Captured Nov 15th, 2012_Part of Life

Yesterday, I spent a great afternoon of quality time with my grandson, Marek. We arrived back home at around 10:30 PM. The skies were clear and bright. I immediately made a pot of coffee and opened the observatory in preparation for a two hour run on a target that has eluded me. While waiting for the run to complete, i entertained myself by searching for meteors from the Leonid Meteor Shower and thinking up catchy phrases to print on t-shirts. Using a common theme, i came up with a phrase that seemed appropriate at the time. But for some reason, i don't believe that "Astronomers do it when it's so cold it will take your breath away" is going to be a big seller. 

I thought i had everything right. The alignment went well, the tracking was dead on, batteries were at full charge and i had a good lock with the autoguider. But after the run, i reentered the observatory and did a quick scan of the photos i had acquired. They were junk. Of the sixty photos i had taken, only a small handful were usable. Upon closer examination, i discovered that one of the cables had gotten tangled and had been pulling against the scope for the entire run. I hadn't checked the cables. Oh well, the forecast is for clear skies tonight...

I like to start each post with a photo. The image i used today was taken from a few shots that were gathered Thursday night before the clouds moved in. Because this is not the first time i have forgotten to check the cables and ruined a set of photos, I thought the Thursday night image was appropriate. The Dumbell Nebula is about 1300 light years distant. Sixteen shots at two minutes each. ISO 1600. 

clear skies...

Captured Sept 15th, 2012_The Milky Way_Numbers

About two hundred years before the birth of Christ, Eratosthenes, the curator of the Great Library of Alexandria, decided he was going to measure the circumference of the Earth. He knew that at noon on a given day, in Syene, a city to the south, a stick planted perpendicular to the ground cast no shadow. So he did the same thing in Alexandria and on the given day, at noon, dutifully measured the angle of the shadow. He divided that angle into 360 and multiplied the result by the distance between the two cities. He then announced to the world the circumference of the Earth. Seems so simple, but he was right. He measured it to within two percent of the the number we have today. With two sticks. While he was at it, he correctly measured the distance to the Sun and Moon. But the powers that ruled the world at that time decided that the Alexandrians were just too smart for their own good. The library and almost all the knowledge contained within it were destroyed. Fifteen hundred years later, Columbus had a hard time convincing a crew to sail with him. They all thought they were going to fall off the edge of a flat world. 

Now for the numbers i want to talk about. If the earth didn't rotate at all, it would be the end of the world as we know it. But the astrophotography opportunities would be incredible! Not having to worry about rotation would allow me to collect HOURS of data without a hitch. At the Equator, the surface of the earth spins around the axis at just over 1000 miles per hour. Since where i live is so much closer to the axis, the speed is more like 700 miles per hour. Eight inches from the North or South Pole, the Earth is spinning at a robust 2.1 inches per hour. And that is about the speed my telescope mount rotates in the opposite direction. If i can get the axis of the scope to line up exactly parallel to the axis of the Earth, i can offset the rotation of the Earth and shoot pictures as if the Earth was not rotating at all. Not an easy task, and i spend an incredible amount of time on acquiring that alignment. But there are other ways....

The magic number is 600. That is the number i commit to memory. I don't even remember where i got it. I would assume i made some sort of google search on how to avoid star trails in photographs. In the next few lines i'm going to explain how to use it. 

The camera i use is a canon t2i. i bought it in a package deal containing two lenses. One lens is a 18mm to 55mm zoom, and the other is a 55mm to 250mm zoom. Nothing special, but not a bad package. The trick to photographing the stars off a fixed tripod is to limit each exposure to a time period that does not show discernible star movement. You can take as many photos as you like, they just have to be very short exposures. How short? Thats where the number 600 comes into play. If i wanted the greatest magnification possible from the lenses listed, i would take the larger lens and set the zoom at 250mm. If i divide 250 into 600 the result is 2.4. That is the maximum exposure i can use at 250mm. I can take as many pictures as i like to gather more light, but each shot can be no longer that 2.4 seconds. There will be no star trails. Just nice crisp stars. Several galaxies and nebula can be captured at these settings. If i were to set the zoom at 100mm, i could acquire shots at 6 seconds each. Once i have all the photos i want, i dump them into the freely available DeepSkyStacker. It does all the work of combining all the light data and aligning the stars in all the shots into one nice photo. 

The photo at the top of this post was taken at the Black Forest Star Party. I was using just the camera on a tripod. the lens was set to 18mm to allow 30 second exposures. (actually,  600/18=33.333 but 30 seconds is the highest autoexposure setting on my camera) The ISO would have been set at 1600 and the fstop as open as i could get it. I don't remember how many photos i collected, probably more than 20. It's a view looking toward the center of our home galaxy, the Milky Way. I used nothing more than the camera, tripod and a wired remote button.

(i know my daughter is going to read halfway thru this post and start mumbling "blah, blah, blah, tech, blah, tech, blah...". But that's ok, i'll explain it to my granddaughter in person.)

clear skies...

Captured Nov 10th 2012_Flame and Horsehead Nebula

Sometimes, less is more. My setup includes an SCT with an 8 inch mirror. Riding piggyback on the SCT is a small guidescope for tracking purposes. But last night, after setting up the alignment, i capped off the main scope and mounted the DSLR camera on the little guidescope. The guidescope has less than 1/3 the magnification of the main scope, but last night, i was going for field of view. 

I love the constellation Orion. This time of year, around midnight, it dominates the sky. And it is just full of interesting targets. The main star in this photo is Alnitak. It is the leftmost star in Orion's belt. Alnitak is about 730 Light years from earth. Just below and to the left of Alnitak is the Flame Nebula (NGC2024). It is about 900 to 1,500 light years away. Also below Alnitak and to the right is the Horsehead Nebula (IC434),1500 light years distant. I've been wanting to include all three components into one photo for some time. Last night was the night.

This image consists of 60 photos at 60 seconds each. ISO1600. I took five darks and five bias. i used no flats. Everything was stacked in DeepSkyStacker and then processed in Photoshop. I really didn't do much processing. Just a generic histogram stretch and a bit of gradient work. That was it. I like this photo, but i think that on the next clear night i get, i will concentrate on the horsehead nebula with the main scope. 

clear skies...

Darks Flats and Bias as I understand them

Before we begin on the files themselves, lets start with a little background information. When my camera is attached to the telescope, there is no aperture adjustment. It is fixed. The only adjustment options i have are ISO and Exposure time. ISO is a measure of light sensitivity. In the days of film, different coatings produced different light sensitivities, but higher ISO films produced a grainier end product. Now it's just a matter of setting the sensitivity of the chip. Exposure time is... well... the time you expose the chip to light. Usually, unless i am dealing with a fairly bright object, i will set the ISO at 1600 and adjust the exposure time depending on the results i get in the histogram. That is not a hard and fast rule. There are several factors that figure into my settings. But that is a whole other blog. For the purpose of this blog, let's say i've decided i want one hour of exposure on the target. In this example, i'm going to set the ISO at 1600. To get an hours worth of light, i'll set the exposure time (shutter speed) to 60 seconds, and plan on taking 60 photos. In the stacking software, these photos are called "Lights" because they contain the light data that will actually create the photo. But sometime in the process i will need to shoot Darks, Bias and Flats. The following is my explanation of  Darks, Flat and Bias as i understand them.

Darks
The chip inside your camera is defective. Yup, sorry. They all are. There are pixels on the chip that will be ON when they shouldn't be. It's just the way it is. During normal photography this isn't much of an issue. But in astrophotography it makes a big difference. Temperature also has an effect on the chip. Turning pixels on depending on how hot or cold the chip is. To battle this, the photographer will take a series of Dark frames. there's no mystery to it. It's just a matter of taking a few photos with the lens cap on at the same ISO, Temperature and Exposure time as the photos. The pros will take Darks before, during and after they have taken their Light frames. But i just do this for fun. As the target photos are taken, the chip heats up inside the camera. I assume that there are more defective pixels as the camera heats up. I could be wrong, but this seems to be working for me. So i take all the Light shots i want, 60 in this case. Then after i am done, i just pop the lens cap on the scope and take 5 Dark frames at the same ISO and Exposure time. I'm not sure how many darks frames i should actually take, but i know if i don't feed SOME into DeepSkyStacker, the results are less than desirable.

Bias
There is a certain amount of electronic noise generated inside the camera when the shutter is activated. This noise has a effect on the chip, causing even more pixel naughtiness. To counteract this, the photographer will record this noise in Bias frames. Many people argue that the bias noise is already recorded on the Dark frames. I don't know. What i do know is that after i have taken my Dark frames, i can change the Exposure time on the camera to the fastest time (in my case 1/4000) leaving the lens cap on, ISO the same and shoot five Bias shots pretty quickly. Does it help much? I don't know. But it's easy, so i will continue to do it.

