Urban Imaging

Schedule doesn’t always allow for a trip to dark skies so sometimes we just have to make due with urban imaging from the driveway. Here is a daylight view of my urban imaging environment.

Like a lot of urban sites I’ve got a @#!%$ LED street light right across the street. Here’s a night time view, as you can see there is light pollution to spare.

Around 8PM a friend and I set  up scopes in my driveway and since the tree in my front yard is just starting to have its leaves pop out it wasn’t stopping much of the glare from the LED monster across the street. With the scopes set up and aligned we started imaging. My first target for the evening was Leo1, a very faint satellite galaxy of the Milky Way. This is one of the targets on my imaging challenge bucket list. Not for its low surface brightness, but because it should be resolvable to stars with my equipment. When I started in this hobby well over 20 years ago I decided that I was going to resolve Sirius B, image deep sky objects in another galaxy and resolve stars outside the Milky Way. I was new to the hobby and figured that it shouldn’t take too long once I figured out how to focus the camera. About three years ago I managed to image deep sky objects in M33. A few months ago I managed to catch Sirius B using my latest setup a SkyWatcher Esprit 120 with a Canon 60Da DSLR.

After capturing 80 minutes of data on Leo1 I moved the scope to my next target, M108 and the Owl. I figured I’d go for a bright target in case the Leo1 effort didn’t pan out. Processing the Leo1 shot provided to be a challenge. The light pollution proved to be a limiting factor in how far I could push the stretch. After a few false starts I ended up with this image.

Leo1 is the faint blue fuzz in the center of the frame. For a better view where you can use your browser to zoom in and have a better look visit my web page on this object.

M108 and the Owl Nebula was much easier, but more time consuming, to process. My usual technique requires masked stretches and split star processing, but for this image split star processing really wasn’t necessary so I simply used starless masks to keep the background under control.

Zooming in on M108 you can see that it is possible to get lots of detail even under light polluted skies.

Even the Owl Nebula turned out reasonably well, given that it really needs more exposure and a longer focal length.

With these results I may try urban imaging more often. There are several mosaics to tackle that may lend themselves to brighter urban skies.

 

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Reprocessing the Helix

 

During the dark sky imaging window in October, 2017 I made it out to capture some data on the Helix. Like most of my images it needs more exposure but I played around with processing it anyway. With the Helix having a low surface brightness at my latitude and because of the shorter than optimal exposure, it was very tricky to bring out the nebula.

My processing started out with my normal masked arcsinh stretch, but somehow I goofed and ended up with an image that had far too much contrast for the data and the colour was off quite a bit.

Now that my schedule allowed a few hours to work on the image again I did some experimenting with the settings I used in the arcsinh stretch. Getting a much better result from the masked stretch I moved on the noise reduction. This got tricky as there was quite a bit of photon noise in the image. The bright sky near the horizon has some light pollution even at our club’s dark sky observatory and the nebula was smack dab in the middle of it.

Using the frequency filter in Images Plus and a suitable mask I managed to get most of the noise under control. Having the ability to control the slope of the filter makes all the difference when tackling this type of noise. After multi-scale sharpening I ended up with an image that after binning by two wasn’t too bad. A final levels tweak and I finally got a Helix Nebula shot that is worth posting.

The image was processed entirely in Images Plus using arcsinh stretches, masked noise reduction using a frequency filter, multiscale sharpening and star reduction. For more information visit my webpage detailing the exposure and camera settings as well as a higher resolution version of the final image.

 

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M96 and Friends

It has been a while since I was able to get out to my favorite dark sky site, the St. Croix Observatory. SCO is the club observatory of the Halifax Centre of the RASC and is a fantastic facility under dark (better than 21 mag/arc-second) skies. Between work schedule, winter weather and the Moon I haven’t been to SCO since November of 2017.

After driving out to the observatory, a pleasant 30 minute drive north of the city, I started to set up my gear. As this was the first clear night with no Moon to speak of in a while there were several other club members there as well, all eager to start in on their own targets. After setting up, sky and polar aligning I started in on centering M96. My plan was to include M95 and several other galaxies in the field. The field I wanted is shown below in a screen capture from ECU.

ECU reported a camera rotation angle of 132 degrees. Using Astro-Tortilla I snapped a few short exposures as I rotated the camera to get the desired field rotation. With the camera set, I fine tuned the frame  centering and acquired a guide star. One a suitable guide star was found I had to wait for the Moon to set. Around 10:30 I finally turned the system loose and went to the warm room where it was a little more comfortable.

