24 replies to this topic

[gustavo_sanchez]

I’ve decided to move this into a separate thread. Simply wording the question, what’s the practical difference between the Continuum filter vs a green or red filter when used in conjunction with a wedge? I have a #29 deep red filter lying around I think.

[hamers]

My understanding is that the choice of ~ 540 nm is that this is one of the design wavelengths at which achromatic/apochromatic telescope are optimized, and corresponds with a peak in visual acuity, so the the optical system of the telescope (and your eye...) are able to achieve as close to the diffraction limit as possible.

https://www.telescop...ochromatism.htm

 

 

 I don't believe there is any reason related to the sun itself...  So a red filter will give give you less resolution at the diffraction limit.  In principle blue might give you better resolution yet, but optical dispersion is more severe at short wavelengths and so the optical correction is not as good.  So in the end the 540 nm has a width that is narrow enough that you reduce effects of dispersion and spherochromatism while still broad enough light that it works for visual and/or photography. 

Edited by hamers, 29 September 2021 - 08:11 PM.

[gustavo_sanchez]

Thanks for the feedback. I appreciate it.

[MalVeauX]

I’ve decided to move this into a separate thread. Simply wording the question, what’s the practical difference between the Continuum filter vs a green or red filter when used in conjunction with a wedge? I have a #29 deep red filter lying around I think.

The practical difference is two things: 1) angular resolution (shorter wavelength = higher angular resolution) and 2) atmospheric seeing disrupting the wavefront (shorter wavelength = more disrupted by atmospheric seeing). Seeing is often bad in daytime for everyone, so longer wavelengths (ie, red) will produce a more steady image at the cost of angular resolution. When seeing is good to excellent, you can benefit the extra angular resolution coming from a shorter wavelength, such as Continuum or any green wavelength filter (they will be nearly indistinguishable frankly in real world results). Our eyes are most sensitive to green and our optics are best figured for green, but again, all of this is at the mercy of the seeing and seeing will never (literally never) allow you to experience the diffraction limited image your system could produce in daytime seeing, so it's not worth fussing over much because you can have the best glass in the world and be in 2 arc-second seeing and you'll see what 2 arc-seconds delivers and nothing more. But again, if seeing is good to excellent, angular resolution can deliver a higher resolution image during fleeting moments of good seeing. You do not need an ultra-narrowband filter for this. You do not need Baader's 540nm filter, any green CCD imaging or visual green filter will work nearly the same and any variation will likely be only attributable to seeing differences per session. Same with red, there's nothing special to it. Also, all optics are very well corrected in green and red. The only wavelength ranges that start to get sketchy for spherical aberration and other issues is when you get down to near UV and some IR, and those issues will come in the form of refractors and SCT with correctors; pure mirrors will not have this issue (but are less commonly used for this purpose by most people, especially visual, as UV and IR are imaging wavelengths only anyways). Also keep in mind, something with a strehl of 0.85 is essentially diffraction limited for this purpose (solar), and you'll likely never even get to that because of atmospheric seeing.

 

Very best,

[hamers]

I agree with Marty on his points above. I had assumed (perhaps incorrectly) you were wanted to doing imaging.  For visual you will always be limited by seeing and the fact that your eyes have a pretty slow response time and so average over the ~ few arc-sec of seeing.  For imaging it is significantly more complicated since you can at least partially "freeze out" the fluctuations due to seeing and align individual images into a single final image with improved resolution.  

Edited by hamers, 30 September 2021 - 09:56 AM.

[gustavo_sanchez]

The practical difference is two things: 1) angular resolution (shorter wavelength = higher angular resolution) and 2) atmospheric seeing disrupting the wavefront (shorter wavelength = more disrupted by atmospheric seeing). Seeing is often bad in daytime for everyone, so longer wavelengths (ie, red) will produce a more steady image at the cost of angular resolution. When seeing is good to excellent, you can benefit the extra angular resolution coming from a shorter wavelength, such as Continuum or any green wavelength filter (they will be nearly indistinguishable frankly in real world results). Our eyes are most sensitive to green and our optics are best figured for green, but again, all of this is at the mercy of the seeing and seeing will never (literally never) allow you to experience the diffraction limited image your system could produce in daytime seeing, so it's not worth fussing over much because you can have the best glass in the world and be in 2 arc-second seeing and you'll see what 2 arc-seconds delivers and nothing more. But again, if seeing is good to excellent, angular resolution can deliver a higher resolution image during fleeting moments of good seeing. You do not need an ultra-narrowband filter for this. You do not need Baader's 540nm filter, any green CCD imaging or visual green filter will work nearly the same and any variation will likely be only attributable to seeing differences per session. Same with red, there's nothing special to it. Also, all optics are very well corrected in green and red. The only wavelength ranges that start to get sketchy for spherical aberration and other issues is when you get down to near UV and some IR, and those issues will come in the form of refractors and SCT with correctors; pure mirrors will not have this issue (but are less commonly used for this purpose by most people, especially visual, as UV and IR are imaging wavelengths only anyways). Also keep in mind, something with a strehl of 0.85 is essentially diffraction limited for this purpose (solar), and you'll likely never even get to that because of atmospheric seeing.

 

Very best,

Thanks Marty, your explanations are very thorough and easy to understand as always. I’ll be going with a green imaging filter to start experimenting.

 

I agree with Marty on his points above. I had assumed (perhaps incorrectly) you were wanted to doing imaging.  For visual you will always be limited by seeing and the fact that your eyes have a pretty slow response time and so average over the ~ few arc-sec of seeing.  For imaging it is significantly more complicated since you can at least partially "freeze out" the fluctuations due to seeing and align individual images into a single final image with improved resolution.  

Actually your assumption was on point. I intend to select a filter to image with a just acquired Meade Herschel Wedge and my Orion 120ST refractor.

[gustavo_sanchez]

I just bought the last Brandon #58 Green filter that Agena had in stock. It should do the trick I hope.

[BYoesle]

Hi Gustavo - do you only have Brandon eyepieces? The Brandon filters have a non-standard thread and if used with any other standard filter thread eyepiece you'll need a filter adapter.

 

For visual you will always be limited by seeing and the fact that your eyes have a pretty slow response time and so average over the ~ few arc-sec of seeing.  For imaging it is significantly more complicated since you can at least partially "freeze out" the fluctuations due to seeing and align individual images into a single final image with improved resolution.

 

Imaging can't create detail that isn't there to begin with, and your eye has a response time resolution of about 13 milliseconds. Imaging just allows the seeing at best moments to be "frozen," but you CAN see every bit of the available detail real-time.

 

You could make the same seeing-related arguments for using inexpensive eyepieces, or cheap float-glass filters verses a Herschel wedge.

 

I personally prefer the Continuum filter, which has now been revised to include IR blocking. Like all Baader filters, it is optically polished and hard-coated, and has been designed for the greatest degree of spectral specificity. Christian Viladrich - who knows a thing or two about solar observation and imaging - has placed the filter curves for green filters here. Christian also notes:

 

The main difference between the 540-10 nm [Contiuum] filter and green filters having a larger bandpass is the reduction of atmospheric dispersion. It makes a difference for observing the Sun at low elevation (say < 30°) with a rather large telescope (say > 200 mm).

 

Note that low solar elevation in the early morning and late afternoon can sometimes provide excellent seeing conditions.

 

As Lorenzo states in the above linked-to thread:

 

...if you take pictures infrequently and don't want to spend too much on the Continuum, a green filter paired with a uv / ir seems like a good second choice.

Emphasis added. In this case, the typical UV/IR filter paired with a #38 seems to offer a relatively insignificant price advantage over the Continuum filter which now incorporates IR blocking.

 

So for me it's a little bit about what higher quality (and cost) brings you. If you're going to the grocery store, a Yugo with so-so tires will get you there. If you you want to win the Indy 500, you'll need the best quality and engineering money can by. And IMHO I see little point to having an expensive APO and a Herschel wedge, and then skimp on the ancillary filtering. I've used both colored filters (#38) and interference filters (Continuum), and prefer the Continuum, even though it's benefits over a #38 with IR filtering may be realized infrequently.

