Double Stacked Continuum Filter

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Double Stacked Continuum Filter

Post by rsfoto »

Hi,

I have to admit that yesterday I learned something new from a Newbee in White Light Solar imaging and that was that there is a double stacked continuum filter which is sold by Baader claiming a total bandwidth of 8 nm instead of 10 nm from the single continuum filter ...

Does that make much sense ?

IMHO Honestly for me the disadvantage of light loss is bigger then the alleged contrast gain ...

What do the experts think about this ?

Thanks :bow

Double stacked https://www.baader-planetarium.com/en/b ... cked).html

Single filter https://www.baader-planetarium.com/en/b ... 40nm).html

If I buy two single continuum I even save Euro € 10.00 :lol:
Last edited by rsfoto on Thu Feb 04, 2021 10:09 pm, edited 1 time in total.


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Re: Double Stacked Continuum Filter

Post by SimonM »

rsfoto wrote: Thu Feb 04, 2021 7:53 pm If I buy two single Solar Continuum filters I even save Euro € 10.00 :lol:
If you head over to the Baader Planetarian website then you can read about the filter (and read the answers to the questions):
A. These "double images" are normal and are caused by the tilt of the two filters. They cannot be avoided and actually are the reason why the filter works so well. We have explained this in more detail on the Important Notes for our (also double-stacked) K-Line Filter. Please check out the following PDF:
https://www.baader-planetarium.com/en/d ... ilter.pdf
As for your second question: A 2" double-stacked Solar Continuum (or K-Line) Filter unfortunately is not possible, because it would require a much larger filter cell than our normal cells.
When you buy the filter it usually comes with an A4 sheet of solar film as part of a pack. So you have everything to use it with a normal scope for imaging only.

I have the Baader Safety Cool Wedge and was considering a double-stacked k-line filter. The Lunt B1200 Calcium filter would be a better choice?

Simon


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Re: Double Stacked Continuum Filter

Post by DeepSolar64 »

Martin Wise would probably have an excellent answer to this question since he uses filters of different wavelengths quite a bit in his continuum observations.

I do have a single 540nm filter and it works well. I have wondered too if the benefits of stacking them would outweigh a dimmer image. I would certainly use them with a Herschel wedge where I could control the brightness of the image a bit.


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Re: Double Stacked Continuum Filter

Post by rsfoto »

SimonM wrote: Thu Feb 04, 2021 8:28 pm
rsfoto wrote: Thu Feb 04, 2021 7:53 pm If I buy two single Solar Continuum filters I even save Euro € 10.00 :lol:
If you head over to the Baader Planetarian website then you can read about the filter (and read the answers to the questions):
A. These "double images" are normal and are caused by the tilt of the two filters. They cannot be avoided and actually are the reason why the filter works so well. We have explained this in more detail on the Important Notes for our (also double-stacked) K-Line Filter. Please check out the following PDF:
https://www.baader-planetarium.com/en/d ... ilter.pdf
As for your second question: A 2" double-stacked Solar Continuum (or K-Line) Filter unfortunately is not possible, because it would require a much larger filter cell than our normal cells.
When you buy the filter it usually comes with an A4 sheet of solar film as part of a pack. So you have everything to use it with a normal scope for imaging only.

I have the Baader Safety Cool Wedge and was considering a double-stacked k-line filter. The Lunt B1200 Calcium filter would be a better choice?

Simon
Hi Simon,

I did read your answer 4 times and still find no answer to my question. Sorry. :?

My question was:

Does the contrast increase justify the light loss and so a possibly slower frame rate ? and the statement buying two filters and saving Euro € 10.00 was more sort of a joke ...

Rainer


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Re: Double Stacked Continuum Filter

Post by rsfoto »

DeepSolar64 wrote: Thu Feb 04, 2021 10:07 pm Martin Wise would probably have an excellent answer to this question since he uses filters of different wavelengths quite a bit in his continuum observations.