Unfortunately, since it was a work day, it had to cut my exposure short after about two hours. Since I was dithering I got about 90 minutes of exposure and grabbed a few darks for hot pixel mapping as I was tearing down the equipment. Although it needs a much longer exposure, hopefully I’ll get out again next month, the shot turned out reasonable well.

It is amazing how many galaxies are in the field. I stopped counting at 20 and there are eight across the face of M96 alone, including an edge on spiral embedded in the left spiral arm at about 9 o’clock.

 

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Sirius B – The Hunt Continues

After getting proper calibration frames the night before I was able to measure the scale in my images which ended up being 0.315 arc-seconds/pixel. Armed with this and a good image of Rigel which has similar separation to Sirius A & B I headed back out into the cold on February 19, 2018 to try my luck again. This time around I used a sub-exposure of 0.1 seconds which I calculated from the Rigel image below and the difference in brightness between the Rigel and Sirius components.

Rigel Image (taken for reference)

Knowing roughly where to look for Sirius made all the difference. After collecting 122, 0.1 second sub-frames and stacking them to produce a stacked image in Images Plus, an arcsinH stretch was used to bring out the dwarf. Sirius B was just visible in the correct spot so the image was enhanced with sharpening and more contrast stretches. Finally the image was combined with my previous effort to show some field stars along with the resolved binary.

Sirius A & B

Measurements made from the image show that the stars have a separation of 11.3 arc-seconds with a PA of 72 degrees. This compares very well with the RASC Observer’s Handbook value of 10.94 arc-seconds with a PA of 72 degrees.

It is interesting to note that the star that I originally thought was Sirius B has been mistaken in several images and sketches I’ve seen, including some on the RASC Sirius B observing challenge page. I’d like to thank Dr. Roy Bishop, a mentor to the whole Halifax RASC Centre, for prompting me to re-examine my original data and to calculate the separation and position angle. If it were not for his coaching I would have made the same mistake as many others and reported the faint, blue star a little less than half way between Sirius A and the bottom of the cropped frame as the white dwarf.

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My Hunt for Sirius B

Imaging Sirius B has been on my astrophotographical bucket list for some time now. Several years ago I tried with an old Meade SN8, but the scope had some optical issues and although it was a reasonable wide field imaging platform, it just wasn’t up to the task of resolving close binary stars.

My next attempt was with a classic 8 inch SkyWatcher Newtonian. I’m still convinced that this system may be able to resolve Sirius B, but I’ve been stymied by the bright halo around the bright A component. The f/5 scope has a large secondary so diffraction is an issue.

These days I’m using an Esprit 120 APO refractor and I thought I’d give it another try. The scope is a joy to use with a very stable focuser and great optics. February 15, 2018 around 7:00 PM I rolled the scope on a ScopeBuggy out of our garage and set it up to cool in the driveway. It wouldn’t be until around nine before Sirius cleared the trees so I went back in to watch the news and plan the evening’s attempt. I had downloaded several images that all supposedly showed the dwarf, including one from the national RASC site on the Sirius observing challenge that I was going to use as a reference. Around 8:30 I went back outside and polar aligned the scope, pointed it at Sirius and started up the autoguider, not that easy a task at -12 degrees!

Heading back inside I have the advantage of using a VNC connection to my tablet running the scope so I could stay warm for the rest of the evening. Since I had no idea of what exposure would work I tried a variety starting at 30 seconds and reducing in two second increments until I saw something close to Sirius A three frames in a row. I was able to see a faint star with exposures from 10 to 5 seconds so I settled on 8 seconds and shot 64 frames. There was a slight breeze so I used the best 42 and stacked them to produce the image below.

Sirius (full field)

Zooming in on the main target

Central Crop

Now things were getting exciting, in close to Sirius A is a faint blue star, slightly elongated due to the breeze moving the scope in some of the subframes. This was the same star labelled as the dwarf in all of the images I had downloaded. From here is where everything went wrong.

I took a couple of calibration frames where I used a planetarium program to send the mount one arcminute north and took a quick image so I would be able to determine direction in the image. I took another image after sending the scope another arcminute north thinking that the first would run out any backlash in the gearing system and I could use this image to measure scale. Finally I took another image with the north button held down and the shutter open, trusting the mount to move north at the sidereal rate. After working through the math I came up with a position angle of 68 degrees (actual is 72) so I was in the right ballpark. When I checked the separation I got almost 17 arcseconds which was off by quite a bit. This was puzzling so I decided to sleep on it and retake my calibration images on the next clear evening.

