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| Reprocessed M31 - now with no green cast! click to flickr |
Showing posts with label Galaxies. Show all posts
Showing posts with label Galaxies. Show all posts
Saturday, September 11, 2010
M31 redux
I was looking back at all the pictures from the New Mexico trip and realized I had yet to reprocess the image of M31. Way back a whole month ago I was wrestling with color balance issues. I just decided to do all the processing in Nebulosity and deal with the color later in Photoshop. I spent a couple hours this morning doing just that.
This is a center crop from the T2i frame, the full frame can be seen here. I'm pleased how much more visible the starclouds and dark lanes are. On some rainy day I just might see if I can find any extragalactic globular clusters and annotate them here. Pretty cool for a 200mm lens.
Thursday, September 9, 2010
Dark helps, Darks help
I made it out to Montebello with my imaging pal last Saturday night. This would be my only chance to get out this dark cycle before being sidelined by minor surgery. I'll be back in action in October but at least I have two images worth of data to process while I sit around in my jammies for a few days.
It was the first trip out after the New Mexico vacation. Montebello provides some reasonable skies considering its proximity to the greater Bay Area but New Mexico it aint. Those of you who live in super dark skies ... count your lucky (bazillion) stars.
Confronted with skyglow again I had to decide on what ISO to image with. I haven't characterized the camera (and probably won't) and frankly get tired reading about S/N and gain vs. exposure time trade-offs. The experimentalist in me says, "just do the comparison yourself". Some day maybe I will, but in that moment I just decided to throttle back down to ISO1600.
I've processed one of the two images I snagged that night - NGC253/288 region with the 200mm EF-L. I rather like wide field frames of objects normally imaged at higher focal length. Not as flashy but it does give another perspective.
Wow ... do dark skies make a difference. Noise was not my issue in New Mexico, even at ISO3200. This image had all kinds of noise that I had to beat down. But dark frames do help, and the more the better. I took 64 darks to throw against this and I still had more noise than I expected. I was also toolazy tired to re-adjust polar alignment and had some trailing so I shortened exposures to 30seconds each (I took 60 for 30minutes of accumulated exposure time).
Below is a MacBook Pro 17 crop of the galaxy and globular cluster.
Stare at the center of our galaxy and look between your feet. This view is just about straight down out of the plane of the Milky Way and NGC 288, the globular cluster, is hovering nearby at 28,000 light-years distant. The Great Sculptor Galaxy, NGC 253 is over 400 times further away at some 11.5 mega light-years distant - one of our "just down the block" galactic neighbors. Nifty. Burnham says 253 was first observed by Caroline Herschel which makes that a double Nifty.
Perhaps under a darker sky in October I'll try this again and put a lot more photons in the bucket. An hour to 90minutes would do this pair some justice.
It was the first trip out after the New Mexico vacation. Montebello provides some reasonable skies considering its proximity to the greater Bay Area but New Mexico it aint. Those of you who live in super dark skies ... count your lucky (bazillion) stars.
Confronted with skyglow again I had to decide on what ISO to image with. I haven't characterized the camera (and probably won't) and frankly get tired reading about S/N and gain vs. exposure time trade-offs. The experimentalist in me says, "just do the comparison yourself". Some day maybe I will, but in that moment I just decided to throttle back down to ISO1600.
I've processed one of the two images I snagged that night - NGC253/288 region with the 200mm EF-L. I rather like wide field frames of objects normally imaged at higher focal length. Not as flashy but it does give another perspective.
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| NGC253 and 288. Canon T2i full frame at 200mm f.l. |
Wow ... do dark skies make a difference. Noise was not my issue in New Mexico, even at ISO3200. This image had all kinds of noise that I had to beat down. But dark frames do help, and the more the better. I took 64 darks to throw against this and I still had more noise than I expected. I was also too
Below is a MacBook Pro 17 crop of the galaxy and globular cluster.
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| crop to the good stuff. click to flickr |
Perhaps under a darker sky in October I'll try this again and put a lot more photons in the bucket. An hour to 90minutes would do this pair some justice.
