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Green in comets is not CN, cyanogen

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#51 Tonk

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Posted 04 January 2015 - 08:58 PM

ha ha ha ha - so these astronomers have been hoisted by their own petard. :lol:


They don't realise that the bright UV emission are from cyano radicals (which their literature sources erroneously call "cyanogen") but have looked up what cyanogen is and got the proper chemistry definition and gone with that. Boy are they confused - and this serves the professional astronomers right for the casual slackness of misnaming things. No sympathy here ;)

#52 Tonk

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Posted 04 January 2015 - 09:28 PM

and I don't think it is visible directly, and even the CN isn't a really strong part of the emission.


The strong CN line is only faintly visible to *some* humans - especially young ones - its closer to the UV end than the Calcium K line which many older folk cannot see in the CaK solar filters (sold as imaging only filters by Lunt etc for this reason). However the CN violet line is an intense emission - it was 2.5 brighter than the C2 lines in ISON. See the height of the leftmost CN peak in this spectrum of ISON taken by Christian Buil. Because of the human insensitivity to the CN violet line the C2 green/blue lines totally dominate in visible intensity - and why comets are not purple (shame!)

20131028_poster_ison_20131024.png

Edited by Tonk, 04 January 2015 - 09:39 PM.


#53 freestar8n

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Posted 05 January 2015 - 01:03 PM

Space.com today:
 

 

n Ng's amazing image of Comet Lovejoy, the gorgeous green glow of the comet and a wispy, narrow appendage can be seen. The greenish hue is likely due to the presence of cyanogen and diatomic carbon, which glow green when illuminated by sunlight.

 

Yahoo link to space.com write up:

 

http://news.yahoo.co...-170406813.html

 

Frank



#54 Tonk

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Posted 05 January 2015 - 01:08 PM

repeat after me

The greenish hue is likely due to the presence of cyanogen ...

repeat, repeat, repeat ... the same old phoney baloney ;)

Edited by Tonk, 05 January 2015 - 01:10 PM.


#55 Tonk

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Posted 10 January 2015 - 10:33 AM

OK - This 1997 film about Hyakutake has the narrator telling us the green glow is cyanogen - so its was obviously a belief current in the late 1990's

https://www.youtube....h?v=H6uCHBqfZlk

#56 freestar8n

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Posted 10 January 2015 - 07:06 PM

Good grief - how did you find that?  It certainly captures a unique period in time - when an amazing comet appeared just before amateur ccd's had become common.  But I doubt many people have seen that video or would reference it.  So I think it gives a good clue that the true source of "cyanogen is green" comes before that video - and also before APOD said it, later.

 

Now I'm thinking it must be in some astronomy book or something.  1997 makes it harder to be a web effect - so maybe it is in an early book somewhere.

 

Frank



#57 Tonk

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Posted 07 August 2017 - 05:02 PM

Frank and anyone else interested in imaging comets - you might be interested in this CN filter.
 

The band region for CN (made from numerous close spaced individual lines) is 385.5nm to 388.2nm. Laser 2000 have a 26nm bandpass filter centred (CWL) on 285nm with >95% transmission which should be ideal for isolating the CN line. This in their BrightLine® single-band bandpass filter range

http://www.laser2000...=FF01-385/26-25

 

and a CWL 387nm FWHM 11nm version

http://www.laser2000...FW-Ex01-Clin-25

Edmund Optics now do a similar steep edge high transmission filters (>95%)  (its their TECHSPEC® Hardcoated OD4 range) but it has a tighter FWHM band width (10nm) but nearest CWL is 394nm - so its an unfortunate close miss for 388nm  frown.gif  The Hardcoated OD4 25nm and 50nm FWHM bandpass filter ranges don't go below 400nm.

 

https://www.edmundop...lter/#downloads

 

(note 12,5, 25 and 50mm diameter filters available)

For other (strong) comet lines
 

C3     - 405.6nm - Edmund Optics do a TECHSPEC CWL 405nm FWHM 10nm - that's only off centre by 0.6nm   (coma)
CO+  - 427nm    - Edmund Optics do a TECHSPEC CWL 430nm FWHM 10nm - that's only off centre by 3.0nm   (ion tail)
C2     - 516nm    - Edmund Optics do a TECHSPEC CWL 515nm FWHM 10nm - that's only off centre by 1.0nm   (coma)


I'm interested in the CN, CO+, C2 set so I can image comets better in moonlight/light pollution situations - I don't think C3 adds much given its weaker than C2 and is found in the same comet region


Edited by Tonk, 07 August 2017 - 05:14 PM.