The next night I planned to take new calibration frames and image Rigel. Rigel is a binary with close to the same separation as Sirius at the moment, but the stars are closer in brightness so resolving the system is much easier. The idea was to use a sequence of images to home in on the correct exposure for the next attempt at Sirius. It turns out that my initial attempts were done with much too long an exposure, saturating the entire area where the dwarf would be located. After determining that two seconds was correct for Rigel, I was able to image and easily resolve Rigel. I took some proper drift shots by exposing for ten seconds with the mount turned off allowing the star to drift through the frame in order to calculate the correct value for the image scale.

Rigel

With the new drift calibration the image scale was found to be 0.315 arcseconds per pixel. I checked the separation on Rigel and got an answer of 9.8 arcseconds with the real value being around 9.5. Much better agreement!

Using the correct image scale of 0.315 arcseconds per pixel I went back to the Sirius image to find that the faint star was definitely not the dwarf. The central crops of Sirius and Rigel, shown above, are both to the same scale. The separation of the two stars in the Rigel system is close to the spacing between Sirius A & B so it is obvious from the two images that the actual dwarf is still within the saturated area of the brighter star. It is interesting to note that the star I had mistaken for the dwarf has been labelled as Sirius B in several images online, including one on the RASC Sirius Observing Challenge page so I’m not alone in my error.

Stay tuned as I’m not ready to give up on this one just yet. Since the target is bright, I can keep trying from home whenever it is clear.

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NGC 891

A fellow astro-imager and I decided to head out to the club observatory for a little photon capturing. As the Sun set we got to work setting up our gear. For a change, the conditions  were near perfect – clear skies, great seeing and since it was fall, no bugs!

After aligning everything we sat around waiting for the end of twilight. This was a night were I planned on experimenting  with AstroTortilla and Backyard  EOS. I’ve been working on a mosaic tool that will rely on precisely  centering a target before moving the scope for each frame in the mosaic. Since I’ve never needed that level of accuracy  before, I took a few minutes to test the setup. After a little tweaking the results were impressive with precise centering of the target. More on the mosaic tool in a future post once I get more of the software  up and running.

With the AstroTortilla experiment out of the way and darkness settling in, it was time to move the scope over to my target for the evening – NGC891. For those not familiar with this galaxy it is the usual faint smudge visually, but photographically  it is an edge on spiral with a nicely  detailed dust lane 27 million light years distant. Here is a crop of the image made from eight, ten minute subs. Masked stretches were used to help control star bloat and mask noise reduction was used to quiet down any background  noise.

The feature  mask tool in Images Plus makes it easy to generate the starless masks and its RL deconvolution  tool was used to sharpen the detail in the dust lane.

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Fireworks Galaxy

With some clear skies in the mid-week forecast an imaging buddy, Art Cole, and I headed out to the St. Croix Observatory  to capture a few images. SCO is the club observatory  of the Halifax  Centre of the RASC, a great facility about 40 minutes out of town with dark mag 6 skies.

I love imaging this time of year. It’s not so cold that you have to wear a parka, it gets dark earlier and there are no mosquitoes! We arrived with a bit of daylight left to make setup easier and as we were the only two at SCO that night we spread out a bit. I must say that the Esprit 120 is a joy to use, making setup much easier than my Newtonian. With the camera at the back end of the scope there is no need for a ladder in any observing position. After setting up my CGE Pro I waited a few minutes to let it get a little darker to start the alignment. Using live view and a grid displayed on the back of my Canon 60Da makes sky and polar alignment a snap. I’m not sure who came up with the all star polar alignment routine in the mount software, but after years of drift alignment he or she has my vote for a Nobel Prize! A few week ago I added a three port USB hub to my system and some Velcro strips for cable management. The combination allows me to control the whole setup, DSLR, auto-guider and scope from a single USB connection to my tablet. Adding Tight VNC to the tablet allows me to control the whole thing from my cell phone from the observatory warm room, a setup that will be very much appreciated once the temperature starts to drop.

With everything set up and darkness above I turned the scope toward NGC 6946, the Fireworks Galaxy, and started calibrating the auto-guider. Phd quickly calibrated and I started the exposure sequence. One reason for picking this target was to capture the rapidly fading supernova that was discovered in May. While my tablet took care of the data capture I set up a zero-G chair and toured the Milky Way with binoculars. After capturing 85 minutes of data I grabbed a couple of quick darks to use as a hot pixel map in my Images Plus workflow. The image was processed using a split star work flow with masked stretches to bring out the galaxy without overly bloating the stars. For details on the workflow please read the pdf from my main website.

