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Pushing the filter envelope: Observing galactic nebulae with handheld binoculars under suburban skies

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#1 C.Hay

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Posted 09 August 2020 - 08:58 AM

Like many, I live under suburban skies. And like many, I lack the inclination and means to drive long distances or install an observatory. Yet I have a burning interest in galactic nebulae. What to do? My solution: make full use of binoculars and make full use of filters.

 

By "handheld binoculars" I mean those which I can hold without any particular support for enough time to get a good view of the object. This extends for me to a 10x70 weighing 2 kilos and a 15x70 weighing less than 1.5 kilos, and naturally includes stabilised binoculars.

By "suburban skies" I mean those in which NELM at zenith is around 5m0. I would define 5m5 as "very good suburban at transition to rural", and 4m5 as "poor suburban". Away from zenith NELM declines, and is regularly 4m-something near the horizon. What can be achieved under such skies?

 

Last night I was out with the 6x24 binoculars after having found a simple way to fit a threaded 1.25-inch adapter to the front barrels. Sky quality was exceptional for my circumstances, with 5m5 in zenith and the bifurcation of the Milky Way between Cygnus and Aquila distinct. For first-light with the filtered 6x24, I chose the three largest nebula complexes in Cygnus: NGC 7000 (North America) with IC 5067 (Pelican); the IC 1318 complex around Sadr; and the Veil Nebula.

 

As the binoculars have 12° FOV, I had high hopes of seeing the whole Veil Nebula floating in wide surroundings, and even of catching the IC 1318 complex in its broader context. Too high hopes, it emerged, but read on:

 

NGC 7000 (North America)
Unfiltered: Nothing doing
Astronomik UHC: Full shape of North America emerges, incl. Florida and Mexico. No sign of Pelican.
Lumicon UHC old-type: Sky background darkened, but no real gain over Astronomik UHC.
Astronomik OIII 12nm: North America now set off better from surroundings. Still no sign of Pelican.
Baader OIII 8.5nm: Best sight! North America floating against truly dark sky background. Eastern margin, where transition to dense star field was still a little unclear in OIII 12nm, is now quite clear. A vague hint of the Pelican.
Astronomik H-Beta 12nm: North America still there in full north-south extent, but reduced in east-west extent and amorphous compared to the view in OIII, more like a long potato than the continent. No sign of Pelican.

 

After each filter change I panned over to the big 68-Cygni Nebula (Sh 2-119), in the wild hope of seeing, with such tiny aperture, the brightest eastern section. No luck, and no surprise!

However, I noticed during each such excursion that North America remained strong and distinct right up to the edge of the 12° field of view. This was a very pleasing effect. It bears out the advantage of fitting filters in front of the objectives rather than behind the eyepieces.

 

Next up: The Veil Nebula with its brightest elements, the western Witch’s Broom NGC 6960 and the eastern Network Nebula NGC 6995.
This was a disappointment. Only with the Astronomik OIII 12nm filters did I get a vague impression of the position and extent of the Witch’s Broom, and a very faint notion of the Network Nebula directly at 52 Cygni.

 

Now for the most ambitious project of the night: The IC 1318 complex around Sadr, the brightest component of which is IC 1318A (DWB 82, also known as Dolphin Nebula), a triangular patch on the northern fringe of the complex.
Nothing seen in any of the filters. Here I was not really disappointed, for my only hope was for IC 1318A in H-Beta (it is my consistent experience in larger binoculars that all elements of the complex respond best to H-Beta). My clear sighting of North America in H-Beta suggests that these binoculars, although 50 years old, have decent transmission at that wavelength. So I think the non-sighting is due to a mixture of insufficient exit pupil and too small image scale.

 

I strained my eyeballs out to get a sighting of the Crescent Nebula NGC 6888, pinning particular hope on the 8.5nm OIII filters, but to no avail. Here, again, this is surely due to a mixture of insufficient exit pupil and too small image scale, probably compounded by a lack of modern coatings on the old binoculars.