I do have a single 540nm filter and it works well. I have wondered too if the benefits of stacking them would outweigh a dimmer image. I would certainly use them with a Herschel wedge where I could control the brightness of the image a bit.
Hi James,

The question here is more " frames per second " and not just increasing brightness during image acquisition ...

One should be careful about adjusting brightness, gamma and contrast while imaging IMHO


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Re: Double Stacked Continuum Filter

Post by marktownley »

The difference in bandpass I think makes no difference - compared to Ha it is still a very much 'wide band' filter. Will the loss of light be an issue? Unlikely as will be used with a wedge or solar film where the light levels are being cut right back anyway.


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Re: Double Stacked Continuum Filter

Post by DeepSolar64 »

rsfoto wrote: Thu Feb 04, 2021 10:17 pm
DeepSolar64 wrote: Thu Feb 04, 2021 10:07 pm Martin Wise would probably have an excellent answer to this question since he uses filters of different wavelengths quite a bit in his continuum observations.

I do have a single 540nm filter and it works well. I have wondered too if the benefits of stacking them would outweigh a dimmer image. I would certainly use them with a Herschel wedge where I could control the brightness of the image a bit.
Hi James,

The question here is more " frames per second " and not just increasing brightness during image acquisition ...

One should be careful about adjusting brightness, gamma and contrast while imaging IMHO


Remember Rainer, I am far more familiar with the visual aspect of solar astronomy so my comments reflect that. :)


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Re: Double Stacked Continuum Filter

Post by SimonM »

rsfoto wrote: Thu Feb 04, 2021 10:14 pm Does the contrast increase justify the light loss and so a possibly slower frame rate?
The Baader "Answer" highlights why you can't easily DIY stack your own double-stack filter successfully, get a 2" version, and why there are some unwanted reflections. What they don't mention is that Wedge deliberately puts the Solar Continuum before the ND filter - which is considered optimal. A camera double-stack 1.25" filter will be after the Wedge’s internal 2" ND filters, if you use them.

The increased contrast is the benefit. The light loss might not matter since you always need some ND reduction in front of a sensor. You get 3 alternative 2" ND filters with the Solar Continuum filter included with the Wedge and the standard 3.0 ND that comes preinstalled.

If you replace the Solar Continuum filter with a double-stack version on your sensor, then the Solar Continuum and the 3.0 ND can also be removed from the Wedge and you can substitute some of the other ND filters, to get the desired frame rate and also not fry the sensor without an ND filter. If k-line works with 3.8 ND film, then so will the double-stacked Solar Continuum with a combination of ND filters in the Wedge. Given that the gains are very small (if any) and with some known disadvantages and it is only for imaging (to keep safe), I wonder, is it really worth it?


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Re: Double Stacked Continuum Filter

Post by MalVeauX »

rsfoto wrote: Thu Feb 04, 2021 10:14 pm My question was:

Does the contrast increase justify the light loss and so a possibly slower frame rate ? and the statement buying two filters and saving Euro € 10.00 was more sort of a joke ...

Rainer
Hey Rainer,

Going from 10nm to 8nm doesn't matter frankly, it won't increase contrast significantly. They're 100 Angstroms wide and 80 Angstroms wide respectively, it's just not narrow enough to isolate a wavelength and reduce all other wavelengths to impact things in a very meaningful way. If your goal is imaging, then it's even less of a useful thing because losing transmission will just cost you lost good frames when seeing is good (slowing down lucky imaging, or at least harming it by the added noise or slower exposure time for freezing seeing purposes, etc, or just no advantage if none of that applies to your transmission profile). Going from 10nm to 8nm will not make a significant impact in contrast compared to simply having more good frames with a single wide bandpass when seeing is really good.

Highest contrast will come from best seeing conditions and critically sampled highest angular resolution unlimited by said best seeing. Whether it's at 500nm, 540nm or 580nm (etc, pick any random number) won't matter at these wide bandpasses as there's no unique structure at this bandwidth to isolate to matter. And the optics you use will likely all have excellent figures in this wavelength range, so that's nothing something to stress either.

