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Stacking Lumicon filters

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#1 bikerdib

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Posted 16 July 2020 - 10:49 AM

Call me crazy (come on, you won't be the first to do so).  Last night I had my 14" Edge set up to do some Jupiter, Saturn and Mars viewing.  But while waiting for those to get high enough for good viewing with the high humidity clouding the atmosphere and the African dust not helping the situation either, I visited some deep space objects.  On the planetary and emission nebula I was using either my Lumicron UHC or O-III filters.  I used to have a Celestron O-III filter and to be honest, on the Western Veil nebula it actually showed more of the feathery nebula towards the end of the nebula because it blocked more of the unwanted light (in my atmospheric conditions anyway).  FYI, I was using my ES 40mm eyepiece for around 97 power.  And for equipment description, I use a Williams Optics 2" diagonal threaded to the back of the scope and the filters are 2 inch.

 

For laughs, while the O-III filter was screwed into the eyepiece, I passed the UHC filter between my eye and the eyepiece basically stacking the filters.  That seemed to bring out a little more of the feathery end of the Witches Broom.  I then tried to stack the filters but Lumicon chose not to thread the filter housing for stacking.

 

So, was it just my imagination the the 2 filters stacked could bring out more of the fainter nebulous region of the Western Veil?  And if that would work, how could I go about stacking the filters?


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#2 MrJones

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Posted 16 July 2020 - 11:34 AM

There's been some talk of filter stacking recently and no reason it couldn't improve contrast under some conditions. I think bigger apertures and great transparency are some of the conditions. I haven't done much of it ... yet. Some filter brands have both sides threaded so are easily stacked. You could also possibly screw one onto the diagonal and one on the eyepiece for setups with diagonals.

 

There's also been some some discussion of the high contrast of the Celestron/Baader OIII filters.

 

https://www.cloudyni...ers/?p=10280902

 

I've also had my best views (most wispy) of the Veil Nebula with one and my C11. 2 nights ago I had my Z12 out on a good night and tried more comparisons between my excellent SVOTek Lumicon OIII and a recently purchased Celestron OIII that has Baader molded into the back of the case. Results are:

 

M27 and M57 - these were brighter and a little more extensive with the SVOTek Lumicon, no doubt which one was better with these

Crescent Nebula - a little dimmer with the Celestron yet a little more of the brightest region running through the 4 stars was visible

Veil - a little dimmer with the Celestron but also a little more detail at the edges on both Eastern and Western parts

 

The Cygnus nebulae might be benefiting from the increased contrast but lower throughput due to the brighter background in that region. Anyway it really seems like it's worth owning a good OIII filter that maximizes both main OIII frequencies and also one that concentrates on just 500.7 nm.


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#3 sg6

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Posted 16 July 2020 - 11:52 AM

For laughs, while the O-III filter was screwed into the eyepiece, I passed the UHC filter between my eye and the eyepiece basically stacking the filters.

By rights what should have happened was no real change, maybe a 5% dimming.

However more likely is that the 2 OIII bands were slightly off center to each other and so what arrived at your eye was a narrower "OIII" bit of the spectrum. And that this for whatever reason resulted in a slightly different/better view/image.

 

The Hb spectra should have been blocked by the OIII anyway, and even if the UHC passed Ha again the OIII should have blocked that. But each would be passing some OIII and exactly what would depend on the overlapping curves from each filter. The result would have to (by rights) be less, or narrower, then just the OIII alone.

 

Was a filter measurement comparison some year ago. Made interesting reading as the peak transmission wavelength tended to drift around a bit. So one OIII filter didn't peak at the same wavelength and another. Some if I recall missed the actual wavelength altogether.


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#4 bikerdib

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Posted 16 July 2020 - 11:58 AM

There's been some talk of filter stacking recently and no reason it couldn't improve contrast under some conditions. I think bigger apertures and great transparency are some of the conditions. I haven't done much of it ... yet. Some filter brands have both sides threaded so are easily stacked. You could also possibly screw one onto the diagonal and one on the eyepiece for setups with diagonals.

 

There's also been some some discussion of the high contrast of the Celestron/Baader OIII filters.

 

https://www.cloudyni...ers/?p=10280902

 

I've also had my best views (most wispy) of the Veil Nebula with one and my C11. 2 nights ago I had my Z12 out on a good night and tried more comparisons between my excellent SVOTek Lumicon OIII and a recently purchased Celestron OIII that has Baader molded into the back of the case. Results are:

 

M27 and M57 - these were brighter and a little more extensive with the SVOTek Lumicon, no doubt which one was better with these

Crescent Nebula - a little dimmer with the Celestron yet a little more of the brightest region running through the 4 stars was visible

Veil - a little dimmer with the Celestron but also a little more detail at the edges on both Eastern and Western parts

 

The Cygnus nebulae might be benefiting from the increased contrast but lower throughput due to the brighter background in that region. Anyway it really seems like it's worth owning a good OIII filter that maximizes both main OIII frequencies and also one that concentrates on just 500.7 nm.

So, you pretty much agree with me about the Celestron/Baader filter being a little better on the Veil.  I actually am thinking about buying another Celestron or Baader.  Kind of sucks though because I just recently did a little house cleaning and sold some filters that I've accumulated over the years and that were duplicates, including a 2" Celestron O-III.  Last night I checked if I could do your suggestion of one in the diagonal and one in the eyepiece, unfortunately with the SCT threaded on diagonal a filter cannot be fitted to the diagonal.  However, I need to pull the scope back out of the carry case to see if the rear of the scope has provision for a filter in it.  It would be a little hassel to have to unscrew the diagonal everytime I wanted to add a filter there though.


Edited by bikerdib, 16 July 2020 - 12:04 PM.


#5 bikerdib

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Posted 16 July 2020 - 12:00 PM

By rights what should have happened was no real change, maybe a 5% dimming.

However more likely is that the 2 OIII bands were slightly off center to each other and so what arrived at your eye was a narrower "OIII" bit of the spectrum. And that this for whatever reason resulted in a slightly different/better view/image.

 

The Hb spectra should have been blocked by the OIII anyway, and even if the UHC passed Ha again the OIII should have blocked that. But each would be passing some OIII and exactly what would depend on the overlapping curves from each filter. The result would have to (by rights) be less, or narrower, then just the OIII alone.

 

Was a filter measurement comparison some year ago. Made interesting reading as the peak transmission wavelength tended to drift around a bit. So one OIII filter didn't peak at the same wavelength and another. Some if I recall missed the actual wavelength altogether.

That is why I said I kind of did it for laughs, I didn't expect as drastic of a change as I got.  And I agree with your reasoning on what happened.



#6 MrJones

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Posted 16 July 2020 - 12:31 PM

So, you pretty much agree with me about the Celestron/Baader filter being a little better on the Veil.  I actually am thinking about buying another Celestron or Baader.  Kind of sucks though because I just recently did a little house cleaning and sold some filters that I've accumulated over the years and that were duplicates, including a 2" Celestron O-III.  Last night I checked if I could do your suggestion of one in the diagonal and one in the eyepiece, unfortunately with the SCT threaded on diagonal a filter cannot be fitted to the diagonal.  However, I need to pull the scope back out of the carry case to see if the rear of the scope has provision for a filter in it.  It would be a little hassel to have to unscrew the diagonal everytime I wanted to add a filter there though.

Some good and bad news - I just verified that my 2" Celestron OIII filter is threaded on both sides. I think all of the Baaders are and also Astronomiks.


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#7 Starman1

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Posted 16 July 2020 - 12:53 PM

It must be an old Lumicon not to be threaded on both sides of the glass.

So some behavior you saw was due to different bandwidths overlapping as well.

 

I've done extensive testing of O-III filters on the Veil Nebula:

7-8.5nm bandwith--the "broom" section of the Witches Broom looks like a hollow tube with filigree on the outside--very detailed and delicate.

on the other end, one segment of "broom" was visible curving away.  On the other side of the Veil, the "rake tines" or "dragon's teeth" had delicate small striae within.

Pickering's Wedge was almost invisible.

 

10nm bandwidth--this filter was junk and the bandwidth missed the 500.7nm O-III line.  I literally threw it away.

 

12-13nm bandwidth--the nebula was brighter, and nebular cloudiness obscured some of the filigree in the broom handle segment.  The Broom end now had 2 distinct curved segments and one thin wisp and was over 3x as wide.

Pickering's Wedge was distinctly seen.  2x as much nebula was visible on the other side of the Veil and the space in between the rake tines was filled with wispy nebulosity.  I could see small clouds and striae of nebula from one side of the Veil to the other.

 

15nm bandwidth--the background sky was getting brighter so much of the nebulosity was getting harder to make out, but all sections, including Pickering's Wedge, were still visible.

 

18-25nm bandwidth--a poorer, more light polluted view, with the nebula suppressed in extent.

 

28nm bandwidth--better than the filterless view, but a poor excuse for a filter.