 

Those of you who have read on up to here may interject that, overall, no great results were achieved. And yet I found the night strangely satisfying and relaxing. Before packing up I looked around without filters through the binoculars, now with heightened sensitivity for and appreciation of the stars and colours that the filters had swallowed.
The view with the 8.5nm OIII filters of the North America Nebula floating with 5 degrees of space to all sides of it will remain with me for long.

 

I aim to continue occasional reports of this kind in this thread. I welcome those of others. I beg you only to gauge and report NELM as accurately as you can, for reports without that information would be impossible to compare to others.

 

CS, Christopher


Edited by C.Hay, 10 August 2020 - 02:22 AM.

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#2 C.Hay

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Posted 18 August 2020 - 06:13 AM

Just spotted a mistake in my text. I mixed up the Witch's Broom and the Network Nebula (Eastern Veil). The passage should read properly:

Only with the Astronomik OIII 12nm filters did I get a vague impression of the position and extent of the Network Nebula, and a very faint notion of the Witch’s Broom directly at 52 Cygni.


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#3 brentknight

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Posted 19 August 2020 - 03:07 PM

Now that Milky Way season is coming around again, I'll have to do some more binocular/filter viewing.  I've got a new site that is much better than my B5 front yard and I'd love to see what difference that makes.

 

Last year I did use UHC and O-III filters on my Nikon 10x50's.  What seemed to work best for me was using a single filter over one objective and using both eye's to view the target.  The brain usually can integrate the view and give you the best of both worlds...  I was surprised that I could pick out M57 pretty easily using this method (but not with 7x35's).


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#4 Rocklobster

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Posted 03 September 2020 - 11:04 PM

Like many, I live under suburban skies. And like many, I lack the inclination and means to drive long distances or install an observatory. Yet I have a burning interest in galactic nebulae. What to do? My solution: make full use of binoculars and make full use of filters.

<...snip...>

That was a very interesting read. Thanks for sharing mate.



Sent from my N10 using Tapatalk


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#5 PEterW

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Posted 05 September 2020 - 05:36 AM

I observe in very similar circumstances, though with poorer skies (never see Milky Way hints). Interesting, I’ve recently got some CLS filters for the front objectives of my 50mm and 2x54 bins and some smaller h-beta for holding in front of the eyepieces or screwed into the eyepieces of the larger binoculars. Maybe I need narrower OIII? My concern is finding stuff if all the stars have been diminished. Maybe one narrow and one wider would work, let brain merging make things appear? Do you have winged eye cups and stray light shields to minimise spurious light?

These objects are my favourites, but I normally “cheat” (night vision user using a narrow hydrogen alpha filter), many of these nebulae are very obvious, so you tend to “nebula hop”’to find the fainter stuff. However we find that transparency is important, there are nights that look the same, but a quick check of a few nebulae shows that one night fainter stuff is worth looking for and another where you can barely see the brighter ones.
Sharpless 119 is fainter, I’d see if you can see hints of IC5067 below the North America and pelican. Also closer to Sadr the “butterfly” shape is the brightest, not sure if this is the patch you refer to?

Thanks

Peter

#6 C.Hay

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Posted 20 September 2020 - 04:30 AM

Peter, I think it may indeed make sense to get narrower OIII, or at least to try them out. On the other hand, I must say that when NELM goes into 4mX territory it becomes nigh impossible to see any of the extended galactic nebulae, no matter what filter. My visual experience with CLS filters has been entirely negative; they seem to be made more for photography. I don't get on well with filter mixing. I find this is strenuous on the brain, which is busy enough trying to assemble an image. Others, however, report that it works for them and can improve with training.

 

I use Bino Bandit stray light shields, which are a huge help.

 

The triangular patch in the IC 1318 complex I referred to is about two degrees north-northwest of Sadr. In binoculars, this is substantially easier than the butterfly nebula directly east of Sadr, which is made difficult by the glare of that star.

