Well it has been a while coming, but the folks at SkyWatcher were able to diagnose the problem they had with my previous Esprit 120 and have shipped me a new replacement scope. I’m very pleased to say that this new unit performs as expected and as advertised, at least in my limited testing. I was able to get out for an hour last night and take a few test shots to verify that the optical problem is no more. The star images are what you would expect from a higher end refractor, no spikes, round and small halos. Below is a quick 12 minute (6 by 2 minute subs) shot of M51 taken with the scope.
Please excuse the poor image quality, it is a result of a very short exposure from an urban imaging site with the Moon in the sky. Even with that limitation there are 15’th magnitude smudges in the upper right that are some of the faint galaxies around the Whirlpool. Of more interest to me is the quality of the star images. Here is a zoom in on the double in the upper left corner.
As you can see the stars are nice and round with no trace of the nasty spikes that showed up on the previous units and these are stars at the corner of the frame, not in the center.
I’d like to say thanks to Joe Wang at Pacific Telescope Sales & Marketing and the folks at Atlantic Photo Supply (local SkyWatcher dealer) for going the extra mile in customer service to satisfy a grumpy customer after my initial purchase had less than stellar performance.
Now if the weather will just cooperate a bit, I can’t wait to see what the Esprit 120 can do under much darker skies.
Well I’ve had a chance to take the Esprit 120 on a good test drive and it has been a bit of a disappointment. The new scope sent from SkyWatcher Canada still has strange spikes on the stars and SkyWatcher Canada tells me that all of their stock seems to have the same problem. Take a look at the star image below.
Not the nicest stellar image; especially since I bought the refractor, in part, to get rid of diffraction spikes from my reflector. It seems there is a problem with at least one batch of the scopes. SkyWatcher has been very good and forthcoming about the issue and is looking into the problem to get me a scope that works as advertised. I know the scope can perform well from several great reviews so stay tuned as I wait for the factory to look into the problem.
Recently I purchased a shiny new SkyWatcher Esprit 120 APO refractor from Atlantic Photo Supply. Unlike what you see in the usual astronomy magazines my new toy had some issues with spikes on all the stars that were not what I expected of a premium refractor. I contacted the good folks at Atlantic Photo supply to let them know and They immediately contacted SkyWatcher and forwarded my initial test images.
Now this blog entry is not about complaining that the scope had issues. Instead it is about the great customer service offered to me by both Atlantic Photo Supply and the folks at SkyWatcher. No one gave me any grief about my test methods or questioned my conclusions, in fact SkyWatcher immediately picked out another scope, tested it and sent it to me with instructions to simply swap out the optical tube and ship it back to them at their expense. With the Christmas holidays fast approaching they got the scope shipped off to Atlantic Photo Supply and it arrived a week later. All that was required of me was to drop the problematic scope off and pick up the new, tested unit.
After hooking everything up I hauled it all out to my driveway for testing. Now my driveway is in an urban location with a bright sky measured at 18 to 19 mag/arcsecond squared on a good night. Initial views through the scope with a 22 mm Nagler eyepiece were spectacular delivering pinpoint stars across the two degree field. Popping in a 5 mm eyepiece showed classic diffraction patterns that were identical both sides of focus with no trace of any colour issues.
Now the views were great, but I didn’t buy the scope to look through; it will be a photographic workhorse replacing my eight inch f/5 Newtonian. Replacing the eyepiece holder with the supplied field flattener and mounting my Canon 60Da I spent a few minutes shooting Deneb to see if the strange spikes were still there and I’m glad to report that the star images were pinpoints edge to edge offering the performance expected of a premium refractor. Next I tried a quick five and a half minute exposure of M42 with the resulting image shown below.
The scope produced a very nice image with pinpoint stars across the field with lots of detail in the core of the nebula. The image above did not use any calibration frames. My 60Da has built in dark suppression so no dark frames were required and the flat field of the Esprit 120 means I did not need any flat frames.
Looking at the stars in a corner of the image you can see that they remain sharp and show no colour fringing.
All in all the scope makes an excellent imaging platform and the customer service from SkyWatcher and Atlantic Photo Supply was second to none, quickly responding to problems with the initial delivered product to get me up and running even over the holidays.
The day started out normally, warm sunny and promising to be another great summer day. The weather forecast called for a mix of sun and cloud with a chance of showers and clearing in the evening. After doing the inevitable cottage chores I started putting the scope together in our shed. Since the drive to the cottage involves some less than smooth dirt roads, I went about aligning the optics and getting all the equipment together.
When supper time rolled around, our family wandered up to our neighbours to join in an 80’th birthday celebration for a long time friend. After shooting pictures at the event I dashed home to let our dog out for a bathroom break and looked up at the sky. Things were getting very dark and it was only 6 PM! It seems our chance of showers had turned into a severe thunder storm warning and a tornado warning! After taking the dog out I was planning to rejoin the birthday party, but the heavens opened up with heavy rain so I ran to the shed and closed the door to protect the scope and then dashed inside the cottage just as the wind started picking up. By the time I got dried off it was raining heavily as you can see from the picture below.After drying off I took a look out the window, just before taking the picture to see a small water spout rip our row boat off the wharf and send it 40 feet down river before landing with a splash! Ten minutes later it was all over and the Sun started to break through the clouds.
By 9:00PM the skies began to clear and the wind died down to zero allowing our kids to enjoy a fire by the rivers edge while I got a chance to do some night scape work.
By about 10:30 it was one of the clearest nights I had at the cottage. I hauled the scope and camera out of the shed and set up to try to capture some data from M20. This has always been a tricky target from the cottage as it skirts the trees for most of time. I managed to image it for about two hours only getting 72 minutes of data where the trees did not interfere. After a little processing it turned out reasonably well.
For details on the image acquisition and processing see my imaging site.
Sometimes things go right despite my best efforts. Friday night was such a night. My local centre of the RASC decided to have a club observer’s evening and like a lot of members I couldn’t resist the first clear night of spring so I packed my car with my gear in the morning and headed to SCO(St.. Croix Observatory) after work for an evening under the stars. When I arrived there was already a small crowd of 21 setting up. I to started out simple enough, I started early so I would have plenty of daylight while setting up my scope then things started to go wrong. With the first stars appearing I aligned on m wrong star and spent 30 minutes wondering why none of the alignment stars were near the center of the field. After discovering my error I realigned correctly and got down to the business of focusing. With a mask and live view focusing is generally an easy task, but with my first target being the galactic jet in M86 I needed a barlow and I soon realized that I didn’t have my 2 inch extension tube and couldn’t get focus. After borrowing one from a friend I managed to get the camera to come to proper focus and the imaging began.
First up was the galactic jet in M86. I had imaged this one before with some success, but my optics at the time left a little to be desired. My first attempt was several years ago with Meade optics (f/4 Schmidt Newtonian) that suffered from a bit of astigmatism and my processing tool kit was a little sparse, but I still managed to get some evidence of the jet.
It was a 300 second exposure that was the sum of ten, 30 second exposures that just barely proved sufficient to show the jet.
This latest attempt was the average of 15, two minute exposures with a longer focal length. The result was pretty noisy and it took a bit of processing in Images Plus. There was a lot of horizontal and vertical banding pattern noise that was easy to clean up using this method as a guide.
The jet is clearly visible at the top of the galaxy and even has a pale blue colour.
Next up was M86 and the heart of Markarian’s Chain. For this one I removed the barlow and imaged at prime focus. M86 is an elliptical galaxy moving toward the heart of the Virgo Cluster and forms the nose in the galactic smiley face below.
The shot is the average of 23, four minute subs for a total of 92 minutes. Processed on Images Plus with my usual masked stretched, split star technique to keep the stars small and bring the galaxies out from the background. When examining the full scale image there are over 30 galaxies in the field.
With my imaging done for the night I packed up and headed home and was treated to a spectacular Moon rise in the approaching cloud. Unfortunately with my camera packed in the trunk with my gear and being on a busy highway late at night I couldn’t stop to image it.
Ever have one of those nights when things just don’t seem to start well? Turns out that this was one of those nights. A friend and I went to our club’s dark sky site to capture a couple of images, I was trying for Thor’s Helmet while my friend was imaging the Cone Nebula. It was nice to set up our scopes without needing gloves, but soon the temperature started to drop and that’s when things started to go wrong.
First thing that failed was the switches used to find the home position on the mount. Some moisture froze and the RA switch stuck forcing manual home positioning. Next up I had an issue with the RA guiding. Seems that I didn’t do a great job in balancing the RA axis and my guiding produced odd double stars. The solution was simple, rebalance and adjust some of the PHD settings, but it cost me 30 minutes of adjustment and realignment. Since it was a work day in the morning this meant a shorter than intended exposure for the evening. After focusing again and starting the exposure I noticed the battery was failing in my trusty intervolometer. Fortunately it lasted through the session and the imaging finally got underway.
The Saint Croix Observatory is a wonderful facility owned and operated by the Halifax Centre of the RASC. The facility has a much appreciated warm room that we made good use of for the rest of the evening while the cameras and scopes did all the work to collect data for our images. By the time we packed up I had collected 112 minutes of data on Thor’s Helmet, an emission nebula surrounding a Wolf-Rayet star. The image was calibrated with flats, flat darks and bias frames. Darks were not used as my 60Da has built in dark suppression that does a great job of removing the dark current from the system. I simply shot three one minute darks to average and use as a hot pixel map and processed the data in Images Plus. After a little post processing the image turned out reasonably well for the shorter than intended exposure.
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.