Sunday, December 31, 2006

Going deeper...

After seeing many great images taken with modified Canon cameras, I finally got up enough courage to attempt one of these modifications myself. Of course I didn't want to try it on my new Rebel XT, which was still under warranty. I decided to pick up a refurbished model on Ebay, do the surgery on it, and sell my original camera which was only 3 months old.
You may be wondering what I am talking about, and why I would want to rip apart a perfectly good camera. The stock Canon cameras have a small piece of filtered glass installed in front of the CMOS sensor (that's the part that converts red, green, and blue light into electrical signals). This filter cuts off a large portion of light in the H-alpha wavelength of 656nm. Above that wavelength the filter pretty much cuts off everything. Why do we care about H-alpha? Because hydrogen is very common in nebulae, and when hydrogen gets ionized due to the energy of a nearby power source such as a star, it then recombines with all the loose electrons flying around. About 1/2 of the time the hydrogen recombines at just the right energy level to release photons at the H-alpha wavelength. So, wherever a nebula is present we will usually see light (photons) emitted in H-alpha. Sure some nebulae are reflection types, but we can capture that light in the normal wavelengths too. Same goes for galaxies.
OK, enough physics, let's get back to the camera. So, we have this filtered glass deep inside the camera and we don't want it there. We have 3 options available right now to deal with this issue:
1. Remove the internal filter and leave the sensor uncovered.
2. Remove the internal filter and replace with clear glass.
3. Remove the internal filter and replace with UV/IR filtering glass.
The problem with option 1 is that the camera can no longer autofocus, but that's OK for use with a telescope, since the scope controls the focus. The only issue with #2 would be with refractor type telescopes where infrared light is not focused at the same point as visible light. This would cause stars to become bloated on images due to the excess IR energy that is out of focus. Option #3 is good for most average use, but does not allow the option of IR or UV photography. I chose option #2 because I wanted to try IR photography. While I do all my imaging through a refractor right now, I am not worried about star bloat because my light-pollution filter cuts off light in the infrared region.
For the clear glass replacement, I chose a pre-cut filter from Life Pixel. Edmund's Optics also sells a larger piece of anti-reflective glass that must be cut to the right size. The glass from Edmund's is thicker than the stock Canon filter, so I was worried about the effect on the camera's auto focus. Life Pixel did not specify a thickness, so I was hoping they matched the stock glass. When I got the glass I noticed it was thicker, so I could have saved some money by buying Edmund's glass. Oh well, now I know better.
The actual surgery is quite tedious and involves many steps. Some good instructions can be found at Life Pixel's DIY page. I followed every step and nervously disassembled and then reassembled the camera. Well, I didn't completely put the case back together just in case anything was wrong. I put in the battery, nervously turned the power switch, and then....nothing. No power, nothing on the LCD screen, just...nothing. I was very frustrated at this point and decided to carefully disassemble the camera again and thoroughly check every connection as I put the camera back together. Again, I attempted to power up the camera and....again....nothing. Well, this time I was really frustrated. I decided to take a break and look over the online instructions on the Life Pixel site as well as this fine tutorial. While looking at one of the pictures it hit me - the door over the memory card slot! The camera won't power up without this door closed. Since I hadn't totally reassembled the camera, I did not close the card door. I ran back upstairs to try again, and lo and behold the camera powered up. Man, did I feel stupid at this point, but very relieved. The only thing left to do was secure all the tiny screws holding the case together, and then wait for a clear night.
