7nm/HBW 2.0nm/25.0mm
https://www.andovercorp.com/products/su ... s-filters/


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Re: G band instead of Ca-k filter

Post by Stardust5858 »

christian viladrich wrote: Sat Nov 28, 2020 10:13 pm Unfortunately not. It should be 430.5 nm. The 433.9-1 nm is off G-band.
Thanks for your help


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Re: G band instead of Ca-k filter

Post by Stardust5858 »

Sorry for being a pain. Would this work, can't find an exact 430nm.

Andover Center Wavelength 430.7+0.4/-0.0 nm
Bandwidth 2.0+0.5/-0.5 nm
Transmission 45%
Blocking 1x10-4 avg. X-Ray to FIR
Size +0/-0.25mm
Thickness 9.5 +0/-nom mm


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Re: G band instead of Ca-k filter

Post by marktownley »

Have you tried plumbing in the shipping costs to the UK from Andover? They are likely to be more than you think. There's customs excise and everything on top too...

From what I can see they don't have stock for that filter.

Have you imaged at 540nm with a continuum filter?


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Re: G band instead of Ca-k filter

Post by Stardust5858 »

marktownley wrote: Sun Nov 29, 2020 11:01 am Have you tried plumbing in the shipping costs to the UK from Andover? They are likely to be more than you think. There's customs excise and everything on top too...

From what I can see they don't have stock for that filter.

Have you imaged at 540nm with a continuum filter?
Yeah, I've thought about all the added cost too. I've a Lunt so only done ha. I'll probably add a Lunt Ca K next year, seems like the best way to go plus WL. Seems most seem to do these tri band observations. I've a white light filter for my birthday next week for my C11 and 80ed.


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Re: G band instead of Ca-k filter

Post by MalVeauX »

Keep in mind what Christian pointed out, you need a big aperture and his seeing was sustained 0.7~0.8 arc-seconds, and as good as 0.3 arc-seconds. This isn't anyone's backyard seeing. This was at a specific location with exceptional seeing conditions. Professional observatory location class. G-band is really a fickle unicorn for most, simply due to the seeing requirements of such a short wavelength. For the same reason few people are able to image high resolution Calcium K (393nm) with enormous apertures.

Very best,


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Re: G band instead of Ca-k filter

Post by marktownley »

MalVeauX wrote: Tue Dec 01, 2020 7:51 pm Keep in mind what Christian pointed out, you need a big aperture and his seeing was sustained 0.7~0.8 arc-seconds, and as good as 0.3 arc-seconds. This isn't anyone's backyard seeing. This was at a specific location with exceptional seeing conditions. Professional observatory location class. G-band is really a fickle unicorn for most, simply due to the seeing requirements of such a short wavelength. For the same reason few people are able to image high resolution Calcium K (393nm) with enormous apertures.

Very best,
100% agree with you here Marty.

Sage advice! :cool:


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Re: G band instead of Ca-k filter

Post by christian viladrich »

Stardust5858 wrote: Sun Nov 29, 2020 9:28 am Sorry for being a pain. Would this work, can't find an exact 430nm.

Andover Center Wavelength 430.7+0.4/-0.0 nm
Bandwidth 2.0+0.5/-0.5 nm
Transmission 45%
Blocking 1x10-4 avg. X-Ray to FIR
Size +0/-0.25mm
Thickness 9.5 +0/-nom mm
Sorry, I was not arround.
Yes, this is the one. Two pieces were still available a few days ago, but now none ...


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Re: G band instead of Ca-k filter

Post by christian viladrich »

MalVeauX wrote: Tue Dec 01, 2020 7:51 pm Keep in mind what Christian pointed out, you need a big aperture and his seeing was sustained 0.7~0.8 arc-seconds, and as good as 0.3 arc-seconds. This isn't anyone's backyard seeing. This was at a specific location with exceptional seeing conditions. Professional observatory location class. G-band is really a fickle unicorn for most, simply due to the seeing requirements of such a short wavelength. For the same reason few people are able to image high resolution Calcium K (393nm) with enormous apertures.

