The Ring Nebual (M57) is a planetary nebula in the constellation Lyra. The image below is a composite stack of nine photos taken the night of October 24, 2009. Each individual photo was captured at f/10, ISO1600. Total exposure time is 9×30sec, or 4 min 30 sec.
M57 - Ring Nebula
Location: at home in Tomball, TX
Cloud cover: less than 5%
Transparency: average (3/5)
Seeing: avg (3/5) or sometimes slightly better
Darkness: no moon, city glow
Wind: almost none
Temperature: 76º-82º
Humidity: 57%-67%
Dew Point: 65º
Time: 10:00 pm – 12:30 am CDT
OTA: 8″ SCT
Guidescope: 70mm refractor
First light with guidescope. Very disappointed to discover PHD Guiding software did not recognize the NexImage and it claimed my scope did not support pulse mode. Fiddled with it longer than I should have. Bottom line: zero success.
Guidescope was very useful for making fine adjustments while D50 was attached to the main scope. Best practice using laptop to view real-time output from NexImage in the guidescope, but eyepiece use works ok, too.
Tried to image Jupiter, photos were awfully blurry. First image seemed to show moon touching jupiter’s limb, no other moons. Tried again with ep. No moons visible, black spot visible at edge. Re-installed D50, tried to re-focus, star image was an irregularly shaped streak even with relatively short exposure times less than 1/10 second. I suspect vibration from the shutter, but it was late and I was tired of trying to debug it.
Finally reverted to visual observation. By this time two distinct black spots were visible. I thought I was seeing a double eclipse, but later cross-ref with SNP and SkyViewCafe indicated one spot was the shadow of Europa and the other Ganymede itself. In the illustration below, the top spot is the shadow of Europa and the bottom spot is Ganymede.
Illustration of Eclipse on Jupiter's clouds
Location: at home in Tomball, TX
Cloud cover: less than 5%
Transparency: average (3/5)
Seeing: below avg (4/5)
Darkness: no moon, city glow
Wind: almost none (see below)
Temperature: 70º-72º
Humidity: 95%+
Dew Point: 69º+
Time: 10:45 pm – 12:15 am CDT
OTA: 8″ SC
First light using Starry Night Pro to control the telescope via serial cable. I have an old version of SNP (4.5) and there are a few minor user interface quirks, but generally I was pleased with the operation. Also first light using DIYPhotoBits to control the Nikon D50 via USB. I was very pleased with the results. I’ve actually modded DIYPB to display images after download using IrfanView, making it much easier to center and check focus.
I started with M57, the Ring Nebula. Exposures above 10 seconds exhibited elongation. It didn’t occur to me until later to use DIYPB’s time lapse feature to collect a set of images for stacking, so I only captured two at that speed. M57 is hardly visible at only 10 seconds, even using ISO1600, so there’s not much to see there.
Next I captured photos of Jupiter and the Galilean moons. Due to the bad seeing and the humidity the image quality was quite poor. The two main bands were visible but murky and the entire image seemed slightly out of focus. I rechecked the focus with the Hartman mask and that was not the problem. The composite photo below shows the relative positions of the planet and its four moons. Io and Europa (on the left) passed in conjunction over the next couple of hours, but it was already late and I didn’t want to stay up for it.
Jupiter and its moons (composite image)
Last I photographed M52, an open star cluster in the constellation Cassiopeia. As earlier with M57, I was unable to get an exposure longer than 10 seconds without elongation. It occurred to me then to use DIYPB’s time lapse feature to take several photos (10, actually) in quick succession then try to stack and merge them later. I tried stacking with RegiStax5, but I was not pleased with the results: the stars looked dull and washed out. I stacked the frames by hand and the result was much better.
Composite image detail of M52(click image for 1000x800 resolution)
This image shows far fewer stars than you might see in a typical photo of M52. This view is representative of what you might see in an amateur telescope. You mileage will vary depending on your telescope and sky conditions.
Tonight I tried my hand at photographing a few Deep Sky Objects. The Hartman mask was extremely useful for focusing, but after tonight it’s clear that I’m going to need to control the D50 by tethering it to the laptop to get best results. Manipulating the zoom controls for the LCD is awkward at best. I may need to spend some time just practicing focusing on a few different stars.
Saturn was actually the first target before the DSOs. I captured a couple of images at ISO 800 and 4 sec exposure that included the moons Titan, Tethys, Dione, and Iapetus (Rhea was transiting and lost in Saturn’s glare). I reduced the exposure time several steps, but it was hard to see much detail in the LCD (another argument for tethered control), so I moved on.
