Jump to content

Banner.jpg.b6007b69ccdf5c69bf18273ddfe023df.jpg

6" Refractor, Hydrogen Clouds and NV (Report)


Recommended Posts

I've been an amateur astronomer for fifteen years, but I think only the last few nights I was priviledged to observe Milky Way's hydrogen regions in all their glory - thanks to NV. The setup was:

  • 6" TS f/5.9 Achromat on TS alt-azimuth mount 
  • PVS-14 with Harder 2100 FOM tube
  • 67 mm TeleVue Plossl, giving 13X magnification and 3-degree field of view
  • H-alpha filters: Baader 7 nm and Antlia 3 nm
  • APM Amici prism for right angle correct orientation view
  • Interstellarum Deep Sky Atlas
  • Bortle class 4 site at Wembury Point, England (SQM showed 20.60). Transparency 6/7. 

 

214771063-10159551110556636-122900573118

 

Initially started with the summer classics - M57, M13, etc, but once I tried the 3 nm filter on the Gamma Cygni region, I literally couldn't pull myself from roaming around this region surrounding Sadr all the three nights. It was mind-blowing. IC1318 and Crescent both photographic in appearance. Glowing, cury, textured emission in high contrast to dark patches and filaments. The dark triangle near LDN889 not only apparent in form, but exhibiting detailed structure. The eyepiece view was quite similar to this picture, if you squint your eye a little: https://bit.ly/3hJ4Ws4

The Crescent showed doubling front in the north and Y-shape in the center, mottled body, almost "electric," I guess, due to the scintillation. Visually was very similar to this picture:
https://www.astrobac...-6888-Large.jpg

Numerous DWB emission clouds and the Sh2-101 Tulip in Cygnus were bright - the whole region all appeared as pierced and surrounded by faint hydrogen emission, which was also easily apparent in the eyepiece. The extent of the nebula seen far exceeded what was shown in the Interstellarum atlas.

NGC 7000 North America's Gulf was very detailed and at high contrast, with bright knots in Mexico and in the north. The IC5067 Pelican was bright, showing three protruding "fingers" and irregular shape. IC 5068, the Cygnus Arc, was bright and apparent, split into multiple irregular regions. IC5146 Cocoon was pretty bright, without much fine detail inside, and apparent central star. Looking at the Interstellarum Deep Sky Guide, I now see that on those emission nebulae I saw about similar level of detail to what Uwe Glahn saw in his 27" reflector. 

The wide field of the 6" showed the whole western portion of the Veil in its field, with irregular bright "claw" of IC1340. NGC 6974/9 with Pickering's Triangle, shown as visible from 12" aperture in the atlas, was pretty bright in the eyepiece. The eastern part had less detail, but its overall irregular shape easily seen. 

Ventured to IC1396 in Cepheus, it appeared very extended and pretty faint, I couldn't see much dark detail, although central round dark region was apparent. Sh2-132, Sh2-157 (bright), NGC7635 and NGC7538 all exhibited some degree of detail, but I am not too familiar with these objects, and left them for another occasion. I don't think I could see the bubble itself with certainty, but it's on a to-do list now.

Going south, M27 was bright and pretty compact, compared to vast hydrogen clouds of Cygnus. I won't mention myriads of well-known and obscure star clusters along the way. I think I could see into great "depth" and could observe less well-known NGC clusters well. (Dolidze-Dzimselejsvili 11 is a really peculiar alignment of stars!) Roaming along the Galactic equator, I have never seen so many stars in the eyepeice in my life. I own mostly Cassegrain designs, but f/5.6 reduced to f/2.3 is something else. Carpets, laces of stars!

I tried switching to "normal eyepiece", but literally couldn't see much, compared to the NV mode. The eye wasn't properly dark-adapted, and, to be honest, after the level of detail seen in NV it felt a little futile. I tried 7 nm H-alpha filter, but it showed significantly less detail than the 3 nm Antlia. From dark nebulae, Barnard's E (B142) in Aquila was apparent without filtering. Some dark nebulae, if overlaid on HII emission, were better seen with the hydrogen filter on.