 

CS, Christopher


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#7 C.Hay

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Posted 04 October 2020 - 01:34 PM

Before retiring the 6x24 binoculars for the winter (the tight eye relief means that the eyecups fog up in cold weather) and moving on to more usual units such as 8x56 and 10x42, I've run a comparison of three different OIII types. The sky was truly suburban at NELM 5m2 (my first post in this thread was under NELM 5m5, which, strictly speaking, is already at the transition to rural).

 

North America (NA) / Pelican

Unfiltered: A vague inkling of NA
Astronomik OIII 12nm: The full extent of North America becomes clear, but its contours not so. I could not make out the Gulf of Mexico. No sign of Pelican.

Baader OIII 10nm: Best view. NA in strong contrast to surroundings, contour of Gulf emerges. Broad nebulosity in Pelican, through which dark nebula LDN 935 becomes visible.

Baader OIII 8.5nm: NA loses extent compared to view in 10nm. Pelican no longer definitely seen.

 

Veil Nebula

Unfiltered: No nebula seen
Astronomik OIII 12nm: A vague inkling of Eastern Veil, similar to the unfiltered impression of the North America Nebula.

Baader OIII 10nm: Now I can make out the extent and curved shape of the Eastern Veil.

Baader OIII 8.5nm: Best view. Shape and extent of Eastern Veil as in 10nm, but standing out clearer. An inkling of a part of the Western Veil directly south of 52 Cygni.

 

From the above and various other explorations in the past I would draw the following interim conclusions:

 

Firstly, each nebula responds in a significantly different manner to each of the three OIII filters used. Hence using three different OIII pairs makes quite as much sense as using three eyepiece pairs in a binoviewer or binoscope does.

 

Secondly, a brighter sky can shift the optimum type of OIII filter towards broader bandwidths. (Under NELM 5m5, 8.5nm was optimal for NA, while under NELM 5m2 10nm became optimal for NA and particularly for Pelican.)

 

I've got 8x56, 10x42, 10x70 and 15x45 binoculars all geared up for filters and aim to continue this series of sporadic observation reports. Cassiopeia, Perseus and Auriga beckon!

 

Christopher


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#8 j.gardavsky

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Posted 04 October 2020 - 02:58 PM

Hello Christopher,

 

this very important shoot out of yours confirms my experience with the 12nm, 10nm and 8.5nm OIII filters.

Both the Pelican Nebula, and the Western Veil (Witch's Broom), are quite sensitive differentiators.

 

Thank you for sharing,

Jiri


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#9 Pcbessa

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Posted 05 October 2020 - 07:24 AM

With the Astronomik UHC in the finder of my 10" Don I can easily see:
North America
Veil
Heart and Soul nebulas
Pacman
Rosette
California (if sky is dark)
Seagull (if sky is dark)

I don't see IC1318 which shows well in my DOB. The nebula likes a dark sky.

I haven't tried others.

#10 C.Hay

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Posted 06 October 2020 - 08:14 AM

Pcbessa, your comments refer to minimum use of filters with telescopes under excellent rural skies. This thread, however, is about maximum use of filters with binoculars under compromised suburban skies.

 

Jiri, thanks for your valuable confirmation of the specific effects of 12nm, 10nm and 8.5nm OIII filters and the role of the Pelican Nebula and the Western Veil in finding these out.

 

Christopher


Edited by C.Hay, 06 October 2020 - 08:15 AM.

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#11 Pcbessa

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Posted 06 October 2020 - 04:38 PM

Hi C Hay, these nebulas are the brightest I can see in my finder (not my telescope), which is the equivalent to a pair of 9x50 binoculars.

And I do see them (Veil, N America, Heart, Soul, Pacman) in full moon, which is the equivalent to Bortle 7 urban skies, albeit not that easy.

When skies get darker, like Bortle 5 then California and Seagull can be seen. So you may want to try these ones. Happy chasing!

#12 PEterW

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Posted 07 October 2020 - 06:08 AM

For hunters of galactic nebulae the “Astrophotography sky atlas” by Bracken is a very handy resource,
though I would guess many are still going to be still beyond even the very sensitive eyes on this forum. Looks like I might need some better OIIi filters.