Sunday, August 22, 2010
Sometimes you just got what you got
I'm pretty slow sometimes but processing this image of M33 taught me something. You can spend as much time as you want processing an image hoping to stumble across some arcane photoshop command-alt-clickery that will extract ever fainter photons that just aren't there. Yeah, sometimes you just got what you got. Be satisfied.
I learned a lot this time around. Blue-Red channel trickery to kill the green weenie. Color halo reduction. All kinds mask selection/load/subtract-ery. Good stuff - and absolutely no way to reproduce how I got to the endpoint. However ... I am repeating to myself ... be satisfied.
At 200mm the image scale for M33 isn't all that great. At least compared to M32. It's smaller than I remembered :). I was also a bit surprised that 60 min didn't pull out more. A late rising moon just below Kitchen Mesa accounts for the still persistent gradient in the lower right corner. The presentation could be improved but dear reader ... there simply ain't no mo' photons. I give you all I have.
You know what? I'm satisfied. Mostly :) Hanging up the hair-shirt for a bit before I tackle another set of data from the New Mexico trip. Click for larger image.
Taken at Ghost Ranch near Abiquiu, New Mexico August 6th, 2010
Canon T2i (stock), 200mm EF-L @ f2.8
Astrotrac Travel System mount
Imaging temperature range: 52-54F
60 60sec exposures @ ISO3200
64 darks, 21 flats (1/5" ISO 100) 21 flatdarks
pre-processed and stacked in Nebulosity
post-processed in PS4
I learned a lot this time around. Blue-Red channel trickery to kill the green weenie. Color halo reduction. All kinds mask selection/load/subtract-ery. Good stuff - and absolutely no way to reproduce how I got to the endpoint. However ... I am repeating to myself ... be satisfied.
At 200mm the image scale for M33 isn't all that great. At least compared to M32. It's smaller than I remembered :). I was also a bit surprised that 60 min didn't pull out more. A late rising moon just below Kitchen Mesa accounts for the still persistent gradient in the lower right corner. The presentation could be improved but dear reader ... there simply ain't no mo' photons. I give you all I have.
You know what? I'm satisfied. Mostly :) Hanging up the hair-shirt for a bit before I tackle another set of data from the New Mexico trip. Click for larger image.
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| M33 Macbook Pro 15 center crop |
Taken at Ghost Ranch near Abiquiu, New Mexico August 6th, 2010
Canon T2i (stock), 200mm EF-L @ f2.8
Astrotrac Travel System mount
Imaging temperature range: 52-54F
60 60sec exposures @ ISO3200
64 darks, 21 flats (1/5" ISO 100) 21 flatdarks
pre-processed and stacked in Nebulosity
post-processed in PS4
Sunday, August 15, 2010
M31 ... now in Color!
I spent a couple, a few 5 hours today trying to get a handle on the color image of M31. First I had to figure out the best settings in Nebulosity for the debayer step. There are no default settings for the T2i - the camera is still rather new. While I could have chosen just about any setting and done the color correcting later (in Nebulosity or PS) my previous attempts were rather garish.
To get a handle on this I took a RAW picture outside in sunlight that included a gray card. Verified in PS that the RGB values were the same (check). Then I opened the file in Nebulosity and debayered with every setting possible (hair shirt? check). Then I wrote down the RGB values reported by Nebulosity for the same spot on the nominally gray card and selected the conversion profile that gave the "most gray" (equal RGB) values (double hair shirt, check).
Next I proceeded to reprocess all the images with the new setting. Which, by the way if you are reading this and happen to be in same situation and don't want to spend 2 hours going through the exercise the answer is ... ta-da ... straight color scaling (not a specific camera like stock 40D or unmodded 300D or whatever).
After all that I cropped and did a Auto Color Balance. Saved every file en route. Then I post processed the image in Nebulosity. The spirit was willing but the body was too weak to start postproc in Photoshop.
