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Tuesday, January 28, 2014

A grande finale of the Cepheus project, mosaic of ten panels with colors

I have planned this Cepheus project for a long time. Finally I have been able to finalize it. I have done some large mosaic images of nebula rich areas in our Milky way. The ultra fast camera optics, Canon EF 200mm f1.8, it's a perfect tool for the job. It has a large, flat and sharp, image field and full open at f1.8, it collects photons very fast. The final image covers an area of about 18x10 degrees. (Full Moon has an apparent size about 0,5 degrees. 720 full Moons are needed to cover this area in the sky.)

To have a color image, each of the panels have been shot three times. This narrowband image is shot with QHY9  (a cooled astronomical camera), Canon EF 200mm f1.8 camera optics full open,  Baader Planetarium Narrowband filter set for an emission of ionized elements, Hydrogen, Oxygen and Sulfur.  (H-alpha, O-III and S-III) The dimensions of the final mosaic image are 12000 x 6500 pixels.

Emission Nebulae in constellation Cepheus 
Mosaic image of ten individual panels, total exposures 92h.
Click for a very large image, 3000 pixels wide and 7MB.

Mapped colors from the emission of ionized elements, R=Sulfur, G=Hydrogen and B=Oxygen.
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About 1:1 detail from the image above
Click for a full size photo

Lots of stars out there.

Cepheus Nebulae in visual spectrum
Composed from the narrowband channels

Image is in Natural color palette from the emission of ionized elements, 
R=Hydrogen + Sulfur, G=Oxygen and B=Oxygen + Hydrogen.
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B&W image with an emission of Hydrogen alpha only

Image of light, emitted by an ionized Hydrogen.
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A labeled image and orientation

Some main objects are labeled here

An orientation in constellation Cepheus. The mosaic image covers an area of ~18x10 dgrees.

Technical details

I have used lots of an older material for this image. I have shot this area for years, with a different instruments, with different focal lengths and apertures. The total exposure time for the final mosaic image is calculated by adding the exposures for the actual mosaic to the exposures for sub-images used.  

List of the sub-images used for a large, 10 panels, mosaic of Cepheus

Panels, shot for a final mosaic

Processing work flow

Image acquisition, MaxiDL v5.07.
Stacked and calibrated in CCDStack2.
Deconvolution with a CCDStack2 Positive Constraint, 33 iterations, added at 50% weight
An extra background normalization in CCDStack for a mosaic match.
Color combine for each panel in PS CS3
Panel composition in PS CS3
Levels, curves and the final color matching in PS CS3.

Imaging optics used for the mosaic image

Meade LX200 GPS 12" reduced to f5
Tokina AT-X 300mm f2.8
Canon EF 200mm f1.8

Cameras and filters

Imaging camera QHY 9, with a QHY filter wheel
Guider camera, Lodetsar
Active optics unit SXV-AO with Meade LX200 12" telescope
Baader Filter set, 7nm H-aplha, 8nm S-II and 8.5nm O-III

Total exposures used for a mosaic image

H-alpha 160 x 1200s Bin 1x1
O-III 66 x 1200s Bin 1x1
S-II 50 x 1200s Bin 1x1

Total exposures 276 x 1200s = 92h


Rick said...

Fabulous image, but weren't you concerned about the performance of the interference filters at F 1.8?? What bandwith were the filters (hope I did not miss this). Anything less than 12 nm is likely to suffer from transmission shift and peak loss, no? I Came across your image when looking for a match to a 105MM Ha shot I just finished, it is almost an exact match in terms of coverage.

J-P Metsavainio said...

I'm well aware about the "blueshift" problem with a faster optics and narrowband filters. How ever, in practise the effect is not too bad and gets easily compensated with just a little more exposure time.
Band width used can be seen at end of the blog post in technical information.