If you want the best 540nm data, couple it with a good long IR blocker and image fast FPS at critical sampling for your pixel size in the best seeing you can get. Emphasis on best seeing. This is far more important than more filters or other configurations. The best data will be sampled to the seeing conditions.

Very best,


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Re: Double Stacked Continuum Filter

Post by rsfoto »

Hi Everybody,

Thanks for the comments ...

Very interesting ...

:bow


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Re: Double Stacked Continuum Filter

Post by marktownley »

I wonder if there are 2 other reason these Baader solar filters are 'double stacked' for solar?

Firstly marketing 'guff' on behalf of Baader - us solar geeks always go for a double stack? I say guff, because as others have said stacking 2 broadband filters makes naff all difference.

Secondly, and possibly the real reason. Way back when a decade or so ago Baader continuum filter had a IR leak that would flood images and make them lacking in contrast. The natural profile of any filter like this is that it transmits highly at the target wavelength and blocks until 700-1000nm and then the transmission starts rising quickly before it is quite transparent to IR. Baader DERFs have the same profile, it's the norm! I know from building CaK filters, it works perfectly if you use CaK PST #1 filter and a double stack K-line. Take out one of the elements of the K-line and it does not, all of a sudden there is a IR flood again. This can be stopped using 'another' filter be it suitable uv/ir blocker or similar target wavelength filter eg 393/10 etc. I think the reason the Baader dichroic solar filters are double stacked is because one alone does not provide significant IR blocking. The early generation continuum filters would not have been 'noticed' as 20 years ago people weren't imaging like we are now, our CCDs are sensitive to these out of band 'leaks', its different now and the build of the filter has changed accordingly.


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Re: Double Stacked Continuum Filter

Post by Carbon60 »

I use a Lacerta wedge for continuum imaging, with the following setup:

I stripped out the ND filter from the output side and replaced it with a 540nm continuum (single, from Baader) and on the input (nose) of the wedge I placed a UV/IR filter to block these unwanted wavelengths. The green output image is very bright (definitely not for visual use). Given that the Lacerta uses the principles of Brewster angle, and the output image is strongly polarised, I use a polarising filter on the camera, or Powermate, and rotate it to an acceptable brightness for imaging at as close to maximum speed as I dare (minimum exposure time of a few microseconds). This almost totally freezes out the effects of seeing, especially at high focal lengths for magnified views. Using polarizing filters (I sometimes need two if the image is particularly bright) and rotating them gives me complete freedom to optimise the amount of light reaching the sensor. I can also easily swap out the continuum filter for any other within the optical range and still optimise image brightness with the polariser(s)

I don't really know what a DS continuum would give me in terms of improved image quality. Maybe it's better for visual, as with imaging we can easily adjust the contrast levels during processing anyhow.

Stu.


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Re: Double Stacked Continuum Filter

Post by SimonM »

marktownley wrote: Fri Feb 05, 2021 6:53 am I wonder if there are 2 other reasons these Baader solar filters are 'double-stacked' for solar?

Firstly marketing 'guff' on behalf of Baader - us solar geeks always go for a double-stack? I say guff because as others have said stacking 2 broadband filters makes naff all difference.

Way back when a decade or so ago Baader continuum filter had an IR leak that would flood images and make them lacking in contrast.
Both reasons are correct. I have the Baader 2" Cool-Ceramic Safety Herschel Prism (Visual/Photographic) with a 2" Solar Continuum and 3.0 ND filters preinstalled after the Wedge. Before buying it, I emailed Baader to ask if it was safe to use without additional UV/IR blocking filters or if they had a whole spectrum attenuation chart available and if using a fast (short focal ratio) scope was still safe. I had a direct (but not immediate) response from Michael Risch at Baader.
We would not be able to sell the product for a decade without complying with safety standards. The Herschel Wedge V means "visual", which means it's recommended for visual use. If you want to be super safe then you can add a UV/IR blocker even if generations of astronomers observed with Herschel Wedges without UV/IR blocker - without damaging their eyes.