Flats
Dirt, dirt, dirt. It's all about dirt. Flats are used to record the dirt within the optics path so it can be removed from the photos. I take Flats when it's handy, but i must admit that i am bad about not even collecting them. The idea is to have the same camera/scope setup and use some even flat light to record the flat frames. What i usually do, when i think of it, is to cover the end of the scope with a white t-shirt (during daylight hours) and point the scope at some empty part of the sky. I'll usually take five shots using the same ISO and Exposure settings as the Light frames. In this example ISO 1600, Exposure time 60 seconds. I don't fret about it. My pics will never make ASTRONOMY magazine. I'm sure that as my skills improve, there will come a time that i wouldn't even dream of processing a photo without Flats. But i'm not there yet.

So there you have it. No mystery to it. Don't worry too much about what to do with the files once you acquire them. I just load them all into a program called DeepSkyStacker and it does the required work. I should probably also mention that i use a camera control program. BackyardEOS is an excellent camera control program and well worth the affordable price.

ok, that's it!

clear skies...

Captured Nov 9th 2012_Messier Object 74

I'm an amateur astrophotographer. And when i say amateur, i mean it in the most literal sense of the word. When someone googles amateur astophotographer, a picture of me pops up with the definition. But i'm proud of my photos and want to share them. They aren't super great. No one is going to confuse them with professional photos, and no one is going to accuse me of stealing images from the Hubble, but they are mine. This blog is not so much a venue to show the photos, but more of a journal of the learning process involved.

In future posts, i will talk about my equipment. how i set it up, the mistakes i made, and the workarounds i have used. Subjects for a rainy day. This post will explain the process i used to capture and develop this image. Messier Object 74 is a face on spiral galaxy in the constellation Pisces. It's about 32 million light years from earth and consists of about 100 billion stars. Much smaller than the milky way which contains somewhere between 200-400 billion stars. M74 is listed as an intermediate target. I cannot make it out in the scope. But the camera sees things that i can't.

Last night, as my wife and granddaughter were watching "Spy Kids 4", i decided it would be a good time to take advantage of the clear skies and open the observatory. I call my observatory "Don's Doghouse". If you saw it, you would understand why. I set the scope to the index marks, and did a four star alignment. Two stars in the east, and two stars in the west. There are a couple nebula i would like to capture in Orion, but it is not yet high enough in the sky. So, i decided to target Messier 74 in the constellation Pisces. I did a 180 second test and saw the distinctive bit of fuzz on the exposure that usually signifies a galaxy. It took a few minutes (almost standing on my head) to get the autoguider locked on a nearby star and guiding the scope. The computer was set to acquire 50 photos at ISO1600. Each photo would be a 180 second exposure. That would yield two and a half hours of exposure time. The computer assumes control of the camera once i start the process, so i don't really have a lot in the process for the next few hours. i step out of the Doghouse once the process starts, and do not enter it again until the run is complete. The idea is to create as little vibration as possible. Although the tripod sits on a 4" thick concrete pad, i won't go near it. NO walking on it, no touching the sidewalls, nothing. Fine with me! Frees me up to wander the yard, sit in my lawn chair, take in the sky, get a cup of tea, harass the granddaughter. 

After two and a half hours, i reenter the Doghouse, shot 5 darks, and 5 bias. I didn't bother with flats. I could shoot some today to throw in the mix. The camera is still attached to the scope. (usually is) But i'm not convinced that the flats add all that much to the final photo. If you don't understand what these are, don't worry. I'll explain them in another post. The 50 photos were loaded into a program called DeepSkyStacker. i went thru the photos one at a time and deselected any pic that showed evident sign of vibration, or alignment errors. Twenty five shots were rejected during this process. Then the dark and bias frames were loaded. DeepSkyStacker is pickier than i am, and can see defects in the photos that i cannot. It rejected twelve more of the photos leaving me with thirteen 180 second exposures. i saved the result as a TIFF file, loaded  into Photoshop and did some minor editing.

I'm not great at Photoshop. i have a lot to learn. But i am capable of stretching the histogram to bring out the color, removing a nasty gradient from the background, and making the background stars a little smaller. I'm particularly proud of the star resizing trick. without it, the stars detract too much from the focal point of the photo. 

So there you have it. I'm unhappy with the reject rate. I think there are some things i can do about it. i do NOT want to shorten the exposure times, though that would help. i would rather concentrate more on getting a better polar alignment. The Clear Sky Chart indicates a relatively good sky tonight after six PM. Good, gives me a chance to practice more. Maybe a nebula.....

comments and advice are GREATLY appreciate...

clear skies....