 

As always, to each their own - and your mileage may vary... 

Edited by BYoesle, 02 October 2021 - 09:58 AM.

[hamers]

For what it's worth... Gustavo's questions and Marty's earlier response prompted me yesterday to do some comparisons of WL imaging with different filter combination, mostly using a color planetary camera so I can see how the RGB components are dispersed differently.  Mostly I want to see how much is from inherently better resolution at a shorter wavelength and how much is due to atmospheric dispersion, which for those of us in northern regions (I'm at 43o N) is important especially in winter.  I haven't analyzed everything yet, but the difference in adding the 540 nm continuum filter is pretty remarkable.  Here's one of the best ones I got, in which I used the Baader continuum 540 nm filter *and* the Baader UV/IR.  This using my Tak TSA-120 refractor, Baader solar film (OD=4.0, intended for imaging).    I'll be going through the rest of the data over the next week or so (cloudy and rain predicted).  But for me, the continuum filter has a pretty dramatic impact on the image quality. 

Attached Thumbnails

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[MalVeauX]

 the continuum filter has a pretty dramatic impact on the image quality. 

The continuum filter is not responsible though, your atmospheric seeing is. And when seeing is bad, a short wavelength like 540nm is actually going to simply be even more difficult to image with due to the disrupted wavefront from the seeing. I stress seeing because people read these things and get attached to the idea that a specific filter or component is a magic bullet and it's really not, seeing is the magic bullet. If the atmospheric seeing is good enough to support the angular resolution of a shorter wavelength, like green or blue or even near UV, then you can record higher angular resolution if you're critically sampling. But again, the filter doesn't produce this, the seeing is what allows it. Seeing is the great gate keeper. And you cannot image beyond your seeing conditions, only up to it, with lucky imaging. And in general, you're virtually never diffraction limited with seeing, you're seeing limited virtually every single time (and for many, all the time). 2 to 3 arc-second seeing is 60mm to 80mm aperture territory in terms of practical resolution potential with red wavelengths which are less disturbed by atmospheric seeing effects, and to image at these tiny apertures at critical sampling with shorter wavelengths with higher angular resolution that are more effected by atmospheric seeing requires significantly better seeing conditions to resolve. To push into larger apertures like 120mm, or more, you need closer to 1~1.3 arc-second seeing conditions and that's in red, to do that in green or blue or near UV you would need sub-arc second seeing conditions. It's quite common for people to use large apertures, fine image scales and resolve nothing more than what a 60mm or 80mm would have, due to the seeing limits they're imaging in.

 

For example, here's a low quality junk achromatic doublet refractor of the same aperture, 120mm F10 (an aperture masked synta 150mm F8 achromatic doublet) operating at F20 on 2.9um pixels (0.25"/pixel). The difference is the seeing conditions were around 0.8 arc-seconds and so I could benefit sampling higher angular resolution beyond even green wavelengths like continuum and instead go into blue or near UV wavelengths, such as 430nm at 10nm bandpass, noted here. This gear is low end, run of the mill, used here. The seeing however is excellent and made the entire difference:

 

 

Atmospheric seeing conditions are everything.

 

If your seeing is poor, you should likely use longer wavelength filtration.

 

Very best,

Edited by MalVeauX, 02 October 2021 - 10:32 AM.

[BYoesle]

Marty, your are correct - seeing is almost everything, especially for daytime seeing, which is generally worse than nighttime seeing.

 

Then again, I usually purchase my equipment based on what I hope it can provide under ideal seeing conditions. Again my reason to purchase a Herschel wedge versus a float glass filter - even though I know the latter will be just as good about 90% of the time.

 

BTW, the Celestron150 f/8 refractor (affectionately known as the "yard cannon") may be relatively inexpensive (and an especially a good deal when purchased used) but I wouldn't call it "low quality junk." It usually seems optically to be of very good quality, especially for narrow band imaging where lateral chromatic aberration is insignificant. For continuum (WL) use it is well-corrected and diffraction limited at 540 nm, and when refocused diffraction limited at 656 nm for H alpha narrow-band use. And because of its lateral chromatic aberration and optimized correction at 540 nm, the Continuum filter is the perfect filter for this scope, whether used at full-aperture or being stopped down due to local seeing conditions:

 

 

Although showing a lot of lateral chromatic aberration, the C6R green 588 nm spot is diffraction limited in this simulation by Mike Jones.