Peter

#13 j.gardavsky

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Posted 07 October 2020 - 06:38 AM

For hunters of galactic nebulae the “Astrophotography sky atlas” by Bracken is a very handy resource,
though I would guess many are still going to be still beyond even the very sensitive eyes on this forum. Looks like I might need some better OIIi filters.

Peter

Hello Peter,

 

there are about 1200 catalogued bright nebulae, most of them (728 objects) are the Lynds (LBN, 1965), followed by Dorschner Gurtler (DG, 1963), Sharpless (Sh2-, 1959), Cederblad (Ced, 1956), ..., and the old NGC/IC objects.

 

The new discoveries of the bright nebulae are coming from the areas of research of the interstellar matter, integrated flux nebulae, and in general of the molecular clouds, and with the sky survey is their number increasing.

Lots of these new objects are visible with our equipments.

 

It is a fascinating area for our hobby,

JG


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#14 C.Hay

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Posted 03 January 2021 - 11:48 AM

After a lull of three months, it is time to take up this thread once more. I present here an amalgam of observations in the current season and in the past one of the Monkey Head Nebula NGC 2174. This nebula, located in the extreme north-eastern corner of Orion, is the youngest sub-region of the stellar association Gem OB1 and is thus linked in evolutionary/physical terms to the Jellyfish Nebula IC 443 in Gemini. 

 

All observations were handheld under a NELM 4m8-5m3 sky in a suburban setting, making use of various binoculars and filters.

 

7x45 binoculars - NELM 5m2: Unfiltered a diffuse impression of nebulosity around the central star HD 42088 (7m6). Couldn't really define the exact boundaries, but the nebula was definitely present. It came as a surprise to me that the Monkey Head can actually be seen with such a small instrument without filters under such a mediocre sky. This surely makes it one of the easiest to see in the winter sky, topped only by M42/43.

 

8x56 binoculars - NELM 5m3: With Astronomik OIII 12nm filters on both eyepieces the nebula is bright and compact, diameter approx. 10'. After switching to Astronomik UHC the nebula is still striking, but much weaker.

 

10x42 binoculars - NELM 5m3: With Astronomik UHC in front of both objectives the nebula is an immediately noticeable little ball, slightly more than 10' in diameter. Boundaries difficult to define. Going from broader to narrower types of UHC filter (sequence from broad to narrow: Baader UHC-S, Astronomik UHC-E, Astronomik UHC) is beneficial. Switching to Astronomik OIII 12nm increases contrast but diminishes the size of the nebula.

 

15x70 binoculars - NELM 4m8 - Gem OB1 association member Chi2 Ori (4m6) 1° to the west of the Monkey Head can be seen naked-eye with direct vision: With Astronomik UHC-E an amorphous nebula of 2/3 full-moon size is immediately striking when scanning the area. The western edge of the nebula appears slightly indented, this is the monkey's face. The bright star HD 42088 sits distinctly off-centre, i.e. to the southeast of the nebula's geometric centre; this is in remarkable contrast to the nebula's perimeter as shown in the Interstellarum Deep Sky Atlas, which shows the star on the western fringe of the nebula.

 

I would hasten to add that I am not out to bash the Interstellarum Deep Sky Atlas. I consider that Atlas excellent and almost always very reliable. I do think, though, that in this one instance it has slightly misplaced the position, while the shape is correct.

 

Concerning observing techniques, it is hard to draw definite conclusions from the above observations; the sample is too small. However, two patterns do seem to emerge:

1. Image scale matters, as borne out by the 15x70 observation, which presented much more detail and a much larger extent of the nebula than the observations at smaller powers. 

2. With large exit pupils around 7mm is becomes expedient to use narrower filters (see the 8x56 observation). With exit pupils around 4mm, the point is reached much sooner within the broad-to-narrow filter sequence at which narrowing the filter starts to drown out the nebula (see the 10x42 observation).

 

CS, Christopher


Edited by C.Hay, 03 January 2021 - 11:54 AM.

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#15 C.Hay

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Posted 13 June 2021 - 01:42 PM

I titled this thread "... observing galactic nebulae ..." and some may argue that, strictly speaking, planetary nebulae don't fall into that category. However, I've been thinking that some PNs may be very suitable targets for binoculars+filters, so allow me to present an exploration of the Owl Nebula M 97 using stabilised handheld 15x45 binoculars under a NELM 4m9 sky with various 2-inch filters over the objectives.

 

Unfiltered: A very faint impression of something going on. Enough to locate the nebula but not really see it.

Baader Blue-CCD: A definite round, nebulous patch with averted vision. Overall best view to my taste, as I'm seeing a greater number of stars with these filters compared to the Astronomik UHC.

Astronomik UHC: Similar to Baader Blue-CCD. More contrast of the nebula to its surroundings, fewer stars.

Astronomik OIII 12nm: Yet more contrast of the nebula to its surroundings but its extent is reduced to little more than stellar.

 

Keep in mind that this is under a miserable NELM 4m9 sky, conditions in which many nebula observers would retire yawning to bed, mumbling tired platitudes such as "petrol in the tank of the escape car is the best investment, not filters".

 

I, for my part, was very pleased by the result acheived with the Baader Blue-CCD and hope to put them through their paces again soon. They seem to deliver good results in this application, enhancing the nebula while letting plenty of stars through despite the slightly constrained exit pupil of 3mm in the 15x45 binoculars. Thanks again to our Jiri Gardavsky for pointing me to these filters!

 

CS, Christopher


Edited by C.Hay, 13 June 2021 - 01:45 PM.

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#16 PEterW

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Posted 14 June 2021 - 12:25 PM

Thanks, will give it a go in my APM 70d next clear night, went after a few messiers after finding the new Hercules Nova, Ursa Major is away from the streetlights, so worth a try.
Peter

Edited by PEterW, 14 June 2021 - 12:25 PM.


#17 j.gardavsky

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Posted 15 June 2021 - 06:34 AM

Just another way: Pushing the filter envelop with H-Beta

 

On a side line of my IFN and LBN observing program,

I have mounted a pair of the Astronomik H-Beta 12nm filters on the 15x85 BA8 binoculars:

 

NGC 7635 Bubble Nebula: Extended bright glow across a triangle of stars, but not enough magnification to get the Bubble extracted.

NGC 7000 North America Nebula: Very nice with uneven distribution of brightness across the nebula. The H-Beta view is perfectly complementary to the OIII.

IC 5067/70 Pelican: Both the head and body of the pelican, better seen than through the UHC filters.

IC 1318 A: NNW of the nebular field surrounding Sadr: Remarkably well standing out.

NGC 6888 Crescent: Surprizingly bright oval

Sh2-101 Tulip: The surprise of the night - the nebula has been seen as "hanging" on one of the bright filaments in the "Fish On The Platter" field.

LBN 159 west off the Ro 5 cluster: A bright companion of the Roslund and nicely standing out.

NGC 6992/95 Veil/Cirrus: Faint and broadened glow, if compared to the view through the OIII filters.

Simes 3-188 Pickering Triangle: Northern part comfortably seen. The H-Beta is the right choice.

NGC 6960 Witch's Broom: As expected, not as good visible as through the OIII filters, the south-western part of the filament with some broadening.

 

June 14th, 2021, around midnight, Erlanger Oberland, Bortle 4.

 

Clear skies,

JG


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#18 C.Hay

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Posted 15 June 2021 - 10:47 AM

Dear Jiri,

 

Thanks for your valuable contribution to this thread. On reading your observing notes, all kinds of things came to mind. I'm putting your notes in italics and responding below them in normal font:

 

NGC 7000 North America Nebula: Very nice with uneven distribution of brightness across the nebula. The H-Beta view is perfectly complementary to the OIII.

Interesting that you found the H-Beta and OIII views perfectly complementary. In much smaller apertures, I have found that H-Beta reduces the east-west extent of North America. Perhaps your 85mm aperture lifts the available light above some critical threshold.

