Friday, September 17, 2010

Lost in the Clouds

Well I pretty much buried M11 (Wild Duck cluster) in the starcloud. It's flying around in there towards the center of the frame. Yes, there.  The white splotch in the center.

I took 71x1min of data which yes, might have been over doing it a bit.  Processed to stretch the contrast between the the starcloud and Barnard's little dark nebulas. Along the way the Wild Duck kinda got lost in the fog. Oh well.

Scutum Starcloud
I've stared at this image for quite some time now and as much as I try to make myself like it ... I just don't. All the standard imager excuses apply (focus soft, tracking could have been better, star bloat, blah blah blah) but that isn't it.  Not really.

I've noticed that I develop an affinity for some images ... despite various flaws. Others are like shirts kept in the closet and rarely worn. Not the garish colored ones or those that "must have shrunk in the wash".   I mean the ones with nothing wrong per se ... just something not quite right and they are passed over again and again.

I showed this image to a friend and his jaw dropped. "You mean that is in the Milky Way? That golden carpet is, like, stars? Every dot? And what is that way cool dark stuff?  Your joking ... really?  That's mind blowing."  When I looked at it through his eyes I started to appreciate it more and more.  I still don't like it much but it sure made a huge difference to see the wonder on my friends face.

Maybe there is a shirt or two in my closet that deserves another chance.

Scutum Starcloud

Taken at Montebello Open Space Preserve, CA Sept. 4, 2010
Canon T2i (stock), 100mm EF-L @ f3.5
Astrotrac Travel System mount
Imaging temperature: 65F ambient, 29C-33C in-camera sensor temp
71 60sec exposures @ ISO1600
64 darks (sensor temps 29-33C to match imaging temp range)
21 flats (1/5sec ISO 100) 21 flatdarks
pre-processed and stacked in Nebulosity
post-processed in PS4

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.

Reprocessed M31 - now with no green cast!  click to flickr
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.

Friday, September 10, 2010

How hot is *your* camera?

Story time ... but with charts and graphs and stuff near the end!

When I was out imaging last week I decided to shoot 30 second sub exposures for the image in the previous post.  The other image (still processing, up soon) used 60 second sub exposures.  So that decision meant that I would have to shoot two complete sets of darks as they must match the exposure time, ISO, and temperature of the light frames.  Typical hair-shirt move.

So at 3:30am I start shooting my darks.  At least it doesn't take a lot of skill.  Block the lens, check the ISO,  set the interval timer, sit back and ponder life's mysteries.

I said it doesn't take a lot of skill, not zero.  I still had to change the exposure time and interval for the two sets.  Thought I did, but hey, it was now after 4am.  Yes, I came home with 2 sets of 30sec darks.  Sigh.  Well, at least I had a lot of 'em.

I knew it was roughly 60F out there so my plan was to shoot my 60sec darks in the garage when the temperature was about the same.  Done.

*Insert LOST backstory sound effect*

Previously I had discussed the idea of a dark library with my imaging pal.  He thought it would be cool if one could measure the temperature of the exposure, bin them by temperature and exposure conditions and then match them to the temperature of the light frames.  Cool Beans. I knew that many DSLR's had temperature sensors from past experience shooting Giga-pans in the hot sun.  Ever see that "your camera is getting too hot" icon?  But how to get at that temperature?

Some searching led me to exiftool - a wonderful utility to extract *all* the hidden goodness from your camera image headers.  A command line utility to boot (a GUI is available for the less righteous - windows only).  But for us Mac and Linux folk it is full on shell time.  Pull up that terminal get crackin!  Some thrashing around and sure enough, with the right incantation I got it to spit out...

28 C

Time to get real sweaty and pull on another hair-shirt.  Some hours later - with shell script higgledy piggledy- a file including a table for each dark exposure was mine for the taking.

*Insert LOST return from backstory sound effect*

I knew that using Live View and heck, just shooting images, would heat up the camera (why have a "too hot" warning otherwise) but I was quite surprised by what I found.  The results are shown in the graph below.