 

22nm bandwidth "Narrowband, UHC-type" filter--A better view than the 18-25nm O-III filters, with more nebulosity visible everywhere.  There must be *some* H-ß emission here.

 

Overall, the amount of nebulosity seen was best in the 12-13nm bandwidths which picked up both O-III lines.  Certain small details were visible with the narrowest filters, but the loss of so much nebulosity didn't seem worth it.


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#8 Jon Isaacs

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Posted 16 July 2020 - 03:53 PM

So, you pretty much agree with me about the Celestron/Baader filter being a little better on the Veil.

 

 

I had a Celestron O-lll filter For a number of years. I see more with a ~14 nm filter..  I generally go two ways with the Veil, a fast refractor with a large exit pupil to take in the entire field and watch the bright "glow" or a large Dob with a large exit pupil. 

 

For my old eyes, the large exit pupil is a help. I'm sure they're not as sensitive as they used to be but they do dilate to greater than 7 mm..

 

Jon


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#9 bikerdib

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Posted 16 July 2020 - 03:56 PM

Thanks for your review report Don.  Actually my Lumicrons are Gen 3 but no threads for stacking.

 

Question, when you did the tests, what Bortle sky brightness were you in?

 

I'm really thinking I may be painting the Celestron filter with a "rose colored" memory.  I say that because I have seen more detail on other objects with the Lumicons than I ever did with the Celestron.  It just seems there is something about the feathery end of the Witches Broom that the Celestron brought out better.  With the Lumicon, I can definately see more hint of the swirling pattern in the handle section of the Broom.  I can't remember ever seeing more than ghostly hints of the Triangle.  I can also see some of the swirling detail in the Eastern Veil with the Lumicron.



#10 bikerdib

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Posted 16 July 2020 - 03:57 PM

I'm also curious what magnification most of you view the Veil with?

 

I am aware that my 14" Edge 40mm eyepiece combo does not give me the best exit puplil but I don't have any eyepieces longer than 40mm.  The 14" Edge definitely isn't my first choice for nebula observing but like I said, I was planning on doing the 3 major planets later and was filling in the time beforehand.


Edited by bikerdib, 16 July 2020 - 04:05 PM.


#11 Starman1

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Posted 16 July 2020 - 05:04 PM

Thanks for your review report Don.  Actually my Lumicrons are Gen 3 but no threads for stacking.

 

Question, when you did the tests, what Bortle sky brightness were you in?

 

I'm really thinking I may be painting the Celestron filter with a "rose colored" memory.  I say that because I have seen more detail on other objects with the Lumicons than I ever did with the Celestron.  It just seems there is something about the feathery end of the Witches Broom that the Celestron brought out better.  With the Lumicon, I can definately see more hint of the swirling pattern in the handle section of the Broom.  I can't remember ever seeing more than ghostly hints of the Triangle.  I can also see some of the swirling detail in the Eastern Veil with the Lumicron.

I did all my tests at a site with 21.35-21.55 mpsas skies. 

I don't pay attention to the Bortle Scale because the descriptions have no relation to what I see in the sky.

My site answers to these descriptions:

the zodiacal light is visible and colorful
the gegenschein is visible
many Messier and globular clusters are naked-eye objects
limiting magnitude with 12.5 in (32 cm) reflector is 17.5 (with effort)
the summer Milky Way is highly structured
M15, M4, M5, and M22 are naked-eye objects
light pollution domes visible in several directions
surroundings are clearly visible, even at a distance
clouds are noticeably brighter than the sky
M33 is not visible

These descriptions come from 5 different classes because they describe my sky at a high-altitude dark site.

Any dark place in SoCal is an "oasis", surrounded by cities at a distance so that multiple light domes are visible.

It is the sky from 30° to the zenith that resembles a true dark site, and from 30° down, a light-polluted site.

It's why I don't mind that the site is a parking lot surrounded by tall trees--no horizon, but also very little in the way of visible light domes.

Naked Eye limiting magnitude about 6.9-7.0 at/near the zenith.


Edited by Starman1, 16 July 2020 - 05:19 PM.

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#12 Starman1

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Posted 16 July 2020 - 05:07 PM

I'm also curious what magnification most of you view the Veil with?

 

I am aware that my 14" Edge 40mm eyepiece combo does not give me the best exit puplil but I don't have any eyepieces longer than 40mm.  The 14" Edge definitely isn't my first choice for nebula observing but like I said, I was planning on doing the 3 major planets later and was filling in the time beforehand.