The image is still too pale, greenish bluish or something. And I have orange star halos, some noise to bang down and so on. After some well deserved rest I'll tackle the image again in Photoshop to see what I can do about color issues. In some sense I like the more muted colors. Going forward I'll have to think about how I will use colors in these images. But, for now, here is M31 in all it's Ghost Ranch glory.
As for all images ... click to see a larger version.
To get a handle on this I took a RAW picture outside in sunlight that included a gray card. Verified in PS that the RGB values were the same (check). Then I opened the file in Nebulosity and debayered with every setting possible (hair shirt? check). Then I wrote down the RGB values reported by Nebulosity for the same spot on the nominally gray card and selected the conversion profile that gave the "most gray" (equal RGB) values (double hair shirt, check).
Next I proceeded to reprocess all the images with the new setting. Which, by the way if you are reading this and happen to be in same situation and don't want to spend 2 hours going through the exercise the answer is ... ta-da ... straight color scaling (not a specific camera like stock 40D or unmodded 300D or whatever).
After all that I cropped and did a Auto Color Balance. Saved every file en route. Then I post processed the image in Nebulosity. The spirit was willing but the body was too weak to start postproc in Photoshop.
The image is still too pale, greenish bluish or something. And I have orange star halos, some noise to bang down and so on. After some well deserved rest I'll tackle the image again in Photoshop to see what I can do about color issues. In some sense I like the more muted colors. Going forward I'll have to think about how I will use colors in these images. But, for now, here is M31 in all it's Ghost Ranch glory.
As for all images ... click to see a larger version.
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| M31 processed entirely in Nebulosity Taken at Ghost Ranch near Abiquiu, New Mexico August 4th and 5th, 2010 Canon T2i (stock), 200mm EF-L @ f2.8 Astrotrac Travel System mount Imaging temperature range: 52-58F 87 60sec exposures @ ISO3200 (taken over two evenings) 64 darks, 21 flats (1/5" ISO 100) 21 flatdarks (still not sure about needing these) pre and post-processed in Nebulosity |
Friday, August 13, 2010
The Abscence of Color
It would appear the imagers job is never done. All images are a "work in progress". You just know you can add some more data ... process a little more ... learn some secret dark art that will make the image pop. I'm not immune.
Friend(s): "So! Did you get any pictures of the sky?"
Me: "Ah, yeah, a few. But there were clouds ... had one good night ... will take me a while to process them"
Friends(s): (losing interest quickly) "oh, ok ... let me see something when they are done then".
What they don't realize is they will *never* be done! sigh. So in order to combat this illusion of progress through motion I will post up what is likely the only good image from the trip ... in B&W. I gray-scaled the image because I am having a nasty time trying to get the colors figured out. All RBG debayering channel sensitivity hoo-ha. Really starting to get me PO'd.
Canon T2i, 200mm EF-L @ f2.8
Astrotrak Travel System mount
87 60sec exposures @ ISO3200 (taken over two evenings)
64 darks, 21 flats (1/5" ISO 100) 21 flatdarks (still not sure about needing these)
preprocessed in Nebulosity
post processed PS4
Color will follow when/if I get that figured out. Just hate throwing away all *that* data.
Friend(s): "So! Did you get any pictures of the sky?"
Me: "Ah, yeah, a few. But there were clouds ... had one good night ... will take me a while to process them"
Friends(s): (losing interest quickly) "oh, ok ... let me see something when they are done then".
What they don't realize is they will *never* be done! sigh. So in order to combat this illusion of progress through motion I will post up what is likely the only good image from the trip ... in B&W. I gray-scaled the image because I am having a nasty time trying to get the colors figured out. All RBG debayering channel sensitivity hoo-ha. Really starting to get me PO'd.
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| M31, M32, M110 (Andromeda galaxy and companion elliptical galaxies) |
Canon T2i, 200mm EF-L @ f2.8
Astrotrak Travel System mount
87 60sec exposures @ ISO3200 (taken over two evenings)
64 darks, 21 flats (1/5" ISO 100) 21 flatdarks (still not sure about needing these)
preprocessed in Nebulosity
post processed PS4
Color will follow when/if I get that figured out. Just hate throwing away all *that* data.
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