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.

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 lazy 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.

crop to the good stuff.  click to flickr
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.

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