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(more) M42 images and a Question


Macavity

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Finally galvanised myself into doing a bit of imaging.

Mostly to try out my Altair Astro 66/400mm ED APO.

Stacked images from the Watec 910HX as ever...

First up a straightforward RGB (3x512s) image of M42:

post-539-0-05442800-1452527772.jpg

Then a go at mono "contrast blending" (512 + 64 +4s) to better show the core:

post-539-0-76473400-1452527823.jpg

Then I tried some narrow band H-Alpha and O(III) images...

But the result ended up a very strange colour. :D

A bit more to learn, clearly!

Almost forgot the question! But basically wondering WHY my H-Alpha and O(III) mono

images (below left and right respectively) seem such a lot fainter than the *unfiltered*

images in the top row! (I adjusted the black level of right one to reduce light pollution).  ;)

post-539-0-24759100-1452539417.jpg

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Glad some people liked 'em! I sense maybe my question is "something and nothing". 

During an internet search, I came across:

http://dg-imaging.astrodon.com/uploads/3/6/0/7/3607549/astrodonnarrowbandfaq.pdf

(See the "Where's the Data" section!)  :eek:

On the other hand, I still vaguely wonder why my narrowband images are so FAINT! 

Perhaps I expected narrow band imaging to be more quantitative (than aesthetic)? ;)

I'd definitely commend the (cheaper) Baader RGB dye filters to Video astronomers. :)

I now sense my expectations re. the 66mm f/6 refractor were a bit unfair. If I do more

"narrow band" nebula imaging it will be perhaps with the trusty old 8" f/4 Newt...

As an interesting diversion, I asked the question: WHICH Colour should one use for

coloring images. I frankly admit I've never been enamoured with the Hubble Palette.

http://mathematica.stackexchange.com/questions/11480/colordatavisiblespectrum-is-wrong - Looks like the jury is still out on this one... :p

Every 2nd'ary school Chemistry student knows what colour elements are anyway! :D

post-539-0-76040500-1452594000.gif

P.S. I was thinking of doing a bit of "RGB" imaging with:

H-Alpha (Red),  OIII (Green) plus a plain BLUE filter...

I sense there is reflection (blue?) nebula around M42. :cool:

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Chris,

Since stars are blackbody (thermal continuum) emitters, only a small fraction of their photon output is within the narrow bandpass of the Ha or OIII filter you are using. They will be much dimmer. I have found in some recent experiments that I need to triple exposure time to get good starfinding and stacking with narrowband filters. Also, in the case of M42, I believe there's quite a bit of reflected light from the core stars in addition to the actual emission line photons, so the nebula itself is dimmer. Of course, your unfiltered shot also includes Ha, OIII, and all the other atomic emission lines together, so again you expect it to be brighter than one emission line alone. And finally, your filters may only pass 85-90% of the light in their bandpass.

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Thanks indeed for feedback on one of my "random wibbles", A! :)

Ultimately, it's hard to deny experiment? And I too see a significant

degree of dimming via narrow band filters. More than I imagined...

With this particular setup (smaller aperture, slowish scope) my nice

"gaussian" signal histograms half merged back into "pedestals",

when I inserted an H-Alpha or an O(III) filters. Not so surprising?

But maybe I needed to see this in practice to appreciate this. :p

I totally agree with all you say above. I too would venture that

there is a (quite) bit of *reflection* nebula in this field as well. ;)

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Didn't really like my blurry RGB M42, so added a Luminence chanel!

(I wan't paying enough attention to the focus of the scope either?)

post-539-0-58711900-1452797123.jpg

As ever, I'm not sure I'd have the application to be a classical imager!

But an interesting (afternoon's) "journey" though? I've learned that my 

ad hoc stretching methods are significantly bettered by "Arcsinh" and

(maybe most!) modern algorithms. I may even understand why too?  :p

I do find IRIS useful to fiddle... If you can get into the interface, it can

do some remarkable stuff e.g. from the domain of expensive software.

If there are any other GIMP'sters out there... I learned that one uses

"Value" as the mode for blending in luminence images with the RGB. ;)

Retrospectively, I notice my stars are now a tad GREEN! (I randomly

played with the colour balance). I discovered a few other *potentially*

useful tricks: *Selective* blurring to get rid of odd black halos around

brighter stars. There's a lot of interesting Astro reading out there...  :)

I suspect I WILL still have a go at "narrow band" with the 8" Newt.

Sixteen+ times more light has go to help a bit with the process...

Even if this is perhaps not one of my more pointful(?!?) exercises! :D

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