Saturday, August 18, 2012

Fabian Neyer's M101 (2012)

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):

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.

Wednesday, May 30, 2012

Rick Johnson's NGC 4754 and 4762 (way back in March 2011)

This lovely duo was described on Cloudy Nights by imager Rick Johnson as “a fantastic pair.” Rick's discussion appears here: Discussion of NGC 4754 and 4762.

The full-size image is here.

14" LX200R @ f/10, L=7x10' RGB=2x10'x3, STL-11000XM, Paramount ME
Nearly all of Rick's posts on CN include a link to his image of some interesting celestial object(s) accompanied by an explanation of the state of observational speculation and science regarding it (them). The discussions are fascinating, and in this case in particular interesting because the galaxies appear to have interacted, yet scientists do not appear to have discussed the matter. Distance estimates are all over the map between 55 and 80 million light years for either galaxy, but the distance estimates seem not to have considered the evidence of interaction.

The image also includes some smudge galaxies and some distant background galaxies, and Rick has researched these, too, as well as two asteroids in the image.

Besides the background information, I like the image itself. It has so much of what I look for in an image.

First off, the stars are the shape that stars should be: they are round. This means something. Rick images with a Meade 14” SCT (LX200R version). I sometimes see round stars in an SCT image, but not often. I do not know all the causes for out-of-round stars in SCTs. I suspect mis-collimation plays a role, but there is more than that. I have spotted what I believe are pinched optics and poorly made (or poorly matched) corrector plates. Usually there are odd spikes that stick out from the stars, sometimes in an understandable pattern, sometimes not.

The fact is, a star is a point source. The shape the point source takes in an image is determined by the imaging system, not by the star. In other words, a star's shape in an image is a snapshot of the imaging system itself. Aesthetically, symmetry is better. I like my stars perfectly round, or, if not, then with symmetrical spikes (as few as possible). Any number of things can take a star out of round. Rick's image has none of them. He's obviously taken the time to work with his imaging system to eliminate each one. In fact, Rick enlightened me on this facet of SCT imaging, and what he said is too good not to pass along:
The spikes you see on SCT images are due to a surprising source, the dirt on the corrector plate. I can't explain it; I was given an explanation by Bob Cox (he did the optics for Mercury through Apollo and the ATM column for years in Sky and Telescope), but it was too technical for me to follow. Somehow a smudge on a corrector plate at the focal point of the scope can create this spike on the equivalent point on the image plane. .... I get these from time to time. If a bright star is on the image field at the point of the smudge on the corrector, it will make a spike or halo or some diffraction artifact. Spider droppings are my main source of these. Since I don't look at images often until months later, they can hang around for a while but only when a bright enough star aligns with the corrector. Bob said if they'd put the corrector "where it belongs at the radius of curvature" this wouldn't happen.
Along the same lines, note that this image was taken at the scope's native focal length, f/10. That would be 3556mm, but Rick said he has extrapolated from the image scale on this image and determined that the focal length was 3660mm. In fact, he says his SCT varies about 100mm—100mm!—in focal length with temperature changes. To get round stars at that focal length takes superior tracking. Initially, I was sure Rick would be guiding off-axis, and I was surprised to hear this image was unguided, as are most of his images.  He says it makes automatic imaging much easier. Rick writes that he makes
a very dense T Point map two hours on either side of the meridian from -15S on toward the pole. I put 800 points in this small area. .... With a dense map it easily can interpolate between points since they are so close together. Takes a couple days to make the map after remounting the scope after its annual spring cleaning but worth the effort!
Ah, Tpoint. I see. And, no surprise that Rick shoots from a Paramount ME. The accuracy in the tracking is a testament to great mechanics and software.

