Lagoon & Trifid in Narrowband

[avandonk]

Finally had a clear night until the fog started to form but I managed to get some narrow band data.
Camera Canon 5DH. Modded 100ED.
Filters Astronomik CCD 13NM HA and OIII, Hutech Hbeta which is not narrowband but passes all blue from Hbeta up to UV.

HA 4x16min, OIII 4x16 min, Hbeta 3x16 min. All at an ISO of 500.

After correcting for flats and stacking I obtained three tiff images which I made identical in size and region etc with Registar. These were then split into RGB components and then recombined with Images plus.

Red data from HA to Red
Green and Blue data from OIII to Green
Blue data from Hbeta to Blue

I did not get good blue data due to fog and a Mercury street lamp. But I can control this some what by using a Hutech LPR or NF in conjuction with the Hbeta filter to restrict the extent of the blue. The fog put a stop to this.

I think this method should give a more 'natural' looking narrowband image. This is a first attempt and any comments are welcome.

Large image 1.7 MB
http://members.optusnet.com.au/~trlee8/LTNB.jpg


Bert

[Garyh]

Very nice Bert, you can tell that its lacking Hbeta for blue but at least you managed a good image out of what you could get!!
Very very Nice!
cheers

[avandonk]

Here is one with the blue data adjusted with curves in PS.

1.7 MB
http://members.optusnet.com.au/~trlee8/LTNB2.jpg

Bert

[Tamtarn]

We're not qualified to make any technical comments but we can certainly show our appreciation of you sharing your image by simply saying ..........

Spectacular...WOW :eyepop:

[dcalleja]

Bert
Its an amazing widefield image. How did you know how much to adjust the blue curve in PS (I presume you just select curves and then the blue layer). I ask because I have no feel for it myself - lack of experience!

[leon]

Looking good there Bert, boy are they bright, but so sharp, great work.

leon

[ballaratdragons]

Well I must say, Bert, after hearing you explain it all at your place last week what you were planning to do (colour split using the above-mentioned filters) I am pleased to see it worked so well.

The final combine has come out stunning!!!

Certainly worth the hard work :thumbsup:

[avandonk]

Managed to get some blue data tonight before the cloud arrived with a Hutech LPR filter as well as the H beta. This at least gets rid of Mercury blue line of street lamp pollution. You can see the dark background is less blue polluted.

Here 1.7MB
http://members.optusnet.com.au/~trlee8/LTNB2.jpg

Thanks all I am amazed how good this works. It is almost as good as having dark skies.

Bert

[Ric]

A great image Bert, those filters have given it a lovely surreal effect, almost like it has been painted.

Very nice indeed.

[Dr Nick]

Incredible! that looks amazing! ;)

[avandonk]

I noticed that the Hutech H beta filter has a peak very close to SII 672.4nm. The blue line on the graph below.

So I tried making a false colour image using this colour allocation.
Red from Hbeta to RED
Red from Halpha to GREEN
Green and blue from OII to BLUE.

Large image here 1.6 mb
http://members.optusnet.com.au/~trlee8/LTNBFC.jpg

Seems to work.

Bert

[avandonk]

Here are the images from the three filters Halpha, OIII and H beta

Bert

[Bassnut]

Nice work Bert, looks smooth. The colour pallete on the 1st image does look very natural, much better than the pseudo Hubble pallet in the green image.

Interesting use of Ha and H beta, works well, I havent tried that.

[iceman]

That's beautiful, Bert. A very nice image.

[jase]

Bert,
Impressive work for a DSLR. The data acquired is smooth which is undoubtedly due to the long exposure times. I note your OIII channel appears weaker than the others. You could boost this with pixel math or simply do without it - i.e create a synthetic green channel in PS (which is created from the Ha and HBeta respectively).

Look forward to seeing more.

[tornado33]

Great work Bert. Would be great to see that applied to the Helix Nebula with its strong O3 as well as Ha emission.
Scott

[avandonk]

Thanks for the tip Scott I will try that next.
Here is another version 1.6MB
http://members.optusnet.com.au/~trlee8/LTNB3.jpg


HAred + Hbeta_red to RED
OIIblue + OIIIgreen to GREEN
Hbeta_blue + 0.29XHA_red to BLUE

The reason for adding 29% of HAred to blue is that whenever you have HA being emitted there is always Hbeta at 0.29 the rate of the HA. Of course some of this Hbeta is lost due to Rayleigh scattering and scattering by dust within the nebula. There is a further complication of variable extinction in the atmosphere of Earth.
The reason for adding Hbeta red to Red is because it sort of simulates SII due to the nature of the Hutech filter. This will do until I get one.
The Hutech Hbeta filter on its own also passes blue due to reflection nebula.
I think this method now gives almost natural looking images from mainly narrowband data.
If anyone has any further ideas Jase?

Bert

[jase]

No further ideas Bert - I think you’ve done this one to death. ;) If you’re not a narrowband purist or attempting to project some scientific data, then you could try subtly blending conventional RGB broadband data with narrowband data. I’ve seen this done before with mixed results. It can improve image aesthetics if done right.

You’re correct, the Ha to Hb emission lines are 3:1 ratio. Keep in mind this is theoretical, the ratios can vary. A blend of ~30% Ha data into OIII is quite common for narrowband work.

“Since most of the Hα emission we detect arises from hydrogen recombination, atomic physics is the only thing that dictates the ratio of Hα to Hβ emission from most ionized intersteller gases. Although it is a slight function of temperature, near 10,000 K, the ratio is about 3:1 in favor of Hα. However, intersteller dust absorbs more blue light than red so that ratios greater than this are typical in observations. Observed ratios of Hα/Hβ should be an intersesting probe of dust in front of and within the ionized gas. Our current plan is to cover at least +/- 30 degrees about the Galactic plane along with several brighter ionized regions, such as the entire Orion-Eridanus complex. The observations began in December, 1999 but may take much of 2000 to complete since we have doubled the Hα exposure time for Hβ observations.” – reference http://www.astro.wisc.edu/wham/science.html

(http://www.astro.wisc.edu/wham/science.html)Indeed, the extinction factor is more prevalent in blue wavelengths (OIII) than red. This is the reason why it’s important to plan an imaging session if you want good results. I typically wait for the object to reach its highest point in the sky before collecting blue data to minimise the extinction factor. Interesting reading - http://cfa-www.harvard.edu/icq/ICQExtinct.html. It’s not hard to calculate once you’ve done it a few times. A stepped imaging approach works well where you collect data based on the objects location in the sky (as it approaches zenith – RRGGBB<object at zenith>BBGGRR). The same applies to narrowband work.

What you also need to consider is normalisation of each channel before the colour combine function. Failing to have equal average sky background brightness across the data will result in unequal weightings across the available dynamic range. If you only use PS you’ll need to calculate this manually by taking samples of the sky. Once you have the right weightings you shouldn't stretch individual channels, but all simultaneously to keep balance. Keep in mind that the right nebulosity colour doesn’t mean the stars will also have the right colour. Sometimes you’ll need to split the two and process them differently, then layer them to get the desired result.