 

For example, in your image above, I assume you stopped down the C6R to 120 nm for improved spherochromatic correction at that wavelength - and not for poor seeing. The difference between 540 nm and 430 nm is a 1.25 times (540nm/430nm) wavelength-based resolution improvement with the G band (430 nm) filter. However, you can't ignore the difference in aperture was 120 mm/150 mm, or 0.80 times the full aperture resolution, which coincidentally is the reciprocal of 1.25 (150/120) - so theoretically there would be no difference between the two if the seeing were perfect. However, the 540 nm Continuum filter used at 150 mm might have been as much if not more favorable resolution-wise if the seeing allowed (Dawes limit = 0.77 arc sec), which one would assume if it was decent at 430 nm (and for the stated 0.8 arc sec), and would have 1.25 times better resolution compared to the 120 mm aperture (Dawes limit = 0.97 arc sec).

 

Just sayin ;-)

[MalVeauX]

 

Although showing a lot of lateral chromatic aberration, the C6R green 588 nm spot is diffraction limited in this simulation by Mike Jones.

 

For example, in your image above, I assume you stopped down the C6R to 120 nm for improved spherochromatic correction at that wavelength - and not for poor seeing. The difference between 540 nm and 430 nm is a 1.25 times (540nm/430nm) wavelength-based resolution improvement with the G band (430 nm) filter. However, you can't ignore the difference in aperture was 120 mm/150 mm, or 0.80 times the full aperture resolution, which coincidentally is the reciprocal of 1.25 (150/120) - so theoretically there would be no difference between the two if the seeing were perfect. However, the 540 nm Continuum filter used at 150 mm might have been as much if not more favorable resolution-wise if the seeing allowed (Dawes limit = 0.77 arc sec), which one would assume if it was decent at 430 nm (and for the stated 0.8 arc sec), and would have 1.25 times better resolution compared to the 120 mm aperture (Dawes limit = 0.97 arc sec).

 

Just sayin ;-)

Yes, precisely!

 

The goal was to specifically show angular resolution at work from a smaller aperture. And that gear, while important, is not nearly as important as the seeing is itself (ie, you do not need a continuum filter and a Tak to do photosphere imaging in poor seeing). Top gear doesn't do anything special in 3 arc-second seeing. But yes, the 120mm at 430nm is the same resolution capability as a 150mm at 540nm as you pointed out, but optics like these faster refractors (yes the C6R synta lens is not a bad lens at all in narrowband, but it's not a Tak is the point; the gear didn't matter as much as the seeing does is the point being made of course) are not as great at short wavelength and seeing becomes challenging too and those shorter wavelengths are even more effected by turbulence. The example was to really highlight how much seeing matters, less so much gear.

 

But yes, from the same cheap humble (but good) 150mm F8 synta lens with 540nm in similar sub-arc second conditions:

 

 

And a comparison from a 200mm F10 (C8 SCT) with 610nm in sub-arc second conditions; again furthering your point that if you lower the angular resolution and increase aperture you can get similar resolution comparing the wavelengths. The difference here though is that red is less effected by seeing than blue is, and it's much easier to image in red with less excellent seeing. But most people won't have sub-arc-second seeing for any of this, again highlighting the gear is less critical for resolution than atmospheric seeing is.

 

 

Seeing is the gatekeeper. Even at small aperture. But again my main point was to stress that excellent gear sits second fiddle to good seeing when it comes to resolution sampling. It's too common for people to want to get an exact filter or scope or whatever thinking it will open a magical portal in the sky and are not soberingly aware of their atmospheric seeing conditions for their area.

 

Very best,

[gustavo_sanchez]

Thanks to all; I think I got great insights based on your discussions on the topic. In my case, my seeing usually is not that great at any times (located among several mountains), but early morning it can somewhat decent. I ordered the Brandon #58 filter (with the Brandon thread to 1.25" adapter, thanks Bob), and understood that the Baader CWL should yield even better results provided my seeing allows it.