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#58 Tonk

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Posted 16 August 2017 - 11:12 AM

This 387/11 nm filter looks perfect for CN line imaging

https://www.semrock....=FF01-387/11-25



#59 Ron359

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Posted 26 October 2018 - 04:02 PM

This 387/11 nm filter looks perfect for CN line imaging

https://www.semrock....=FF01-387/11-25

If I can revive this thread;   Tonk, the 'pros' seem to agree with you on this filter, having been pointed to it by another amateur.  Have you used one since your post?  I've been following these campaigns (see links). So ran across their discussion and then this CN thread in further searches.  I am thinking about getting one, but its 'pricey' and I'm uncertain how well it work with small scope aperture.  

 

http://wirtanen.astr...ml#Jorma_update

 

http://www.psi.edu/41P45P46P#useful



#60 Tonk

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Posted 29 October 2018 - 11:59 AM

Its on order in my case as I'm using a 50mm with a KAF 16200 based camera on an FSQ106. This aint cheap! The delay ordering this was due to my 16200 camera needing an electronics redesign around the A/D converter to USB circuit (but that is another story)

 

My comet NB system (includes two other comet specific wave lengths) will be going live next Feb in a remote hosting facility in southern Spain (zero light pollution, excellent seeing in a high(ish) altitude desert climate and good horizons for the necessary long exposure imaging).

Note that my aim is not to detect low contrast features in the coma (though this would be interesting for some bright comets) - but to extend imaging into bright moon periods.

The PSF issue is a little bit worrying with the Semrocks but as comets are not point features this is mitigated. Note that the PSF star "halo" is seen worst around very bright stars. The aim would be to loose the stars in these images in post processing. I have the maths techniques for this mastered a long time ago - but we will see how it goes.

Note that these Semrock filters are for laser microscopy - each one is matched to a known dye used for staining biological samples. A laser light of an excitation  wavelength is used to cause the stained area to fluoresce at a different specific wavelength and the filters are matched to these wavelength for imaging the sample. So it just so happens that a number of the Semrock filters are accidentally matched to comet emission lines - its pure luck.

 


Edited by Tonk, 29 October 2018 - 12:54 PM.

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#61 Tonk

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Posted 29 October 2018 - 12:16 PM

Note that the Maryland uni reviewer is using a mounted filter with a an overall depth of 5mm. I've gone for the unmounted version which has a 2mm substrate profile

The Semrock filters are 2mm thick and Astrodon are 3mm meaning using these side by side in filter wheels has a problem with the locking screws. The solution is using 49mm x 1mm silcone O-rings (ebay) to raise the thinner filter and match heights for the locking screws. Adjust the diameter part if using smaller filters

Regarding the star halos seen using the SemRock  filters. The University of Maryland concludes "[its] not constructed with high-quality optical glass". This is highly unlikely given the filter application in laser florescence microscopy imaging. Its more likely due to a lack of an (unneeded) anti-reflection coating. Uncoated filters are prone to reflecting part of the light back to prior lens elements that then reflect it forwards again. The path length of these reflections is such the star light in the reflection is no longer in focus at the sensor plane - hence the halo (as observed in the link - http://wirtanen.astr...lter_test.shtml)..  Multiple reflections give stepped halos of decreasing brightness at increasing radius, each with sharp boundaries


Edited by Tonk, 30 October 2018 - 11:17 AM.


#62 Tonk

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Posted 29 October 2018 - 01:01 PM

having been pointed to it by another amateur.


Was this HappyLimpet here on CN?

#63 Ron359

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Posted 29 October 2018 - 03:03 PM

Its on order in my case as I'm using a 50mm with a KAF 16200 based camera on an FSQ106. This aint cheap! The delay ordering this was due to my 16200 camera needing an electronics redesign around the A/D converter to USB circuit (but that is another story)

 

My comet NB system (includes two other comet specific wave lengths) will be going live next Feb in a remote hosting facility in southern Spain (zero light pollution, excellent seeing in a high(ish) altitude desert climate and good horizons for the necessary long exposure imaging).