The last night before returning home I explored Sagittarius, literally bumping into M22 very low on the horizon while scanning manually, and it was a sight to behold! Definitely a top globular in my book now, replacing M13, along with Sadr surroundings being visually more engaging and richer than even the great Orion Nebula! And then... M8 Lagoon was almost a live photograph - silky-smooth whirlpool, bright and detailed flower-like center with stars, dark patches - it's difficult to describe! Looking at monochrome photographs of the Lagoon, I think visually what 6" showed that night comes quite close. I could spend the whole night on that object alone (or the Sadr!) but that was my first overview "mission" so I had to move on. The M20 Trifid was very bright, almost laser-etched on the sky background with irregular patches dividing it easily seen as pitch-black filaments. This photograph is similar to what was seen in the eyepiece (although yes, there was noise in the tube, and it wasn't that deep, so squint to get an idea):
https://bit.ly/2TesrQo

In that area further, M17, Omega, was very bright and high-contrast as well - I could see the Omega shape in it, so now I finally get why it's called that, and the center emission region was extremely bright and knotty. M16 Eagle appeared as an eagle with wings open, and although there was lots of texture, I couldn't see Pillars of Creation that night, but definitely worth a try at a higher elevation and with a barlow.

Suddenly, my visual astronomy life is enriched with so many objects, exhibiting so many details. Comparing what I've seen with Uwe Glahn's and Ronald Stoyan's sketches in the Interstellarum Deep Sky Guide, on extended emission nebulae a 6" aperture with FOM 2100 NV under Bortle 4 sky shows more detail than unaided 27" reflector under very dark sky, and definitely exceeds 14". Could it get any better? On the way home, I had the opportunity to visit the Stonehenge!

Max

215956601-10159552864611636-454637502024

 
  • Like 10
Link to comment
Share on other sites

Excellent report. I use 3nm filters almost exclusively for nebulae from the city, but interesting to read that your 3nm worked so well under darker skies too - and clearly improved on the 7nm. Thanks for posting - we need more night vision disciples on SGL!

  • Like 1
Link to comment
Share on other sites

A really good combination, 6" Achromat and NV, no need to worry about colour correction when you have a black and white view of the sky. 😀

Must be very portable ( the scope is a little wide, however being fast not to long) which is great to visit those dark sites.

How do you find views of the Nebulae compare between London and  
Wembury Point when using the 3 nm H filter? From Gavster photos the background is really dark outside of London, you can tell when he has been to the Isle of Wight.

  • Like 1
Link to comment
Share on other sites

Yeah, through the filter this 6" is really an apo! I wish the field was flat, but I think I'm fine with that instrument. Honestly, I haven't tried 3 nm in the city. I've tried 7 nm on Rosette with the 90 mm refractor and it was disappointing, and M42 was OK'ish, but the whole experience still a far cry from Gavin's pictures. Rural sky was a completely different story. 

  • Like 1
Link to comment
Share on other sites

18 hours ago, Maxim Usatov said:

Yeah, through the filter this 6" is really an apo! I wish the field was flat, but I think I'm fine with that instrument. Honestly, I haven't tried 3 nm in the city. I've tried 7 nm on Rosette with the 90 mm refractor and it was disappointing, and M42 was OK'ish, but the whole experience still a far cry from Gavin's pictures. Rural sky was a completely different story. 

In London skies I'm told that a faster scope is better as it allows for turning up the gain in the NV device. All your refractor scopes needs to be around F6. 

Flat stars, getting those in a refractor is an expensive proposition, i.e. a Petzval design. Maybe adding TS flat would help you out there? Very much a hack. 

Link to comment
Share on other sites

@Maxim Usedv. Beautiful review, a great comet hunter, William Bradfield, used an achromat of this type. Very nice photography of Stonehenge, if one goes to the UK to see Stonehenge is a must!

  • Like 1
Link to comment
Share on other sites

  • 6 months later...

Decided to get out for an hour of two to a nearby car park under reasonably dark sky, about 1 hr driving from London. Conditions were very windy with temperature decreasing rapidly, so instead of carefully observing each object I decided to just give a quick tour over some of the targets.