In the meantime I decided to try a few test shots indoors. At the top of this post you'll see a comparison image of some colored spools of thread. The top image has no external filter installed. You are seeing UV, visible, and IR wavelengths all at the same time. All color is washed out and you can see how sensitive the camera is to red. The second image shows how the CC1 filter from X-Nite brings back normal colors for whenever you want to take family or vacation photos, or whatever. This filter essentially mimics the stock Canon internal filter. You'll notice in that picture how much my auto focus is off. The thicker glass threw off the auto focus, but I can tweak that sometime. The lower picture shows the view through a Hoya R72 infrared filter. This gets tricky because you cannot see anything through the viewfinder with this filter installed. Your eye is not sensitive to IR, so it essentially looks black. To get the image framed and focused properly, you have to take a trial-and-error approach and take many images on a tripod. By the way, I am using 58mm filters along with a step-down ring to fit the 52mm threads on my lens.
The weather cooperated the following weekend, with some unusually warm weather for mid-December. This also brought lots of fog. I decided to go out anyway and try out my newly modded camera. I started off taking about an hour's worth of "junk" images to get the camera up to operating temperature. Then I turned my telescope to Monoceros, a visually bleak constellation with some wonderful objects. My deepest image with the stock Rebel XT had been the Rosette Nebula, which you saw in the previous post. That was 80 exposure of 3 minutes each, stacked in ImagesPlus. This time I only tried 20 exposure of the same length for testing purposes. I was shocked at the stacked result. I got slightly better results in 1/4 of the exposure time. Other objects with less H-alpha emissions, or none at all, will not show this kind of improvement. But this short test proves the modification is well worth the effort for objects like the Rosette. A comparison image of the Rosette Nebula is at the bottom of this post. Next, I moved over to M42 and snapped only 20 images to check the results. The stacked image above shows a nice improvement in red sensitivity in this region. I then went over to the Horsehead Nebula area and planned to taking a lot of exposures here. After about 30 exposures were taken, I came back outside and noticed a thin layer of fog hanging over. I decided to stop the exposures and pack up for the night since it was getting late. I kept 26 of the exposures, although I should have threw out a few more due to the fog. The stacked result above blew me away. In just a short amount of time I had captured a huge amount of deep red H-alpha emissions. Just compare it to my first attempt in my previous post about Orion. The new image also indicates a problem that occurs when the mount is tracking too well. There are vertical lines appearing due to the noise from the camera's internal CMOS sensor, which is generated every time an image is read into memory. Normally a small amount of tracking error in the mount can compensate for this by shifting the image slightly between frames. Some people actually move the camera slightly between exposures. I never worried about this because my tracking was never perfect. That night I must have been lucky with my polar alignment!
Since that night I have been busy with the holidays and haven't gotten a chance to get back out. I plan to spend a lot of time in Orion and Monoceros while they are in prime position for the next couple of months. Then it's galaxy season, which doesn't always required a modded camera, but it should be fun anyway. This post should get me caught up to present day, just in time for New Year's Day. Time to go celebrate the end of 2006, and the beginning of what hopefully is a great year for everyone.

Thursday, December 28, 2006

Going deep...

Over the Thanksgiving holiday I got very lucky with the weather - four days off work and four clear nights forecast. This kind of thing is typically unheard of for someone with lots of new astro equipment, so I was praying that the forecasters would not let me down. The night before Thanksgiving I setup my equipment before it was totally dark and got prepared for some imaging. I haven't mentioned it before, but there's a lot of stuff that needs to be connected to make this whole system work:

USB cable from laptop to Canon Rebel XT USB port
USB to serial convertor to Canon Rebel XT shutter port
DC adapter from power strip to Canon Rebel XT
USB laptop port to Shoestring Astronomy GPUSB unit
GPUSB interface cable to EQ6 autoguider port
Firewire cable from laptop to firewire hub
Firewire cable from firewire hub to DMK camera
Power cable to firewire hub
Power cable to mount
Power cables to dew heaters on each scope

So you can see that there's lots of stuff to trip on, and I have on more than one occasion. All these cables are necessary to automate the process as much as possible. The ImagesPlus software uses the USB and serial cables connected to my Canon Rebel XT camera to control camera settings, download images, and control the camera's shutter. ImagesPlus makes the process so easy. The software has a routine that measures focus, so you can quickly dial in the focus before getting started. Once you have achieved the best focus, you simply enter the number of exposures, the delay between exposures, the ISO setting, and any prefix to the file name. Then you click "Release" and the software begins taking exposures.
But there's a little more to be done for longer exposures. My mount can typically allow exposures up to 90 seconds without any guiding. That's without any precise polar alignment or drift alignment. To go longer we need something to keep the mount pointed precisely. That is where autoguiding comes into play. There are three basic elements to the autoguiding system:
1. A camera such as a dedicated CCD guide cam or webcam
2. Software to read the camera images and issue correction signals
3. A hardware interface to the mount's guide port
In my case I use the DMK21AF04 firewire camera as my guiding camera. I purchased this camera because it excels as a planetary imager with it's high frame rate and low noise. I tried to pick equipment that can have more than one use, and the DMK fits that role perfectly. The DMK is mounted in the C8, which has the f/6.3 reducer installed. Without the reducer my field of view would be very small, and the f/10 ratio would require much brighter guide stars. Going down to f/6.3 gives me a bit larger field of view and requires less exposure time for dimmer guide stars. On my laptop I am running MetaGuide software which works with lots of different webcams. Metaguide captures the frames coming in from the camera and stacks several to overcome small movements due to poor seeing. The software then determines which way to correct the mount, and issues guide corrections to the GPUSB interface from Shoestring Astronomy. This little device converts the guide commands to signals that the mount can recognize. What all of this boils down to is that I can run my exposures much longer. What makes it so convenient is that I can get everything setup in about 30 minutes, then start a long image sequence and walk away. While I am inside sipping cocoa or having a snack, the rig is snapping away pictures and keeping itself guided along the way. I just go out from time to time to check the progress and make sure nobody has ran off with any of my equipment. Sometimes I even catch a quick nap, which is hard not to do when you are imaging through the night.
Over the holiday weekend I managed to spend two nights out and capture three objects very nicely. The first was M45, which was in the previous post. The second was the Rosette Nebula, which consisted of 80 exposures of 3 minutes each at ISO 800 (top picture). The third was the California Nebula, which consisted of 50 exposures of 2 minutes each at ISO 1600 (bottom picture). Beyond just capturing a bunch of images, I learned a lot in the process. Every night I go out I learn more, and that's a big part of the reward of this hobby.

M45 - The Pleiades

The Pleiades cluster is a bright nearby grouping of stars visible to the naked eye even from moderately light-polluted skies. It is estimated to be 440 light years away, which is why I say "nearby." In astronomical terms that's not too far away! It is also know as the Seven Sisters, named after the seven daughters of Atlas and Pleione in Greek mythology. The main stars of this cluster are hot and blue, which is due to their relatively young age of about 100 million years old (1/50th the age of our Sun). The intense blue light given off by these stars illuminates a dust cloud that the stars are currently passing through.
This has been a challenging object for me, both in imaging and processing. My image above is the result of 70 exposures of 3 minutes each taken at ISO 800. It seems like even more time might be required to improve the results. I also need to work on my processing skills as it was difficult to really bring out the fainter details without raising the overall noise level too much.
Below is a NASA image map that identifies the major stars of the Pleiades.

Comet Swan

It was nice to have a brief visit of a passing comet shortly after getting my astrophotography rig. This was Comet Swan, named for the SWAN instrument aboard the sun-orbiting SOHO spacecraft. The instrument makes images available to the public, and the skilled eyes of astronomers all over the world, both amateur and professional, can use these images to discover their own comet. This comet, also classified as C/2006 M4, is a non-periodic comet, which means it will not come back for at least 200 years, if at all. Comet Swan suddenly increased brightness from magnitude 7 to magnitude 4 shortly before my image was taken. I didn't have ideal imaging conditions as the comet was low on the horizon at dusk and would disappear behind trees not long after it was dark enough to image. The images were aligned on the comet nucleus and stacked in ImagesPlus.

Orion - The Hunter

Since I first started taking an interest in the night sky during childhood my favorite constellation has always been Orion - The Hunter. This winter constellation stands out prominently among the rest, dominating the southern sky. Riding along the celestial equator, the three bright stars that make up Orion's belt are hard to miss. The Giza pyramid complex in Egypt is said to be a map of these three stars. To the ancient Egyptians, this constellation represented the god of death and the underworld. Greek mythology has a couple of different versions, one being that Orion was accidentally killed by Artemis after a dare by her brother Apollo. The other version had Apollo summoning a giant scorpion to kill Orion. The latter might explain why Orion and Scorpius occupy similar parts of the sky in opposite seasons.
It is easy to see why so many civilizations regarded this constellation with so much attention. You can't help but stare at it when stepping out on a cold winter night. The great yellow star Belelgeuse dominates Orion's shoudler, while the bright multiple star Rigel stands at one of Orion's feet. And of course you can't miss the three stars of Orion's belt - Alnitak, Alnilam, and Mintaka. Straight below the belt you will find Orion's sword, and a large nebula complex appropriately called the Orion Nebula. This was also classified by Charles Messier as M42 and is a large cloud of illuminated dust visible to the naked eye (assuming your sky is dark enough). There are actually two Messier objects here, M42 and M43. Nearby is what is referred to as the Running Man Nebula, because it really looks like a man running. This is classified as NGC 1977, but is also part of a complex of other nebulae NGC 1973 and NGC 1975. This is all part of an extremely large area called the Orion Molecular Cloud Complex. This area covers nearly the entire constellation, hundreds of light years across and 1,500 to 1,600 light years away from us. A very active star forming region, the complex also contains Barnard's Loop as well as the famous Horsehead Nebula, also known as Barnard 33. Near to the bright star Alnitak and the Flame Nebula, this region is high in H-alpha emissions which give it a reddish glow behind the dark dust. The Flame Nebula (NGC 2024) is also a pretty sight, getting it's bright illumination from Alnitak. The bright energy of Alnitak knocks electrons loose from the hydrogen gas there, and when these electrons and ionized hydrogen recombine, they give off a bright glow.
This area represents a challenging object for imagers due to the very bright star Alnitak next to the very dim details we want to capture. Also, the deep red H-alpha regions around the Horshead Nebula are difficult to capture with a stock camera due to the internal filtering (more about that later). But with time and persistence, decent results can be obtained. Below are my first attempts at two regions of the Orion Molecular Cloud Complex.

Observing in suburbia

Many people will travel to darker sites, or even build their own observatory to enjoy viewing & imaging celestial objects. The idea of packing everything up and driving to some location in the middle of nowhere does not appeal to me, at least not on a regular basis. This is not something I would do alone and I definitely do not want to leave my wife home alone all night. An observatory is just not an option as the neighborhood association would have a fit with such a structure. Someday I might have an observatory in a remote area of the southwest, but that will probably have to wait until retirement (and even then only if I'm lucky!). For now I am stuck with my suburban Atlanta location and it's light polluted skies. On top of that, my neighbor installed motion-detecting lights on the front and back of his house. What is really annoying is the front light, which has one light pointing out on the driveway, and another pointing diagonally back towards my yard - right at my observing location. He has conveniently aimed the motion sensor high enough to activate upon any car passing by, which in my neighborhood is about every two minutes. I could move over to the other side of the yard, but then I would have no view of Polaris, which is necessary for my mount's polar alignment. For the moment, I have resorted to clamping some aluminum corner pieces from a canopy we had on the deck to the fence, and hanging moving blankets between the pieces to block the neighbor's lights. Eventually I will build a small patio area so I have a flat, stable surface for my rig. Then I'll put up those aluminum canopy pieces around the patio to hold "light-blocking panels" which haven't been built yet. They will consist of a square PVC pipe frame with black duck cloth covering the entire area. These will make very lightweight panels that can be stored easily in the garage. It's the closest thing I can have to an observatory, and it's the best I can do in suburbia.

Wednesday, December 27, 2006

Stack 'em up!!

One thing I learned & loved very quickly was the technique of stacking many exposures to increase the signal-to-noise ratio. Things like light pollution and a mount with less-than-perfect tracking all work against us to limit how long we can take an exposure. If you can't take 10-minute exposures, no problem. You can take 2 or 3 minute exposures and take lots of them to get almost the same results. Software like ImagesPlus makes this task easy and offers many different options to stack images. I still don't understand them all, but the results clearly speak for themselves. Take a look at what happens when I add 20 more 90-second exposures to the 10 I took the night before (top picture). Nice improvement! And then look what happens when I add another 30 exposures.The results get even better - now I have dust lanes appearing in my Andromeda Galaxy. This is where I realize that I didn't line up my camera very well on different nights. You can see the mis-alignment on the corners. Oh well, all part of the learning experience. I'll keep going back to this object and adding more exposures.

Now I'm hooked!