Note that my aim is not to detect low contrast features in the coma (though this would be interesting for some bright comets) - but to extend imaging into bright moon periods.

The PSF issue is a little bit worrying with the Semrocks but as comets are not point features this is mitigated. Note that the PSF star "halo" is seen worst around very bright stars. The aim would be to loose the stars in these images in post processing. I have the maths techniques for this mastered a long time ago - but we will see how it goes.

Note that these Semrock filters are for laser microscopy - each one is matched to a known dye used for staining biological samples. A laser light of an excitation  wavelength is used to cause the stained area to fluoresce at a different specific wavelength and the filters are matched to these wavelength for imaging the sample. So it just so happens that a number of the Semrock filters are accidentally matched to comet emission lines - its pure luck.

 

Thanks!  couple of questions - what other comet specific NB filters do you use?  Do you use the Lumicon 'comet' filter' - I know its intended for visual but should work for imaging those C bands?  

 

On your scope -won't the FSQ glass and coatings absorb much of the CN uv band?  I figured the thickness diff would be a problem but 'workable' with re-focusing etc.  I'll be starting with the smaller size -yeah due to the cost and other stuff we'll see how it works if worth going larger!   And I agree comets are 'fuzzy' objects so the halo of the semrock shouldn't be much problem unless you're at really high mag.-image scales.   



#64 Tonk

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Posted 29 October 2018 - 04:23 PM

Do you use the Lumicon 'comet' filter' - I know its intended for visual but should work for imaging those C bands?


No - the band pass is too broad for my purposes (reducing moonlight - and the amount of passed starlight flux)
 

 

won't the FSQ glass and coatings absorb much of the CN uv band?


Its barely UV if at all! The official range for violet in the visible spectrum is 380–450 nm - so technically the center of the CN line (287.5nm) is 7.5nm into the visible part of the spectrum. What you really need to be worried about is the QE of your camera at that wavelength. (My KAF 16200 is 38% @ 380nm - peak is 60% in green - 34% @ 750nm far red)

On a side note - I did the calculations regarding Doppler shift for moving comets. The fastest comets in retrograde orbits moving towards Earth while Earth is moving towards the comet (the max closing velocity of Halley is a good example) produces a Doppler shift of only 0.1nm - so the line will not fall outside a 11nm band pass filter if your comet/filter center lines are reasonably matched to within a few nm - +/- 3nm is good.

(until 3 years ago I was sharing an office with laser spectroscopists @ Univeristy of Leeds - so I did a lot of brain picking)


Edited by Tonk, 29 October 2018 - 04:37 PM.


#65 Tonk

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Posted 30 October 2018 - 02:52 PM

I've just had confirmation from Semrock that these filters do not have an anti-reflection coating an there is not an option to add a coating.



#66 Lumicon

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Posted 05 December 2018 - 04:27 PM

Lumicon makes a visual Comet Filter that covers OIII and C2. But the Lumicon Comet filter is too broad for astrophotography because the S/N ratio would be too poor. Also, it doesn't cover (CN)2.

 

It seems that what we need is a set of very narrowband (3-5nm) filters. One for the (CN)2 line, one for the OIII line, and one for the C2 lines. With the exception of OIII, the existing filters that cover those lines are too broad. This makes for a poor signal to noise ratio, true narrowband filters are the only thing that is going to work.  The narrowbands would be for astrophotography only, they would not work for visual.

 

Astrodon already offers your choice of 3nm or 5nm filters for OIII. But I don't know of any filter that covers (CN)2 or C2 in a narrowband. Astrodon could make narrowbands in these lines, but the development costs are high and I don't think that there is enough potential sales to cover the development costs.

 

How much interest would there really be for these? Does anybody know of a rich person or organization who would place a special order with Astrodon and cover the development costs?  :-)

 

Doug


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#67 Tonk

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Posted 05 December 2018 - 05:50 PM

Also, it doesn't cover (CN)2


You really need to read this whole thread. Its CN radicals that emit the 387nm light. (CN)2 - the proper cyanogen molecule** - has never been detected in comets with any certainly at all (it is largely spectrally inactive being a 4 atom linear molecule) and has nothing to do with the CN spectral lines. The major source of CN radicals in comets is the disassociation of HCN - hydrogen cyanide

** - some astronomers for a 100+ year old historical reason I explained quite a few posts up, call CN radicals "cyanogen" but this is entirely incorrect and the practice is decreasing in more recent published papers. This use of cyanogen for CN is a misnomer and leads to people looking up the (CN)2 formula for chemist's cyanogen - (a different stuff) - as you have apparently done.


