Baader Contin Filter DS

[Solar B]

I was all ready to rock with a 2” Contin 

in the wedge & a 1.25” on the EP

when the clouds rolled in 😅

Baader sell a stacked Contin filter so 

I was interested to see if 2 will make 

any difference 🤷‍♀️

Brian 

[Stu]

Interested to hear the results Brian! I’m will be buying a 1.25” filter too (either new or used) so if it makes sense to stack them I can do that in the CoolWedge.

[johninderby]

Found a couple of reviews that claim that contrast is doubled using the DS filter but this review had a couple of pics.

One thing to note though is that the proper DS filter has the filters angled.

http://myphotojourney.co.uk/baader-herschel-prism-single-vs-double-stacked-solar-continuum/

Edited July 6, 2020 by johninderby

[AdeKing]

15 minutes ago, Stu said:

Interested to hear the results Brian! I’m will be buying a 1.25” filter too (either new or used) so if it makes sense to stack them I can do that in the CoolWedge.

I've used my 1.25" continuum filter on the end of the eyepiece in my Cool Ceramic wedge, but didn't notice much difference, though hardly a fair assessment though given the absence of any significant features.

I'll see if I notice more of a difference the next time there is a spot to look at.

[Solar B]

I'll certainly report back Stu if/when I get the chance ... obviously try it to , it does 

look promising 're Johns link and that's what I was hoping for a little more granulation 

detail but as Ade suggests stacking 2 may make no visual difference.

Brian 

 

[johninderby]

Bit more info.

The double stacked Solar Continuum filter consists of two 1.25" filters which are slightly tilted against each other. They are held in a special cell. Filter substrate thickness: 2 mm (each filter glass)

 

[Peter Drew]

It makes sense to me.  Provided that you use sufficient aperture to reveal granulation, double stacking the filters should dim the image slightly, granulation is sometimes overwhelmed by the image brightness.  Ha observers notice how surface detail is enhanced when thin cloud temporarily passes by.  Tilting the filters probably just reduces the chance of unwanted reflections.     🙂

[bomberbaz]

I am a little unsure as to how this will work as the filter is designed to let through light along the 540nm wavelength.

Does this stacking of filters work along the lines that the second filter hopefully captures any extraneous light that got through the first filter or are there other dynamics that I am overlooking.

[johninderby]

It  makes it a narrower band filter. Bit like double stacking an HA scope gives finer detail.

Edited July 6, 2020 by johninderby

[Solar B]

8 minutes ago, bomberbaz said:

I am a little unsure as to how this will work as the filter is designed to let through light along the 540nm wavelength.

Does this stacking of filters work along the lines that the second filter hopefully captures any extraneous light that got through the first filter or are there other dynamics that I am overlooking.

No your quite right they're centred at 540nm so 2 shouldn't make any difference ? & I remember they're purpose being questioned at launch but that was before anyone had tried one I think and Peter's quite right the tilting will be to prevent reflections just like an ERF is or should be 🙂

Brian 

[Stu]

Interestingly I tried a 1.25” Lunt Herschel Wedge at the weekend but with a polarising filter as I don’t have a 1.25” continuum filter. I tried it in the Telementor and the Scopetech and saw no granulation at all. I then tried the Tak with the CoolWedge and continuum and the granulation was immediately obvious. I then tried the Lunt in the Tak and whilst I could detect the granulation it was not really obvious. The two variables are obviously the wedge and the filter. Hopefully I’ll be able to do some more comparisons when I get a 1.25” Continuum filter but I was surprised how little was visible without it. 

[Stu]

7 minutes ago, Solar B said:

No your quite right they're centred at 540nm so 2 shouldn't make any difference ? & I remember they're purpose being questioned at launch but that was before anyone had tried one I think and Peter's quite right the tilting will be to prevent reflections just like an ERF is or should be 🙂

Brian 

Presumably though there is sample variation so the net result will be a narrower bandwidth? If they were both absolutely identical in terms of band pass frequency then it should make no difference.

[bomberbaz]

3 minutes ago, Stu said:

Interestingly I tried a 1.25” Lunt Herschel Wedge at the weekend but with a polarising filter as I don’t have a 1.25” continuum filter. I tried it in the Telementor and the Scopetech and saw no granulation at all. I then tried the Tak with the CoolWedge and continuum and the granulation was immediately obvious. I then tried the Lunt in the Tak and whilst I could detect the granulation it was not really obvious. The two variables are obviously the wedge and the filter. Hopefully I’ll be able to do some more comparisons when I get a 1.25” Continuum filter but I was surprised how little was visible without it. 

what aperture and F ratio were the scopes in question stu?

Steve

[Solar B]

2 minutes ago, Stu said:

Presumably though there is sample variation so the net result will be a narrower bandwidth? If they were both absolutely identical in terms of band pass frequency then it should make no difference.

I just don't know ... however if it does work I'll be interesting in trying the real thing or obtaining another 2" contin for the wedge.

 Brian 

[David Smith]

On 06/07/2020 at 21:19, johninderby said:

It  makes it a narrower band filter. Bit like double stacking an HA scope gives finer detail.

