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Ha Clip Filter 6nm or 12nm

Snjór
29 Jun, 2019 18:51
Hi,

I thinking of getting Ha filter for Canon crop sensor  DSLR and not sure I understand difference in 6nm or 12nm  other than huge price difference.  Could someone with more knowledge explain. I read Astronomik web pages but still at a loss. My usage would be wide field images with camera lens from very bright København, DK. Thanks!

Sigga
Magellen
29 Jun, 2019 19:11
Hi Sigga,

I am using both HA NB filters on a DSLR  (Canon EOS 600D). They say, the stronger the light pollution, the narrower your filter should be. True enough, but the narrower your filter, the longer the single exposures should be.

Depending on the light train, my exposure times per frame start at 5 Minutes (f/2, 12nm filter) and go up to 20 Mintues (f/6, 6nm filter). If you have guiding and a resonable fast lens, I would go for the 6nm filter. Without guiding, I think you could consider the 12nm filter, even if it is less effective.

HTH Fritz

PS: Please PM me for a more technical description
Edited 29 Jun, 2019 19:17
koten90
30 Jun, 2019 04:57
Actually Halpha emits in 656,281nm, not 657 or 655. Nor even 656,3 or 656,2.
The light you capture outside that emission line is not Halpha, so it not interesting. That light comes from LP, Moon or any other source.
It is so true that all filter broader than 4nm let you catch even NII (Nitrogen) emission line.

At the same trasmittance, a narrower filter will give you the same amount of signal, with a clearer contrasted background which is a must have to capture faint filaments of gas that normally would vanish in the glow of broader filters.

The only problem I can see is for very very fast focal ratios: below f/3,5 you can have some problem. I don’t know how to explain it, but it would result as if light had its nanometers shifted, so the signal cannot pass through the filter. I hope someone could give us a technical explanation of this phenomenon.

In conclusion, I absolutely suggest almost anyone to buy the 6nm and don’t mind if it is for canon, sbig or other sensor. It is quite always better.
astroCH
30 Jun, 2019 06:56
Hi Sigga,
imaging under light pollution I quite tricky… I have both CLS-CCD and Ha 12nm for my modified DSLR. The Ha 12nm works well on bright targets, such Rosetta, Orion or so. My local dealer suggested me to buy the 12nm over the 6nm for my small refractor (60mm aperture, 255mm focal length) : framing and focusing would have be to challenging with a 6nm filter as the emission line are really more restrictive (= almost completely dark image on liveview). The CLS-CCD works very good on almost every targets as the emissions lines from OIII and SII are also transmitted…but your camera isn't modified and filters don't increase the % of transmission…it will just cut off the artificial light like mercury and sodium street lamps. That's actually what I need while imaging near my city.
So why not considering a CLS or L-Pro filter for your wide field image taken in DK?
My humble advice would be to forget Ha (6nm and 12nm) and go for a light pollution filter, like the CLS-CCD from Astronomik or L-Pro from Optolong, as your DSLR isn't modified.
Hope it will help you choosing the best one ;-)
Cheers, Christophe
koten90
30 Jun, 2019 07:32
Stop it, stop it: if you haven't a mod-DSLR you cannot use an Halpha filter!

For Christopher: the Astronomik CLSCCD has a transmission graph that looks like a UHC filter (narrower and more color-changing, not so good for non-nebular subjects); viceversa, Astronomik UHC-E is much more similar to a CLS filter.

the focusing issue with Halpha and live view is easy to solve: just focus on a bright star such as Vega or Deneb (if you use Astrobackyard EOS to control the shooting, you will have a helpful module to focus at best considering FWHM and having a histogram to avoid sensor saturation). I have a friend in Florence who focused a TS 90/600 + 0,8x reducer with Canon 450D Baader mod. and Astronomik 6nm. Vega reported an FWHM 2,8pixel! smile
Edited 30 Jun, 2019 07:33
eigenVector
30 Jun, 2019 14:05
Alessio Pariani
… If you haven't a mod-DSLR you cannot use an Halpha filter!

This is so important. Narrowband on dslr in general is very ineffective itself even if it were modded.
astropilch
30 Jun, 2019 18:09
Hi Sigga

My  images were taken with a 12 nm Ha clip filter and modded 450 d. I'm under Bortle 6 skies.  It's one of the best asto purchases I've ever made!!

Regards
Alan
Edited 30 Jun, 2019 18:10
Snjór
01 Jul, 2019 11:25
Hi all,

Thanks so much for responding and information, I have better understanding now and lots to think about and consider.

Best wishes and clear skies to all,
Sigga
gnomus
01 Jul, 2019 11:44
Hi Sigga

I cannot help with the DSLR side of things, since I stopped doing DSLR Astrophotography a few years back.  When I was using a DSLR, I did use a general Light Pollution filter - one of the IDAS ones.  I remember finding this purchase complicated enough, since there are so many different IDAS 'models'.

I think folks are correct - that an Ha filter won't be much use with an un-modded DSLR.  Are you wanting to use the filter for LP, or to get into NB imaging?  If it's the latter, then you might want to consider if you're at the stage of getting a dedicated mono camera.  I found it very easy to spend lots of money going down the DSLR route when, if I'd stopped to think about it, I always knew I was going to end up with a dedicated cooled-CCD astro camera.  In my view, your image capturing skills, and your processing would easily justify such an investment.

In general the narrower the better for NB - although (with Astrodons) there is a case for a 5nm Ha over a 3nm Ha (due to hydrogen beta … whatever that is).  But the Astrodons (and the Chromas) are absurdly expensive.  The Astronomik 6nm filters are worth considering (I have a set - please PM if you want a detailed review).  The other filters worth considering are the Baaders - I'd look especially at the Baader 'Ultra Narrowbands'.  They are relatively new.  If these are any good - and I haven't used them or seen any reviews - then they would be a much cheaper alternative to the Astrodons/Chromas.