After my first weekend out with the new rig it was two weeks later before the weather cooperated and allowed some imaging. It was mid-October now and the weather had briefly turned cold, but at the same time brought much clearer skies. I actually didn't intend to start any DSO imaging yet, I wanted to keep getting familiar with all the equipment and polar alignment techniques. However, the first time I looked at M31 through the William Optics Zenithstar 80 FD, I couldn't help but run back inside and grab the camera. It was too beautiful NOT to photograph. I only snapped about 10 exposures at 90 seconds each, with the camera set at ISO 1600.
I could tell from the exposures being downloaded to my laptop that this would turn out pretty good. I also took some 120 second exposures, but my lack of good polar alignment created too much star trailing to use these images. Next, I moved over to M45 and again took only 10 exposures at 90 seconds each. I then moved over to the Double Cluster (NGC 884 & NGC 869) to try my hand at the monthly imaging contest on the Cloudy Nights website, where I spend much of my time on the forums. I finished the night by taking a few exposures of M42 in Orion, although it was still low in the sky and a streetlight was shining almost directly in my scope. Later I took some dark & bias frames before tearing down for the night. The next day I took some flat frames using a simple technique of holding two layers of a t-shirt over my telescope with a rubber band and taking some exposures in Av mode. I then used ImagesPlus software to calibrate, align, and stack all my images. I love this software and consider it one of the best investments I made for the entire setup. Without it I truly would be lost, or at least not enjoying things as much! These images posted here represent almost no processing, but I was excited about my initial results. At this point, I knew I was completely hooked!

My first "Astrophoto"

Let's now go back in time a few months to the first night out for the new rig. It was September 30, 2006 and the full moon was out. Since my wife is Taiwanese, and this was their "Mid-Autumn Festival" we were out carrying on the tradition of cooking BBQ under the bright moonlight. After a lot of meat, seafood, and veggies were put on the grill I rushed out to the yard to power up the mount as the moon began to rise through the trees. The sky was still not quite dark enough to do a star alignment, and I was in a hurry to snap a pic of the moon still rising though some distant trees. What was interesting was that the mount slewed right to the moon without any star alignment. OK, the moon is a big target, but that impressed me. I probably didn't get the camera at the right exposure setting, but I was happy with the result. Later when the moon was a bit higher I snapped a few pics of the big bright full moon. The night of a full moon is not great for imaging, but I was bound and determined to do something with this new rig. Well, that's about where the fun ended. Now I can look back and laugh, but I spent several frustrated hours that night trying to figure out why my mount's GOTO function was not even close. After using a dob, I was moving the mount manually sometimes (i.e. unlocking each axis and moving it). This was after the mount was powered up and aligned, so I was obviously throwing off the mount's alignment without realizing it. Now I know better, but that first night had me nearly pulling my hair out. Oh well, newbie mistakes, and not the first.

Saturday, December 23, 2006

Better late than never....

When I got started with my new telescope earlier this year, my intent was to document my progress through a blog or my own dedicated website. A decent website costs money so I started looking around at all the different blog sites out there. I signed up for one and later didn't like it, signed up for another, then started getting overwhelmed in CSS and HTML stuff. About the same time we started remodeling our kitchen, which caused my blog, and my astronomy hobby, to be put on the back burner for a while. Well, the kitchen turned out great even though it's still not 100% complete today. Still have some backsplash to install but we are almost there. Another side effect of the kitchen remodel was my aggravation of an old shoulder injury. Even after all the hardest work was behind us, my shoulder continued to hurt for a couple of months. This made hauling my telescope, an Orion XT10i Dobsonian, a difficult chore. The XT10i collected dust during the summer while the weather was too hot and humid for viewing. As fall approached, my thoughts turned to astrophotography, which meant lots of new equipment to buy, and lots to learn. The dob was a nice telescope, but my light-polluted suburban Atlanta skies made viewing frustrating and disappointing. I had a good collection of accessories including some Siebert and Hyperion eyepieces, a NexImage webcam, and a Moonlite CR2 focuser. This would probably be a killer setup in dark skies. In my skies it was still a pretty good performer, but I always was left wanting more. I kept thinking about astrophotography, which my original budget did not allow. In September I was finally in a financial position to afford a decent starter rig. That's when I got started in what has turned into a full-blown obsession for me. The dob is gone now, but new set of toys takes it's place. This is where I will start documenting my journey into the world of astrophotography, and finally get around to getting this darn blog started.