Edited by Tonk, 05 December 2018 - 06:25 PM.


#68 Tonk

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Posted 05 December 2018 - 05:59 PM

How much interest would there really be for these? Does anybody know of a rich person or organization who would place a special order with Astrodon and cover the development costs?  :-)


A small number of folk are buying Semrock NB filters - 387nm filters for (CN) under the direction of the University of Maryland's comet Wirtanen citizen science monitoring program, The filter is used for comet morphology studies. I've also bought Semrock 427nm (CO+) and 513nm (C2) - yes it was expensive!!

Semrock are already making these for fluorescence microscopy to match light emitted from specific laser activated dye molecules so the development cost came from elsewhere. The missing feature of the Semrock filters is they are not anti-reflection coated (they dont need to be for the designed application). Adding anti-reflection coatings would improve matters. Semrock wont do this - I asked.

The band widths for these filters dont need to be as narrow as 5 or 3nm. The optimal filter band widths where determined for the Hale-Bop filter set produced in the mid 90's under NASA's direction and are 6nm for CN, 6nm for CO+ and 12nm for C2 - the latter is a complex set of peaks so all that a narrower band pass does is loose available flux. The literature often refers to the full set of comets filters as the HB filter set (it includes 4 continuum band passes as well as filters for other species such as H2O+, NH etc).


Edited by Tonk, 05 December 2018 - 06:23 PM.

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#69 Tonk

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Posted 05 December 2018 - 06:08 PM

These are the filters I'm using

q7eBKe5Ejj9T_620x0_wmhqkGbg.jpg

These are the band passes of these filters. The CN and CO+ band passes are 2x HB ideal (FWHM =  13nm compared to HB ideal of 6nm). The C2 is near ideal (16nm compared to the HB ideal of 12nm)

CN - V6AV2neuhKJW_620x0_wmhqkGbg.jpg

CO+ - UzOAWRN6p5Bu_620x0_wmhqkGbg.jpg

 

C2 - BMb57E5TN3lf_620x0_wmhqkGbg.jpg


Edited by Tonk, 05 December 2018 - 06:17 PM.


#70 Lumicon

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Posted 05 December 2018 - 07:05 PM

Tonk,

 

I think that you probably have the best filters available for (CN)2 and C2. Sadly, they are still not good enough. :-(  They are technically narrowband by conventional definitions, but still too broad. Astrodon defines narrowband as less than 10nm.

 

In designing the "ideal comet set filters" I would err on the side of too narrow in order to increase the signal to noise ratio. NASA has better telescopes than most of us.  :-) But also, the trend has been to go narrower recently because of improved camera sensors. If you want definition, go narrow.

 

I doubt there would be a market for two different C2 filters for the two lines at 511nm and 514nm, but they could be squished into a narrowband centered on 512.5. I would make the (CN)2 narrower than 6. The OIII is already available in many widths, we make OIII in 3nm and 5nm. If you want wider, they are readily available.

 

Of course, Astrodon filters would include all the usual anti-reflective astrophotography coatings. You can't blame Semrock because they were not designed for astrophotography.

 

But again, only the OIII is available at this moment. So we can only dream.

 

Doug



#71 canopus56

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Posted 05 December 2018 - 09:40 PM

In addition to Tonk's 2015 post #38 above, for persons interested in more background on the green color, I found the following to be a readable reference.

 

Biver, N. Cometary spectroscopy. 2011. In Astronomical Spectrography for Amateurs. J.-P. Rozelot and C. Neiner (eds). EAS Publications Series, 47 (2011) 165–188. https://doi.org/10.1051/eas/1147006 (Pay-walled)

 

Biver notes that ammonia (NH3), water (H20), and acetylene (C2H2) get broken up by sunlight and then recombine into a myriad of by-products and constituents - NH2, H+, OH-, C2, etc.

