Astrophotography is a unique hobby, that is at once science, art & craft. It’s a very satisfying hobby that utilizes all your brain-cells and makes you fulfilled from a creative standpoint as well. See individual sections in the menu as well.
I have created a website with links of all astrophotography related tips and tricks. See www.astrophotolinks.com.
Process of Astrophotography
The planets are usually bright enough that normal exposures are enough to capture the object. For example, to take picture of Moon, an exposure of 1/250 s. is sufficient, Jupiter can be captured with exposure of 1/50 or so. Such short exposure only require a large aperture and correct magnification.
Deep sky objects are a different story. These objects are usually very dim. Except for couple of very bright nebulae, most objects require a minimum of 30 second exposure. Most objects require exposure of 5 minutes or more. When taking long exposures, we are confronted with 4 issues:
1. The longer the exposure, more is the ‘noise’ i.e. heat within the camera that gets recorded as false signal. That creates unwanted grains.
2. There is so much man-made light pollution that the ambient light starts overpowering the light emitted from your target. This necessitates that individual picture cannot be shot over for more than a few minutes. But, in those few minutes, we do not get enough data! We require more data!
3. Most of these objects are so far away that the photons (light is made of photon, individual packets of energy) come intermittently i.e. signal may be received at a specified pixel in some images only, not all images. For example, a galaxy’s spiral arms’ outer edges may be so dim that the light emitted by the stars in that area may send one photon our way every few minutes. Therefore, multiple pictures have to be taken to get at least one photon in one of your pictures.
4. Earth moves! Every second! Even at the shortest focal lengths, say, 120 mm, the Earth moves enough that the target as well as all the neighborhood stars move in the picture when shot over 15 seconds, creating ugly star trails.
Tracking & Autoguiding
To overcome all the constraints, astrophotographers use high quality mounts that track movement of the objects as they move from East to West in Earth’s sky. Even then, the tracking is not perfect. At higher focal lengths, these mounts give proper tracking of up to 1 minute or so. To overcome this, astronomers use a process called ‘autoguiding’. Autoguiding entails using another camera to lock on to a bright star close to the object being shot. A computer is used to receive a picture of that star every few seconds. A software checks if the star is moving from the locked position and gives instructions to the mount to correct its movement so that the star returns back to the locked position. This process ensures that we are able to take pictures of few minutes without any unwanted star trails.
After multiple pictures are taken, we use softwares that help us combine data from multiple pictures, remove extra noise and extract fainter portions of the picture without overexposing the brighter portions.
Equipments & Software that I use
QSI 683wsg. A CCD Camera that can cool the sensor by about 40 degrees Celsius than ambient temperature. This reduce the noise substantially due to lesser heat. Most of my earlier pictures were shot by a Canon T2i DSLR camera, but, I am using QSI 683 since last 6 months.
1. AG Optical Telescope (Dall Kirkham) – Focal Length 1650 mm. Aperture 250 mm. Focal Ratio f/6.7. For my camera, the magnification comes to approx 75 times.
3. Stellarvue SV80S Refractor – Focal length 480 mm. Focal Ration f/6. For my camera, the magnification comes to approx 21 times.
I now use Paramount MX mount, which is definitely better than the Losmandy G11 mount that I used couple of years back. As I have said earlier, proper tracking is way more important than a better scope. It’s all about guiding.
For Autoguiding – Maxim DL
For Stacking – Maxim DL
For Processing – Pixinsight
For Final touches – Photoshop Essentials