 

It's conversations like this what I like the most of CN, when you guys start "flowing down" your experience and knowledge, it's better to just sit back, listen, and enjoy. 

 

I'll do my best to report on my own findings when the time comes.

[Great Attractor]

Another point: the photosphere has more contrast in green than in red (mainly important for visual observing). Here's my old video (using a 150 mm Newtonian + PGR Chameleon with neutral gamma setting) comparing a few filters, from IR to Solar Continuum (note it's an old version of this filter, so on an unfiltered camera it only works properly with an UV/IR-cut):

 

https://vimeo.com/48074377

[hopskipson]

I've been using my SSM lately during my sessions and can attest to the fact that it's all about the seeing.  I try to catch the fleeting moments of sub-arcsecond seeing when I can.  I'm sometimes amazed that my seeing will suddenly drop to 0.8 and hover there for about 3 seconds and that is enough to capture 25-50 really good frames to stack.  I might have to wait a while but it's definitely worth it.  Sometimes I can get lucky and when I hit the capture button the SSM will stay low and sometimes not so much.  But when it comes together I can capture something like this:

 

 

as opposed to this:

 

[hamers]

For anyone interested:  There are some good papers in the scientific literature describing the how seeing depends on wavelength and other factors that might be of interest.  

The classic paper by Fried analyzed light propagation through turbulent media and predicts that seeing-limited resolution improves slightly at longer wavelength, with

resolution ~ lambda^0.2.   This trend is consistent with Marty's comments above, noting that in some cases a filter at longer wavelength might yield better results.  Experimental measurements by  Boyd (J. Optical Society of America, vol. 68, p. 877) attempted to validate Fried's calculations by doing experimental measurements of seeing as measured by the sharpness of the solar limb measured in the visible (550 nm) and mid-infrared (10 microns) and various seeing conditions,  and found a factor of 1.8 improvement at 10 microns, consistent with the idea that resolution improves as the 0.2 power of wavelength.   If the theoretical work of Fried and experimental work of Boyd hold over narrower regions of the visible, then one might expect that the resolution at 700 nm would be  (400/700)^0.2=0.89 times that at 400 nm. Or equivalently, a seeing of 2 arc sec at 400 nm would give  1.78 arc sec at 700 nm.  So, a red filter would be expected to give a slight improvement if seeing was totally dominated by turbulence.

 

Because seeing depends on other factors in addition to turbulence, there are some empirical studies of how seeing depends on other weather factors such as scattering due to humidity.  Kopeika and co-workers have published a number of papers measuring seeing at different wavelengths under different weather conditions, and then developing an equation that predicts the seeing based on wind speed, relative humidity, and temperature. Their work is totally empirical:  do a  lot of measurements, and then try to fit the data to an equation. They represent their data as the "modulation transfer function" (MTF), (bigger MTF= better resolution) and how the MTF varies the humidity, temp and wind speed at different wavelengths between 400-700 nm, and give some qualitative explanations for why the data looks as it does.  They show, for example, that steady winds improve resolution by dispersing aerosols that form, with more significant improvements at short wavelengths (opposite to turbulence), while higher temperatures and higher humidity levels lead to reduced resolution.  Your own mileage will vary and I would expect that the influence of these different factors may depend a lot on your local weather situation,  but there are some interesting points in these paper that could help to guide whether a filter is helpful or whether simply having more photons (yielding shorter frame acquisitions times) would help the most.    

 

The "Solar Astronomy" book by Christian Viladrich (and other cloudy-nighters), in the discussion of the 540 nm continuum filter says that it is intended to reduce atmospheric dispersion,  which is not accounted for in any of the above works. Atmospheric dispersion can be measured pretty easily just by looking at a star or planet at high magnificantion with a one-shot color camera and measuring the shift in blue vs. red components.  I recently measured about 0.7 arc-sec for an object ~ 25 degrees above the horizon. (in Wisconsin in January the sun never gets higher than ~26 degrees aloe the horizon).   So atmospheric dispersion may not be completely negligible either and could factor in the best "width" if filter under conditions of exceptionally good seeing. 