 

"The main radicals are C2, responsible for the famous cometary 'Swan bands' and the green tint of cometary comae, CN (violet), C3, NH, NH2 and OH (Fig. 2) (at 166)."

 

Swan Bands Wikipedia (in the green region of the visible spectrum)
https://en.wikipedia.../wiki/Swan_band

 

https://en.wikipedia..._blue_flame.png

 

The green color in the visible spectrum around 530nm is produced by C2 molecules being excited by the Sun and then emitting photons as they drop to lower energy states. Although CN is present in comet gases, it primary emits below 480nm and its relative abundance is far less than C2.

 

A table of comet emission lines by source molecule and wavelength are attached.

 

I have not seen a calibrated spectrogram for Comet 46P. 

 

Color  Wavelength interval
Red  ~ 700–635 nm
Orange  ~ 635–590 nm
Yellow  ~ 590–560 nm
Green  ~ 560–520 nm
Cyan  ~ 520–490 nm
Blue  ~ 490–450 nm
Violet ~ 450–400 nm
or Purple

From: https://en.wikipedia.org/wiki/Color

Attached Thumbnails

  • 20181203CometSpectroLinesBiven.jpg

Edited by canopus56, 05 December 2018 - 09:48 PM.


#72 Tonk

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Posted 06 December 2018 - 05:48 AM

In designing the "ideal comet set filters" I would err on the side of too narrow in order to increase the signal to noise ratio. NASA has better telescopes than most of us.  :-) But also, the trend has been to go narrower recently because of improved camera sensors. If you want definition, go narrow.

NASA commissioned the filters for a global research program - various academic institutions bought the filter sets  to use on a range of scopes owned by those institutions. Some of these scopes were no more capable than scopes available to (some) amateurs.

 

I think this is the difference between what we using them for and your angle on higher definition imaging applications. I'm involved in some citizen science projects measuring production rates of various chemical species - I really only need a photometer to count photons to do the job at hand so definition doesn't really bother us. As for S/N the scopes we are using are cited on a mountain at a very dark sky site in southern Spain to help cut down on the N part.

 

It would be nice to have really narrow band filters for pretty pictures - but right now there aren't any frown.gif  . If some narrower ones ever appear i would be interested.

 

 

I doubt there would be a market for two different C2 filters for the two lines at 511nm and 514nm, but they could be squished into a narrowband centered on 512.5.


Due to the complexity of the C2 spectrum the lines at 511nm and 514nm are only slightly stronger that the multitude of other C2 peaks surrounding these two characteristic peaks - picking the center point and deciding how wide you should go is fine. There is absolutely no reason to have separate filters in this region.

Semrock by a complete chance do a 514nm/3nm filter that could be used for C2

https://www.semrock....d=FF01-514/3-25

 

 

I would make the (CN)2 narrower than 6.


Please can you stop using (CN)2 - its CN - just go and read some of the literature on the subject wink.gif. Here's one -http://www.astro.umd...ions/filter.pdf - see table 1 (which defines the HB comet filter set). As I have mentioned only astronomers have had the (very bad) habit of calling the reactive CN radical species "cyanogen". However cyanogen is the name organic chemists (I'm a PhD qualified one smile.gif ) have always had for the very different molecule (CN)2. I'm not splitting hairs here - they (CN and (CN)2) are two totally different substances and they have very different spectra.

By the way the Semrock CN filter (387/11) has been tested by a number of groups and it is able to reveal morphological features in comet comas with apertures as low as 10" - so it is good enough for the application. The comments from Jorma Ryske are that careful calibration is needed. See here - http://wirtanen.astr...ml#Jorma_update.

Note that in the above link - when comparing Ryske's results using the 387nm Semrock with those using the HB CN filter on the Lowel scope you can see reflected light from the dust tail dominating and obscuring parts of the CN cloud in Ryske's image compared to the Lowel image. This is the clear difference between using a 6nm bandwidth HB CN filter to the 11nm bandwidth Semrock filter.

This result is useful - imaging gas rich and dust poor comets will get the best out of the wider Semrock filters. Dust rich and gas poor comets on the other hand will be a dead loss to any NB comet filter. The cutoff between these extremes of comet types will not favour the Semrocks compared to much narrower band pass filters - but there are plenty of comets out there to image and a fair proportion of the less dusty will come up good in NB.  

