September 29, 2007
Here is a new Crescent! This is the prior image but added to it is nearly 27 minutes of additional 5.7-second exposures taken through a 13nm H-alpha filter. Like the earlier image, this additional data was gathered through the Vixen R135S at f/4.8 with the DSI Pro, unguided on an LXD75 mount. The H-alpha data was stacked in Registax and then combined with the older image in DeepSkyStacker. Further processing was done in Registax. The natural next step would be to combine these in color, but I have not figured out how to do that yet, especially for these images which would not process in Envisage. In the meantime, I am delighted to see more of the nebula!
Here is another of the three images from this last week. This is the core of M31, the Andromeda Galaxy. Imaging with the DSI Pro through a scope with a focal length of 720mm, I can't fit the entire galaxy in the frame (not even close). But these dust lanes around the core are more than I can see visually, and much more sharply defined. The image is about 15 minutes 40 seconds of 4-second exposures, taken through the Vixen R135S at f/5.3 on the LXD75, processed in Registax.
The nights were beautiful the week of the new moon in September. I had one great night of imaging. Here is one taken toward the end of the night. I was waiting for the Pleiades to come up over the trees, and was too tired to think of another target than this one, a visual favorite. The cluster NGC 7789 in Cassiopeia is too large to shoot with the DSI Pro at a 720mm focal length (the Pleiades are even larger, and I didn't even try), but I aimed well within NGC 7789's borders and started shooting, anyway. The stars in this shot are within the cluster. I think they are lovely. Yes, they need color. I will get to that, eventually, but I am still so amazed to see these images, even in black and white, that I just haven't bothered yet. The scope was the Vixen R135S, at f/5.3, unguided on the LXD75. This is 11 minutes 16 seconds worth of 4-second exposures processed in Registax.
In early September, on a Saturday near the new moon, the skies cleared off and water vapor was down to an acceptable level. I didn't get the camera working until quite late and did not spend much time imaging, but towards the end of the session I turned the camera on M29. This image is about 10 minutes worth of unguided 4-second exposures with the DSI Pro through the R135S. Surely it would be better in color. I will be trying that, soon (though maybe not on this cluster).
M29 is called "M29" because it is #29 in Messier's catalogue of things that might look like comets but are not (he wanted a checklist to avoid mistaking a non-comet for a comet). M29's appearance always confused me until last night, because it could never be mistaken for a comet, I thought; it is quite obviously a small group of stars. But last night I saw M29 in my 50mm finderscope. Sure enough, it looked like a patch of fuzz, perhaps a possible comet. Of course, through the much larger R135S, as in the image, one would never think that.
The Crescent Nebula, NGC6888, is on the cover of September's Sky & Telescope. I wanted to see what I could do from the backyard. I also wanted to try out a new Vixen focal reducer designed for use with the R135S. With the focal reducer, I am imaging at f/4.8. That's still 648mm, but faster than the images at f/5.3, stacked below, of M57. This image of the Crescent is about 38 minutes worth of 8-second, unguided images, stacked and stretched in Registax. It is not as deep as I'd like. I thought I'd see more of the nebula. Perhaps under darker skies, or with an Ha filter. Next time, maybe.
I've been working toward a new image of M57. I wanted to capture both stars in the middle of the ring. The clouds here finally broke in August. On August 9th, I was able to set up the Vixen R135S on the LXD75. The image posted here was taken at f/5.3 through the DSI Pro. The stars are smaller points in the Vixen than through the achromat. Also, with the newtonian, I need no IR filter, as all wavelengths line up on one plane. This image is 10 minutes worth of 8-second exposures stacked and stretched in Registax, unguided. One can see three stars inside the loop of the ring, and one star on the outer edge. If the photometric measurements of others around the web are correct, stars dimmer than magnitude 16 appear in this image.
In late June we had a brief break in the monsoon---one night of clear skies, not very transparent, until around 3 am. I used the Orion 100mm achromat, the LXD75, and the DSI Pro. Once again, the exposures were unguided. This image is a combination of 239 2-second exposures and 131 2.8-second exposures; that is just over 14 minutes total. The exposures were dark-subtracted, combined, and processed entirely in Envisage. The result shows less detail than I had hoped, probably because I was so excited to get set up and start taking pictures that I forgot to install the V-block filter in the achromat. That may explain why some of the stars are so large. Also, I was still learning the software, and I saved the individual frames in a format that made them harder to process afterward. Moreover, transparency was not great. As I stretched the histogram, I found that, in order to make the background black, I had to sacrifice lots of nebular brightness. Finally, I took this from my backyard, which sports Bortle scale 4.5-5 skies.
I was delighted to receive great advice from a few members of my club, the North Houston Astronomy Club. One, Paul Downing, downloaded my image from here, applied a Kernel low pass filter to the image and did some additional stretching. His result is posted here, with mine on the left and his on the right:
I was surprised that this image could be obtained from my data. I do not have the filter capability in the free software that I own (that I know of---I haven't explored all of its contours yet), but I realized that I have been using rather blunt instruments for stretching. Here is a better stretch obtained using DeepSkyStacker:
It looks much more like a globular cluster now. I am surprised that the data was there. Compared with a visual observation, this is pretty astonishing.
This image is just 6 exposures, 5.7 seconds each. Like the others posted before this one, the exposures from which it was created were captured, and darks were subtracted, in Envisage. But these exposures were also combined and processed in Envisage. Actually, I had reached the end of an imaging session and wanted to see if I could glimpse M57 on the computer screen in a 1 second exposure (what I have used as my “Live” setting in the Autostar capture software). I could, so I decided to take a few more exposures. What surprised me about the image is that, notwithstanding the short exposure time, the central star is visible, something I had never seen before. Scope: Orion 100mm f/6 achromat. Mount: LXD75. Camera: DSI Pro. This image was also unguided.
This image is 107 exposures: 20 images 1 second long and 87 images 8 seconds long. The exposures were captured, and darks were subtracted, in Envisage. They were stacked and processed in Registax 4. Scope: Orion 100mm f/6 achromat. Mount: LXD75. Camera: DSI Pro. This image was also unguided.