Another thing I like about this image is its modesty. Rick doesn't say, and it's not readily apparent, but there is another distortion from NGC 4754 on the lower side, moving to the left and down, opposite the one that is going right and up. If one stretches the image quite a bit, it's obvious. Rather than force the galactic spike into open view with selective processing, Rick has let the data speak for itself. It's a very dim feature, Rick's data barely catches it, and he has let it be. Rick is out to explore the universe. Letting the data do the talking is part of that mentality. Of course, there is some processing involved, and sometimes stretching of galactic centers and stars needs to be adjusted so that they do not blow out or unduly distract, but the data from the sky is left in the image, which is why you will see asteroid trails, for another example.

Finally, where does Rick find these targets? At this focal length, a great deal more of the universe opens up. I applaud Rick for going a step deeper and introducing us to the wonderful objects further out. I have some new goals for my own imaging after having seen some objects from Rick.

I asked Rick for a little biography, and he sent this:
I first got interested in astronomy when a article in some magazine (Life?) in 1953 mentioned that in the spring of 1954 Mars would be the closest it had ever been since the 200" scope was built, and it would answer once and for all whether the canals were real or an illusion. Of course that didn't happen, but I was convinced it would and also that I wanted to see first hand. I priced a 6" scope at about $200 ($1675 in today's dollars). No way that would happen! I found an astronomy book at the library that said, “Build your own 6" scope for $35” ($300 today). That was still steep but possible (gas was $0.25 at the time). I ordered my own copy of the book (long lost) and ordered the mirror blanks and grinding kits. Turned out you made the eyepiece lenses as well! The instructions you got were 3 pages long. Totally useless. I struggled for over a year but by opposition in May I was ready. All I saw was an orange-red amoeba-like blob. I was disappointed until Life published the 200" photos that failed to decide the issue after all. I later learned the mirror I'd made was great but the eyepieces I'd made were awful. A local amateur loaned me a good eyepiece and I was in heaven until I could afford my own. By 1955 I was photographing the moon and have been at it ever since. Finally after retiring and building my dream observatory, I can take images far beyond anything I ever dreamed of taking 57 years ago.
After watching the tremendous gains in both equipment and knowledge over those nearly 60 years, I wish I could stick around to see what the next 60 years bring!
You are living the dream, Rick! It gives me hope for my own future.

Rick images from the shores of a lake in rural Minnesota, not far from Paul Bunyan State Forest. He images about 150 objects a year and is currently fourteen months behind in processing data! What a wonderful problem to have. Please keep'em coming, Rick.

Saturday, May 26, 2012

M13, by Markus Blauensteiner

A link to the full image is here: full resolution image

This M13, by Markus Blauensteiner, struck me as nicely captured and processed.  The image has depth. The sheer number of stars recorded here gives some idea of M13's grandeur.  It's a remarkably clear image at that depth for a focal length of only 500mm.  Markus said, “This was a night with extra good seeing conditions!”  Consistent with the depth and clarity is the detail in the galaxy at the upper left of the image, NGC 6207.  Of course, Markus has also caught IC 4617, in between NGC 6207 and M13.  That's a pretty dim target.  The image is stretched enough to show it clearly but the stretches were controlled so that neither noise nor lack of contrast play a role in the image. The middle of the globular is not overstretched and blown out, as is so easy to do either during capture or processing.  Just very nicely done.

The colors are vivid without being overdone, and the contrast between the blue, white, yellow, and orange stars is not only eye-catching but informative.  Notice the bright orange star left of the cluster?  Now notice the yellow one lower-left of it.  See the nice difference in color?  That's careful color processing.  Markus says he calibrates by B-V index, and it shows.

Exposure times were 20 x 3 minutes for luminance, 1x1 bin; and RGB 8 x 3 minutes, 2x2 bin.  The scope, described below, has a natural focal length of 500mm and an aperture of 150mm.  Capture occurred at the Gahberg in Upper Austria (which looks like a dark, rural place).  Markus generally images from a small, private observatory there.  I believe there is a picture on Markus's website.

The link is to Markus's website is here:

He's posted several other images.  Looking them over is good time spent.

