The Basics: Equipment
How did I capture these images?
Good question. This site is a collection of images taken from very small areas of the night sky. Before I get in to the various types of objects that are shown on this site I want to take a moment to describe the basic process of getting an image.
A camera is connected to a telescope using various adapters. The camera collects the photons emitted from the object using the telescope as the lens. The CCD cameras I use are made for astrophotography and are different from your typical 35mm camera or cell phone camera. I use cameras that have low noise characteristics and the ability to cool the sensor chip. This is required because the objects are dim and they require the shutter to be open from 5-30 minutes per exposure to get enough data. This creates a lot of heat in a standard 35 mm camera chip and with heat comes noise. Noise appears as the snowy or grainy items seen in some images and it must be minimized by cooling the camera chip.
In addition to the cooling capabilities of a CCD camera I also “stack” several images to increase the signal to noise ratio so the images appear less grainy. Stacking is a process of taking several individual exposures and combining them using special software. So how many individual exposures are used for my images? Just click on an image on my site and another page will open that gives some basic facts about the object and image capturing information. So if you see L=10×600 seconds, R=10×600 seconds, G=10×600 seconds, and B=10×600 seconds this means the following:
L stands for a luminance or clear filter, there are 10 exposures and each is 600 seconds or 10 minutes long. R would mean a red filter, G a green filter, and B is a blue filter. So in the example above the total time to capture the image is 24,000 seconds or 400 minutes or 6.67 hours. That is a long time for a shutter to be open! I use software to combine all of these individual images and Photoshop to refine the image. Sometimes you will see SII= 10×600 seconds, Ha=10×600 seconds, OIII= 10×600 seconds. SII stands for single ionized Sulfur, Ha is Hydrogen alpha, and OIII is double ionized Oxygen. SII, Ha, and OIII are filters I use to only allow light emitted from those gasses onto the camera chip. These appear as black and white images when captured but during processing I add false color to give them their unique look.
Ok, so now we know that a camera is attached to a telescope. Now you may be thinking, how does he keep the shutter open for such a long time and not have the image appear blurry or streaked? The best way is to install the telescope to a mount that rests on either a tripod or pier to keep the assembly stable. Ok, we addressed the stability issue but there is another very important consideration to avoid the blurs and streaks. The Earth rotates at about 1,000 miles per hour and we need a way to compensate for this. The solution is simple but in practice it is tricky. The telescope and camera are attached to a tracking mount that matches the rotation speed of the Earth which allows the telescope to follow the object and keep it steady during the entire time the camera shutter is open. This is a very simple explanation but in practice this is much trickier than it sounds. The mount needs to be aligned with the exact rotation point at the North Pole and the success of the image is highly dependent on your ability to get this polar alignment accurate. To further complicate things, every mount has mechanical errors which need to be addressed. This is done by “guiding” the mount using another camera that is aimed at the same part of the sky as the imaging camera. This camera measures the error in the mount and sends the proper correction back to the mount so it can correct itself. This is called guiding and it is a mandatory requirement for astrophotography.
Ok, so we have a camera connected to a telescope that rests on a tracking mount that is corrected by a guide camera. Whew, that’s a mouthful! But we are not quite finished yet. All of the items need to be controlled and synchronized using control software via a computer. The software helps locate the target in the sky, control the camera shutter, control the telescope focus, send the guiding corrections to the mount, and save all of the captured images to a folder on the computer. It does several other things but these are the basic functions.
As you can see from my brief overview there are a lot of components required for taking an image. The equipment can be expensive and the learning curve can be steep. However, don’t let this discourage you if you want to try your hand at some imaging, I’ve seen some decent images of bright objects captured with a cell phone camera held up to an eyepiece on a cheap telescope. Heck, I’ve even used a rubber band to fasten a Logitech webcam to an eyepiece to capture video of some planets!
Ok, the previous paragraphs describe the equipment used for capturing most of the images on my site. However, there are a few objects that have different requirements and these are the sun and planets. Everyone knows that looking at the sun will temporarily blind you and with a telescope this effect is magnified to the point where permanent eye damage will occur. The telescope I use to capture the sun has special filters that only allow a very narrow wavelength of light to pass to your eye and this allows me to safely see and image the sun. The images on my Solar page use this telescope and a video camera resting on top of one of my mounts. Why video instead of the CCD camera? The sun is very bright so short exposures must be used but the problem with short exposures is that our atmosphere is constantly moving by local winds, jet streams, etc. and it this movement that will cause a CCD camera to capture moments of bad “seeing” and the image will appear distorted and out of focus. A video camera captures the good and bad “seeing” over time and processing software allows me to remove the bad frames and keep the good ones. When you click on a solar image and the attachment page opens you will see a description of the capture info. For full disk images I like shooting about 500 frames of video and for the close ups I like shooting about 800-1000 frames. The full disk images are mosaics, meaning that the picture you see is really six separate videos of six separate areas of the sun that are combined to form one image. I like this method because it allows me the ability to zoom in a bit and still have a clear picture.
The planets require larger telescopes with long focal lengths to image successfully. I used a 10” SCT type telescope for the images on my planet page. I used a video camera attached to the telescope for the same reason I use video for the sun, to average out the good and bad “seeing” moments. Jupiter and Saturn are bright so the exposure on the video are short and I usually capture at 30-60 frames per second. I try to capture 1000-3000 frames of video and drop the bad frames and keep the good frames.
Well that wraps up the basics on the equipment so lets move on to the actual images. Go to the About tab and choose an item from the drop down menu.