Horsehead in the fog...
alias IC434 in the city lights!
|I know I'm not the first to try to image the Horsehead Nebula under the heavily light polluted conditions of a city! |
But this image was obtained from captures made with a webcam under the conditions illustrated below:
60s digital view, taken during the aquisition of the individual frames that have been added to obtain the final image of Horsehead Nebula.
To get more informations about the used webcam : click here !
IC 434 Horsehead Nebula
You want to know how I did this ?
Then follow me...
|Imaging Conditions : >|
WebCam Philips VestaPro modified (version 1) equipped with B&W sensor SONY ICX098BL on my 8" Celestron + 3.3 Meade Reductor + Celestron LPR Filter .
Checking of the telescope's collimation on Betelgeuse, focused by the aigrette method.
Capture of 94 40s individual frames.
Note: for the treatment 2 images were eliminated...
Parameters of acquisition: Gain 70%, Gamma 50%.
Here is one of the 94 rough images - Reduced to 80% >
Obscure nebula is perceptible on this individual frame.
Acquisition of 11 darks, telescope closed.
Acquisition of 11 ULP by pointing the orange horizon, the telescope being closed by a white translucent bag.
Rem: The use of LPR filter is undoubtedly for much in the success of this attempt. Indeed, by reducing the parasitic radiation of urban lighting, I could increase the exposure time and thus appreciably improve the signal report/ratio on noise of each rough image...
The images preprocessing...
|Preprocessing and combination of the images: |
To make Dark, Flat and other registrations, I 've used the IRIS software as described in my Web pages...
This image has been obtained after preprocessing and combination with Iris!
The result is already quite good, in spite of the combination of a great number of images. Nevertheless, the image remains quite "disturbed". The difference between the signal and the sky's bottom was rather weak. So, I had to be rather severe about the adjustment's level of the visualization's thresholds.
You can also notice the presence of small "artefacts" and the "Whiting Eye effect" quite visible on the most brilliant stars...
|Processing or magic of the layers! |
Caution: The only aim of this stage is to make the image as beautyfull as possible.
I wished to act on three aspects of the image:
These three requirements being sometimes contradictory from the point of view of the actions to carry out, I decided to treat them independently on three layers...
Note: The three layers result from the image obtained with IRIS.
Background : Softening preserving the structure, To soften More. - Merging : Normal
Copy 1 : no treatment - Merging : Soft light
Copy 2 : Contraste/Luminosity to keep only the most brilliant stars, Gaussian of ray 1 to 2, manual Correction with the fuzzy round brush of more "deformed" stars- Merging : To clear up
The merger of these three layers enabled me to obtain the image presented at the beginning of this article: -)
B&W Image Fred GUINEPAIN + Color Image François MEYER
Article rédigé en janvier 2003
(C) Fred GUINEPAIN - 1999-2007