Setting:

Date: 6 Feb 2022
6" TS f/5.9 Achromat on TS alt-azimuth mount 
PVS-14 with Gen3 Harder 2100 FOM tube, 2" APM Amici prism
67 mm TeleVue Plossl, giving 13X magnification and 3-degree field of view
Filters: H-alpha Baader 7 nm and Antlia 3 nm, 642 nm IR Astronomik, DGM NPB Nebula filter
Bortle class 4 site at White Hill Car Park near Kingsley, Hampshire (RG25 3EJ)
SQM showed 20.34 - moon was 42% setting at 23:36

NGC 2024 the Flame Nebula
IC 434 the Orion's Dagger and B33 the Horsehead Nebula

Started observing at about 21:30 when the moon was still up and sky pretty bright, with the 7 nm H-alpha filter the Flame was remarkable, very bright object with tree-like dark lane structure, similar to a Stoyan's Interstellarum Deep Sky Guide sketch of 18" reflector view under dark sky. Horsehead was very remarkable and pretty bright. The smooth background emission of the Dagger was filling the field of view, the head's dark silhouette was detailed - almost photographic picture. Typically I could see a single dark lane in the center of the Flame and the hint of the structure in London's Bortle 8 sky, and I am generally unable to make out the head's shape, although I can definitely see a dark spot in the emission. Completely different story on a darker sky. Horsehead details are similar to 18" reflector Stoyan's sketch, and the Dagger is brighter and more extending through the 6" NV setup.

Barnard's Loop
The loop was pretty bright, very much extended, northern part appears to be brighter and exhibiting structure. Panning through it, its presence was obvious - an object completely invisible in this setup in Bortle 8.

M42 and M43, NGC 1977 the Running Man Nebula 
Of course, always a magnificent sight, Huygens region extremely bright, photographic amount of details in extensions. The picture in 6" NV was closer to a photograph rather than any sketch I've seen, although I don't think I could see its very outer loop that almost touches Iota Orionis. NGC 1977 was considerably faint - just a glow around the three stars. No wonder I don't see it at all in the city.

Switching to Antlia H-alpha 3 nm increased contrast and brought more details out on the Barnard's Loop, but for some reason it made little improvement on other objects above, which is somewhat opposite to what I concluded during the previous session, where 3 nm was strongly preferred for the views of the Gamma Cygni region. Someone has mentioned that the Antlia filter showed darkening towards the edge of the FOV. In my setup this effect was noticeable, but did not at all hurt the observations - something completely negligible.

NGC 2237-9/46 the Rosette Nebula and the surroundings
Magnificent object, considerably bright, fits great in the FOV, complex multi-layered shape with good contrast against the background, great amount of emission and dust details, appearing photographic in the 6" NV setup, definitely exceeding any sketches I've seen. Visually, the Rosette and the Horsehead/Flame nebulae appeared almost identical to what is shown on the photographs here: https://www.cloudyni...otography-r3149

Panning north from the Rosette, hydrogen clouds appeared everywhere in the FOV. Bracken's atlas names this Sh2-273, spanning about 3 degrees, but Interstellarum's atlas confines Sh2-273 to 1-degree nebulosity surrounding the NGC 2264 Christmas Tree Cluster. In 6" NV I could see hydrogen clouds extending all the way from the Rosette to the Christmas Tree and beyond - the whole area north to the Rosette is drained in hydrogen. I have marked the nebulosity surrounding NGC 2264 as faint, but that's only because the contrast is low, the nebulosity is superimposed on the hydrogen background.

Panning south, Sh2-280 and Sh2-282 appear pretty bright and extended, both fitting the same FOV. Interstellarum atlas shows 282 as a considerably fainter object. Sh2-284 is pretty faint, lacking details.

IC 2177 the Segaull Nebula, Sh2-292, Ced90
Pretty bright, very extended and curved shape. Sh2-292 round, pretty bright and distinctive. Sh2-297 (Ced 90) pretty brigth and distinct at the tip of the Seagull. Not much details seen, but interesting shapes.