We are sorry we do not offer such a chart.

We would not give the advice (up to 8") on our website if it would not have been tested properly. This means if the Wedge is recommended for 8" it can be used for 6" without any problem. Because it is logical that the aperture and not the focal length [determine] how much energy comes into focus.

Herschel Wedges are well known to be used for decades without problems as one of the safest methods for solar observation. Nevertheless, you are questioning the technical descriptions, the advice and the details on our website for a product that we sell for more than 10 years in the same kind.

We cannot urge somebody to believe us or to trust us - but we ask for your understanding that we cannot discuss every information on our website in every depth. If you still fear to use the Herschel Wedge it's understandable. Many people fear to look through a telescope to the Sun, even with proven filters, and then our advice can only be: If someone is not comfortable with something it's better not to do it.
Michael, along with Martin Rietze at Baader, have both been solar chasers for many years, and the Baader Team travel to all the main solar eclipses.

Around 2015, Baader did change the Solar Continuum filter and also repackaged it in a 6mm holder. Others have analyzed the spectrum and determined that the filter was updated to block the IR that is harmful. The preconfigured Wedge is completely safe for solar viewing without any additional filters. The product as preconfigured passes all the safety standards, which specifies all the bands of wavelengths and the attenuation required. An additional separate Polarising filter isn't required for safety but it does cut the glare which some people are susceptible to (I'm not).

The Brewster prism absorbs a small amount of the energy and passes through most of the remaining energy so that only 4.6% is reflected up. This is still a combination of white light, UV, and IR. The Solar Continuum filter blocks the UV and filters the IR component to a lesser extent. The ND 3.0 filter also attenuates the IR component, but not as much as WL and collectively they meet the safety standards with both filters in place. The filters supplied are 2" and fit above the prism.

The Photographic version of the Wedge is the same as the Visual but includes 3x additional 2" ND filters that are 0.6 ND, 0.9 ND, and 1.8 ND. The instructions state that these can be used only for Imaging and not for Visual and also that there should not be any filters in the front of the Wedge which has a thread for filters because it is a common component e.g. used with Baader ClickLocks. The double-stack Solar Continuum filter is not manufactured as a 2" filter (too much tilt to fit in a carrier), so cannot be used in the Wedge, hence Baader needed another method to make the product comply with safety standards and also the perceived lack of contrast. So it is likely that they chose to add the UV/IR dielectric coatings on the existing Solar Continuum filter (used before the 3.0 ND filter) and so avoid the need to supply a separate UV/IR cut filter.

The Wedge does (just) have space for three low profile filters after the prism. Adding an additional 2" ND or UV/IR cut filter to the Wedge if desired, to ease the swapping of EPs is possible. Users react only to visible light and are not alerted to the dangers of IR, so using a Polarising filter cuts only the visible light and so appears safe, but IR is not attenuated. UV/IR filters are no more effective at blocking IR than an ND filter and both are only about 50% effective compared to blocking visible light.

Simon


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Re: Double Stacked Continuum Filter

Post by christian viladrich »

Hello,
By definition, the "continuum" is (are) the region(s) of the solar spectra where there is no line. So it makes no difference at all to have a single or double stack continuum filter (whethever its color).


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Re: Double Stacked Continuum Filter

Post by christian viladrich »


UV/IR filters are no more effective at blocking IR than an ND filter and both are only about 50% effective compared to blocking visible light.

Simon
It depends a lot on the filter :
- the IR blocking of UV/UR cut filters is usually through dielectric coating, they cut IR up to about 1050-1100 nm.
- ND filters block light by absorption. Some can cut IR up to 1500 nm.

For example, these old ND filters from Celestron become fairly transparent in IR :
Image

Baader ND are much better :
Image


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Re: Double Stacked Continuum Filter

Post by christian viladrich »

Polarizing filters should be used with care :
Image


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