I asked Markus about his scope, a  LICHTENKNECKER FLATFIELDKAMERA, and he reported:
The flat-field-camera (FFC) is a quite rare sort of telescope. It is derived from the so called “Schmidt-Camera”, which was used as a Richfield telescope in astrophotography. The problem with the Schmidt-Camera was that the film cassette was placed INSIDE the telescope. So, this wasn`t very practicable with SLRs and digital sensors.

So, in the 80s, a manufacturer named LICHTENKNECKER had the idea to put a secondary mirror in place of the film cassette. The company had the ambition to get a FLAT, fully corrected field for the APS-C format (25,1 mm × 16,7 mm) without the need of extra corrector systems.

The result was a system that looks like a Schmidt-cassegrain, but the secondary mirror is not fixed at the front lens, but about at the half of the tube.

The FFC has NO focuser, the camera and filter wheel are fixed directly on the telescope by a T2-thread.

For focusing, you have to open a little “door” in the tube, grab into the  tube and focus by twisting the secondary mirror.

So it is not possible to focus automatically, you always have to do it by hand.

You may adapt a focuser, but the quality of the picture is better the closer the chip is to the back of the scope. The optimal distance between the scopes back end and the camera chip is 55mm.

If the scope is once collimated (which is quite tricky), you have got a very quick system (f/3.5!!)  which makes beautiful stars up to the corners of DSLR-chips.

Here's a link to my equipment.  The second picture shows the FFC with the little "door" for focusing (right to the telrad):
Looks like a fast and precise set of glass.

Finally, I just wanted to note that Markus caught this image with an Atik 16HR, an older camera by today's standards and one that can be picked up quite inexpensively.

Thanks to Markus for the opportunity to blog this image and for the information about the camera, website, and history.

Thursday, May 3, 2012

M33, by Nicola Montecchiari (April 2012)

This M33 from Nicola Montecchiari is available in larger version here:

Nicola's website is SkyMonsters.

I like the shot in particular for its resolution, its vivid colors, and for the way Nicola incorporated H-alpha data into the image.  I've seen images that capture M33's nebulosity before, but not this vividly.  The image suggests M33 is a busy place!  The data was gathered with the VISAC with reducer, at f/6.4 or 1280mm, with deconvolution applied.  The image demonstrates the kind of resolution possible at that focal length and also the capabilities of the instrument.

Nicola lives in Italy and shoots mainly at three places, all delightfully rural spots.
1) Porliod (AO), Italy - 45 48N, 7 30 E
2) Pian dell'Armà (PV), Italy - 44 42 N, 9 12 E
3) Tortorici (ME) (Summer time) - 38 01 N, 14 49 E

He has been fond of astronomy since a child, a gift his father shared.  He started attempts at imaging in the early 90s but became more involved since 2000.  More biography is available on Nicola's website.

His equipment includes the following, in his own words:
- Canon 50/1.8 for wide fields
- FSQ85ED for medium fields (with an w/o reducer)
- Vixen VISAC for narrow fields (with and w/o reducer)

- Canon EOS 450D modded with baader filter.
- QSI583wsg as CCD camera
Nicola has two mounts: a Takahashi EM200 but also a Vixen SP used when traveling abroad (say, in Namibia).

Finally, Nicola recommends:
- Shoot always color and be careful to correctly balance the colors. This doesn't mean to copy what other people have done, but pursue your own view of it without distorting the physics of what you shot.
- Be humble
 Congratulations, Nicola, on a wonderful image.

Thursday, April 26, 2012

The Astro-Imagers Blog

I see many wonderful images of the sky from around the world.  There are a lot of talented imagers out there!

I began this blog to showcase and remember some of the best I've seen, both so that I can learn from their work and so that I can preserve a record of images.  I also learn about the sky in the process.  No two images are alike, and each imager catches, preserves, and promotes something different in the image.

Sit back, enjoy, and perhaps learn something about the sky, imaging, and those who make it their passion.

Polaris B