Last February 18th the sky was unexpectedly clear. The moon was also out, so I took advantage of the circumstances by shooting a Hydrogen-alpha image of the Rosette Nebula, one of the targets I had always wanted to image.
This was kind of a hurried shot, as I had this feeling I would only have one shot at imaging this object this season. So I took a few shortcuts: I binned my guide chip 2x2 (which a lot of the experts recommend anyway) for extra sensitivity, and used 10-second guide exposures (thank goodness for a great mount!), which helped me luck into a guide star. I normally try to dither my exposures, moving the guide star around every few exposures, but in my quest for going as long as I can in one night I decide to forego that.
As a possible result of those shortcuts, I lost a couple of exposures to weird tracking (no idea why, but the guider and mount seemed to recover anyway). I lost a couple more images as the Rosette set behind some trees. Ah, well.
In addition, on processing my image I found quite a smattering of dark pixels all over the image. This is either my dark library (I have over ten darks for this temp/exposure/bin setting, though), or a plain result of not dithering. So I had quite a bit of cleaning up in Photoshop, but I might still have missed a few. This, plus my relative lack of experience with processing H-alpha images, is the reason behind the delay of my post.
Details:
Scope: Borg 76ED f/6.6 (500mm focal length)
Mount: Takahashi EM200
Camera: SBIG ST-8XE with CFW-8a filter wheel and a Custom Scientific 4.5 nm H-alpha filter
Exposures: 10 x 15 minutes (2-1/2 hours total)
Images captured and calibrated in CCDSoft. DDP applied in MaximDL. Levels and curves applied in Photoshop. Noise reduction and smoothing applied with Noise Ninja.
Enjoy,
Eric
This was kind of a hurried shot, as I had this feeling I would only have one shot at imaging this object this season. So I took a few shortcuts: I binned my guide chip 2x2 (which a lot of the experts recommend anyway) for extra sensitivity, and used 10-second guide exposures (thank goodness for a great mount!), which helped me luck into a guide star. I normally try to dither my exposures, moving the guide star around every few exposures, but in my quest for going as long as I can in one night I decide to forego that.
As a possible result of those shortcuts, I lost a couple of exposures to weird tracking (no idea why, but the guider and mount seemed to recover anyway). I lost a couple more images as the Rosette set behind some trees. Ah, well.
In addition, on processing my image I found quite a smattering of dark pixels all over the image. This is either my dark library (I have over ten darks for this temp/exposure/bin setting, though), or a plain result of not dithering. So I had quite a bit of cleaning up in Photoshop, but I might still have missed a few. This, plus my relative lack of experience with processing H-alpha images, is the reason behind the delay of my post.
Details:
Scope: Borg 76ED f/6.6 (500mm focal length)
Mount: Takahashi EM200
Camera: SBIG ST-8XE with CFW-8a filter wheel and a Custom Scientific 4.5 nm H-alpha filter
Exposures: 10 x 15 minutes (2-1/2 hours total)
Images captured and calibrated in CCDSoft. DDP applied in MaximDL. Levels and curves applied in Photoshop. Noise reduction and smoothing applied with Noise Ninja.
Enjoy,
Eric
Attached Image:
