After a bit of a dry spell a couple of RASC members and I made it out to the St. Croix Observatory (SCO). SCO is the local Centre club observatory with dark skies and a great roll off facility. One thing that we really appreciated was the warm room as it was -10 degrees C during the imaging run!
After setting up and polar aligning, the wind picked up and caused a lot of guiding problems. The result was fat, but round stars and a blurred nebula. The image below is a simple stretch of the calibrated and stacked data.
The image is definitely not one of my best but with a little work I was able to rescue it, well sort of…All the processing was done with Images Plus employing split star techniques, masked stretching and star reduction. The masked stretches help to control the star bloat that would otherwise ruin the image. for those that want some details on the type of processing involved, check out this paper on the technique.
The image is the average of 40 three minute subs calibrated with bias, flats and flat darks. No dark frames were used as my Canon 60Da has built in dark suppression so they are not necessary. A single dark was used as a hot pixel map using the adaptive high/low pixel reduction functions of Images Plus. When I first started using this technique I was skeptical, but after making some measurements the technique really does work and it save quite a bit of time when you don’t have to shoot darks at the end of an imaging run.
Clear skies and keep imaging.
The evening was surprisingly clear for one with clouds in the forecast so I headed out to SCO, the observatory of the Halifax Centre of the RASC for some time under the stars. As I finished polar aligning several other member arrived and began lugging their equipment out and setting it up. The first target for the evening was M45. I was able to collect about 40 minutes of data before my second target, M1, rose high enough in the sky to image.
I used short exposures to preserve colour in the stars and lots of subs to bring out the nebulosity around the brighter stars. The short sub-exposures prevented saturation of the fainter stars so more of the colour gets maintained during the stretching process and after the initial stretch, split start processing ensured that the star colour was preserved throughout the rest of the processing.
While working on a camera comparison for a RASC Journal column I stumbled across some strange things with Nikon cameras. It seems that filtering is applied to their raw images, producing some strangely clipped histograms in both bias and dark frames.
Bias frame histogram
While trying to explain the clipped histograms and the very quiet light frames I came up with a simple class of statistical filter that reproduces all the histogram features and gives great noise reduction with very little blurring of the image. One of the nicest features is that the blur is so well controlled that masks are not needed and the filter can be applied even before any stretches are applied to an image.
The filter is a version of a simple average kernel. The difference is that the central pixel of the kernel is replaced only if it is less than the average of the pixels within the kernel. This means that for images like darks and bias frames, the histogram will be clipped at the average which is usually the peak of the histogram. Any data below the average likely contains noise, while data above the average tends to hold the detail in the image. In order to accomplish this with standard filtering tools available in most image processors all we need to do is to apply a small kernel averaging or box filter to the image on another layer. Set the blend mode of this new layer to lighten and presto – a great noise reduction filter.
Image without filter
Image with filter applied
As you can see from the M8 shots above there is very little blurring of the of the image while the noise in the dark areas of the image is reduced. The filter applied to the filtered image uses a 7 by 7 kernel averaging filter and the lighten blend preserves detail throughout the shot.
Using this noise reduction technique and a LMS combine of a longer exposure and a shorter barlowed shot to get core detail the M42 image below gives an HDR rendition of one of my favorite deep sky objects.
Mother Nature finally cooperated with an astronomical event and we had some clear skies that coincided with the September 27’th lunar eclipse. Living next to the ocean and less than an hour away from the world’s highest tides makes lunar events especially interesting. As the Sun set below the horizon and twilight began, a fellow RASC member and I headed to DeWolfe Park, on the shores of the Bedford Basin, to catch images of the event. Quite a few other people showed up, intent on getting some memorable pictures as well. Some brought tripods and DSLR’s, others came with point and shoot cameras and even cell phones, all aiming their cameras to photograph what the press had been billing as a “Supermoon Eclipse” (I really hate that term).
As the darkness arrived everybody started snapping images of a spectacular Moon rise. The image below shows a sequence of shots from just after Moonrise until about 9 PM local time. I was hoping to be able to capture images this way right through the eclipse, but the field of view of my system proved inadequate for the task and I had to settle for the moonrise sequence below.
A little before 10 PM we began to notice the penumbral portion of the Earth’s shadow as a slight darkening of the lunar limb. Finally things started to progress to the actual eclipse and into totality with the Moon turning a faint red colour. As the eclipse proceeded I snapped several images roughly equally spaced from the first sign of the umbral shadow to totality. After a little work in an image processor stitching them together, I was able to get a reasonable eclipse sequence.
All in all I got to spend a very pleasant evening under some urban skies with several other people who were interested in imaging and viewing the night sky. We may even have picked up a new club member or two as several people stopped to chat and seemed quite interested in the RASC.
For some more information on the images please visit my main web site at nightanddayastrophotography.com.
This summer I found a little time to get some imaging done. Form the backyard M17 skirts the treetops in the south. The day started off with a little work putting out our wharf and the usual lawn/field mowing required on the first trip to the cottage each year. The clouds came and went all day long and I was getting a little concerned toward the end of the day as the clouds took their time moving off, but as luck would have it the Clear Sky Chart was right and we were treated to a terrific Mira River sun set.
With the warm summer breeze calming down and the equipment set up, I got to work capturing some M17 data. I didn’t get quite as much as I’d like as it kept dipping into the trees, but after an hour and a half I managed to get 48 minutes of data that did not have the tops of spruce trees interfering.
More details on the exposure and the processing can be had here on the main image pages of the web site.
I’ve been working on my web page for some time now my latest updates have added web galleries and of course this blog. As time goes on I’ll be posting details on some on going astrophotography projects.
My setup consists of a SkyWatcher eight inch imaging Newtonian on a Celestron CGE Pro mount and a Canon 60Da. Guiding is done with an Orion Star Shoot Autoguider and a four inch refractor. As my primary imaging site is just over forty minutes away at the St. Croix Observatory, I never manage to get the really long exposures I’d like, but with a little processing the images are passible.
My main website contains most of my images as well as some details on image processing, a little theory on image noise and other tips and tricks of the craft.
Thanks for taking the time to visit and stay tuned for additional posts as I get breaks in my schedule to get out under the stars.