My two most-used magnifications were 107x (8.6x/inch) and 140x (11.2/inch).

It is brighter at a lower power, but details get lost.

For emission nebula viewing with a 14", I'd recommend nothing below 80x, and nothing above 150x.


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#13 Supernova74

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Posted 16 July 2020 - 05:17 PM

no your not crazy 

i must admit Astronomy can be trial and error at times going against what filter is designed for what purpose at times it can suprise you I made a mistake once viewing Jupiter with an OIII filter was suprised it even worked to a certain degree with the banding structure on the planet I didn’t even know you could use UHC on the planets.no set rules in this game you generally do discover thease things by mistakes some work and some don,t.ive also accidentally stacked to filters one on the diagonal end and the other on the eyepiece barrel.



#14 Starman1

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Posted 16 July 2020 - 05:23 PM

no you're not crazy 

i must admit Astronomy can be trial and error at times going against what filter is designed for what purpose at times it can surprise you I made a mistake once viewing Jupiter with an OIII filter was surprised it even worked to a certain degree with the banding structure on the planet I didn’t even know you could use UHC on the planets.no set rules in this game you generally do discover these things by mistakes some work and some don't.i've also accidentally stacked two filters one on the diagonal end and the other on the eyepiece barrel.

One little tidbit: a UHC filter makes seeing Antares as double 100% easier.  It dims the red giant by about 3 magnitudes or more while barely dimming the companion.

When the two stars are closer to the same magnitude, Antares becomes really easy to split.


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#15 bikerdib

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Posted 16 July 2020 - 06:46 PM

Thanks again Don.  I say my 14" Edge isn't my scope of choice for nebula because my ES 16" truss newt gives much better views.  And your sky conditions are MUCH better than where I regularly observe.  I live in a small town of 1200 people but I'm only about 25 miles from the edge of Houston and that distance is shrinking quickly.  With the usual high humidity the sky glow can be pretty bad these days.  Back when I started here 46 years ago the conditions were much better but Houston just keeps spreading and more and more people unfortunately think they have to light up their yards so it looks like daytime 24 hours a day.  As to magnification (and related exit pupil size) we are pretty close to what I normally use.  Thanks for the tip about Antares, I need to try that.



#16 bikerdib

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Posted 16 July 2020 - 06:47 PM

Supernove, I have tried my UHC filter on Jupiter too and while it helps, I much prefer either a variable polarizing filter or my Baader Moon and Skyglow on it.



#17 bikerdib

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Posted 16 July 2020 - 06:49 PM

Jon, I know about old eyes.  Being 64, I can only wonder what I could have seen with my current equipment back when I started the hobby.  Between the pesky floater trains and mild cataracts (so far) things just aren't what they used to be.



#18 Miranda2525

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Posted 16 July 2020 - 11:25 PM

There really is no point in stacking nebula filters. OIII and UHC are good to have and use separately.



#19 Supernova74

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Posted 17 July 2020 - 02:48 AM

well there is another alternative regarding planetary observing is useing An ADC (atmospheric turbulence correcter) and even tho imagers use them thay can also be used for visual purposes.

i think thay do work to a certain degree however I’ve seen three exsamples from mainly ZWO,Omegon and Altair Astro which look exsactly the same,I’m not sceptical on there performance some what but I am in quality as for $100-150 for a device which has prisms working conjunction with each other to block or improve the atmospheric turbulence is a little debatable to be honest is the glass thay useing any good I don’t know just seem cheap and in this world cheap does,nt useally perform very well in amateur Astronomy.



#20 Miranda2525

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Posted 17 July 2020 - 03:06 AM

Personally, when viewing planets, the largest factor, (for me), is the seeing.

 

Once the seeing is excellent, I find no use in filters on any of the planets except for Venus, which is unusually bright.

On Venus I use a 13% neutral density filter. The rest of the planets, I personally don't find using any to be majorly useful. I've tried a lot of them.

 

That's just me. Experimenting is fun for some.


Edited by Miranda2525, 17 July 2020 - 03:07 AM.


#21 Supernova74

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Posted 17 July 2020 - 03:10 AM

Personally, when viewing planets, the largest factor, (for me), is the seeing.

 

Once the seeing is excellent, I find no use in filters on any of the planets except for Venus, which is unusually bright.

On Venus I use a 13% neutral density filter. The rest of the planets, I personally don't find using any to be majorly useful. I've tried a lot of them.

 

That's just me. Experimenting is fun for some.

Yes you definitely need some kind of filter on venus.blue an purple work well.yes I do find on most of the planets that coloured filters just does,nt look natural.


