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11/30/-1
    
Sunday, November 1st, 2009
An experiment with narrow band imaging.

So I got the new camera, a Canon 1000D, and I also picked up an Astronomik 12nm Hydrogen Alpha CCD Clip-In Filter for Canon EOS Cameras. Can the name be more of a mouthful? Technically, I think 12nm is more of a medium band filter, but still it seems to be referred to as a "narrow band filter", so I'll call it the same. But I'll be calling it the Ha filter from here on out.

The bottom line objective here is to increase imaging productivity by implementing a narrow band filter that can be used during a full moon. The image acquired during this time will then be added as luminence data to normal one shot color (OSC RGB) images I'm taking either here or in the desert.

The Pictures In This Gallery - NGC 281
I've only had it a few days and so far only one test subject has commenced. NGC 281 happens to be a subject that I have a 2 hours of OSC RGB on, it has a very nice dust lane and interesting structure and it responds well to Ha, so it's my target for now. Currently the moon is full, which - for the first time since I've been observing - is GREAT! A perfect test.

The images I'm posting in the gallery are of the original shot, the Ha shot, and the combined shot. I'm just now learning how to do the processing of Ha shots and the combining techniques into the OSC RGB shots, so I'm on a learning curve, but I think the first light results are pretty good and I'm totally stoked about the potential here.

Picture 1 - 01-NGC281-2h.jpg
This is a 2 hour shot during a new moon weekend in a dark sky. I was very pleased with this shot as it was though I wished I had more time on it to bring out the fainter details of the structure.

Picture 2 - 02-NGC281-Ha-2h30m.jpg
This is the ha only data shot during the full moon which was not only extremely bright, but it was only 43 degrees away from NGC 281!

Picture 3 - 03-NGC281-HaRGB-4h-30m.jpg
The combined shot using Ha as luminance and OSC RGB as color.

Scope: Vixen R200SS 200mm @ f/4 w/Vixen R200SS Coma Corrector
Mount: Orion Sirius EQ-G with GoTo
Guiding:  Meade DSI Pro and PHD Guiding
Guide Scope: William Optics ZenithStar 66 SD
Camera: Canon EOS 20D (unmodified) for OSC RGB and Canon 1000D (Modified) for Ha data
Special Settings: None
ISO: 1600
Exposure: 2 hours OSC RGB (24 x 300s) 2.5 hours Ha (18 x 600s)
Processing Software: Acquired in Nebulosity with high dithering, Stacked in Deep Sky Stacker (Kappa-Sigma Clipping for all frames), Levels, Curves, Astronomy Tools, Gradient XTerminator and Noise Ninja in Photoshop
Support Files: 24 flats, 24 bias, one dark used as a bad pixel map
See Gallery below for image



Image Gallery For This Session
01 NGC281 2h 02 NGC281 Ha 2h30m
03 NGC281 HaRGB 4h 30m
   

01-NGC281-2h.jpg
Click picture above for larger version
If the picture seems too bright or too dark, try adjusting the brightness below.
Brightness:
|
  



Comments:
On 11/04/09 at 02:52pm Diego wrote:
Beautiful image. I agree with Barry, the star field is a little bit diminished in the last image, but it is still the best of all. Congratulations!

On 11/04/09 at 12:43am Neil Heacock wrote:
Thanks for the tip Gerald. I'm totally new at this type of combining, so I'm interested in different methods. your points are excellent. Much appreciated!

-Neil

On 11/03/09 at 06:03am Gerald (oldwexi@aon.at) wrote:
Thats a very good image!
But you could improve the final result. The color can get better if you use the
Ha Data in the R-channel instead as Luminance!
Using Ha as Luminance destroys the correct colors with nebulae!!!
Why?
The Ha is distributed to green and blue also if you
use Ha as Luminance! Therefore you got the pinkish hue of the nebula and the star colors diminishing.
LRGB makes only sense with star clusters and some galaxies, not with nebulae.
To improve the already excellent image
make a (Ha+R)/G/B image out of the data you already have.
(oldwexi@aon.at

On 11/02/09 at 11:37pm Neil Heacock wrote:
The Ha data is basically red. There is essentially no blue or green. So in order to blend it as luminosity it needs converted to grayscale. But as captured, it's basically monochrome red.

This also means that with a one shot color camera, where only 1 in every 4 pixels is a red pixel because of the RGGB bayer matrix of the chip, 75% of the pixels are rejecting the data (or more accurately, not seeing any data). That's a key reason why monochrome cameras are better, because 100% of the pixels are being used for every photon that comes in regardless of the filter in front of the chip.

If it was green data I was capturing, then 50% of the pixels would be collecting data. But alas, our universe doesn't seem to like green as much as we do...

-Neil

On 11/02/09 at 11:15pm Barry wrote:
It's cool, alright. Wow, 4 1/2 hours of data. Do you have to shoot in grey scale with the Ha filter or does the filter negate the color collected by the camera?

On 11/02/09 at 09:02pm Neil Heacock wrote:
Yeah, the star field is diminished, but that's part of the objective. Smaller, less bloated stars. But I still want all of the stars. You'll notice that the Ha shot is actually missing stars altogether from the OSC RGB shot. So in the combine method, I'm trying to get as much of the data from both images as possible.

The fact that I "enhanced" a dark sky shot from my front yard is *very* exciting to me!

-Neil

On 11/02/09 at 08:01pm Barry wrote:
The nebula is certainly enhanced in the Ha and combined shots. The star field is somewhat diminshed but overall, the combined shot is the most pleasing. Nice work.



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