Sunday, November 22, 2009
Soul Nebula closeup finalized
After a long, frustrating period, we finally had kind of clear skys!
Actually, I started my imaging session Three times last night and back everything up at between.
Weather was so volatile, since misty clouds from open see are impossible to predict.
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After all I was able to capture more H-alpha and enough O-III and S-II to build a decent three band narrowband image.
Two versions , as usually, first one in HST-palette and the Second one in "natural colors" mixed from same material as HST-image.
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Two color chemes,
HST Palette as S-II=Red, H-a=Green and O-III=Blue.
Second image is in natural colors composed from narrowband data. Channels are balanced so, that image match to visible spectrum, H-a + 24%S-II=Red, O-III=Green and O-III + 15%H-alpha=Blue.
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Processing work flow:
Image acquisition, MaxiDL v5.07.
Stacked and calibrated in CCDStack.
Deconvolution with a CCDSharp, 30 iterations.
Levels, curves and color combine in PS CS3.
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Telescope, Meade LX200 GPS 12" @ f4.65
Camera, QHY9
Guiding, SXV-AO @ 11Hz
Image Scale, 0,8 arcseconds/pixel
Exposures:
H-alpha 16x1200s Binned 1x1
O-III 3x600s, binned 3x3
S-II 9x600s, binned 3x3
Top of that, some color data from an older wide field image is used.
Wider view to the Soul Nebula. Area of the current image is marked with a frame. -
A Starless version of the Nebula.
I place it here, since it looks kind of nice and the actual Nebulosity can be seen better this way.
Friday, November 20, 2009
Colors in Astro Images
I made two animations to show difference between different Color schemes used in my images.
At an image of the Elephant's Trunk Nebula abowe, differen color variants are animated together.
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First is pure Hydrogen alpha channel, second is a RGB-broadband image, next is H-aRGB mix. After that, there is pure Narrowband compositions from three channels, H-a, S-II and O-III. First of them is a "Natural Color" composition mixed so, that resulting colors are close to visible spectrum to human eye. Last image is a "Mapped Color" composition, where all three channels are mapped to selected color. In this case the mixture is S-II=Red, H-a=Green and O-III=Blue, this combination is generally known as a Hubble-palette (HST), after a Palette used in images by Space Telescope Hubble.
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What is the truth then?
Deep space targets are generally so dim, that human eye is not cabable to see any colors from them.
Closest to real colors is the RGB image, if colors are balanced correctly.
Usually a pure white Star is used to measure a correct color balance between Red, Green and Blue data.
Next closest is the H-aRGB mix, where H-alpha filtered image is used to boost contrast and details in image.
It tend to distor the Red balance in image though.
Third, in reality order, is a Narrowband mixture, where different channels are mapped to visible colors as closely as possible by the wavelenghts.
I'm using a mixture by Richard Crisp.
H-a is mapped to Red with about 20% S-II, O-III is Green and the Blue is mixed from O-III and about 15% H-alpha to compensate missing H-beta.
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The Hubble palette is least realistic color scheme. It's made famous by wonderful pictures from the Hubble Telescope. This palette is developed to maximize visual difference between different ionized Elements in Nebula. Even though it's used in sientific purposes, it's beautiful as well. I use HST-palette for esthetic reasons only, with that tool I'm able to reveal some of the hidden beauty.
An other good reason to use it is, that it's a de facto standard and makes possible to compare images from different narrowband imagers.
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An other animated example of color palettes, the Pelican Nebula.
Thursday, November 19, 2009
An image portfolio
I have opened a portfolio for my Astro Images under a Zenfolio service.
At this moment it's more like a test version, please, have a look.
Comments are welcome.
Tuesday, November 17, 2009
Clouds and more clouds
We have all the darkness but no clear skys.
This must be the worst location on Earth to do astro photographing!
We have about half a Year too light nights to shoot anything (location is 65N)
and top of that, winters are very cloudy.
The whole Week looks like this.
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