This awesome, deep image of M101 is my favorite of the object. There are so many things to like here.
First of all, Fabian Neyer spent over 40 hours obtaining luminance data. This is a fabulously long time. The point is well-taken, though. The image shows not only the dim outer spiral arms of M101, but the Milky Way's galactic cirrus in the area. It also shows stellar streams around NGC 5485! The dimmest galaxies in the image has been cataloged at magnitude 25! That is real depth. Fabian describes his skies as "mag 5."
There is also a wealth of detail in the M101 core and in all its satellite galaxies. I love those dark lanes in M101's heart, the individual clusters of stars in the spiral arms, and the numerous tiny galaxies strewn around the background.
The color is also great. M101's color is tough to get right. The galaxy is nearly white in its center, but there is clear H-alpha emission in the inner spiral arms. The outer arms are bluish, but not so blue that the color jumps out at you and says, "Blue!" The color is more subtle, and Fabian has caught it very well. There is still room in the outer spiral arms for a whiter or even redder cluster, and that makes contrast great.
The star colors are just how I like them, too. They are not so strong as a human being would never see in space but are rather subtle hues that merely make clear the information about the star's temperature. I find this kind of star color much more realistic and believable. When I look at a deep sky image, I'm not looking at the stars, so I want them to add background and sparkle, like the gypsophila in a bouquet. The galaxy and its satellites are the issue, and that's where my attention should be drawn. This image does that nicely.
While we are talking about stars, notice the shapes of them here. The stars are round, and their edges are nicely controlled. They are just a hair fuzzy for my taste, but there is neither the blobbiness of uncontrolled optics or poor baffling, nor is there annoying blooming from the camera. This is a testament to the system, but any camera with real blooming control will allow it. The real praise in my book goes to the telescope. Fabian's TEC 140 puts up a wonderful star image, something that I am unable to manage with my Newtonians, of course. This is Fabian's first light with the TEC 140.
Finally, I learn something about the sky from this image. M101 has always been large and spread out, but notice how much of the spreading is toward NGC 5485? That may signal some sort of relationship between the two. It's just enough to make me wonder, and that is just the sort of thing that makes astronomy fascinating.
I asked Fabian for a short bio:
After two years of visual astronomy, I started with astrophotography in 2002. During the first couple of years I mainly used DSLR cameras for data collection (and a Borg ED refractor). Since about 3 years ago, I use the STL11000M for astrophotography and more recently switched to TeleVue and TEC refractors.
I also asked why he spent so much time on M101. I like his answer so much that I am thinking of following him down the same road:
I usually image well known objects, for example, the Heart and Soul Nebula, Orion Nebula, and also the Pinwheel galaxy that probably were imaged by other astrophotographers a few of hundred times already. The interesting part, however, is to show new details of an object not seen before. Fortunately, the amateur astrophotographer has the the time to accumulate as many hours as he wishes - compared to professional observatories where this is very expensive. Probably the most contributing reason to spend so many hours on a single object is the opportunity to reveal new nebulas, the outer-most spiral arms of a galaxy, or even unknown stellar streams.
For me what matters in the end is not the number of images I produce every year but the image quality and uniqueness of an image, so that I also enjoy looking at it years later.
With regard to that goal, light pollution simply forces me to accumulate so many hours. The situation in my observation area got worse over the last years, and so the total exposure time has to increase. I recently was able to compare two observation sites and the effect of light pollution (quite impressive I think): http://www.starpointing.com/lightpollution.html#lpexample
Impressive, indeed. I took two nights last fall shooting M45, and it was just enough to get past the noise generated by subtracting light pollution from the image. I can see why Fabian gathers so much luminance data. I think he is helped by the precision of the TEC 140. The uniformity of the star shapes makes gathering data over many nights much easier, I am guessing, while retaining the detail that the scope of capable of showing.
Fabian included one other note on the length of the exposure:
This may sound a bit weird, but the total time invested in an image is not only the time you spend under the night sky but also the time for image processing. So if your daily work (I'm working on my PhD, which is quite time-consuming) and other hobbies are time-consuming too, there is not so much time for image processing. For example, at the moment I would have absolutely no time to process an image every month. So by accumulating more hours for an image, I also reduce the yearly time I spend in image processing. The additional time for pre-processing (i.e., image calibration, image alignment, image stacking) due to the higher number of images is only in the range of 1 hour (which is nothing compared to the time I spend for post-processing).
That's interesting, too. My own take is that the more data one gathers, the easier the processing and post-processing is. Deep, precise data helps everything: depth, detail, color, lack of noise. Everything is more easily controlled in the post-processing. There is just so much more to work with. The solution to most post-processing problems is more data.
Thanks, Fabian, for the opportunity to blog this image. It is awesome, and I've learned some things.