First just follow the blue diamonds.  Start with the camera turned off and equilibrated out in the garage.  Ambient temperature steady at 60F.  Set timer to expose for 60seconds, wait 15seconds, take another.  Wash, rinse, repeat.  See temperature climb.  See temperature rise to over 90F!  Yikes.

OK.  Say you are willing to put in a 60sec delay between exposures to give the sensor time to "cool down".  Follow the red diamonds.  Better, but hey, still pushing a 20F rise in 45minutes.

Even a two minute interval doesn't buy much and I'm not waiting around that long.  An ambient temperature of 38F allows for shorter intervals and the temp levels off quicker.  But instead of a brisk 40F you are actually imaging at a balmy 60F.

A check of my light frames shot in the field show the same effect.  Only difference is the camera *starts* warm since I have taken test exposures, focused with Live View and whatnot.  Those first few shutter clicks get you warmed up in a hurry.   Guess we know where all that energy stored in the battery goes.  Huh.

The bad news is self-evident.  The good news is that it is at least possible to know the temperatures of your frames and match darks accordingly.  The not so good news it that doing that is a bit of a pain.  The great news is that one can get just fine images not worrying about this.   More shooting, less fussing = more fun.  But for those of us with a closet full of hair-shirts ... no rest for the weary.  Dang, yet another advantage those cooled-CCD folks have.

How does one use exiftool to get at all this?  I'll post what I've learned later.  For now I leave you with this handy tip.

If you are ever caught out lost and freezing in a forest ... just curl up around your DSLR and hit the shutter every minute or two until help arrives.   You heard it here first.

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.

Saturday, September 4, 2010

The First is Last

This is the last of the images from our 2010 trip to New Mexico.  I just realized that this picture of the southern Milky Way ...

[south from this latitude anyway - would be amazing to see this at the zenith! note to self, must travel with gear south of the equator]

... was the very first of the trip way back on August 3rd.  I remember being so excited to finally have a break in the monsoon storms.  I waited about 9 days for that.  It was still cloudy that night and I shot 16 60sec exposures before the clouds came charging through.  It was first light for the 100mm EF-L lens - I hadn't even taken a terrestrial shot with it yet.  Still had that, ahhhh, new lens smell.

Old Friends.  click to flickr
Only 16min of data but it probably would have taken me an hour to pull out this signal from the skyglow back home.

There is the Trifid and Lagoon floating in the shoals of their inky pool.  The globular cluster M28 off to the left looking almost star-like in this wide field.  Thousands of stars masquerading as one.  The open cluster M23 sparkling jewel like, just peeking into the frame in the upper right.  The comfort of old friends revisited. 

Taking a picture of this area is like photographing Half Dome in Yosemite - standing next to hundreds of tourists all pointing their cameras at the amazing vista. One of the most photographed areas of the sky.  Iconic. You have seen hundred of pictures.  You have seen it dozens of times with your own eyes.  Yet you are drawn to take yet another picture as a keepsake of this particular meeting.  You almost have to.

In the end 3 partial nights dodging clouds and moving from object to object.  I had one perfect night when I snagged an hour each of M33 and M32 before the moon rose.  Six images.  Hours and hours of processing images late into the night after returning home.  Simply perfect.

But now I'm out of data.  Must. Get. More.   Hmmm,   It's been about a month.  Dark moon cycle.  Hey Marek ... wanna go to Montebello tonight and shoot some stars?  I'm in!

Southern Milky Way
Taken at Ghost Ranch near Abiquiu, New Mexico August 3rd, 2010
Canon T2i (stock), 100mm EF-L @ f3.2
Astrotrac Travel System mount
Imaging temperature range: 60-62F
16 60sec exposures @ ISO3200
50 darks, 20 flats (1/5" ISO 100) 20 flatdarks
pre-processed and stacked in Nebulosity
post-processed in PS4