Go on, Sigga.  You know you need a dedicated CCD  smile   smile    As I say, feel free to PM if you want to discuss this 'route' in more detail.

Regards

Steve
suburbanastronomer
01 Jul, 2019 17:24
Hi Sigga,

A lot of valid points but talk about information overload! I have  a few images taken through a 6nm clip filter with my filter modified Canon 60 on my astrobin page that will give you an idea of what  sort of results you can expect. As Allesio pointed out, if your DSLR is not filter modified, only a small portion of the Ha will get through to the sensor and only the  red pixels will be able to pick up Ha. So  you'll need to take a lot of exposures to get results that you'll be satisfied with. The good thing is that since bandpass is fairly narrow, you'll be able to use your lens wide open (or close to) without having to worry about coma. I typically would capture 20 or more 300 second subs with my  Rokinon 85mm f1.4

clear skies!

Marc
UN73
01 Jul, 2019 18:53
hi sigga,

i suppose you mean a modded cam? otherwise your exposuretime won´t be a pleasure anymore like others mentioned before. if you combine ha with rgb it makes a huge difference even if your sky isn´t heavily polluted.

keeping the lens wide open means that there will be a shift in the wavelength that the filter will let through. for apertures in the range of f/2 (which is quite daring for most lenses) the 6 nm one isn´t supposed to be superior to the 12 nm one. the wider the aperture the more light will fall onto the filter in a steeper angle which is apparently the reason for the shift.

the 12 nm is easier to work with if you use enlarged liveview for focusing your widefield and work with a non-goto mount like the star adventurer. i suppose with the 6 nm filter you wouldn´t see even the brightest stars for focusing in liveview anymore.

bye,
ulf
Starminer68
01 Jul, 2019 19:01
Hi, Sigga,

I totally agree with all comments above: DSLR without modification AND cooling is no good for DSO. I am a fan of Canon, so I started with the lightest Canon D100, upgraded it with power adaptor instead battery, even with Orion cooling box….. Finally I gave it up and bough ASI 1600 MM-Pro, cannot be happier  smile  You can use your DSLR for widefield photos, collages etc. but if we are talking about serious DSO astrophotography - CCD is the only way to go (choose only mono). as to filters: avoid cheap clones, they are unpredictable (could be ok or garbage). I would suggest Astrodon Ha 7 nm-OIII 7 nm-SII 6 nm or Baader planetarium CCD filter set, a bit pricy but top quality, no nasty halo around bright stars etc, Per aspera ad astra!  smile
olaskarpen
01 Jul, 2019 19:19
https://www.astrobin.com/378563/?image_list_page=3&nc=&nce=

I only have good experiences with dslr with narrowband.

https://www.astrobin.com/full/352556/B/

Nikon mono mod D600
Edited 01 Jul, 2019 19:25
Snjór
01 Jul, 2019 19:27
Thinking hat on and pulled down tight!
Starstarter86
03 Jul, 2019 08:21
For your consideration: This is what you get with an unmodded DSLR, @340 mm f/4.8 and a 7nm Ha-Filter after 8h of imaging 10min-Frames:

https://www.astrobin.com/398949/B/?nc=user

I dare say not very impressive smile
Gernot_Obertaxer
05 Jul, 2019 07:26
Check out my latest image smile I used a Astronomik 12nm for the h-alpha picture.

The focusing and the framing ( Canon6Da) was not that easy!

I think with the 6nm you wont see anything on the liveview screen.

CS Gernot
Morian
05 Jul, 2019 13:39
Hej Sigga.
Har set dit opslag.
Prøv at forstille dig at jo lavere nm dit filter er jo finere af det material du vil image kommer igennem, lidt ligesom en si ,altså jo lavere nm tal er jo mere fint er sièn…ok?
Jeg har Canon 500da og 6D (ikke modifiseret) i DSLR camera men mht imaging med dem syntes jeg dark nebula eks.LDN,LBN osv er optimale for disse sensor og ikke så meget Nebulaèr da deres sensore ikke er så følsomme, men det er bare min mening.
Hvis jeg var dig vil jeg spare de penge på det clip in filter og bruge dit camera til de ovenstående objekter jeg har nævnt og evt spare sammen til et mono ccd.
Med Venlig Hilsen morian (alias Morten)
Morian
05 Jul, 2019 13:40
Hej Sigga.
Har set dit opslag.
Prøv at forstille dig at jo lavere nm dit filter er jo finere af det material du vil image kommer igennem, lidt ligesom en si ,altså jo lavere nm tal er jo mere fint er sièn…ok?
Jeg har Canon 500da og 6D (ikke modifiseret) i DSLR camera men mht imaging med dem syntes jeg dark nebula eks.LDN,LBN osv er optimale for disse sensor og ikke så meget Nebulaèr da deres sensore ikke er så følsomme, men det er bare min mening.
Hvis jeg var dig vil jeg spare de penge på det clip in filter og bruge dit camera til de ovenstående objekter jeg har nævnt og evt spare sammen til et mono ccd.
Med Venlig Hilsen morian (alias Morten)
Snjór
07 Jul, 2019 22:48
Thank you all for help, info and suggestions! I have much to think about now!

Sigga
bobzeq25
07 Jul, 2019 23:47
Narrower is better.  People think wider will allow shorter exposures, but what you get is just noise, so you don't really win.  Narrower is also, as you noted, a lot more expensive.  A common tradeoff.
 
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