NGC 2359 the Thor's Helmet
By the time I've got to it, SQM was 20.64, the Moon almost set but transparency wasn't great. The helmet was faint, appeared irregularly shaped through the 7 nm H-alpha filter, pretty small at 13X mangification. I wasn't sure if I saw the horns or just the brighter central part of it which appeared to be C-shaped. Wind and chill began to kick in at this point. The helmet was completely invisible unfiltered or through the DGM filter. With 3 nm H-alpha, there wasn't enough light to confirm any more details, and the 12 nm view was too bright lacking contrast. More magnification, better transparency and aperture would be desirable here.

M51 the Whirlpool Galaxy, and other objects
Unfiltered view was bright with spiral arms seen - definitely an improvement compared to NV through 90 mm refractor last year, but still very small through this setup at 13X magnification. At this point SQM showed 20.81 at zenith, but 20.48 in the direction of M51 which was elevated at about 45 degrees. Doubling power to 26X reduced contrast, with no additional details seen. 642 nm IR view helped darken the background a little and was the most preferred view at 13X without barlowing. DGM filter - no improvement over unfiltered. Interstellarum Deep Sky Guide shows more details seen in 14" reflector, so this galaxy wants aperture and good zenith placement.

At this point I had to start to shut down as it became too windy and chill at 6 deg. C. Quick glimpse mode - M108 appeared a small edge-on spiral with bright stellar-like nucleus. M97 the Owl Nebula was very faint and round - I wonder if [OIII] filter would help here. M81 - the Bode's Galaxy and M82 - the Cigar Galaxy, both very bright. M81 didn't show much details but M82 three dark lanes visible. Something for other other time.

IMG_9322.jpg

IMG_9314.jpg

  • Like 5
Link to comment
Share on other sites

On 07/02/2022 at 13:20, Maxim Usatov said:

Switching to Antlia H-alpha 3 nm increased contrast and brought more details out on the Barnard's Loop, but for some reason it made little improvement on other objects above, which is somewhat opposite to what I concluded during the previous session, where 3 nm was strongly preferred for the views of the Gamma Cygni region. Someone has mentioned that the Antlia filter showed darkening towards the edge of the FOV. In my setup this effect was noticeable, but did not at all hurt the observations - something completely negligible.

I was looking at HH and Flame nebula last night:

  • SQM 20.89
  • Transparency: Medium
  • Scope: LZOS 130/F6 with TV 67 mm 
  • NVD: OVNI M 2100 FOM
  • Filters: Baader 6.5 nm f2 and Antlia 3 nm Pro H-Alpha


I swapped between both the Baader and Antlia. On previous nights I thought there was not much difference between the two filters, the transparency was better on that night.

Last night Sunday 6 February the Antlia seemed a little better at pulling out contrast, however the difference between the two is not as much as I expected.

I'm coming to the conclusion that the Chroma might be the way forward, however given the Chroma's cost I'd like to observe with one before buying.
 

Edited by Deadlake
Link to comment
Share on other sites

I'm in about the same position, but would not expect Chroma to be significantly different. We're talking about 10% transmission difference. But, of course, maybe there are other factors in play here. We need to get together somewhere and test this all out! I'm also wondering if I'm loosing anything with my telescope being a Chinese achromat and not a premium apo. Theoretically at low mags and narrowband observations there should be literally zero difference.

  • Like 1
Link to comment
Share on other sites

1 hour ago, Maxim Usatov said:

I'm in about the same position, but would not expect Chroma to be significantly different. We're talking about 10% transmission difference. But, of course, maybe there are other factors in play here. We need to get together somewhere and test this all out! I'm also wondering if I'm loosing anything with my telescope being a Chinese achromat and not a premium apo. Theoretically at low mags and narrowband observations there should be literally zero difference.

@GavStar is not far, he has a Chroma. Maybe when the moon is not in control and the weather is good we can do a comparison. 
I don't know anyone on CN that has both filters to do a comparison.
The only thing I have too go on is that I've never seen a Chroma 3 nm H-Alpha filter for sale in the second hand market I do see Antlia 3 nm Pro's advertised.