Very best,
This is completely true.


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Re: G band instead of Ca-k filter

Post by MalVeauX »

Heya,

Just because it was asked, you can get filter mounts with threaded cells that will hold a 25mm filter.

https://www.ebay.com/itm/Eyepiece-Filte ... 236afeeb55

If you search eyepiece filter mount 28mm for 25mm filter you'll find lots of these out there.

I bought this exact one and it held my EO 430nm no problem.

But I still don't recommend the 430nm filter. :P

Very best,


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Re: G band instead of Ca-k filter

Post by DeepSolar64 »

MalVeauX wrote: Wed Dec 02, 2020 6:09 pm Heya,

Just because it was asked, you can get filter mounts with threaded cells that will hold a 25mm filter.

https://www.ebay.com/itm/Eyepiece-Filte ... 236afeeb55

If you search eyepiece filter mount 28mm for 25mm filter you'll find lots of these out there.

I bought this exact one and it held my EO 430nm no problem.

But I still don't recommend the 430nm filter. :P

Very best,

So you recommend the 540Nm filter?


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Re: G band instead of Ca-k filter

Post by MalVeauX »

DeepSolar64 wrote: Thu Dec 03, 2020 5:53 am
MalVeauX wrote: Wed Dec 02, 2020 6:09 pm Heya,

Just because it was asked, you can get filter mounts with threaded cells that will hold a 25mm filter.

https://www.ebay.com/itm/Eyepiece-Filte ... 236afeeb55

If you search eyepiece filter mount 28mm for 25mm filter you'll find lots of these out there.

I bought this exact one and it held my EO 430nm no problem.

But I still don't recommend the 430nm filter. :P

Very best,

So you recommend the 540Nm filter?
Yes, it's a good filter, it's as short wavelength (high angular resolution) as I would go, visually, unless you have exquisite seeing conditions. Even then, it's not needed, a polarized filter and something like a red filter will often be more useful simply because seeing will generally always be poor, and red will steady the seeing more than green will.

Very best,


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Re: G band instead of Ca-k filter

Post by DeepSolar64 »

I hope in time to get a Sodium D line Quark for my AT72EDII refractor. With 72mm of aperture it shouldn't require an ERF but only a UV/IR cut filter.

http://www.daystarfilters.com/Quark/NaQuark.shtml


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Re: G band instead of Ca-k filter

Post by krakatoa1883 »

Stardust5858 wrote: Sun Nov 29, 2020 9:28 am Sorry for being a pain. Would this work, can't find an exact 430nm.

Andover Center Wavelength 430.7+0.4/-0.0 nm
Bandwidth 2.0+0.5/-0.5 nm
Transmission 45%
Blocking 1x10-4 avg. X-Ray to FIR
Size +0/-0.25mm
Thickness 9.5 +0/-nom mm
I have one purchased from the Andover dealer in Italy. It works fine, very sharp and contrasty. It requires plenty of light so I put it just behind the Baader wedge (on 100mm ED refractor) with no neutral filters inside. For using this filter seeing needs to be really good.


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Re: G band instead of Ca-k filter

Post by marktownley »

krakatoa1883 wrote: Wed Dec 09, 2020 8:34 am For using this filter seeing needs to be really good.
And this is the key takeaway from this thread!


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Re: G band instead of Ca-k filter

Post by DeepSolar64 »

I might go for Gband if I had consistently better seeing. I don't, especially this time of year :(


Lunt 8x32 SUNoculars
Orion 70mm Solar Telescope
Celestron AstroMaster Alt/Az Mount
Meade Coronado SolarMax II 60 DS
Meade Coronado SolarMax II 90 DS
Meade Coronado AZS Alt/Az Mount
Astro-Tech AT72EDII with Altair solar wedge
Celestron NexStar 102GT with Altair solar wedge
Losmandy AZ8 Alt/Az Mount
Sky-Watcher AZGTI Alt-Az GoTo mount
Cameras: ZWO ASI178MM, PGR Grasshopper, PGR Flea
Lunt, Coronado, TeleVue, Orion and Meade eyepieces

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