 

IC 5067/70 Pelican: Both the head and body of the pelican, better seen than through the UHC filters.

Yes, I've also found the Pelican responds well to H-Beta, especially its body, if I recall correctly.

 

IC 1318 A: NNW of the nebular field surrounding Sadr: Remarkably well standing out.

This is to be expected. IC 1318A (also labelled DWB 82 in the Interstellarum Deep Sky Atlas) is the brightest part of the whole complex. It leaps out at me in 18x80 binoculars with Astronomik H-Beta 12nm.

 

NGC 6888 Crescent: Surprisingly bright oval.

This is a big surprise indeed. I always though the the Crescent was an OIII object. Must follow this up!

 

Sh2-101 Tulip: The surprise of the night - the nebula has been seen as "hanging" on one of the bright filaments in the "Fish On The Platter" field.

Another surprise to follow up with 80mm binoculars with H-Beta.

 

NGC 6992/95 Veil/Cirrus: Faint and broadened glow, if compared to the view through the OIII filters.

That this is broadened with H-Beta is valuable information. Must follow this up too. Emission nebulae that are star-forming regions often have H-Beta at their margins. The Veil, however, is a supernova remnant. A further suprise!

 

Simeis 3-188 Pickering Triangle: Northern part comfortably seen. The H-Beta is the right choice.

Once again, a very interesting observation. I've seen Pickering's Triangle quite clearly in 10x42 binoculars with Astronomik OIII 12nm under a mediocre NELM 5m5 sky. This led me to believe it was a pure OIII object and never try H-Beta here - apparently a mistake to rectify at the next opportunity!

 

CS, Christopher


Edited by C.Hay, 15 June 2021 - 10:51 AM.

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#19 j.gardavsky

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Posted 15 June 2021 - 12:19 PM

Hello Christopher,

 

and thank you very much for your comments.

 

With increasing age, my eyes' sensitivity has shifted towards the shorter wavelength, and this has been the reason why I am increasingly using the H-Beta and the blue(RGB)CCD filters.

 

Pickering Triangle:

This Triangle, together with the Funnel, is inside of the SNR shell, and herewith the energy required for the collision ionisation of oxygen may be less than in the rapidly expanding shell. This may explain the comfortable visibility also through the H-Beta filter.

 

The Veil:

The impression of a broader Veil through the H-Beta filter may be due to a thin layer of the collisionally ionized oxygen, followed by a larger volume of the UV ionized hydrogen.

 

A counter example of the SNR missing a significant OIII emissions are the Barnard's Loop and the Lambda Orionis Nebula, with their expansions possibly stopped by the Monoceros molecular clouds intruding into Orion, see also https://www.cloudyni...the-binoculars/

 

Crescent Nebula:

I have observed this nebula just a few times (23x) through the binoculars and through the 6" F/5 achro refractor.

The refractor showed the details better through the H-Beta filter, if compared to my OIII filters (5nm, 10nm, 12nm).

 

Sometimes, the observing sessions bring something, not noticed before.

 

Liebe Grüße,

Jiri


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#20 C.Hay

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Posted 18 July 2021 - 08:20 AM

The Swan is high in the sky and it is time to present observations of the Crecent Nebula NGC 6888 with 8x56 binoculars. One observation was a year ago, the other this week. First my notes and the sketch I made on 21 June 2020, 0 to 1 o'clock, under a NELM 5m0 sky:

 

Baader OIII 8.5nm: Distinct impression of nebulosity surrounding a couple of 7mag stars and extending a little to the east, approx. 10' in diameter.

Astronomik OIII 12nm:No longer so clear whether it is just an unresolved grouping of stars.

But back to Baader 8.5nm the stars are suppressed while the nebulous glow remains: thus a definite sighting. For further confirmation I checked with unfiltered 15x70 binoculars: no condensation of stars is to be seen there that could produce an unresolved nebulous impression with the 8x56 bins.