 

Bottom line: There is probably no "universal" choice of best filter, and any filter choice will depend greatly on local weather conditions and the position of the sun. !  As Marty and Bob Y. point out, seeing indeed controls (almost) everything, but how seeing depends on wavelength may not be so easy to predict and may be different in, say, Wisconsin vs. Florida vs. Arizona.  Papers like Kopeika's can perhaps provide at least a qualitative basis for making choices.  

 

I can's post the papers to CN due to copyright, but if a smallish number of people want me to send them by email I can probably do that. 

 

Papers:

D.L. Fried, "Optical Resolution through a randomly-inhomogeneous medium for very long and very short exposures",  Journal of the Optical Society of America 1966,  vol. 56, p. 1372-1379 

Robert W. Boyd, "Wavelength dependence of seeing",  Journal of the Optical Society of America 1978, vo. 68, pp. 877-882

 

R. Kopeika, et al.,  "How weather affects seeing through the atmosphere", Optical Engineering 1986, vo. 25, p. 505

Edited by hamers, 03 October 2021 - 03:01 PM.

[chemman]

Thank you Bob Hamers for that intensly analytical dissertation on thus subject.  As a scientist it is the only approach I can use to what I do in solar.  Deviations for me may ease into my work and deviations may be necessary due to availability of specific technologies to me but the numerical proven solution I know is almost always (there is the Quantum Mechanics in me) the correct solution that will yield consistant results.   

 

It turns out that I live where I do for one reason only.  I can drive to 12,000 feet above sea level in less than 2 hours.  I find it very interesting that my house is 8 miles down a back road, I travel 8 miles, as the crow files,  to get to my favorite viewing location 2 miles high.  If the additional 6 miles of atmospheric conditions cooperate,  say jet stream and clouds, seeing conditions are literally out of this world.  I live here for the seeing, well and the snow, trees, scenery,  mountains,  lake, cool weather, snow and a few other reasons, lol.  

 

Chuck

Edited by chemman, 04 October 2021 - 11:31 AM.

[PatrickVt]

1.  On solar imaging:  I'm not sure what you are looking for here but I assume you are looking for camera advice.  A monochrome astro camera is the recommended camera.  

 

2.  On which light filtering (solar film, glass filters, wedges, etc):  I would recommend a solar wedge, for sure.  I've used all of these that you have mentioned and my solar wedges provide far better views and especially images than any of the others.  Of course, I'm referring to a solar wedge with Continuum and UV/IR Cut filter as well as the necessary polarizer/ND.    

 

3.  On safety while practicing solar astronomy:  Safety is important.  Know your equipment.  Understand all your equipment.  Know the purpose of each component.  Never leave the equipment unattended during daylight.  Before putting light on your eye or camera, always take a quick look at your imaging train to ensure all is correct for safe solar imaging.  If you need checklists, by all means create some checklists.  

 

Patrick

[hamers]

Thank you Bob Hamers for that intensly analytical dissertation on thus subject.  As a scientist it is the only approach I can use to what I do in solar.  Deviations for me may ease into my work and deviations may be necessary due to availability of specific technologies to me but the numerical proven solution I know is almost always (there is the Quantum Mechanics in me) the correct solution that will yield consistant results.   

 

It turns out that I live where I do for one reason only.  I can drive to 12,000 feet above sea level in less than 2 hours.  I find it very interesting that my house is 8 miles down a back road, I travel 8 miles, as the crow files,  to get to my favorite viewing location 2 miles high.  If the additional 6 miles of atmospheric conditions cooperate,  say jet stream and clouds, seeing conditions are literally out of this world.  I live here for the seeing, well and the snow, trees, scenery,  mountains,  lake, cool weather, snow and a few other reasons, lol.  

 

Chuck

Yeah, sorry if it was too much of a dissertation !!  I do a lot of one-of-a-kind optics-based instrument development and this kind of quantitative approach to optimizing measurement problems is pretty much in my blood and sometimes I just can't help myself...  I'm glad you appreciated it !

Bob

[gustavo_sanchez]

1.  On solar imaging:  I'm not sure what you are looking for here but I assume you are looking for camera advice.  A monochrome astro camera is the recommended camera.  