Dumb question of the day but how does stacking 2 filters with the same band pass result in a narrower overall band pass

[Merlin66]

I have a spreadsheet I downloaded (from someone - I think on SolarChat) which shows the result of stacking two Gaussian transmission curves.

The peak transmission drops and the bandwidth tightens due to the multiplication of the transmission curves.

Say if each curve has a peak of 90% transmission, the the combined peak would be (0.9 x 0.9) = 0.81%

Likewise if you multiply each point "down the curve" the resultant bandwidth reduces. If each filter is identical, the bandwidth reduction will be around 30%.

I'll upload the spreadsheet when I find it.

 

Gausian curve addition.XLS

Edited July 7, 2020 by Merlin66
spreadsheet added

[bomberbaz]

18 minutes ago, Merlin66 said:

I have a spreadsheet I downloaded (from someone - I think on SolarChat) which shows the result of stacking two Gaussian transmission curves.

The peak transmission drops and the bandwidth tightens due to the multiplication of the transmission curves.

Say if each curve has a peak of 90% transmission, the the combined peak would be (0.9 x 0.9) = 0.81%

Likewise if you multiply each point "down the curve" the resultant bandwidth reduces. If each filter is identical, the bandwidth reduction will be around 30%.

I'll upload the spreadsheet when I find it.

 

Gausian curve addition.XLS 210 kB · 0 downloads

This is interesting. I currently use a combo of continuum and polarising filter in my filter stack. I wonder if I could maybe lose the polarising filter and use a second Continuum filter to achieve a more detailed but similar bright result.

BTW. I have viewed without the polarising filter already. I won't be losing my eyesight. 

[Merlin66]

IMHO double stacking the Continuum filter brings limited benefits. There are no defined emission/ absorption features in that region of the spectrum.

A polarising filter is always useful to reduce excess light. Note: what ever solar filter system you use must have at least an ND5 reduction (for visual)

Some polarising filters still pass some IR wavelengths - best to double check with the supplier.

 

[Solar B]

Yeah have to agree with Ken .... I tried again latterly this evening .... this time with a

100mm F11 , at first I thought yes I am able to see a little more granulation but think 

I was imagining it all as switching back to the single 2" Contin I felt provided a sharper 

image from the cool wedge , not conclusive but there you go.

Brian

[bomberbaz]

8 hours ago, Merlin66 said:

IMHO double stacking the Continuum filter brings limited benefits. There are no defined emission/ absorption features in that region of the spectrum.

A polarising filter is always useful to reduce excess light. Note: what ever solar filter system you use must have at least an ND5 reduction (for visual)

Some polarising filters still pass some IR wavelengths - best to double check with the supplier.

 

Yes sorry I should have said in addition to the mandatory ND5 which is a permanent part of the wedge.  Don't want someone misunderstanding my comment re the polarizing filter. 

9 hours ago, bomberbaz said:

This is interesting. I currently use a combo of continuum and polarising filter in my filter stack. I wonder if I could maybe lose the polarising filter and use a second Continuum filter to achieve a more detailed but similar bright result.

BTW. I have viewed without the polarising filter already. I won't be losing my eyesight. 

 

[Rusted]

Granulation is aperture, seeing and magnification dependent.
I like my SC simply for reducing the glare in visual white light.
I don't do WL [nor visual] often enough to be able to confirm increased clarity of granulation.
Particularly by comparison with and without the filter.
It sounds like the sort of project to be practised [diligently] when the sun is featureless.
Or, when the sun is actually visible for more than fleeting moments in this overcast!

 

[Solar B]

11 hours ago, Rusted said:

Granulation is aperture, seeing and magnification dependent.
I like my SC simply for reducing the glare in visual white light.
I don't do WL [nor visual] often enough to be able to confirm increased clarity of granulation.
Particularly by comparison with and without the filter.
It sounds like the sort of project to be practised [diligently] when the sun is featureless.
Or, when the sun is actually visible for more than fleeting moments in this overcast!

 

Agreed 

I think SCs do help with bringing out a touch more detail but they're real benefit I find 

is with focusing here the limb or AR (remember those) can be fine tuned.

As for DS SCs well I think this could display a tad more detail but it'll be subtle 

Brian 

 

[Stu]

On 06/07/2020 at 21:34, bomberbaz said:

what aperture and F ratio were the scopes in question stu?

Steve

The Telementor is 63mm, and the Scopetech 80mm. I was surprised at how little I could see compared with the Tak, although I know my Tak setup is about as good as it gets in a 4”.

[bomberbaz]

 

16 minutes ago, Stu said:

The Telementor is 63mm, and the Scopetech 80mm. I was surprised at how little I could see compared with the Tak, although I know my Tak setup is about as good as it gets in a 4”.

So it appears as I have previously read that 100m/4" is indeed the magic number aperture wise for getting granulation to show in white light.

Now I only have a fairly basic 4" achro until something better comes along in the 2nd hand market and it has yet to be given a bash at white light but I am hopeful that it will be good enough to give me some granulation when used with a continuum filter. 

[JeremyS]

I was speaking to veteran observer Alan Heath the other day. He regularly sees granulation in his >80 year old 3-inch Broadhurst Clarkson refractor.