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Object: Messier 45
Type: Open Cluster
Distance: 407 light years
Constellation: Taurus
Date: 18 January 2009
Equipment: SXV-H9, Zeiss 135mm lens, ATIK filter wheel, Astronomix LRGB filters
Subframes: 30 x 300s full resolution subframes (luminance), 20 x 200s RGB 2x2 binned, 16 flats/flat darks (no darks) in luminance, channels calibrated and stacked in AIP4Win. Final processing in AstroArt and PSP7.
It really has been an exceptionally poor winter for imaging so far, has it not? On the few nights that stars are actually visible, there has been a mist lurking around, robbing the sky of any sort of clarity needed for deep-sky work. This particular evening was not really much better but it had been so long that I’d thought I’d give it a go on something bright, like M45, an object I’d never really had much luck in imaging in terms of capturing the delicate nebulosity that suffuses its stars.
Seeing started poor and a high haze became increasingly heavy during this imaging session. I shot what were going to be the luminance frames for the image (200s at full resolution through a UV/IR blocker) first, followed by the red and green frames at 2x2 resolution, and all the while the sky background on the images was getting brighter and brighter. When I finally shot the series of 200s blue frames, I was amazed at how burnt out the stars looked compared to the red and green channels – perhaps an indication of just how “blue” the Pleiades are (or perhaps the lens has a touch of chromatic aberration). I was going to shoot a series of frames at shorter exposures, but by then the stars were virtually hazed out, so I gave up.
The blue frames were a write-off, so I used the luminance channel as the blue one, and pieced together an RGB composite in Paint Shop Pro. This was a bit fiddley as I’d resized the 2x2 binned red and green channels in AIP4Win to match the full resolution luminance channels. In PSP, not only were those images very slightly smaller than the “unresized” ones, there was a bit of rotation as well, probably because I’d had to reverse the equatorial mount between the red and green frames.
The high haze had also caused some horrible gradients across the raw images, and the stacked ones took quite a bit of processing to flatten them out.
It was all a bit much for the AstroArt RGB processing package, which couldn’t stack the colour frames and introduced a load of new coloured gradients anyway, hence a bit of laborious trial and error work to rotate and resize the composites in PSP7 to get something that could be aligned accurately enough to avoid odd and unequal flaring effects on the stars.
With all of this heavy processing, the final image isn’t too brilliant. The brighter stars are still a bit burnt out – you can’t pick out the three small stars just west of Alcyone, for example, which the best shots can clearly resolve. The nebulosity around Merope and is also rather restricted and doesn’t show the “brush-strokes” you see in really good images of this area of the sky.
Whether that’s down to the poor conditions at the time, a poor processing technique and/or insufficient resolution from the 135mm telephoto lens, I’m not sure.
Type: Open Cluster
Distance: 407 light years
Constellation: Taurus
Date: 18 January 2009
Equipment: SXV-H9, Zeiss 135mm lens, ATIK filter wheel, Astronomix LRGB filters
Subframes: 30 x 300s full resolution subframes (luminance), 20 x 200s RGB 2x2 binned, 16 flats/flat darks (no darks) in luminance, channels calibrated and stacked in AIP4Win. Final processing in AstroArt and PSP7.
It really has been an exceptionally poor winter for imaging so far, has it not? On the few nights that stars are actually visible, there has been a mist lurking around, robbing the sky of any sort of clarity needed for deep-sky work. This particular evening was not really much better but it had been so long that I’d thought I’d give it a go on something bright, like M45, an object I’d never really had much luck in imaging in terms of capturing the delicate nebulosity that suffuses its stars.
Seeing started poor and a high haze became increasingly heavy during this imaging session. I shot what were going to be the luminance frames for the image (200s at full resolution through a UV/IR blocker) first, followed by the red and green frames at 2x2 resolution, and all the while the sky background on the images was getting brighter and brighter. When I finally shot the series of 200s blue frames, I was amazed at how burnt out the stars looked compared to the red and green channels – perhaps an indication of just how “blue” the Pleiades are (or perhaps the lens has a touch of chromatic aberration). I was going to shoot a series of frames at shorter exposures, but by then the stars were virtually hazed out, so I gave up.
The blue frames were a write-off, so I used the luminance channel as the blue one, and pieced together an RGB composite in Paint Shop Pro. This was a bit fiddley as I’d resized the 2x2 binned red and green channels in AIP4Win to match the full resolution luminance channels. In PSP, not only were those images very slightly smaller than the “unresized” ones, there was a bit of rotation as well, probably because I’d had to reverse the equatorial mount between the red and green frames.
The high haze had also caused some horrible gradients across the raw images, and the stacked ones took quite a bit of processing to flatten them out.
It was all a bit much for the AstroArt RGB processing package, which couldn’t stack the colour frames and introduced a load of new coloured gradients anyway, hence a bit of laborious trial and error work to rotate and resize the composites in PSP7 to get something that could be aligned accurately enough to avoid odd and unequal flaring effects on the stars.
With all of this heavy processing, the final image isn’t too brilliant. The brighter stars are still a bit burnt out – you can’t pick out the three small stars just west of Alcyone, for example, which the best shots can clearly resolve. The nebulosity around Merope and is also rather restricted and doesn’t show the “brush-strokes” you see in really good images of this area of the sky.
Whether that’s down to the poor conditions at the time, a poor processing technique and/or insufficient resolution from the 135mm telephoto lens, I’m not sure.
There are certainly better shots of M45 out there than this one. I think I’ll give up on it for now…
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