After a bit of quality time spent with Images Plus I had a passable galaxy image with an open cluster, NGC 6939, in the upper left as a bonus.

Zooming in on the galaxy reveals a faint “star” that wasn’t there before May. The supernova is highlighted by the white arrow.

Compare this with an older and much poorer image taken several years before the supernova.

For more image details and to see a blink of the two galaxy images please visit my main website page for this image. It still amazes me that images confirming a supernova can be captured with a simple DSLR camera and a small amateur telescope. Galileo would be impressed with what his humble telescope has made possible.

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Summertime SkyWatcher Esprit 120 Imaging

With a clear weekend in the forecast and some cottage time coming up I finally got a chance for some imaging time. Skies at the cottage in Marion Bridge are reasonably dark with the Milky Way clearly visible.  I’ve been itching to get out for the final testing of my Esprit 120. After SkyWatcher shipped me a replacement Esprit to replace a unit with pinched optics, I noticed a strange distortion in some of the stars in several of my images. The distortion only showed up after saturation boosts so I wanted to do some more testing to figure out what was causing the problem. After shooting several star fields at varying altitudes I very pleased with the results. It turns out that the distorted stars were due to atmospheric dispersion and saturation boosting during processing. Aligning the three colour channels before any other processing completely solves the problem and the scope produces stunning images as advertised.

First up is a shot of M13. I was imaging the cluster as one of my test shots to verify the atmospheric dispersion problem. The shot was taken from our cottage and the cluster was almost directly overhead.

The image is a 50 minute exposure with round stars right to the corners. Several field galaxies are visible in the full res version of the shot with NGC 6207 in the upper right of the image.

Since the night was supposed to be clear until morning the next target up was M57. This was a chance to check how much true resolution I was going to loose by moving from an eight inch reflector to a 4.7 inch refractor as I have an image of this target taken with my reflector.

The shot is a 69 minute exposure made from a stack of 23, three minute subs. The 15’th magnitude galaxy PGC62532 is easily visible to the upper left of M57 and there are galaxies down to 17’th magnitude in the field.

Over several nights I managed to capture over five hours on Ngc7497. This is an unimpressive nearby galaxy about 60 million light years distant. The interesting part about imaging this galaxy is the gas and dust that fills the field. The dust is much closer than the galaxy being inside the Milky Way. The shot could use over ten hours to really bring out the detail in the very faint dust field, but all in all it turned out quite well given that is was shot with a DSLR.

Once vacation ended it was back to the work day grind, but with another clear weekend I couldn’t resist a little more imaging time. This time several members of the local RASC Centre headed out to the St. Croix Observatory (SCO), the Centre’s roll off observatory in some dark skies about 40 minutes outside the city. Since I had to get into work at a reasonable time the next morning I had to image something bright in the limited time I had so I decided to give M8 a try. The seeing was not the best with PHD showing around two arcseconds guide errors so I wasn’t sure how the stars in the field would turn out, but the software did a great job and the stars were very tight and circular all the way to the corners of the image.

With the weather here in Nova Scotia this has been a productive summer of imaging and the Esprit 120 seems to be a great imaging platform, performing as advertised.

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M51 Update

After reshooting some flats to get rid of a gradient in the lower part of the image I was able to push the stretch a bit more and managed to get a more detailed image of the main galaxy (M51) in my last post. The image below is a crop of the central portion of the Esprit 120 image from my last post after applying the new flats.

M51Esprit_crop

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Finaly an image off the Esprit 120

It’s been a few months since I’ve had clear skies during a dark sky imaging window. I’ve been itching to get out and get a good test of my new SkyWatcher Esprit 120 APO. Several members of the Halifax Centre of the RASC arrived at the St. Croix Observatory (SCO) and we all sat around until just past 11PM when the clouds parted revealing some of the most transparent sky I seen at the site. The Milky Way was visible right to the horizon.

After setting up and polar aligning  I swung the scope around to M51 and started imaging. When the first image came off the camera I was very pleased to see that I didn’t give up much in terms of resolution compared to my eight inch Newtonian. The refractor produces a nice crisp image with a slightly wider field.

M51Esprit

As an added surprise there is some of the IFN visible throughout the field, but I have to redo my flats to really bring it out as my current flat is causing a lighter strip across the bottom of the image.

Here is a version off the Newtonian for comparison. The image is a shorter exposure so it is not stretched as much, but as you can see the core resolution is no better then the Esprit.

m51_da

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