Next I tried M13, the globular cluster in Hercules. This actually turned out to be the best subject of the night. One of the photos had some jitter from the wind shaking the telescope (did I mention it was occasionally quite breezy?). Most were fairly good, however, with nearly round stars — limited by the sharpness of the focus, most likely. Click the image to see a very large full-sized photograph. If you look closely you can see stars of several different colors in the cluster. M13: FL 2032mm, ISO 800, 30sec exposure, f/10.
M13
Next came M57, the Ring Nebula in Lyra. I captured several images, but they all showed noticeable wind jitter. I’m certain this is telescope vibration and not tracking error because the motion vector varies from one photograph to the next. I merged the four best frames in Registax, stretched to compensate for the motion vector, applied a gamma correction to increase the brightness, then reduced the image size to improve the apparent sharpness of the focus. M57: FL 2032mm, ISO 800, 30 sec exposure, f/10.
M57 - The Ring Nebula
The next target I tried was M27, the Dumbbell nebula. However, even with a 30 sec exposure at ISO 800 there was almost no trace of any nebulosity in the photo, so I moved on.
I decided to re-balance the telescope forward to compensate for the extra weight of the camera on the back. This, of course completed wrecked the scopes alignment so I had to restart. After alignment I focused the camera on Mizar (ζ UMa). It’s a nice blue double, but it’s included here for more than aesthetic reasons. According to SNP, the separation between Mizar A and B is 14 arc-seconds. In the unprocessed photo, the distance between the centers of the stars is approximately 19.3 pixels (along a diagonal). This puts the resolution for the camera at about 0.725 arc-seconds per pixel. By comparing similar measurements of other doubles I should be able to calculate the actual resolution more accurately. Mizar: FL 2032mm, ISO 800, 1/2 sec exposure, f/10.
Mizar A and B
After rebalancing I Attempted several images of the Whirlpool galaxy M51. The cores of M51 and its companion galaxy both appeared tiny and featureless over several photographic attempts.
Tonight I got my first shot of the moon with the D50 and the C8. This was about an hour before sunset. Aiden was my big helper while I assembled the telescope. Then he stood on the stool and looked through the eyepiece at the moon.
The number of craters visible in the high-resolution image is really amazing. Central peak uplifts are visible in many of the larger craters. However, the focus was not tight enough in general to pick up the terrace edges (although you can make out traces here and there). You can click on the image below to see the full-sized photograph, but be prepared to wait! The big photo is 2.3MB at a whopping 2900×2900.
You can see some severe vignette in the corners from the 1.25″ universal T-adapter. The photo is actually a composite of two separate shots because the moon did not fit in the camera’s image sensor at this high magnification.
Telescope: Celestron C8, FL 2032mm, f/10
Camera: Nikon D50, ISO 800, 1/1000s
1st quarter moon in daylight
Another warm night. Tonight I tried using ISO 800 and got this picture at 1/320s. The focus is a lot sharper tonight than I had last night. I really need to make a Hartman mask for the 70mm Meade refractor.
thick crescent moon
Update: clicking the photo should work now!
It was hot outside tonight, even for Houston in the summer. It was still 93ºF after sunset! I got this shot with the Meade refractor using ISO 200 at 1/100s. There’s just a touch of blur from me supporting one end by hand. I was tired and didn’t want to mess with pulling out the GEM tonight in the heat. Click the image to see full resolution photo.
waxing crescent moon
I took this late at night between our house and the neighbor’s. There were scattered light clouds and I don’t think the sky was ever completely clear. Technical details: Nikon D50, Tamron lens @ 300mm, f/6, ISO 200, 1/200s. Click photo to enlarge.
June 7th Full Moon
A few days later I woke up at 5:30 with the realization that the gibbous moon would be high in the sky. I know, I know, too much time thinking about lunar orbital characteristics and not enough time thinking about… hmm… what else is there again? Anyway, you can hardly blame me: the adapter for mounting the camera to the scope had just arrived the day before. (Technically, there’s a T-Ring for the Nikon D50 mated to a universal 1.25″ T-adapter.)
Oooh. Nice craters. The photo was taken just before sunrise. Other tech stuff: 70mm Meade refractor w/ 600mm FL, f/8.57, ISO 200, 1/200s.Click photo to enlarge.
June 10th Gibbous Moon
I took this last one a couple mornings later just after sunrise. This one is framed in the blurred branches of a tree. You can just make out some craters along the terminator. Tech stuff: Tamron @ 300mm, f/6, ISO 400, 1/1600s. Click photo to enlarge.