 

2.  On which light filtering (solar film, glass filters, wedges, etc):  I would recommend a solar wedge, for sure.  I've used all of these that you have mentioned and my solar wedges provide far better views and especially images than any of the others.  Of course, I'm referring to a solar wedge with Continuum and UV/IR Cut filter as well as the necessary polarizer/ND.    

 

3.  On safety while practicing solar astronomy:  Safety is important.  Know your equipment.  Understand all your equipment.  Know the purpose of each component.  Never leave the equipment unattended during daylight.  Before putting light on your eye or camera, always take a quick look at your imaging train to ensure all is correct for safe solar imaging.  If you need checklists, by all means create some checklists.  

 

Patrick

Patrick, thanks for the contribution. My post was meant to be posted on another topic, regarding "Best of Solar" topics. Sorry for the confusion. Please carry on with the original purpose of this topic.

[skaiser]

OK

 starting to look at branching out from night sky imaging to Solar.

Doing a lot of reading.

I am leaning toward the   2" Baader Herschel Prism Version P ,and a  green filter and UV/IR ? to get started.

I'm looking at using this with my AT92 , 92mm f/5.5 apochromatic triplet refractor.

I may have missed this in reading.

Do I need some sort of main aperture filter to protect my optics from any light concentrated heat?

Any long term degradation of optics from imaging the sun with this type setup?

 

Thanks for any help

take care

[PatrickVt]

You should have no problem with your AT92.  Unless you plan to leave the scope out in the sun all day, every day for years, I don't see how the sun would or could damage the telescope.  

 

For white light solar viewing with any of the various branded Herschel wedges, you do not need any type of front mounted energy rejection filter.  

 

Worth noting however is that the Baader photographic solar wedge is not to be used for visual observing as delivered.  I believe you would need to add an ND filter or swap out the ND filter for a stronger one for visual observing.  I think that is the only difference between the visual version and the photographic version.  I'm sure someone with more knowledge on the Baader solar wedges will confirm or correct this info.  

 

Patrick

[BYoesle]

Worth noting however is that the Baader photographic solar wedge is not to be used for visual observing as delivered.  I believe you would need to add an ND filter or swap out the ND filter for a stronger one for visual observing.  I think that is the only difference between the visual version and the photographic version.

Both the Baader V (visual) and P (photographic) Herschel wedges include a built-in ND3.0 filter and therefore are safe for visual use. However, it is removable in both versions. Visual use should ALWAYS use the ND3.0 filter. 

 

I am leaning toward the   2" Baader Herschel Prism Version P ,and a  green filter and UV/IR ? to get started.

 

They both also come with a 2 inch Continuum 540/10 nm filter (with IR blocking), so no additional "green" filter is needed. I would consider additional IR blocking if only using the ND filters and/or polarizer filter without the Continuum - see Polarizing and ND filter transmission curves here.

 

The P version also comes with additional ND1.8, 0.9 and 0.6 ND filters which can be substituted for the ND3.0 for IMAGING USE ONLY. The additional filters are what accounts for the added cost of the P version.

 

 

Baader HW Manual.

 

For me personally I find that in addition to the ND3.0, an ND0.6 makes the brightness level more comfortable, and this includes my using either a polarizer (public outreach), or the Continuum filter which provides the best overall optical performance due to both telescope optical issues and atmospheric dispersion issues. See related thread here.

Edited by BYoesle, 19 November 2021 - 02:36 PM.

[PatrickVt]

I never realized that the Baader P wedge came with the ND3 too.  I thought the ND3 only came with the V version while the P came with lesser ND filters.  I was thinking it was kind of the same idea as the old Baader solar film being available in two ND strengths.  Thanks for pointing that out.

 

Perhaps Baader should really rename the P version as a VP version.  I probably would have been more inclined to purchase the Baader P if I knew this info about these two models.  At the time, I was afraid to commit to photography or visual only.  

 

Anyway, I learned something today so I can call it a day now! 

 

Patrick

[wargrafix]

Marty is certainly right about seeing being the final chapter in having successful images.