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#22 BillP

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Posted 17 July 2020 - 04:43 PM

7-8.5nm bandwith--the "broom" section of the Witches Broom looks like a hollow tube with filigree on the outside--very detailed and delicate.  on the other end, one segment of "broom" was visible curving away.  On the other side of the Veil, the "rake tines" or "dragon's teeth" had delicate small striae within. Pickering's Wedge was almost invisible.  . . .
 
12-13nm bandwidth--the nebula was brighter, and nebular cloudiness obscured some of the filigree in the broom handle segment.  The Broom end now had 2 distinct curved segments and one thin wisp and was over 3x as wide.
Pickering's Wedge was distinctly seen.  2x as much nebula was visible on the other side of the Veil and the space in between the rake tines was filled with wispy nebulosity.  I could see small clouds and striae of nebula from one side of the Veil to the other.  . . .
 
Overall, the amount of nebulosity seen was best in the 12-13nm bandwidths which picked up both O-III lines.  Certain small details were visible with the narrowest filters, but the loss of so much nebulosity didn't seem worth it.

 
Given those two descriptions, seems like you would want to have both a 12-13nm and a 7-8.5nm handy and not just one.  What brands were each of those?

 

 

 

<filters>


Edited by BillP, 17 July 2020 - 04:48 PM.


#23 Starman1

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Posted 17 July 2020 - 06:13 PM

Two Baader O-III--one older (claimed 7nm) and one newer (claimed 10nm, but measured less)

[Celestron is a re-badged Baader, so should fall into the range]

These were one-line O-IIIs, picking up only the 500.7nm line.

 

And TeleVue II (12nm), Lumicon Gen.3 (11nm), and Astronomik O-III(12nm) contemporary filters.

Also, one older Lumicon O-III (13nm)

These were all 2-line O-III filters, also picking up the 495.9nm line.

 

There is also an O-III line at 493.1nm, but the output is tiny compared to the other two lines.

It is picked up by narrowband filters that also pass the 486.1nm H-ß line.

 

Yes, some tiny details were visible in the single line filter with great detail.

But even with the 12.5", the image was very dark and the loss of nebulosity was disappointing.

It wouldn't be an issue for photographers, who can just increase the length of exposure.


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#24 MrJones

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Posted 21 July 2020 - 09:36 AM

Two Baader O-III--one older (claimed 7nm) and one newer (claimed 10nm, but measured less)

[Celestron is a re-badged Baader, so should fall into the range]

These were one-line O-IIIs, picking up only the 500.7nm line.

 

This is wrong. The Celestron/Baader visual OIII filters have ~10-30% transmission at 496nm.

 

https://www.cloudyni...2#entry10283093

 

This is a clever design to maximize contrast with less expensive materials to make a high contrast filter. A main problem is variation in the results as can be seen in the same link.



#25 Starman1

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Posted 21 July 2020 - 11:57 AM

My two Baader O-IIIs had transmissions of (rounded off): 7nm--20% 496nm, 89% 501nm

8.5nm--13% 496nm, 90% 501nm

Those fall in the range of the Celestron filters.

 

Now, how does that work on the spectral lines?

Normally, the 495.9nm line has about 25-30% the energy of the 500.7nm line (and the 493.1 O-III line < 1%)

Let's call that 30 and 100.

My first filter reduced 30 to 6 and 100 to 89.  Instead of a 1:3.33 ratio of brightness, it was now 1:15

The 2nd filter reduced 30 to 3.9 and 100 to 90.  Instead of a 1:3.33 ratio, it was now 1:23

 

In essence, both filters reduced the presence of the 495.9nm line significantly, to a level where the presence of the line was inconsequential in the image.

 

Compare that with my TeleVue Bandmate II O-III filter, with a transmission of 99.2% at 495.9nm and 98.4% at 500.7nm.

The corresponding energy values become 29.8 and 98.4, a ratio of 3.3: 1, very close to the actual value of the O-III balance.

 

I grant you, technically the Baader O-III filters had SOME output at 495.9nm, but with such a reduced output at an already reduced output, to all intents and purposes, they had no noticeable output at 

the 495.9nm wavelength.  Perhaps they would not be ideal for imaging, where a narrower bandwidth with 0 output at 495.9nm might be preferred.

 

But for the best use on an O-III emission nebula, they are neither optimum for visual use nor astrophotography.

And the FWHM bandwidth figures for both would not include the 495.9nm line.


Edited by Starman1, 21 July 2020 - 11:59 AM.



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