 

 

 

Of course, Astrodon filters would include all the usual anti-reflective astrophotography coatings. You can't blame Semrock because they were not designed for astrophotography.


I'm not blaming Semrock smile.gif - they are however getting more orders than usual for the 387nm CN filter since the Wirtanen project kicked off in September.

 

The reflection problem only really upset the aesthetics of bright stars if you are doing pretty pictures. The comet features for that vast majority of comets that can be imaged should not be noticeably affected (not many are that bright). You can always remove the stars from the narrow band comet images (via statistical rejection stacking) and overlay with a regular anti-reflection LRGB image of the star field (when the comet has gone). So its is doable - just more pretty picture post processing work than normal.


Edited by Tonk, 06 December 2018 - 06:44 AM.


#73 Tonk

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Posted 06 December 2018 - 06:22 AM

I have not seen a calibrated spectrogram for Comet 46P.


I have on FB - it has a weak CN line compared to the strong C2 line groups. I'll see if I can get a copy up here ...


OK - this is the FB spectrum link

https://www.facebook...70693552968598/

 

And here it is inline: (its not been background calibrated)

Spectrum: 46P/2018.11.04
Cepheid Observatory, RBT, India
Vorion Scientific Observatory, AHD, India

47316066_1970693612968592_28439208370886


Edited by Tonk, 06 December 2018 - 06:46 AM.


#74 JoRy

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Posted 24 January 2019 - 03:09 PM

Just found this interesting topic of photographing CN cyano radical emission in comets gas jets. I purchased this Semrock 387nm narrowband filter last spring and have tested it with my 12" Newton and QSI690 since autumn 2018. I participate also to 4*P Coma Morphology campaign and sent my first results of comet 21P/Giacobini-Zinner to campaign. They publish my results in http://wirtanen.astr...ml#Jorma_update and give a conditional recommendation for using this filter.

 

There really are challenges using this filter. For example in my case getting reasonable quality UV flat was a long process. But finally it really is possible to get reasonable results of comets CN gas jets and rotation effect with amateur size telescopes using this filter.

 

This filter has changed my comet photographing technique quite much so that I'm nowadays using practically only this filter trying to resolve CN radical gas jets and then some R channel exposures to resolve dust tail. Results are perhaps ugly but I think these have more value for comet research.

 

My last and so far perhaps best image/animation can be found from this SW gallery link http://spaceweatherg...pload_id=150891 showing 46P/Wirtanen's rotation and pinwheel effect taken 11th January 2019. Same observation with bit more technical specs is also here in Finnish Astronomical Association Ursa portal https://www.taivaanv...ions/show/80336 (sorry partly finnish language).

 

Jorma


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#75 Ron359

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Posted 24 January 2019 - 04:13 PM

Just found this interesting topic of photographing CN cyano radical emission in comets gas jets. I purchased this Semrock 387nm narrowband filter last spring and have tested it with my 12" Newton and QSI690 since autumn 2018. I participate also to 4*P Coma Morphology campaign and sent my first results of comet 21P/Giacobini-Zinner to campaign. They publish my results in http://wirtanen.astr...ml#Jorma_update and give a conditional recommendation for using this filter.

 

There really are challenges using this filter. For example in my case getting reasonable quality UV flat was a long process. But finally it really is possible to get reasonable results of comets CN gas jets and rotation effect with amateur size telescopes using this filter.

 

This filter has changed my comet photographing technique quite much so that I'm nowadays using practically only this filter trying to resolve CN radical gas jets and then some R channel exposures to resolve dust tail. Results are perhaps ugly but I think these have more value for comet research.

 

My last and so far perhaps best image/animation can be found from this SW gallery link http://spaceweatherg...pload_id=150891 showing 46P/Wirtanen's rotation and pinwheel effect taken 11th January 2019. Same observation with bit more technical specs is also here in Finnish Astronomical Association Ursa portal https://www.taivaanv...ions/show/80336 (sorry partly finnish language).

 

Jorma

Thanks for posting your results here, I have been wondering if tonk or anyone else had gotten images with the semrock filter.   Your 12" Boren-simon scope (noted on SW) also has a very fast f/ ratio doesn't it?  That would make these images 'easier' to capture than a scope with slower f/ratio?  


Edited by Ron359, 24 January 2019 - 06:19 PM.



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