June 12th Morning Gibbous Moon
This morning I woke up early enough to catch the waning crescent moon before sunrise. This photo was taken with the Nikon D50 through a Meade 70mm refractor (FL=600mm, f/8.57, ISO200, 1/100s). Click on the picture below to see the full sized (1280×1024) image. The photo is unprocessed except for cropping.
Waning Crescent Moon
Venus was nearby, so I also snapped this photo. FL=80mm, f/4.2, ISO400, 1/200s. You can really see the smudges on the CCD sensor in the early morning light. Click on the picture to see the full-size original (it’s really big, 3008×2000, you’ve been warned!)
Crescent Moon and Venus
I attached the Nikon D50 to the C8 SCT last night for the first time. Of course I was excited to see what kind of pictures I could take with it, but I also had concerns about how I was going to focus the camera. The view port on a SLR is pretty small, which is challenging on its own. Add the fact that the camera will be attached to the bottom of a telescope pointing nearly straight up, and seemingly simple procedure like focusing becomes a significant challenge. So I did a little research and I found an interesting page on Arcturus Observatory / Comet Man web site that discussed using a Hartman mask to focus. Then I wondered: could I make a Hartman mask? Would it work?
Following that idea, I found a sheet of heavy weight art paper, set the C8’s lens cover on it, and traced a circle of the inner diameter of the OTA. Using a standard Swiss Army pocket knife I made three cutouts: two circles and a triangle. It was quick, cheap, and amazingly useful. Here’s the mask and the pad or art paper from which it was made:
Hartman Mask
My wife said it looks scary. Maybe that’s because I was holding the mask over my face saying, “ooooo,” but I don’t see how that could have any effect. Besides, the circles are much farther apart than my eyes, so I couldn’t see a thing.
Anyway, the real fun began when I set up the C8 and used the mask to focus on a star. I got distracted for a while just watching the pattern coalesce and split as I turned the knob. Of course the real test was whether it would work with the camera attached. I wanted to try getting a picture of Saturn and its moons. First I aligned the scope and slewed to Regulus, which was the nearest bright star to Saturn. Then I removed the eyepiece and the star diagonal and attached the camera to the visual back using the T-ring and T-adapter. Then I started capturing images.
The following focus trial images were taken at ISO 400 with a 2 second exposure time. It took several trials for me to establish a procedure and I won’t include the first six or seven photos for that process. Let’s just say there was not a lot of instant gratification here. In any case, I was still exciting to see if I could make the mask work.
Like many digital cameras, the Nikon D50 allows you to “zoom in” on a portion of an image during playback. After each image I magnified the diffraction pattern as much as possible to gauge the focus.
Hartman Focus - 1
As you can see, the pattern is pretty distinct. This means the image is not in focus. I turned the knob about 20°-30° and took another picture.
Hartman Focus - 2
The pattern is smaller and brighter. That’s good because it means I’m turning the knob in the right direction. After a little more knob action I took this one:
Hartman Focus - 3
Now the diffraction pattern has mostly disappeared (no rings or dark centers), but the spots are still distinctly separate. Notice the triangle shape of the bottom left spot.:
Hartman Focus - 4
In this image the star appears pretty well focused. Keep im mind I was looking at this outside, bent at the waist, squinting at a little LCD screen smaller than the image you see here. I gave the knob a little more twist and took another picture to see if the image could get any sharper.
Hartman Focus - 5
Oops! Too far! Notice how the triangle has inverted from the earlier images. I turned the knob back 3/4 of the way to its previous position.
Hartman Focus - 6
Now that looked like pretty good focus. Also, it was getting late and the mosquitoes were starting to gather in larger numbers. I was anxious to move on to imaging Saturn.
After slewing to the ringed planet I captured 17 images at different ISO settings and shutter speeds. The best picture of Saturn was taken at ISO 400 with the shutter speed 1/4 second.
Saturn Solo
The best picture of Saturn’s moons was taken at ISO 400 with the shutter speed 5 seconds.
Saturn's Moons
By this time it was getting late and the mosquitoes were driving me crazy. I disassembled everything and finished for the night.
The human eye seems to have a better dynamic range than the D50. I combined the two previous images as a composite that represents how Saturn appeared when observing visually. The picture is rotated 90° and made extra-wide to show the faint moon Iapetus on the left. The image size is reduced on this page, but you can click on it to see the full-sized composite image.
Saturn (composite image)
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