CrescentNebula BinocularSketch June2020

The left part of the sketch shows the extent of the nebulous area seen. The direction of the shading has no meaning. Wolf-Rayet 136 (WR 136), the source of the nebula, is marked by two small arrows.

The right part shows the brightnesses of field stars. WR 136 is 7m5. I find this little parallelogram of field stars very helpful in locating the nebula.

 

In the night of 12 July 2021, at 1 in the morning, I gave the Crescent another look with the same 8x56 binoculars, again under a NELM 5m0 sky, but this time applying a broader range of filters:

Unfiltered: WR 136, the 7m2 star and the 8m2 star form a little group that is not much more striking than several similar groups in the field of view. No nebula.

Astronomik OIII 12nm: The little group of stars is now slightly more striking compared to others in the field than it was unfiltered, particularly with averted vision.

Baader OIII 10nm: The effect noticed with Astronomik OIII 12nm becomes stronger. With averted vision I would say some kind of nebulosity is there.

Baader OIII 8.5nm: Best view. Field stars are further suppressed compared to 10nm. The nebular impression, however, remains. I can't really define its boundaries this night beyond saying it is located between the three stars (in contrast to the night of 21 June 2020, when I was confident enough to produce the above sketch; this is probably because I'm more tired this time).

Astronomik H-Beta 12nm: Field stars are reduced to roughly the same extent as with Baader OIII 8.5nm. No nebular impression at all at the site of the Crescent. Lots of nebular mottling throughout the  IC 1318 region around Sadr (Gamma Cyg).

 

The consistently good effect of the tightest OIII filter in my collection on the Crescent Nebula leads me to wonder whether even tighter filters, such as the new Baader 6.5nm or the Astronomik 6nm, might deliver further gain. This question intrigues me so much that I've asked both firms whether they would lend me filter pairs for such tests. If they do, I'll report here. The Veil is an obvious candidate. The Pacman and the OIII sections of the Pelican are bright enough to possibly benefit from ultra-tight OIII filtering. Various other candidates in the autumn and winter sky and in Sagittarius/Serpens leap to mind.

 

CS, Christopher


Edited by C.Hay, 18 July 2021 - 08:23 AM.

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#21 j.gardavsky

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Posted 18 July 2021 - 01:36 PM

Hello Christopher,

 

this is an excellent, and for me very interesting observing report on the Crescent Nebula!

And my hat off, you have got it through the binoculars as small as 8x56!

 

The Baader 8.5nm OIII eyepieces are, in spite of the frequently seen critical remarks by some vendors, are a very good choice when the problem is to extraxt a nebula from the bright field stars, and/or from the surrounding glows, like the reflected light on the molecular clouds.

I have been using the Baader 8.5nm OIII in past, later replaced with an even narrower Astrodon 5nm OIII. And one of the reasons for going narrower have been in my case some details in the Cirrus/Veil.

 

Thank you very much, and wishing you clear skies,

Jiri


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#22 Oscar56

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Posted 18 July 2021 - 02:23 PM

Fascinating read.

 

The second comment in this thread the observer noted using just a single filter on one ocular. Is that the normal technique?  I will need to acquire a step down ring to attach a filter. 



#23 C.Hay

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Posted 19 July 2021 - 09:06 AM

Jiri, thanks for your comments, which provide fresh insight, as so often. Do you no longer use the 8.5nm filters at all, preferring to go for Astrodon 5nm each time - or do you switch between the two? Which objects benefit particularly from 5nm? 

 

Oscar56, I've tried mixing filters - i.e. a different one on/in each barrel of binoculars or binoscopes - and find it very strenous on the brain to no gain. Using just one filter on one side is even worse. That said, I can imagine configurations in which different filters are used with benefit. I think the precondition for me would be that image brightness on both sides is identical. Then the brain at least isn't troubled by that part of things.

