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 Post subject: Narrowband imaging of M82
PostPosted: Sat Mar 08, 2014 10:03 am 
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Location: Bolton
Last night I had an opportunity to continue my experiments with narrowband imaging using a monochrome LX-webcam and filter-wheel. Although there was some hazy cloud around, the moonlight wasn't too bright, and M82 was high enough in the sky to work with.
I was using the camera on my StarWave 80ED, operating at f/4.6 (using my Celestron focal reducer), and the filter-wheel was loaded with Hydrogen-alpha, Oxygen-III and a blue "nebula" filter. These are the results with each filter:
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File comment: 30x 1-min with H-alpha filter
m82h.jpg
m82h.jpg [ 32.29 KiB | Viewed 2702 times ]
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File comment: 30x 1-min with O-III filter (the hazy cloud got a bit thicker during these exposures)
m82o.jpg
m82o.jpg [ 32.32 KiB | Viewed 2702 times ]
Attachment:
File comment: 30x 1-min with blue "nebula" filter
m82n.jpg
m82n.jpg [ 29.98 KiB | Viewed 2702 times ]

This morning I processed and stacked them, using the H-alpha image for the Luminosity & Red channels, O-III for Green and "nebula" for Blue:
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File comment: LRGB stack from 3x 30-min filtered exposures
m82_7mar.png
m82_7mar.png [ 38.61 KiB | Viewed 2702 times ]

I noted that the supernova (2014J) seemed to have faded noticeably since last month.
And I also remembered that I'd done some similar tests with M82 back in October, using a Celestron 80mm f/5 achromat, so I've managed to align these two images for comparison:
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File comment: M82 in October 2013 and March 2014
m82_sn.gif
m82_sn.gif [ 15.14 KiB | Viewed 2702 times ]

As well as the apperance of the supernova, this clearly shows the difference in optical quality between the simple achromat and ED 'scopes!
But it was a clearer night back in October, so I caught a little more of the fainter parts of the galaxy then.


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 Post subject: More experiments with imaging of M82
PostPosted: Mon Mar 24, 2014 9:55 am 
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For a comparison with my recent narrowband experiment, last night I fitted my original Philips SPC880 camera: this has the original tri-colour (RGB) CCD and firmware (i.e. not the RAW bayer-mode output). This was certainly a lot less hassle than using the monochrome camera and filter-wheel: just a single framing and focusing operation, rather than having to re-focus for each of the colour filters. And then the post-processing was a bit more straightforward too.

I'd not done such a good job with my polar-alignment this time - the image drifted about a third of the way across the field over the hour, and most of the individual frames showed slight trailing. So after calibrating with Offsets and Darks, Registering and stacking (using Sigma-clipping), I applied some Richardson-Lucy deconvolution, after which the stars looked much less elongated.

Finally I used the Colour Stretch and even tried some Wavelet filtering too:
Attachment:
File comment: M82 on 23-Mar. 38x 90-sec with Philips LX webcam through StarWave 80ED at f/4.6
m82_23mar.png
m82_23mar.png [ 86.99 KiB | Viewed 2634 times ]
The supernova is fainter now, but still quite distinct.


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