I'd expect a brighter image with your scope one F stop advantage.

The only difference is the shape of the stars etc, not the brightness of the image. I'm sure other people will comment. :)

Edited by Deadlake
Link to comment
Share on other sites

Remember that it’s not just the transmission and width of the 656.3nm you need to worry about, there are a lot of nanometers of photons out there that you want to keep out! Very few companies provide transmission  spectra in optical density units…. You want the biggest OD everywhere apart from 656nm. Chroma are rare in providing this data, most only give % transmission…. making it very easy to hide small slightly less blocked bands. You can always stack filters together, thus massively driving down the photons you don’t want, with little effect on the ones you do.

Peter

 

 

 

 

 

 

 

 

 

Link to comment
Share on other sites

I’ve got Chroma 3nm filters that I’d love to try out on a 6” F/5.9 scope, if we ever get the chance to arrange a meet up. Am based in north London, but often working in evenings so rarely get the chance to observe outside the city. 

Link to comment
Share on other sites

2 hours ago, PeterW said:

Remember that it’s not just the transmission and width of the 656.3nm you need to worry about, there are a lot of nanometers of photons out there that you want to keep out! Very few companies provide transmission  spectra in optical density units…. You want the biggest OD everywhere apart from 656nm. Chroma are rare in providing this data, most only give % transmission…. making it very easy to hide small slightly less blocked bands. You can always stack filters together, thus massively driving down the photons you don’t want, with little effect on the ones you do.

The Antlia performance drops below F3, maybe that is what is being seen?

Antlia H-alpha Pro narrowband filter optimizes the FWHM (full width half maximum) to 3nm bandpass. As the bandwidth becomes narrower, the 3nm Pro narrowband filters enhance contrast of emission targets by lowering the unwanted background signal. Antlia H-alpha 3nm Pro filters are designed to deliver 88% transmission at the 656.3nm line which provides you with the maximum signal and well defined nebulae structures.

Conventional broader narrowband filters cause a heavy loss in transmission due to the strong Center Wavelength (CWL)-shift. We guarantee T>88% within 1nm range of the center bandwidth, which means that the 3nm Pro narrowband filter can guarantee high transmittance for working with both long focal ratios and fast optical systems. Blue-shift data shows that Antlia 3nm Pro filters can be used with nearly all systems as fast as f/3 with minimal loss in emission signal and meets the requirements of fast optics like Hyperstar and RASA.

The out of band blocking specification is rated OD5 (0.001%) which delivers an excellent SNR(signal to noise ratio) and effective cut-off rate to minimize interference from other wavelengths. Improved sharp cut-off astrophotography 3nm Pro filters are designed to minimize halos around bright stars.

Application and Performance

High transmittance and smallest bandwidth to maximize contrast

Steep spectral profile minimizes halos around bright stars

A single substrate to eliminate internal reflections   

Narrowband Objects: H-alpha Emission Nebulae, Planetary, Wolf Rayet Nebulae and Supernova Remnants

Use in light polluted areas and dark sites

Extends imaging time when the moon is up

Antlia narrowband Pro filters can be used down to F/3 systems with slight loss of signal

All Antlia Narrowband filters are edge blackened to eliminate internal reflections from stray light

Superior optical reliability reduces post image processing

This filter is not suited to deep sky objects that do not contain H-alpha emissions.

Technical Specifications

Basic Substrate: Schott optical substrate

Filter Thickness:   2mm+/-0.05mm for 2'' mounted

FWHM (Full width at half maximum): 3nm

CWL (Central Wavelength): 656.3nmnm

Peak Transmission: >88%

Blocking: > 5 OD(0.001% out of band blocking) @ 300-1000nm

Surface Quality: S/D (scratch/dig)= 60/40 (Refer to MIL-O-13830)

Transmitted Wavefront: Lambda/4 or better.

Parallelism: less than 30 arcsec

Single / Non-glued substrate

  • Like 1
Link to comment
Share on other sites

3 hours ago, Maxim Usatov said:

@Highburymark Would be very interested in a test and would be happy to bring the refractor. I'm based in West London. Perhaps, at a star party, or we can agree to drive out to a parking lot somewhere, weather permitting?

@Highburymark Do you have transport to make it out of London?
@GavStar is another option as he has the chroma filter.

Options:

1) We could meet at Walton-on-Thames Green, there is the pub nearby where we could opion... SQM will be bad, say 19 if we are lucky????

2) We could meet further out, maybe if I can get sign off my back garden. SQM 20.89, however I suspect slightly lower.

This could take some time given the moon is well in control at present.

Martin

  • Like 1
Link to comment
Share on other sites

On 08/02/2022 at 10:10, Maxim Usatov said:

@Highburymark Would be very interested in a test and would be happy to bring the refractor. I'm based in West London. Perhaps, at a star party, or we can agree to drive out to a parking lot somewhere, weather permitting?

Where was the filter placed, in front of the EP because longbond’s tests state this will minimise bandshift? 

According to Ed placing the filter between the EP and NVD might be the best location as the Antlia 3nm filter is destined to run at F3 ish (Baader 6.5 nm designed to run at f2). I’d drop the speed to close to F3 to test as faster for the Antlia might not be beneficial.

The chroma works at F4, so this might be a better choice as it can be placed in front of the EP and hence a 67 mm can be used so the system runs faster.

Also different results reported based on observers SQM, not any easy comparison.

Link to comment
Share on other sites

The 3 nm Antlia was placed in front of the EP.

I have a little hard time understanding why it has to work specifically at f/3. Antlia's site says it works "down to f/3", so I understand anything slower than that should be fine.

@Highburymark I'd be happy to give you a lift.

 

Edited by Maxim Usatov
Link to comment
Share on other sites

1 hour ago, Maxim Usatov said:

The 3 nm Antlia was placed in front of the EP.

I have a little hard time understanding why it has to work specifically at f/3. Antlia's site says it works "down to f/3", so I understand anything slower than that should be fine.

@Highburymark I'd be happy to give you a lift.

 

Look at Ed's post's 34, 47, 47, 50, 52 and 54 here:

https://www.cloudynights.com/topic/775073-band-shift-and-filter-position/page-2

Looks experimental, I've modified my afocal adapter to give it a go tonight. I might get different results with the Antlia and the Baader (F2) filter which is also likely the outcome, but as I'm trying one I might as well try the other.

If what Ed has reported works for the Baader and the Antlia is means @joko will need to redesign the OVNI adapter to allow filters can be placed between the EP and the NVD.


IMG_5821.thumb.jpeg.4d4b4bf157dc6da3f5940313fe417356.jpegIMG_5822.thumb.jpeg.7b5283cd9039695072dd843304bd51b2.jpeg
 

Edited by Deadlake
Link to comment
Share on other sites

A high-speed filter, like the 6.5 nm f/2 Highspeed filter from Baader, is optimized to perform within the specified focal ratios range - f/3.4 to f/1.8 in this case. I don't know specifically how this done but imagine the bandpass is somehow blue-shifted (in concentric circles?) to compensate increasing angles of incidence with increasing distance off-axis, to match the light cone coming from a fast optical system. I don't think Antlia specifies an optimal range for their 3 nm filter, they just say "down to f/3," so this looks like a normal filter to me. I assume Antlia's filter is not "high-speed" per se, i.e. the bandpass is not variable with the off-axis distance. Maybe I am just imagining things, of course. 

  • Like 1
Link to comment
Share on other sites

The chroma for example is specified to work at F4, just right for an imaging Newtonian.

The confusion for me is the Antlia is half way as ok down to F3. I'm presuming the Antlia filter works best at the slowest part of the optical path, however I'm hoping that placing it between the EP and NVD will improve the contrast but I suspect it will not. 

Chroma here we come? 

Link to comment
Share on other sites

Moon was just too powerful to draw any conclusion. I suspect the Antlia gets no benefict from being placed in between the EP and NVD as expected however the Baader seems too and provides a brighter image all over the field of view compared to beimg placed before the EP. Will need to repeat when the moon is set.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.