 

I have once had excellent results in a 5-inch binoscope with Baader Blue-CCD screwed into the eyepiece on one side and Astrodon BB (Exoplanet Blue Blocking) on the other. The Baader Blue-CCD cuts off wavelengths above 505nm, while the Astrodon BB cuts off 500nm and below. The two thus transmit totally different parts of the spectrum. However, the brightness of Venus rendered by them in the eyepiece is practically identical. The Astrodon BB gives sharper planetary edges (as does any good yellow longpass filter), while the Baader Blue-CCD brings out detail on the planetary surface. The combined image showed clear indentations at the terminator, plus, for the very first time for me, an inkling of detail on the illuminated surface of Venus. The experiment was thus very worthwhile. I haven't had any such success by mixing filters on galactic nebulae yet, but never say never.

 

CS, Christopher


Edited by C.Hay, 19 July 2021 - 09:08 AM.

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#24 j.gardavsky

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Posted 19 July 2021 - 12:00 PM

Jiri, thanks for your comments, which provide fresh insight, as so often. Do you no longer use the 8.5nm filters at all, preferring to go for Astrodon 5nm each time - or do you switch between the two? Which objects benefit particularly from 5nm? 

 

 

CS, Christopher

Hello Christopher,

 

I have parted with the Baader 8.5nm OIII filters.

 

Just from scratch where the Astrodon 5nm OIII has shown some advantage:

 

25x100 FB binos: Some more brightenings on the NGC 7000 NA

25x100 FB binos: NGC 6992/95 Cirrus/Veil east, norh-east more contrast

6" F/5 achro 73.5x: Crescent Nebula bright oval very well detached from the skies

6" F/5 achro 23.4x: Sh2-221 G160.4 +02.8 SNR in Auriga, faint oval glow (also through the Baader 8.5nm H-Beta)

 

The extra large SNR Sh2-221 in Auriga has been so far one of the toughest object for the OIII and H-Beta vision.

It is a bicolor object with partially separated OIII and H-Beta diffuse emission areas,

https://astroanarchy...-in-auriga.html

and it's been tough even for the Leica L Plan f=32mm eyepiece, which delivers an excellent contrast with its minimum of glass inside.

 

The other nearby big bicolor SNR, the Sh2-224, has been easy, if compared to the Sh2-221.

 

Best regards,

Jiri


Edited by j.gardavsky, 19 July 2021 - 02:11 PM.

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#25 C.Hay

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Posted 22 July 2021 - 05:48 AM

Dear Jiri,

 

Thanks for your report on the gain provided by moving from OIII 8.5nm to even tighter filters. I must say I wasn't aware of Sh2-221. I gazed in delight at the photographs to which you linked. Sh2-221 plus Sh2-216 is a wonderful pair of objects in a seven-degree field.

 

You noted further above that vendors - indeed, even the manufacturers! - tend to persuade people that OIII filters narrower than 10nm, and H-Beta in general, can only be used visually with instruments of at least 8 inches of aperture. A related idea is that such filters need pristine skies to be useful visually. Your and my experience empirically disproves both notions. It is a pity that vendors and manufacturers underplay the visual potential of their narrowband filters, as this systematically prevents the majority of the amateur community from trying them out at all.

 

Another myth that your and my experience puts to rest is that using filters on top of eyepieces doesn't work. My 8x56 observations are made precisely that way. All of your binocular observations are, too. The argument that the wavelengths transmitted become increasingly displaced towards the edge of the field of view is valid, of course. It fails to appreciate, though, that the inner half of the field is unaffected by this displacement (don't pin me down on the "inner half", I haven't explored that precisely; sometimes it seems to me that only the inner third is unaffected, sometimes the inner two thirds, so "inner half" is a first approximation). My 8x56 bins have a field of 6.3°, so 3° of clean view remain in the centre - quite large enough to frame most objects.

 

In support of the above assertions, I offer my 8x56 observations under a NELM 5m5 and also NELM 4m5 sky of the Seagull Nebula IC 2177 with H-Beta on top of the eyepieces as reported here: https://www.cloudyni...culars-to-boot/

 

CS, Christopher


Edited by C.Hay, 22 July 2021 - 06:08 AM.



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